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Biological Science: Assignment no. 2 Garcia, Pauline Jessica M. BSA I-20

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Page 1: Biology Assignments

Biological Science: Assignment no. 2

Garcia, Pauline Jessica M.

BSA I-20

Adrian Guinto

July 10, 2012

Page 2: Biology Assignments

Biological Science: Assignment no. 2 2

QUESTIONS FOR CELLS1. Explain the events that made it possible to observe and understand cell structure and function.

Light microscopy

Scientists first saw cells by using traditional light microscopes that were plagued by optical aberrations. Scientists gradually got better at grinding glass into lenses and at whipping up chemicals to selectively stain cellular parts so they could see them better. Robert Brown (1773-1858) is generally credited with being the first to appreciate that the nucleus was an important component of the cells of plants and animals (1833). By the late 1800s, biologists already had identified some of the largest organelles (e.g., mitochondria, and Golgi).

Researchers using high-tech light microscopes and glowing molecular labels can now watch biological processes in real time. The scientists start by chemically attaching a fluorescent dye or protein to a molecule that interests them. The colored glow then allows the scientists to locate the molecules in living cells and to track processes—such as cell movement, division, or infection—that involve the molecules.

Fluorescent labels come in many colors, including brilliant red, magenta, yellow, green, and blue. By using a collection of them at the same time, researchers can label multiple structures inside a cell and can track several processes at once. The technicolor result provides great insight into living cells—and is stunning cellular art.

Electron microscopy

In the 1930s, scientists developed a new type of microscope, an electron microscope that allowed them to see beyond what some ever dreamed possible. The revolutionary concept behind the machine grew out of physicists' insights into the nature of electrons.

As its name implies, the electron microscope depends not on light, but on electrons. The microscopes accelerate electrons in a vacuum, shoot them out of an electron gun, and focus them with doughnut-shaped magnets. As the electrons bombard the sample, they are absorbed or scattered by different cell parts, forming an image on a detection plate.

Although electron microscopes enable scientists to see things hundreds of times smaller than anything visible through light microscopes, they have a serious drawback: they can't be used to study living cells. Biological tissues don't survive the technique's harsh chemicals, deadly vacuum, and powerful blast of electrons.

Electron microscopes come in two main flavors: transmission and scanning. Some transmission electron microscopes can magnify objects up to 1 million times, enabling scientists to see viruses and even some large molecules. To obtain this level of detail, however, the samples usually must be sliced so thin that they yield only flat, two-dimensional images. Photos from transmission electron microscopes are typically viewed in black and white.

Scanning electron microscopes cannot magnify samples as powerfully as transmission scopes, but they allow scientists to study the often intricate surface features of larger samples. This provides a window to see up close the three-dimensional terrain of intact cells, material surfaces, microscopic organisms, and insects. Scientists sometimes use computer drawing programs to highlight parts of these images with color.

2. When cells were first described, what was observed during this initial discovery?

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Biological Science: Assignment no. 2 3

The invention of the microscope allowed the first view of cells. English physicist and microscopist Robert Hooke (1635–1702) first described cells in 1665. He made thin slices of cork and likened the boxy partitions he observed to the cells (small rooms) in a monastery. The open spaces Hooke observed were empty, but he and others suggested these spaces might be used for fluid transport in living plants. He did not propose, and gave no indication that he believed, that these structures represented the basic unit of living organisms.

3. Describe what is now known as cell theory.The cell theory states that “all organisms are made up of one or more cells, within which the life process of metabolism and heredity occur.” It only means that cell is considered as a unit of structure, function heredity and development.

4. Why are most cells small?Cells are so small so the surface area and volume of them can be proportional to each other. This helps with the efficiency of the cell's absorption and waste expulsion processes. Also by the cell's smallness, communication from the nucleus to other organelles is fast and the cell can be regulated while the conditions for diffusion are still ideal.

5. Define cytoplasm and nucleoplasm.The cytoplasm is the gel-like substance residing within the cell membrane holding all the cell's internal sub-structures (called organelles), outside the nucleus. All the contents of the cells of prokaryote organisms (which lack a cell nucleus) are contained within the cytoplasm. Within the cells of eukaryote organisms the contents of the cell nucleus are separated from the cytoplasm, and are then called the nucleoplasm. Nucleoplasm, also called nuclear sap or karyoplasm, is the fluid usually found in the nucleus of eukaryotic cells. This fluid contains primarily water, dissolved ions, and a complex mixture of molecules. Its primary function is to act as a suspension medium for the organelles of the nucleus. Other functions include the maintenance of nuclear shape and structure, and the transportation of ions, molecules, and other substances important to cell metabolism and function.

6. Compare and contrast the function of a solution and a colloid in cell structure.The cell, the fundamental unit of life, is composed of a vast network of membranes of colloidal dimensions (about 6-8 nanometers wide) that present an enormous dynamic surface area as well as compartmentalize cell functions. These membranes are colloidal assemblies of diverse composition, especially proteins and phospholipids. The outer cell membrane, the plasma membrane, is electrically polarized and contains colloidal protein aggregates called ion channels whose structure ("conformation") can change in the presence of specific chemicals, such as neurotransmitters, or voltage changes across the membrane resulting in cell responsiveness to stimuli and signal conduction (the "action potential").

7. What is a cell membrane?The cell membrane is the outer layer of the living cell. It gives form to the cell and controls the passage of materials in and out of cell.

8. How do materials move through a cell membrane?

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Biological Science: Assignment no. 2 4

Materials move into and out of cells through active transport, diffusion, and osmosis.

Active transport occurs when the cell must use energy to actively move the materials up (against) their concentration gradient.

Diffusion is passive. This means the cell need not expend energy, the material simply moves from an area of higher concentration to areas of lower concentration. (For example, cook bacon in the kitchen and the smell fills the entire house.)

Oxygen and carbon dioxide diffuse across the phospholipid bilayer. Other substances diffuse through proteins embedded in the membrane; this is called facilitated diffusion.

Osmosis is the movement of water through a semi-permeable membrane (also called a selectively permeable or differentially permeable membrane), into the solution with the higher solute concentration. This is also a passive process.

9. What are the possible dynamics of cell contents when the osmotic pressure within the cell is not equal to that outside the cell?

Reverse osmosis

Reverse osmosis is a separation process that uses pressure to force a solvent through a semi-permeable membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.

Forward osmosis

Osmosis may be used directly to achieve separation of water from a solution containing unwanted solutes. A "draw" solution of higher osmotic pressure than the feed solution is used to induce a net flow of water through a semi-permeable membrane, such that the feed solution becomes concentrated as the draw solution becomes dilute. The diluted draw solution may then be used directly (as with an ingestible solute like glucose), or sent to a secondary separation process for the removal of the draw solute. This secondary separation can be more efficient than a reverse osmosis process would be alone, depending on the draw solute used and the feedwater treated. Forward osmosis is an area of ongoing research, focusing on applications in desalination, water purification, water treatment, food processing, etc.

10. How do materials move between cells?Cells make use of passive and active processes to transport substances across its membrane.

11. Describe the nucleus: what is it; what is in it; and what is its function?Nucleus is a specialized organelle, which contains the organism’s hereditary material i.e. DNA (Deoxyribonucleic Acid). Inside the nucleus, a dense, spherical body called nucleolus is present. The nucleus contains structures, which regulates the cell cycle, growth, protein synthesis and reproductive function.

12. Give a brief description of each of the following structures:

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a. Endoplasmic reticulum-is a series of membranous channels that transverse the cytoplasm of most eukaryotic cellsb. Ribosome-is a large complex of RNA and protein which catalyzes protein translation, the formation of proteins from individual amino acids using messenger RNA as a template. Golgi apparatus-is a cluster of flattened membranous sacs which is responsible for the storage, modification and packing of materials produced for secretory export.c. Lysosomes-are single-walled membranous sacs responsible in digestion of nutrients, bacteria and damaged organelles.d. Mitochondrion-are double-walled membranous sacs with folded inner partitions, they release energy into usable ATP which happens during cellular respiration.e. Fat droplet-f. Plastid-are organelles responsible for photosynthetic activity, manufacturing and storage of chemical compounds in plants.g. Vacuole-are membranous sacs that store and release various substances within the cytoplasm. It is also responsible for the cell’s enlargement and water balance. h. Microfilament- these filaments are primarily structural in function and are an important component of the cytoskeleton, along with microtubules and often the intermediate filaments.i. Microtubule-are thin, hollow tubes that support the cytoplasm and transport materials within the cytoplasm.j. Cilium-are minute cytoplasmic projections that extend from the cell surface and responsible to move particles along cell surface or move the cell itself.k. Flagellum- are minute cytoplasmic projections that extend from the cell surface and responsible to move particles along cell surface or move the cell itself.l. Centriole- is a cylindrically-shaped cell structure found in most eukaryotic cells, though it is absent in higher plants and most fungi. The walls of each centriole are usually composed of nine triplets of microtubules

13. Compare and contrast eukaryotic and prokaryotic cells.Eukaryotic cells have more elaborate interior organization, while prokaryotic cells resemble one another in form, having little internal organization and a strong cell wall encasing their exteriors.

QUESTIONS FOR CELL DIVISION1. Compare and contrast prokaryotic and eukaryotic cell division. Which is less complex and why?

Mitosis or eukaryotic cell division is a process of cell duplication, or reproduction, during which one cell gives rise to two genetically identical daughter cells. It is used by single celled organisms to reproduce; it is also used for the organic growth of tissues, fibers, and mibranes.

Meiosis or prokaryotic cell division, on the other hand, is a division of a germ cell involving two fissions of the nucleus and giving rise to four gametes, or sex cells, each possessing half the number of chromosomes of the original cell. It is useful for sexual reproduction of organisms; The male and female sex cells, e.g. the spermazoa and egg, fuse to create a new, singular biological organism.

2. In both eukaryotic and prokaryotic cell division, the genetic information must be duplicated before the cell begins to divide. Why?

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All eukaryotic organisms have evolved an organized process of cell division, which enables the genetic information to be accurately copied and distributed to the daughter cells. The process of duplication of the genetic material is called DNA replication. During each cell cycle several hundreds to thousands of replication origins on several chromosomes are activated resulting in the accurate duplication of several million bases of DNA, once and exactly once. Any errors in copying even a single base can be mutagenic and potentially detrimental to the organism. To ensure high fidelity execution of such a complex task, this process is highly regulated both at the cellular level as well as at the level of individual origins on chromosomes.

Lesions in DNA, which arise from exogenous (for example UV radiation) and intrinsic sources (for example free radicals), can compromise the integrity of genetic information and cause cell death. The process of replication is especially vulnerable to these lesions, since it relies on an intact template DNA strand. Cells have therefore evolved checkpoint mechanisms, which respond rapidly to the presence of DNA lesions and replication problems and lead to the adjustment of the DNA replication program, adding a further layer of regulation.

Our lab uses the budding yeast as a model system to understand how these highly conserved processes are interrelated. Yeast offers the advantage of using elegant genetic tools in combination with quantitative biochemical methods and modern genomic and proteomic approaches to elucidate the components of these pathways and their mechanism of action. We study two related aspects of DNA replication. One part of our research focuses on the mechanistic understanding of how post-translational protein modifications such as phosphorylation and ubiquitylation regulate DNA replication during an unperturbed cell cycle. In addition, we study the relationship between DNA replication and the checkpoint in the context of DNA damage.

3. Cell division is a brief and distinct stage in a cell’s life history, compared to the rest or a cell’s life. Describe what happens during interphase. Interphase which is the non-dividing stage is devoted enlargely to cell growth. Dividing cells spend some of the 90% of their time. The chromosomes are not seen as distinct structures. The nucleolus is not visible, nuclear membrane is still present, centrioles, chromosomes and DNA duplicate.

4. Define karyokinesis and cytokinesis. Karyokinesis is the process of change that takes place during the division of

a cell nucleus at mitosis or meiosis.

Cytokinesis is the process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells. It usually initiates during the late stages of mitosis, and sometimes meiosis, splitting a mitotic cell in two, to ensure that chromosome number is maintained from one generation to the next.

5. Describe, with the use of labeled diagrams, each of the stages in eukaryotic cell division.

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6. Define syncytium and coenocyte in terms relating them to cell division.A coenocyte is a multinucleate cell which can result from multiple nuclear divisions without their accompanying cytokinesis, in contrast to a syncytium which results from cellular aggregation followed by dissolution of the cell membranes inside the mass. The only exception is the (incorrect but too-well-established-to-be-changed) use of the word syncytium in animal embryology to refer to the coenocytic blastoderm of invertebrates.

7. Compare and contrast binary fission, budding, cloning, conjugation, transformation, and transduction. Binary fission- the cell starts by duplicating its DNA to create two complete sets, and then growing to a size much larger than it usually is. As the cell grows, the sets of DNA move to opposite ends of the cell. Once the cell has achieved the right size, it splits in two, creating two daughter cells with identical DNA. Binary fission is classically used when an organism is living in a stable environment.

Budding- is a form of asexual reproduction in which a new organism develops from an outgrowth or bud on another one. The new organism remains attached as it grows, separating from the parent organism only when it is mature.Since the reproduction is asexual, the newly created organism is a clone and is genetically identical to the parent organism.

Conjugation is the process by which one bacterium transfers genetic material to another through direct contact.

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Biological Science: Assignment no. 2 8

Transformation- is the exchange of genetic material between strains of bacteria by the transfer of a fragment of naked DNA from a donor cell to a recipient cell, followed by recombination in the recipient chromosome.

Cloning- is the creation of an organism that is an exact genetic copy of another. This means that every single bit of DNA is the same between the two.

Transduction- is a method of genetic recombination by which DNA is transferred from one cell to another by a viral vector. Various bacteriophages transfer DNA from one species of bacteria to another.

8. Define haploid and diploid, using the terms fertilization and zygote.

A haploid is a set of chromosomes containing one member of each chromosome pair. It can also be defined as the number of chromosomes in a gamete (a cell with only one pair of chromosomes) of an organism. It is symbolized by "n" or "1n." A diploid is a set of chromosomes containing two sets of chromosomes (one male and one female). The symbol for a diploid is "2n" because it is double the haploid.

9. Define the following terms with labeled illustrations, comparing and contrasting the roles these parts play in different stages of a cell’s life history: chromosome, chromatid, centromere.

Chromosome- structure composed of deoxyribonucleic acid (DNA) contained within a cell's nucleus

(center) where genetic information is stored. Human have 23 pairs of chromosomes, each of which has recognizable characteristics (such as length and staining patterns) that allow individual chromosomes to be identified. Identification is assigned by number (1-22) or letter (X or Y).

Chromatid- either of two parallel filaments joined at the centromere that make up a chromosome and that divide in cell division, each going to a different pole of the dividing cell and each becoming a chromosome of one of the two daughter cells.

Centromere- the clear constricted portion of the chromosome at which the chromatids are joined and by which the chromosome is attached to the spindle during cell division.

10. With carefully labeled illustrations, describe all the steps in meiosis.

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QUESTIONS FOR REPRODUCTION1. Define asexual reproduction and discuss the different types that exist.

Reproduction is the biological mechanism by which species give rise to offspring and perpetuate their genetic material. Asexual reproduction is the reproductive process that involves only one organism and results in two or more organisms. Single celled organisms, such as archaea, bacteria and protists, commonly reproduce asexually. Certain fungi and some plants do as well. An advantage of asexual reproduction is that it results in more rapid proliferation of the species. Another advantage is genetic stability. When certain desired traits are observed in commercial plants (color, disease resistance, flavor, etc.), that plant is often encouraged to reproduce asexually in order to keep those traits

Different Types of Asexual Reproduction: Binary fission is the simplest form of asexual reproduction. The parent cell simply divides into

two parts that are about equal. Each of the new cells, called daughter cells, becomes a separate individual. Each of the new offspring then grows to a normal size. Binary fission is the usual method of reproduction of one-celled organisms including protozoa, bacteria, and many algae. Binary fission is also the process by which multi-cellular organisms grow.

Budding is another type of asexual reproduction. New individuals develop as small growths or buds on the surface of the parent organism. The new organism may break off and live

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independently or remain attached and live as a colony. Budding is different from binary fission because the offspring and parent are not the same size. Yeast, hydra, sponges, and some worts reproduce by budding.

Spores are special cells that some individual organisms produce. A thick, tough outer coating that protects the inner cell usually surrounds spores. When released by the parent, each spore may grow into a separate individual. Fungi, algae, and protozoa can reproduce by spore formation.

Regeneration is the ability to re-grow lost body parts. Starfish, earthworms, hydra, and planarian can regenerate in to new individual. A planarian that is cut into several pieces will regenerate into several new worms.

Vegetative propagation is new cells separating from the parent and forming a complete, independent individual. Plants can reproduce asexually by vegetative propagation. Roots, stems, and leaves are called vegetative structures. Some plants reproduce vegetative by special structures such as bulbs, corms, tubers, runners, and rhizomes. Farmers and gardeners have taken advantage of different plants' ability to reproduce asexually for generations. Artificial vegetative propagation allows gardeners and farmers to grow plant with certain traits. A "cutting" is any vegetative part of the plant used to produce a new individual.

Cloning is a scientifically-engineered reproductive technology that involves infusing the genetic material from a parent organism in to an (nucleus removed) of another cell.

2. Compare and contrast asexual and sexual reproduction: What are the benefits and shortcoming of each?Asexual reproduction involves only one parent, and the resulting cells are generally identical to the parent cells while in sexual reproduction, two parents contribute to the formation of a new individual, during this process, a new combination of traits can be produced. Sexual reproduction is more complex than asexual reproduction, requiring that parents find one another.

3. Describe with the use of illustrations both types of gametogenesis: spermatogenesis and oogenesis. The male testes have tiny tubules containing diploid cells called spermatogonium that mature to become sperm. The basic function of spermatogenesis is to turn each one of the diploid spermatogonium into four haploid sperm cells. This quadrupling is accomplished through the meiotic cell division detailed in the last section. During interphase before meiosis I, the spermatogonium’s 46 single chromosomes are replicated to form 46 pairs of sister chromatids, which then exchange genetic material through synapsis before the first meiotic division. In meiosis II, the two daughter cells go through a second division to yield four cells containing a unique set of 23 single chromosomes that ultimately mature into four sperm cells. Starting at puberty, a male will produce literally millions of sperm every single day for the rest of his life.

OogenesisJust like spermatogenesis, oogenesis involves the formation of haploid cells from an original diploid cell, called a primary oocyte, through meiosis. The female ovaries contain the primary oocytes.

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There are two major differences between the male and female production of gametes. First of all, oogenesis only leads to the production of one final ovum, or egg cell, from each primary oocyte (in contrast to the four sperm that are generated from every spermatogonium). Of the four daughter cells that are produced when the primary oocyte divides meiotically, three come out much smaller than the fourth. These smaller cells, called polar bodies, eventually disintegrate, leaving only the larger ovum as the final product of oogenesis. The production of one egg cell via oogenesis normally occurs only once a month, from puberty to menopause.

4. List the main human male reproductive structures (internal and external), explain their function. Penis — The penis is the male organ for sexual intercourse. Semen, which contains sperm, is

expelled (ejaculated) through the end of the penis when the man reaches sexual climax (orgasm). When the penis is erect, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.

Scrotum ―The scrotum is the loose pouch-like sac of skin that hangs behind the penis. It contains the testicles (also called testes), as well as many nerves and blood vessels. The scrotum has a protective function and acts as a climate control system for the testes.

Testicles (testes) ―The testes are oval organs about the size of large olives that lie in the scrotum, secured at either end by a structure called the spermatic cord.

Epididymis — The epididymis is a long, coiled tube that rests on the backside of each testicle. It functions in the transport and storage of the sperm cells that are produced in the testes. It also is the job of the epididymis to bring the sperm to maturity, since the sperm that emerge from the testes are immature and incapable of fertilization.

Vas deferens — the vas deferens is a long, muscular tube that travels from the epididymis into the pelvic cavity, to just behind the bladder. The vas deferens transports mature sperm to the urethra in preparation for ejaculation.

Ejaculatory ducts — these are formed by the fusion of the vas deferens and the seminal vesicles. The ejaculatory ducts empty into the urethra.

Urethra — the urethra is the tube that carries urine from the bladder to outside of the body. In males, it has the additional function of expelling (ejaculating) semen when the man reaches orgasm. When the penis is erect during sex, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.

Seminal vesicles — the seminal vesicles are sac-like pouches that attach to the vas deferens near the base of the bladder. The seminal vesicles produce a sugar-rich fluid (fructose) that provides sperm with a source of energy and helps with the sperms’ motility (ability to move). The fluid of the seminal vesicles makes up most of the volume of a man’s ejaculatory fluid, or ejaculate.

Prostate gland — the prostate gland is a walnut-sized structure that is located below the urinary bladder in front of the rectum. The prostate gland contributes additional fluid to the ejaculate. Prostate fluids also help to nourish the sperm. The urethra, which carries the ejaculate to be expelled during orgasm, runs through the center of the prostate gland.

Bulbourethral glands — the bulbourethral glands, or Cowper’s glands, are pea-sized structures located on the sides of the urethra just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to lubricate the urethra and to neutralize any acidity that may be present due to residual drops of urine in the urethra.

5. Give the precise route that sperm takes from where it is formed to where it leaves the body.The sperm start off in the seminiferous tubules and then are stored in the eppididdymus. From here they are carried by the ductus deferens or vas deferens which takes a route from through the ingiunal canal backwards over the top of the urinary bladder and down behind it. Here the sperm

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pass through the seminal vesicle then the prostate. Here it joined the urethra which carries it down and out through the penis.

6. Give the precise route that an egg takes from where it is formed to where it become an embryo, and then the path it takes when the baby is born. Female make, within their bodies, special cells called ova (eggs). The male produces cells in his body called sperm. When a male sperm cell joins with an ovum inside the female's body, we say the ovum has been fertilized. The ovum grows and changes from one cell into billions of cells which form the earliest stages of a baby, called an embryo. The ovum does this by a process called mitosis.This cell mass them divides into three sections: an outer layer, an inner layer called the trophoblast, and an inmost mass of cells from which the embryo grows. The growing embryo is attached to the wall of special chamber inside its mother's body. This is called the womb or uterus and here it stays for the nine months it needs to develop into baby ready to be born. This period is known as the gestation period. While the embryo is in the womb, it receives its food direct from its mother's body through the placenta. The embryo is joined to the placenta by a cord called the umbilical cord. When the baby is born, the doctor cuts this cord and the place where it was joined to the baby's baby becomes the navel

7. Describe a complete menstrual cycle.Menstruation is also called menstrual bleeding, menses, catamenia or a period. The flow of menses normally serves as a sign that a woman has not become pregnant. (However, this cannot be taken as certainty, as a number of factors can cause bleeding during pregnancy; some factors are specific to early pregnancy, and some can causeheavy flow.)

Eumenorrhea denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal). The average blood loss during menstruation is 35 milliliters with 10–80 ml considered normal. Women who experience Menorrhagia are more susceptible to iron deficiency than the average person. An enzyme called plasmin inhibitsclotting in the menstrual fluid.

Painful cramping in the abdomen, back, or upper thighs is common during the first few days of menstruation. Severe uterine pain during menstruation is known as dysmenorrhea, and it is most common among adolescents and younger women (affecting about 67.2% of adolescent females). When menstruation begins, symptoms of premenstrual syndrome (PMS) such as breast tenderness and irritability generally decrease. Many sanitary products are marketed to women for use during their menstruation.

QUESTIONS FOR CELLULAR RESPIRATION1. Under what circumstances might cellular respiration occur in the presence of oxygen, and when

might oxygen be unnecessary?

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The Citric Acid Cycle or Krebs Cycle begins after the two molecules of the three carbon sugar produced in glycolysis are converted to a slightly different compound (acetyl CoA). Through a series of intermediate steps, several compounds capable of storing "high energy" electrons are produced along with two ATP molecules. These compounds, known as nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), are reduced in the process. These reduced forms carry the "high energy" electrons to the next stage. The Citric Acid Cycle occurs only when oxygen is present but it doesn't use oxygen directly. Electron Transport requires oxygen directly. The electron transport "chain" is a series of electron carriers in the membrane of the mitochondria in eukaryotic cells. Through a series of reactions, the "high energy" electrons are passed to oxygen. In the process, a gradient is formed, and ultimately ATP is produced. Glycolysis literally means "splitting sugars." Glucose, a six carbon sugar, is split into two molecules of a three carbon sugar. In the process, two molecules of ATP, two molecules of pyruvic acid and two "high energy" electron carrying molecules of NADH are produced. Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP. This process is called fermentation.

2. Although it has been stated that the oxidation of glucose to pyruvate releases, energy, what exactly is meant by term oxidation?Oxidation can be defined very simply as, the "addition" of oxygen. An alternative approach is to describe oxidation as the loss of hydrogen. It was derived from the observation that almost all elements reacted with oxygen to form compounds called, oxides. A typical example is the corrosion or rusting of iron as described by the chemical equation:4 Fe + 3 O2 -----> 2 Fe2O3 The logical starting point in the discussion of oxidation-reduction reactions is the atom, and the terms and conventions used by chemists in describing this phenomenon.All atoms are electrically neutral even though they are comprised of charged, subatomic particles. The terms, oxidation state or oxidation number, have been developed to describe this "electrical state" of the atom. The oxidation state or oxidation number of an atom is simply defined as the sum of the negative and positive charges in an atom. Since every atom contains equal numbers of positive and negative charges, the oxidation state or oxidation number of any atom is always zero. This is illustrated by simply totaling the opposite charges of the atoms as shown by the following examples.

3. The first series of chemical reactions in cellular respiration, in which glucose is converted to pyruvate, is called glycolysis. Expand on what happens during this series of reactions.We all need energy to function and we get this energy from the foods we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration, a catabolic pathway for the production of adenosine triphosphate (ATP). ATP, a high energy molecule, is expended by working cells. Cellular respiration occurs in both eukaryotic and prokaryotic cells. It can be aerobic respiration in the presence of oxygen or anaerobic respiration. Prokaryotic cells carry out cellular respiration within the cytoplasm or on the inner surfaces of the cells. More emphasis here will be placed on eukaryotic cells where the mitochondria are the site of most of the reactions. It has three main stages: glycolysis, the citric acid cycle, and electron transport.

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Glycolysis: Glycolysis literally means "splitting sugars." Glucose, a six carbon sugar, is split into two molecules of a three carbon sugar. In the process, two molecules of ATP, two molecules of pyruvic acid and two "high energy" electron carrying molecules of NADH are produced. Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP. This process is called fermentation. The most pressing need of all cells in the body is for an immediate source of energy. Some cells such as brain cells have severely limited storage capacities for either glucose or ATP, and for this reason, the blood must maintain a fairly constant supply of glucose. Glucose is transported into cells as needed and once inside of the cells, the energy producing series of reactions commences. The three major carbohydrate energy producing reactions are glycolysis, the citric acid cycle, and the electron transport chain. The overall reaction of glycolysis which occurs in the cytoplasm isrepresented simply as:C6H12O6 + 2 NAD+ + 2 ADP + 2 P -----> 2 pyruvic acid, (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 H+.

4. Why are exzymes important in glycolysis?Glycolysis means sugar-splitting. Glycolysis is part of a universal metabolic pathway for the catabolic conversion of glucose to Energy. The process of Glycolysis is catalyzed by about ten different enzymes.

5. How are both glycolysis and Kreb cycle related?glycolysis is the 1st step of cellular respiration and is common to both aerobic and anaerobic organisms because it occurs in the absence of oxygen. the product of glycolysis is pyruvate which is oxidised to ACETYL CO A and it is acetyl COA that enters mitochondria and takes part in kreb's cycle.

6. Describe anaerobic fermentation; compare and contrast it to other ways cells have to obtain energy. Integrate anaerobic fermentation into the larger picture, explaining the role it plays in most plants and in some microorganisms.Anaerobic fermentation means the “absence of oxygen”, the opposite of aerobic fermentation. It is a complicated process which is 100% natural and is carried out on micro-organisms. Under anaerobic conditions, the pyruvate molecule can follow other anaerobic pathways to regenerate the NAD+ necessary for glycolysis to continue. These include alcoholic fermentation and lactate fermentation. In the absence of oxygen the further reduction or addition of hydrogen ions and electrons to the pyruvate molecules that were produced during glycolysis is termed fermentation. This process recycles the reduced NADH to the free NAD+ coenzyme which once again serves as the hydrogen acceptor enabling glycolysis to continue. Alcoholic fermentation, characteristic of some plants and many microorganisms, yields alcohol and carbon dioxide as its products. Humans cannot ferment alcohol in their own bodies; we lack the genetic information to do so. These biochemical pathways, with their myriad reactions catalyzed by reaction-specific enzymes all under genetic control, are extremely complex.

7. How do ATP and ADP differ, and why are they important in cellular respiration?ATP stands for Adenosine Tri-Phosphate, and is the energy used by an organism in its daily operations. It consists of an adenosine molecule and three inorganic phosphates. After a simple

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reaction breaking down ATP to ADP, the energy released from the breaking of a molecular bond is the energy we use to keep ourselves alive. ATP is used to provide energy for muscle cells, for active transport and to transport molecules and proteins through the plasma membrane. It is the energy that powers your body while ADP is what is left after the energy is released. ATP is important in cellular respiration because cells use ATP to supply their energy needs while ADP stores energy made from cellular respiration. When a cell has energy available, it can store small amounts of it by adding a phosphate group to ADP molecules, producing ATP.

8. What happens during the Kreb cycle?The Krebs cycle is a series of reactions which occurs in the mitochondria and results in the formation of ATP and other molecules which undergo further reactions to form more ATP.

In general, the Krebs cycle consists of the bonding of the two carbon acetyl coenzyme A with the four carbon compound called oxaloacetic acid. The resulting compound, which has six carbon atoms, undergoes a series of chemical reactions, resulting in the formation of energy (in the form of ATP, NADH, and FADH2) and oxaloacetic acid, which can then bond with another molecule of acetyl coenzyme A so that the cycle can run again.

The Krebs cycle occurs two times for each glucose molecule from glycolysis, since it occurs for each of the two molecules of acetyl coenzyme A formed by the oxidation of the two molecules of pyruvic acid. For each turn of the Krebs cycle, one molecule of ATP, three molecules of NADH, and one molecule of FADH2 (a coenzyme similar to NADH) are formed. Therefore, for one glucose molecule, the Krebs cycle results in the formation of two molecules of ATP, six of NADH, and two of FADH2. The NADH and FADH2 then undergo the electron transport chain, resulting in the production of more ATP.

9. What is the electron transport chain, what role do the cytochrome play in this chain, and where might such an electron transport chain exist? Why?The electron transport system occurs in the cristae of the mitochondria, where a series of cytochromes (cell pigments) and coenzymes exist. These cytochromes and coenzymes act as carrier molecules and transfer molecules. They accept high-energy electrons and pass the electrons to the next molecule in the system. At key proton-pumping sites, the energy of the electrons transports protons across the membrane into the outer compartment of the mitochondrion.Each NADH molecule is highly energetic, which accounts for the transfer of six protons into the outer compartment of the mitochondrion. Each FADH2 molecule accounts for the transfer of four protons. The flow of electrons is similar to that taking place in photosynthesis. Electrons pass from NAD to FAD, to other cytochromes and coenzymes, and eventually they lose much of their energy. In cellular respiration, the final electron acceptor is an oxygen atom. In their energy-depleted condition, the electrons unite with an oxygen atom. The electron–oxygen combination then reacts with two hydrogen ions (protons) to form a water molecule (H2O). The role of oxygen in cellular respiration is substantial. As a final electron receptor, it is responsible for removing electrons from the system. If oxygen were not available, electrons could not be passed among the coenzymes, the energy in electrons could not be released, the proton pump could not be established, and ATP could not be produced. In humans, breathing is the essential process that brings oxygen into the body for delivery to the cells to participate in cellular respiration.

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10. What types of substances can be fed into the respiratory chain of reactions? And what happens to them once they have been fed into this chain of reactions?

All reactions of glycolysis and the citric acid cycle take place in the cell's cytosol. The respiratory chain is located in another compartment: it occurs at the inner mitochondrial membrane. It is here that ATP is generated under consumption of oxygen and this is why mitochondria are often said to be the cell' 'power plant'. The process is also called oxidative phosphorylation. It resembles photophosphorylation that is part of photosynthesis. Both processes need intact membranes that form intact compartments separated from the rest of the cell to function.

In summary can the respiratory chain be characterized as the process during which NADH + H+ and FADH2 are oxidized under consumption of oxygen and water and ATP are generated.

While FAD accepts both electrons and protons transport cytochromes only electrons.

QUESTIONS FOR PHOTOSYSNTHESIS1. Give a brief history of how basic fundamentals of photosynthesis were first discovered.

Tracking atoms through Photosynthesis: Scientific theory

Scientists have tried for centuries to piece together the process by which plants make food. Although some of the steps are still not completely understood. The overall photosynthetic equation has been known since the 1800s: In the presence of light, the green parts of plants produce organic compounds and oxygen from carbon dioxide and water. Using molecular formulas, photosynthesis with this chemical equation:

6CO2 + 12H2O+ Light energy C6H12O6 + 6O2 + 6H2O

The carbohydrate C6H12O6 is glucose. Water appears on both sides of the equation because 12 molecules are consumed and 6 molecules are newly formed during photosynthesis. This simplify the equation by indicating only the net consumption of water:

6CO2 + 6 H2O + Light energy C6H12O6 + 6O2

This chemical change is the reverse of the one that occurs during cellular respiration. Both of these metabolic processes occur in plant cells. However, plants do not make food by simply reversing the steps of respiration.

The splitting of Water

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One of the first clues to the mechanism of photosynthesis came from the discovery that the oxygen given off by plants through their stomata is derived from water and not from carbon dioxide. The chloroplast splits water into hydrogen and oxygen. Before this discovery, the prevailing hypothesis was that photosynthesis split carbon dioxide (CO2 C + O2) and then added water to the carbon (C+ H2O [CH2O]).

This hypothesis predicted that the O2 released during photosynthesis came from CO2. This idea was challenged in the 1930s by C. B. van Niel of Standford University. Van Neil investigated photosynthesis in bacteria that make their carbohydrate from CO2 but do not release O2. Van Neil concluded that atleast in these bacteria; CO2 is not split into carbon and oxygen.

Experiment tested to verify Neil’s theory:

CO2 + 2 H2O [CH2O] + H2O + O2

A significant result of the shuffling of atoms during photosynthesis is the extraction of hydrogen from water and its incorporation into sugar. The waste product of photosynthesis, O2, is release to the atmosphere.

2. What are the different photosynthetic pigments and why are there different ones?

Pigments are chemical compounds which reflect only certain wavelengths of visible light. This makes them appear "colorful". Flowers, corals, and even animal skin contain pigments which give them their colors. More important than their reflection of light is the ability of pigments to absorb certain wavelengths.

There are three basic classes of pigments. Chlorophylls are greenish pigments which contain a porphyrin ring. There are several kinds of

chlorophyll, the most important being chlorophyll "a". This is the molecule which makes photosynthesis possible, by passing its energized electrons on to molecules which will manufacture sugars. All plants, algae, and cyanobacteria which photosynthesize contain chlorophyll "a". A second kind of chlorophyll is chlorophyll "b", which occurs only in "green algae" and in the plants. A third form of chlorophyll which is common is (not surprisingly) called chlorophyll "c", and is found only in the photosynthetic members of the Chromista as well as the dinoflagellates. The difference between the chlorophylls of these major groups was one of the first clues that they were not as closely related as previously thought.

Carotenoids are usually red, orange, or yellow pigments, and include the familiar compound carotene, which gives carrots their color. These compounds are composed of two small six-carbon rings connected by a "chain" of carbon atoms. As a result, they do not dissolve in water, and must be attached to membranes within the cell. Carotenoids cannot transfer sunlight energy directly to the photosynthetic pathway, but must pass their absorbed energy to chlorophyll. For this reason, they are called accessory pigments. One very visible accessory pigment is fucoxanthin the brown pigment which colors kelps and other brown algae as well as the diatoms.

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Phycobilins are water-soluble pigments, and are therefore found in the cytoplasm, or in the stroma of the chloroplast. They occur only in Cyanobacteria and Rhodophyta. Phycobilins are not only useful to the organisms which use them for soaking up light energy; they have also found use as research tools. Both pycocyanin and phycoerythrin fluoresce at a particular wavelength. That is, when they are exposed to strong light, they absorb the light energy, and release it by emitting light of a very narrow range of wavelengths. The light produced by this fluorescence is so distinctive and reliable, that phycobilins may be used as chemical "tags".

3. Describe the differences between autotrophs and heterotrophs.

Living organisms obtain chemical energy in one of two ways: Autotrophs store chemical energy in carbohydrate food molecules they build themselves. Food is chemical energy stored in organic molecules. Food provides both the energy to do work and the carbon to build bodies. Because most autotrophs transform sunlight to make food, we call the process they use photosynthesis. Only three groups of organisms - plants, algae, and some bacteria - are capable of this life-giving energy transformation. Autotrophs make food for their own use, but they make enough to support other life as well. Almost all other organisms depend absolutely on these three groups for the food they produce. The producers, as autotrophs are also known, begin food chains which feed all life. Heterotrophs cannot make their own food, so they must eat or absorb it. For this reason, heterotrophs are also known as consumers. Consumers include all animals and fungi and many protists and bacteria. They may consume autotrophs or other heterotrophs or organic molecules from other organisms. Heterotrophs show great diversity and may appear far more fascinating than producers. But heterotrophs are limited by our utter dependence on those autotrophs that originally made our food. If plants, algae, and autotrophic bacteria vanished from earth, animals, fungi, and other heterotrophs would soon disappear as well. All life requires a constant input of energy. Only autotrophs can transform that ultimate, solar source into the chemical energy in food that powers life.

4. List some of the most important nutrients to a plant, and tell where they are most likely to come from.

The Non-Mineral Nutrients are hydrogen (H), oxygen (O), & carbon (C).These nutrients are found in the air and water. In a process called photosynthesis, plants use energy from the sun to change carbon dioxide (CO2 - carbon and oxygen) and water (H2O- hydrogen and oxygen) into starches and sugars. These starches and sugars are the plant's food.

Mineral NutrientsThe 13 mineral nutrients, which come from the soil, are dissolved in water and absorbed through a plant's roots. There are not always enough of these nutrients in the soil for a plant to grow healthy. This is why many farmers and gardeners use fertilizers to add the nutrients to the soil.The mineral nutrients are divided into two groups: macronutrients and micronutrients.

Macronutrients Macronutrients can be broken into two more groups:

Primary and secondary nutrients.

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The primary nutrients are nitrogen (N), phosphorus (P), and potassium (K). These major nutrients usually are lacking from the soil first because plants use large amounts for their growth and survival.The secondary nutrients are calcium (Ca), magnesium (Mg), and sulfur (S). There are usually enough of these nutrients in the soil so fertilization is not always needed. Also, large amounts of Calcium and Magnesium are added when lime is applied to acidic soils. Sulfur is usually found in sufficient amounts from the slow decomposition of soil organic matter, an important reason for not throwing out grass clippings and leaves.

Nitrogen (N)-Nitrogen often comes from fertilizer application and from the air (legumes get their N from the atmosphere, water or rainfall contributes very little nitrogen)

Phosphorus (P)-Phosphorus often comes from fertilizer, bone meal, and superphosphate. Potassium (K)-Potassium is supplied to plants by soil minerals, organic materials, and

fertilizer. Calcium (Ca)-Sources of calcium are dolomitic lime, gypsum, and superphosphate. Magnesium (Mg)-Soil minerals, organic material, fertilizers, and dolomitic limestone are

sources of magnesium for plants.

MicronutrientsMicronutrients are those elements essential for plant growth which are needed in only very small (micro) quantities. These elements are sometimes called minor elements or trace elements, but use of the term micronutrient is encouraged by the American Society of Agronomy and the Soil Science Society of America. The micronutrients are boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn). Recycling organic matter such as grass clippings and tree leaves is an excellent way of providing micronutrients (as well as macronutrients) to growing plants.

Boron (B)-Sources of boron are organic matter and borax Chloride (Cl)-Chloride is found in the soil. Iron (Fe)-Sources of iron are the soil, iron sulfate, iron chelate. Manganese (Mn)-Soil is a source of manganese. Molybdenum (Mo)-Soil is a source of molybdenum.

5. How does chlorophyll work?The chlorophyll is found in the thylakoid membrane. chlorophyll is the pigment that absorbs in red and blue and reflects green, which makes plants look green. chlorophyll captures the sun's energy and is used as energy to complete the photosynthesis process (light dependent reaction.)

6. Where is chlorophyll usually located, and why?The primary link between ling things and sunlight is chlorophyll. It is found in all photosynthetic organisms. It is found in leaves. Chlorophyll is a pigment necessary for photosynthesis.Chlorophyll is contained in structures called chloroplasts. Chlorophyll in the chloroplasts traps light during photosynthesis. It absorbs energy from the colors of the spectrum. The chlorophyll reacts in the same way in the presence of light. Its structure traps light energy and converts it to chemical energy.

7. What is noncyclic photophosphorylation?Non Cyclic photophosphorylation operates in a zig-zag manner and involves two chemically and physically distinct photosystem (PS I and II), linked together by electron transport chain. Noncyclic photophosphorylation produces oxygen, NADPH and ATP.

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Noncyclic photophosphorylation requires both photosystem I and photosystem II, which are linked in series. This linkage produces net oxidation of an electron donor (of water to oxygen) and reduction of NADP+to NADPH.

8. What is cyclic photophosphorylation?Cylic photophosphorylation occurs on the thylakoid membrane. In cyclic electron flow, the electron begins in a pigment complex called photosystem I, passes from the primary acceptor to ferredoxin, then to cytochrome (a similar complex to that found in mitochondria), and then to plastocyanin before returning to chlorophyll. This transport chain produces a proton-motive force, pumping H+ions across the membrane. This produces a concentration gradient that can be used to power ATP synthase during chemiosmosis. This pathway is known as cyclic photophosphorylation, and it produces neither O2 nor NADPH. Unlike non-cyclic photophosphorylation, NADP+ does not accept the electrons; they are instead sent back to photosystem I.

9. How do plants synthesizes carbohydrates?Carbohydrates (comprising carbon and water) are sugar compounds which are manufactured or "synthesized" by green plants (and other organisms) when exposed to light. This carbohydrate manufacturing process is called photosynthesis after the Latin words "photo" meaning light and "synthesis" meaning putting together.

QUESTIONS FOR HOMEOSTASIS1. Explain what it means for a cell to be isosmotic, hyperosmotic, and hypoosmotic with regard to the

surrounding medium.IsosmoticA condition in which the total number of solutes (i.e. permeable and impermeable) in a solution is the same or equal to the total solutes in another solution. Hypo-osmoticA condition in which the total amount of solutes (both permeable and impermeable) in a solution is lower than that of another solution. HyperosmoticA condition in which the total amount of solutes (both permeable and impermeable) in a solution is "greater" than that of another solution. 2. Why is ammonia converted into either urea of uric acid in most organisms?Ammonia, a breakdown product of nitrogen metabolism, has toxic effects within the body. The liver converts it to urea for excretion in the urine.

3. What are the different methods animals have to cope with nitrogenous wastes?FishFish excrete nitrogenous waste as ammonia; this is unusual because ammonia is highly toxic therefore storage in the body can pose a risk. However, fish are able to cope due to their

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environment – the large volumes of water they reside in allow them to continuously excrete ammonia (without the need for storage) directly into the water, diluting the ammonia to non-toxic levels.There are two extremes of environment which fish have to adapt to however – marine and freshwater. The difference in concentration of salt between these two environments has led to slightly different methods of dealing with nitrogenous waste. Osmoregulation of fish living in fresh water requires them to excrete large volumes of dilute urine. This is due to osmosis, which allows large volume of water to enter body fluid from the surrounding hypotonic freshwater. The converse is true for marine fish, the hypertonic water means water leaves bodily fluid by passive osmosis, in an attempt to conserve water small amounts of concentrated urine are released. Fish still have kidneys however, despite nitrogen excretion being handled by the gills. Instead the kidneys are involved in the excretion of excess water and divalent ions, e.g. Mg2+ and SO42-. Amphibians

As with fish the type of nitrogenous excretion depends entirely on environment. Typically tadpoles use the same method as fish – ammonia excretion via the gills. However adult amphibians produce urea as they do not remain constantly in the water. The urea is stored, diluted in the bladder, but as amphibians may be prone to desiccation they have adapted the ability to reabsorb water from the urine when needed. This requires them to have relatively large bladders for storage. Amphibians do not drink to obtain water; instead they are able to absorb water through a region of the skin called the ventral pelvic area.

BirdsAll birds excrete a paste like substance called uric acid (which contains the waste nitrogen) independent of habitat. It initially begins as watery urine which travels down the ureters, from the kidney to the cloaca. The cloaca is a unified exit for the gastrointestinal, urinary and reproductive systems. In the cloaca, the urine mixes with faecal matter from the digestive tract and as much water is removed as possible to produce a dry, crystalline paste containing uric acid. A small amount of watery urine may be excreted as well.

ReptilesThe method of nitrogen excretion depends on the habitat; aquatic reptiles (e.g. turtles) will mainly excrete ammonia (possibly urea) as with fish. Whilst reptiles living in drier conditions (e.g. lizards, snakes & tortoises) excrete uric acid – the low toxicity, crystalline paste. This helps to conserve water and during development in the egg, a build-up is not fatal. Uric acid, as with birds, is excreted from the cloaca. The kidneys of reptiles do not have loops of Henle and so they are unable to produce concentrated urine also, whilst a large bladder is present in chelonians (turtles) snakes and some lizards do not have a bladder at all.

MammalsAll mammals produce primarily urea (sometime ammonia) which is excreted in urine. Mammals are able to osmoregulate and maximise water conservation by varying the concentration of urine depending on the hydration of the body. Mammals living in environments with plentiful access to fresh water will excrete large amounts of dilute urine. Mammals living in dry or marine environments will excrete small amounts of concentrated urine. Osmoregulation in mammals is mainly controlled by the hormone ADH, its release (when a mammal is dehydrated) will result in the reduction of water loss and increased reabsorption of water in the kidneys by the loop of Henle.

4. Trace the movement of nitrogenous waste removal through a kidney from the renal artery to the ureter. After plasma enters the proximal tubule, it passes through the coils, where usable materials and water are reclaimed. Salts, glucose, amino acids, and other useful compounds flow back through

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tubular cells into the blood by active transport. Osmosis and the activity of hormones assist the movement. The blood fluid then flows through the loop of Henle into the distal tubule. Once more, salts, water, and other useful materials flow back into the bloodstream. Homeostasis is achieved by this process: A selected amount of hydrogen, ammonium, sodium, chloride, and other ions maintain the delicate salt balance in the body. The fluid moving from the distal tubules into the collecting duct contains materials not needed by the body. This fluid is referred to as urine. Urea, uric acid, salts, and other metabolic waste products are the main components of urine. The urine flows through the ureters toward the urinary bladder. When the bladder is full, the urine flows through the urethra to the exterior.

QUESTIONS FOR HORMONES1. What are hormones, and how are they delivered from where they are produced to their target

area?Hormones are chemicals that transfer information and instructions from one set of cells to another. They are responsible for maintaining and controlling the activities of the cell.

When a hormone is secreted, it travels from the endocrine gland through the bloodstream to the target cells designed to receive them. Along the way to the target cells, special proteins bind to some of the hormones. Also, the target cells have receptors that attaches into specific hormones that shall only communicate with specific target cells. The hormone then locks onto the cell’s specific receptors. This combination transmits instructions to the internal metabolism.

2. What is the difference between endocrine and exocrine glands?The difference between the two is that endocrine glands are ductless meaning they release hormones directly into the bloodstream where they can be transported to cells in other parts of the body, while exocrine glands release secretions in the skin or inside of the mouth.

3. What are two groups of plant hormones, and how do they affect plants?

Plant hormones are chemical messengers that affect a plant's ability to respond to its environment. Hormones are organic compounds that are effective at very low concentration; they are usually synthesized in one part of the plant and are transported to another location. They interact with specific target tissues to cause physiological responses, such as growth or fruit ripening. Each response is often the result of two or more hormones acting together.

Because hormones stimulate or inhibit plant growth, many botanists also refer to them as plant growth regulators. Many hormones can be synthesized in the laboratory, increasing the quantity of hormones available for commercial applications. Botanists recognize five major groups of hormones: auxins, gibberellins, ethylene, cytokinins, and abscisic acid.

4. What is a plant’s photoperiod?Photoperiod, also called light duration and day length (or daylength), refers to the length of the light period as contrasted to darkness within a day. Day length controls or influences several plant growth and development processes that determine or affect crop yield.

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5. Describe how hormones affect diabetes.Hormones called insulin and glucagon which are secreted by the pancreas work together to maintain a steady level of glucose, or sugar, in the blood. Diabetes occurs when there is too much sugar in the blood this happens because the pancreas fails to produce insulin or can’t produce normal amounts of it.

6. Compare the similarities and differences of male and female sex hormones.The major female and male hormones can be classified as estrogens or androgens. Both classes of male and female hormones are present in both males and females alike, but in vastly different amounts. Most men produce 6-8 mg of the male hormone testosterone (an androgen) per day, compared to most women who produce 0.5 mg daily. Female hormones, estrogens, are also present in both sexes, but in larger amounts for women.

Estrogens are the sex hormones produced primarily by a female's ovaries that stimulate the growth of a girl's sex organs, as well as her breasts and pubic hair, known as secondary sex characteristics. Estrogens also regulate the functioning of the menstrual cycle.

In the majority of women, ovarian hormones appear not to play a significant role in their sex drive. In one study of women under the age of 40, 90 percent reported experiencing no change in sexual desire or functioning after sex hormone production was shut down because of the removal of both ovaries.

QUESTIONS FOR BRAIN AND THE NERVOUS SYSTEM

1. What protective layers envelope the vertebrate brain? According to Florian E. W. Schmidt, Ph.D. (1999), the vertebrate brain is protected by the meninges or the three connective tissue membranes enclosing the brain. The outermost meninx is the dura mater which encloses Arachnoid mater and the innermost pia mater.

2. How are vertebrate brains similar in basic construction?The vertebrate brain is basically an anterior enlargement of the nervous system. It is subdivided into three basic regions – the forebrain, the midbrain, and the hindbrain. Each region contains major divisions – Telencephalon and Diencephalon in the forebrain, Mesencephalon in the midbrain, and Metencephalon and Myelencephalon in the hindbrain. The brains of the vertebrates look like a series of bulges in the neural tube in their early development. It is difficult to see the differences in the early embryonic brains of the vertebrates.

3. What do the terms forebrain, midbrain, and hindbrain refer to?The brain is made of three main parts: the forebrain, midbrain, and hindbrain. The forebrain is responsible for a variety of functions including receiving and processing sensory

information, thinking, perceiving, producing and understanding language, and controlling motor function. There are two major divisions of forebrain: the diencephalon and the telencephalon.

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The diencephalon contains structures such as the thalamus and hypothalamus which are responsible for such functions as motor control, relaying sensory information, and controlling autonomic functions. The telencephalon contains the largest part of the brain, the cerebrum. Most of the actual information processing in the brain takes place in the cerebral cortex.

The midbrain and the hindbrain together make up the brainstem. The midbrain is the portion of the brainstem that connects the hindbrain and the forebrain. This region of the brain is involved in auditory and visual responses as well as motor function.

The hindbrain extends from the spinal cord and is composed of the metencephalon and myelencephalon. The metencephalon contains structures such as the pons and cerebellum. These regions assists in maintaining balance and equilibrium, movement coordination, and the conduction of sensory information. The myelencephalon is composed of the medulla oblongata which is responsible for controlling such autonomic functions as breathing, heart rate, and digestion.

4. What are the three basic types of neurons? motor neuron: neurons that relay signals from the central nervous system to the other parts of

the body

sensory neuron: neurons that transmit information to the central nervous system from the senses of sight, hearing, taste, touch, and smell, as well as those that transmit pain signals

inter neurons: relay signals between neurons or groups of neurons, are responsible for the processing of information by the brain, like the logic circuits of a computer. also serve to relay signals from place to place within the central nervous system.

5. Define myelin sheathing and explain its function.Myelin Sheath is the insulating envelope of myelin that surrounds the core of a nerve fiber or axon and that facilitates the transmission of nerve impulses, formed from the cell membrane of the Schwann cell in the peripheral nervous system and from oligodendroglia cells. Also called medullary sheath.The main purpose of a myelin layer (or ''sheath'') is to increase in the speed at which impulses propagate along the ''myelinated'' fiber. Along ''unmyelinated'' fibers, impulses move continuously as waves, but, in myelinated fibers, they hop or "propagate by saltation."Myelin increases electrical resistance across the cell membrane by a factor of 5,000 and decreases capacitance by a factor of 50. Thus, myelination helps prevent the electrical current from leaving the axon.When a peripheral fiber is severed, the myelin sheath provides a track along which regrowth can occur. Unmyelinated fibers and myelinated axons of the mammalian central nervous system do not regenerate.

6. What is the all-or-nothing principle?The all-or-nothing principle Refers to the phenomenon where the strength of a nerve impulse is not dependent on the strength of the stimulus. Instead, there is a threshold level of stimulus strength that must be reached before the nerve will fire an impulse (at full capacity). Below the threshold, the nerve will not fire at all. In cardiology, it refers to the same phenomenon observed in the heart

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muscle, which will either contract fully or not at all. In studies of behavior, it refers to the same phenomenon where a behavioral stimulus will either produce a complete response or no response at all. Also called all-or-nothing phenomenon, all-or-none law, all-or-none responsiveness, etc.

7. Shortly after being released, what normally happens to neurotransmitters?When a nerve impulse reaches the end of the axon, the impulse makes some of the sacs fuse with the axon’s membrane. Each fuse sacs releases neurotransmitters into the synapse. The neurotransmitter molecules diffuse across the synapse and bind to receptors on the next neuron or effector cell.

8. How does a nervous impulse pass down a neuron?The passage of a nerve impulse through a neuron starts at a dendrite, it then travels through the cell body, down the axon to an axon terminal. Axon terminals lie close to the dendrites of neighboring neurons. When the nerve impulse reaches an axon terminal it causes the release of a chemical ( called a neurotransmitter ) that travels across the gap (the synapse) between a terminal and the dendrite of the neighboring neuron. Neurotransmitters stick to receptors in the neighboring dendrite and trigger a nerve impulse that travels down the dendrite, across the cell body, down the axon etc.

QUESTIONS FOR BONES AND MUSCLES1. What substances are found in skeletal systems? Explain their function.

Because bone is made up of minerals and it is hard, many people think that it is not living material. But a bone is a living animal consists of both living tissue and non-living substances. Within the "alive bone" are blood vessels, nerves, collagen, and living cells including: osteoblasts (cells that help form bone), and osteoclasts (cells that help eat away old bone). In addition, bone contains cells called osteocytes, which are mature osteoblasts that have ended their bone-forming careers. These cells engage in metabolic exchange with the blood that flows through the bones. The nonliving, but very important, substances in bone are the minerals and salts. Cartilage matrix has an affinity for basic dyes (basophilia). The principal constituents of ground substance are proteoglycans, which consist of protein combined with complex carbohydrates such as chondroitin sulfate and keratan sulfate. The acidic sulfate groups account for the basophilia of the matrix. The proteoglycans are themselves attached to hyaluronic acid to form giant molecules which form a hard gel because their strong negative charges repel the chains. They tie up almost all of the water molecules in cartilage and are attached as gigantic molecular complexes to collagen fibrils. Typically the concentrations of proteoglycans are higher right around the cells, giving bluer rings called territorial matrix. The paler matrix away from the cells is called inter-territorial matrix. Mineral is a substance that the body needs to carry out all of the bodily functions like thinking, breathing and moving around. One of the minerals that the body needs is calcium. Calcium is a major part of bone, and this is where the body stores its calcium. The less calcium the bone has, the weaker it will become. In case the body does not get enough calcium from the daily intake of food, it will take the calcium it needs from the bones. The skeleton holds up your body like the trunk on a tree.

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2. How do muscles work antagonistically?

Muscles work antagonistically when they work in opposition to each other. For example, a person uses certain sets of muscles to open his hand and splay his fingers wide. In order to close the hand and make a fist, however, an antagonistic set of muscles would have to be used. Antagonistic muscles are important for balance, extending limbs, holding objects aloft, and contracting limbs, among other things.

There are many groups of antagonistic muscles in the body. The most famous of these pairings is the biceps and the triceps on the arm. Additional antagonistic muscles include the chest and back of the torso, as well as the quadriceps and hamstrings of the leg.

3. The vertebral column is made of which types of vertebrae? Where are they example of each.The Vertebral Column (Spinal Column) supports the head and encloses the spinal cord.The spinal column is comprised of 26 individual bones; these bones are referred to as vertebrae. The spinal column is divided into 5 different areas containing groups of vertebrae and is grouped as follows:7 cervical vertebrae in the neck.12 thoracic vertebrae in the upper back corresponding to each pair of ribs.5 lumbar vertebrae in the lower back.5 sacral vertebrae which are fused together to form 1 bone called the sacrum.4 coccygeal vertebrae that are fused together to form the coccyx or tailbone.The vertebrae are referred to by their name and number, counting down from the top of the spinal column as follows:The cervical vertebrae are C1 - C7The thoracic vertebrae are T1 –T12The lumbar vertebrae are L1 – L5The sacrum and coccyx do not have numbers and each is thought of as one bone. Spinal nerves exit the sacrum and coccyx at levels (Foramen) within the main structure of each vertebra.

4. What is the function of the pacemaker?Pacemakers consist of a pager-sized housing device that contains a battery and the electronic circuitry that runs the device, along with one or two long thin electrical wires that travel from the pacemaker housing device to the heart. The housing device is implanted below the skin in the shoulder area. The thin wires, which can conduct electrical impulses, are then threaded from the housing device through a vein that runs in the chest, to the heart.In some patients, only one of these long, thin electrical wires, called leads, are implanted into one of the chambers of the heart. Most patients who receive pacemakers have two leads implanted, one going to the right atrium of the heart and one going to the right ventricle of the heart (this is shown in FigureThe pacemaker and leads can be programmed in several complex ways to analyze the heartbeat and then determine if the pacemaker should electrically stimulate the heart to contract.In the most common type of program, the electrical leads implanted in the right atrium and/or right ventricle can perform two functions. These leads can serve as sensors, detecting if electrical impulses generated by the SA node have occurred and if such electrical impulses have been conducted by the AV node down into the ventricle.The same electrical leads also can transmit an electrical impulse from the pacemaker's battery down into the right atrium and/or right ventricle. If the lead implanted into the right atrium does not

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detect that the SA node has fired and created an electrical impulse, the pacemaker sends an electrical impulse to the right atrium, taking over the function of being the heart's "spark plug."If the lead implanted into the right ventricle does not detect that an electrical impulse has made it through the AV node down into the ventricle, the pacemaker generates an electrical impulse that is conducted via the electrical lead in the right ventricle to the ventricles. In this manner, the pacemaker "supervises" the heart and ensures that it continues to contract at a rate adequate to pump sufficient blood throughout the body.

5. Describe muscle contraction and relaxation.

Many of our organs are made up of muscles that help them perform specific functions. Muscles can relax and contract. Relaxation and contraction of muscles cause movement of body parts. You can smile, frown, and wink your eyes due to the contraction of your facial muscles.

6. Explain the fundamentals of the sliding-filament theory.

A muscle consists of bundles of cylindrical, elongated cells called muscle fibers. Each muscle fiber consists of a plasma membrane called sarcolemma, surrounding the cytoplasm or sarcoplasm. The sarcoplasm contains mitochondria, sarcoplasmic reticulum, and hundreds or thousands of tiny fibers called myofibrils. Each myofibril consists of contractile portions known as sarcomeres that extend between two dark lines called the Z-line. A sarcomere contains two types of protein filaments actin and myosin. The striations of skeletal and cardiac muscles are due to the arrangement of these myofilaments. The light bands (I bands) are due to the thin actin filaments, while the dark bands (A bands) are due to the thick myosin filaments.

The shortening of the sarcomeres within the myofibrils causes contraction of a muscle. When a sarcomere shortens, the actin filaments slide past the myosin filaments and approach each other. As a result, the I bands shorten. It is important to note here that the length of the filaments does not change even as the sarcomere shortens. This movement of actin filaments in relation to myosin filaments is called the sliding filament theory.

QUESTIONS FOR THE INTERNAL TRANSPORT OF PLANTS 1. Describe the conducting tissues of plants.

The xylem is the principal water-conducting tissue of vascular plants. It consists of tracheary elements, tracheids and wood vessels and of additional xylem fibres. All of them are elongated cells with secondary cell walls that lack protoplasts at maturity. Bordered pits are typical for tracheids, while wood vessels are marked by perforated or completely dissolved final walls.

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The xylem takes also part in food storage, support and the conduction of minerals. Xylem and phloem together form a continuous system of vascular tissue extending throughout the plant. The principal conductive cells of the xylem are tracheary elements, of which there are two types, tracheids and wood vessels. Both are elongated cells with secondary cell walls that lack protoplasts at maturity. They are completed by the xylem fibres and parenchyma cells. Much speaks on behalf of the origin of xylem fibres and wood vessels from the tracheids.The other vascular tissue is the phloem. Its principal function is the conducting of assimilates and food. It is composed of the sieve elements, of which two types can be distinguished, sieve cells and sieve-tube members. Phloem elements do typically have sieve plates instead of final walls. Sieve-tube members of angiosperms are associated by living companion cells.The phloem is the principal food-conducting tissue of vascular plants. Its elements are elongated, just like those of the xylem. In contrast to tracheids and wood vessels, mature phloem elements contain a protoplast and sometimes even a nucleus. Phloem elements may be of primary or secondary origin though the early primary phloem, the protophloem, is frequently destroyed during elongation of the resepctive organ.The main conducting elements of the phloem are the sieve elements, of which there are two different types: sieve cells and sieve-tube members. Sieve cells have narrow pores, their sieve areas are quite uniform in structure, and they are distributed evenly on all walls. One of the principal differences between sieve cells and sieve-tube members is the presence of sieve plates in sieve-tube members, that are absent in sieve cells. Sieve cells are the only type of food-conducting cells in most seedless vascular plants and gymnosperms, whereas in angiosperms only sieve-tube members are present. Sieve-tube members occur end-on-end in longitudinal series called sieve tubes. They are in contact via plasmodesmata. Typically, the final walls are interspersed with primary pit areas (groups of plasmodesmata), that later on develop into sieve plates. Sieve tubes in the phloem of angiosperms are flanked by one or several plasma-rich, nucleated companion cells, that do not occur in gymnosperms.

2. What are the theories concerning how materials are conducted throughout plants? What is the function of the roots, and how do they work? Pressure-Flow Theory for Nutrient TransferAfter sugars are produced in photosynthesis, these sugars must be transported to other parts of the plant for use in the plant's metabolism. Part of the pressure-flow theory is that the sucrose produced is moved by active transport into the companion cells of the phloem in leaf veins. This raises the concentration of sucrose molecules in the companion cells above that in the sieve tubes, so they can then move into the sieve tubes by diffusion. With the concentration of sucrose now greater in the sieve tubes than external to them, water molecules will move into the sieve tubes near those photosynthesis locations by osmosis. With a larger amount of water in the tube, its fluid pressure will be higher than at distant locations in the tube, and the pressure difference will cause flow in those directions.At some distance from the photosynthetic source, there may be a region, say in a fruit, where sugar is needed. This theory suggests that the sucrose is transported into the fruit by active transport, raising the sugar concentration in the fruit relative to the sieve tube. In response to this concentration difference, water will follow the sugar into the fruit by osmosis.The movement of the water from the sieve tube into the fruit lowers the fluid pressure at that location, continuing to produce the pressure gradient that leads to bulk flow of water to the fruit, carrying the dissolved sugar with it.

Phloem, the Medium for Plant Energy Transfer

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In the stems of plants is a layer of living tissue called phloem that forms a medium for the movement of a sugar-rich fluid (sap) and which is therefore a key part of the energy transport within vascular plants. Part of the phloem is made up of sieve tubes which are constructed of specialized sieve tube cells with no nuclei. The sieve tubes permit the flow of sugar solution under the influence of a fluid pressure differential according to the pressure-flow theory. Phloem also contains companion cells for the sieve tubes which aid in the transport of sugars to the tubes.

3. The functions of the plant root system include: Anchorage and support. The plant root system anchors the plant in the soil and provides

physical support. Redwood trees (a gymnosperm) about 100 meters tall have stood erect for thousand years only because millions of individual fibrous roots dig into the ground, even though the depth of penetration is only up to about 5 meters. In general, however, taproot system provides more effective anchorage such that they are more resistant to toppling during storms.

Absorption and conduction. The plant root system absorbs water, oxygen and nutrients from the soil in mineral solution, mainly through the root hairs. They are capable of absorbing inorganic nutrients in solution even against concentration gradient. From the root, these are moved upward. Plants with a fibrous root system are more efficient in absorption from shallow sources.

Storage. The root serves as storage organ for water and carbohydrates as in the modified, swollen roots of carrot, sweet potato (camote) and yam bean (sinkamas). Fibrous roots generally store less starch than taproots. Some roots are capable of storing large amounts of water;

Photosynthesis. Some roots are capable of performing photosynthesis, as in the epiphytic orchids and aerial roots of mangrove.

Aeration. Plants that grow in stagnant water or other watery places have modified roots called pneumatophores to which oxygen from the air diffuses.

Movement. In many bulb- and corm-forming plants, contractile roots pull the plant downward into the soil where the environment is more stable.

Reproduction. The plant root system also serves as a natural means of perpetuating a species. In mature Norfolk Island pine and certain plants, suckers are commonly seen growing profusely around the trunk from horizontally growing roots.

QUESTIONS FOR CIRCULATORY SYSTEM1. Describe the similarities and difference between closed and open circulatory systems.

The circulatory system consists primarily of blood, the heart and a network of blood vessels. The main functions of the circulatory system are gas exchange, hormone and nutrient distribution, as well as waste elimination. The heart pumps the blood throughout the body, which is transported by the blood vessels to the necessary tissues and organs. Gas exchange involves spreading oxygen throughout the body and removing carbon dioxide waste. Oxygen must be delivered to all functioning body cells in order for them to metabolize, or carry out their functions and activities.

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Blood also transports helpful nutrients and antibodies so that the body's immune system may be healthy and responsive.

Open Circulatory SystemThe open circulatory system is the simpler of the two systems. Here, the heart pumps blood into open cavities, where blood vessels carry the blood throughout the body at a low pressure. There are two major differences between the open and closed system. First, the open system bathes all organs and tissues throughout the body with blood and, second, there are no arteries or major veins to increase blood pressure and direct distribution. Animals with an open circulatory system typically have lots of blood and low blood pressure.

Closed Circulatory SystemLarger and more active animals, including all vertebrates, have a closed circulatory system. This more complex system includes two major processes: pulmonary and systemic circulation. In the former process, deoxygenated blood is passed through the lungs in order to receive oxygen. Afterward, systemic circulation distributes the newly oxygenated blood throughout the body. In a closed circulatory system, blood is directed through arteries to veins throughout the body. As opposed to bathing all tissues and organs with blood, the blood remains in vessels and is transported at high pressures to all extremities of the body at a rapid rate.

Advantages of the Open SystemThe open circulatory system requires less energy for distribution. This system is more suited to animals that have a slower metabolism and a smaller body. Due to the absence of arteries, blood pressure remains low, and oxygen takes longer to reach the body cells. If an organism has a low metabolism, meaning it is generally less active in such processes as locomotion, digestion and respiration, it has less of a need for oxygen. Also, since oxygenated blood takes more time to reach the extremities of the body, the open system is only feasible in smaller animals.

Advantages of the Closed SystemThe closed system operates with a much higher blood pressure. In addition, it is more efficient in that it uses much less blood for even higher and faster levels of distribution. Since oxygenated blood may reach the extremities of the body much faster than with an open system, organisms with a closed system may metabolize much faster, allowing them to move, digest and eliminate wastes much more quickly. In addition, due to the efficient distribution of antibodies, immune responses are much stronger, helping the body to fight off infection more powerfully.

2. How does the insect tracheal system affect its circulatory system?In smaller, less active insects, tracheal gas exchange is by simple diffusion. Larger, more active insects such as grasshoppers improve upon diffusion by forcibly ventilating their tracheae, analogous to breathing in mammals. Contraction of abdominal muscles compresses their internal organs, forcing air out (like exhaling). Relaxation of abdominal muscles enables air to be drawn back in (like inhaling).Aquatic insects, whether adult or larva, also rely on tracheal tubes for gas exchange. Some insects, such as mosquito larvae, remain tied to the air and exchange gases at the water's surface. Others may bring a bubble of air under water with them. Even truly aquatic insect larvae—with gills through which O2 diffuses from the water—still transport the O2throughout the body with a gas-filled tracheal system.Because the tracheal tubes carry oxygen from the air directly to the cells, insects don't need to carry oxygen in their hemolymph, like mammals do in their blood. This is why insect hemolymph isn't red: the oxygen-carrying molecules (hemoglobin) make mammalian blood red.In the fish gill, low-oxygen blood enters the capillaries, encountering water at the end of its travel through the gills, which is thus relatively low in oxygen. As blood travels in the direction opposite to the water, it encounters

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"fresher" water with ever-higher oxygen concentrations. Thus, along the capillary, a steep diffusion gradient favors transfer of oxygen into the blood.

3. What is the role of the Malphigian tubules, and how do they interact with the circulatory system of what kinds of animals?Pre-urine is formed in the tubules, when nitrogenous waste and electrolytes are transported through the tubule walls. Wastes such asurea and amino acids are thought to diffuse through the walls, while ions such as sodium and potassium are transported by active pump mechanisms. Water follows thereafter. The pre-urine, along with digested food, merge in the hindgut. At this time, uric acid precipitates out, and sodium and potassium ions are actively absorbed by the rectum, along with water via osmosis. Uric acid is left to mix with feces, which are then excreted.Alternative modes of actionComplex cycling systems of Malpighian tubules have been described in other insect orders. Hemipteran insects use tubules that permit movement of solutes into the distal portion of the tubules while reabsorption of water and essential ions directly to the hemolymph occurs in the proximal portion and the rectum. Both Coleoptera and Lepidoptera use a cryptonephridial arrangement where the distal end of the tubules are embedded in fat tissue surrounding the rectum. Such an arrangement may serve to increase the efficiency of solute processing in the Malpighian tubules.

4. Compare and contrast several different types of hearts.

The different types of vertebrate hearts and how they evolved:

Two-Chambered Heart

All vertebrates have a closed circulatory system with one central heart. The oldest type of vertebrate heart is the two-chambered heart that is still used by all modern-day fish, like our little friend here. The two-chambered heart is a very muscular organ consisting of one atrium , which is a heart chamber that receives blood returning to the heart and one ventricle, which is a heart chamber that pumps blood out of the heart.

The two chambers are separated by a single one-way heart valve which ensures that blood travels in only one direction, out of the ventricle and into the blood vessels, where the blood makes a single loop through the circulatory system. First, the blood travels to the gills, the respiratory organ in fish that transfers oxygen from the surrounding water to the blood. The oxygen-rich blood then flows through the tissues, and finally, returns back to the heart.

Three-Chambered Heart

The two-chambered heart has served fish quite well for a very long time, but when amphibians evolved and crawled out onto land, a major evolutionary change took place in their circulatory system; they developed double circulation which basically means that they have two separate circuits of blood flow.

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One circuit, called the pulmonary circuit, leads to the respiratory organs to oxygenate the blood. The second circuit, called the systemic circuit, carries oxygenated blood to the various body tissues. As a result of the double circulation, amphibians have a three-chambered heart consisting of two atria and one ventricle.

Blood is pumped first through the pulmonary circuit where it is oxygenated and then returns to the heart through the left atrium. It then enters the left side of the common ventricle, and from there, most of the oxygen-rich blood is pumped through the systemic circuit to distribute the oxygen to the tissues before it is returned to the right atrium of the heart. From there the blood flows into the right side of the common ventricle before it is pumped back out into the pulmonary circuit.

Because the ventricle is shared by both circuits, some mixing of oxygen-rich and oxygen-poor blood does occur. However, mixing is reduced by the presence of a ridge in the centre of the ventricle that somewhat separates the left and right side of the ventricle.

Four-Chambered Heart

Once the three-chambered heart evolved, the logical next step in the evolution of the heart was to completely separate the ventricle into two distinct chambers to ensure that oxygen-rich and oxygen-poor blood from the two circuits do not mix. This evolutionary progression between three- and four-chambered hearts can be seen in various species of reptiles.

Reptiles generally have three-chambered hearts, but different species of reptiles have walls of varying sizes that partially separate the ventricle. The lone exceptions are the crocodile species, which have a complete septum, creating a four-chambered heart that is very similar to the four-chambered heart found in birds and mammals, including humans.

5. Follow the entire route of blood through a vertebrarate circulatory system.

The metabolic activity of any tissue is limited by its blood supply. The changes in metabolic activity associated with endotherm and the change from gill to lung respiration has led to changes in vertebrate circulatory systems.

Vertebrate Circulatory Systems

Vertebrates have evolved an intricate closed circulatory system that consists of a heart and three principal types of blood vessels: arteries, capillaries, and veins.

Arteries carry blood away from the heart and have thick, elastic, muscular walls that can dilate or contract to control blood pressure within the vessels. Because blood in the arteries has been relatively recently pumped out of the heart, arterial blood pressure tends to be high. The blood in arteries is usually rich in oxygen, since it is being pumped out to the body to provide oxygen and other nutrients to the cells. The only exceptions are the pulmonary arteries, which carry blood to the lungs to pick up its supply of oxygen. Since blood in the pulmonary arteries hasn’t yet reached the lungs, it is oxygen poor.

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Arteries are too large to service every little cell in the body. As arteries get farther from the heart, they begin to branch into smaller and smaller vessels, which eventually branch into thousands of capillaries. The walls of the smallest capillaries are only one cell thick, allowing nutrients, waste products, oxygen, and carbon dioxide to diffuse between the blood and the surrounding tissues. After providing nutrients and oxygen and picking up waste, capillaries begin to merge into larger and larger vessels, eventually converging into veins.

Veins carry blood toward the heart. The blood in veins is not pushed by pumping of the heart, so the blood pressure and forward momentum of the blood in veins is lower than in arteries. Blood in veins is largely pushed along by the contractions of the skeletal muscles as the organism moves around. To ensure that the blood in veins flows toward the heart, veins contain unidirectional valves. Venous blood has already provided nutrients to cells, so it is usually deoxygenated, giving it a characteristic blue color. The lone exception, once again, is the pulmonary veins. Since this blood is flowing back to the heart from the lungs, it is fully oxygenated and bright red.

6. What is the function of a lymphatic system?The lymphatic system helps to defend the body against disease, maintain fluid balance and absorb liquids from the intestine and transport them to the blood. It also collects and returns fluid that leaks from blood vessels and absorbs fats and vitamins. The lymphatic system also defends against invading microorganisms and disease.

QUESTIONS FOR BLOOD1. Analyze, compare, and contrast the contents of the blood of a vertebrate and an insect.

In vertebrates, blood is composed of blood cells suspended in a liquid called blood plasma. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume), and contains dissipated proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), and blood cells themselves. Albumin is the main protein in plasma, and it functions to regulate the colloidal osmotic pressure of blood. The blood cells are mainly red blood cells (also called RBCs or erythrocytes) and white blood cells, including leukocytes and platelets. The most abundant cells in vertebrate blood are red blood cells. These contain hemoglobin, an iron-containing protein, which facilitates transportation of oxygen by reversibly binding to this respiratory gas and greatly increasing its solubility in blood. In contrast, carbon dioxide is almost entirely transported extracellular dissolved in plasma as bicarbonate ion. Insects and some mollusks use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed circulatory system. In most insects, this "blood" does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen. Jawed vertebrates have an adaptive immune system, based largely on white blood cells. White blood cells help to resist infections and parasites. Platelets are important in the clotting of blood.[2] Arthropods, using hemolymph, have hemocytes as part of their immune system. Blood is circulated around the body through blood vessels by the pumping action of the heart. In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, and venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled. Medical terms related to blood often begin with hemo- or hemato- (also spelled haemo- and haemato-) from the Greek word αἷμα (haima) for "blood". In terms of anatomy and histology, blood is considered a specialized form of

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connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of fibrinogen.

2. How does blood clot?There are two major facets of the clotting mechanism – the platelets, and the thrombin system.The platelets are tiny cellular elements, made in the bone marrow, that travel in the bloodstream waiting for a bleeding problem to develop. When bleeding occurs, chemical reactions change the surface of the platelet to make it “sticky.” Sticky platelets are said to have become “activated.” These activated platelets begin adhering to the wall of the blood vessel at the site of bleeding, and within a few minutes they form what is called a “white clot.” (A clump of platelets appears white to the naked eye.) The thrombin system consists of several blood proteins that, when bleeding occurs, become activated. The activated clotting proteins engage in a cascade of chemical reactions that finally produce a substance called fibrin. Fibrin can be thought of as a long, sticky string. Fibrin strands stick to the exposed vessel wall, clumping together and forming a web-like complex of strands. Red blood cells become caught up in the web, and a “red clot” forms.A mature blood clot consists of both platelets and fibrin strands. The strands of fibrin bind the platelets together, and “tighten” the clot to make it stable.In arteries, the primary clotting mechanism depends on platelets. In veins, the primary clotting mechanism depends on the thrombin system. But in reality, both platelets and thrombin are involved, to one degree or another, in all blood clotting.

3. How does heart beat?The atria and ventricles work together, alternately contracting and relaxing to pump blood through your heart. The electrical system of your heart is the power source that makes this possible. Your heartbeat is triggered by electrical impulses that travel down a special pathway through your heart:

SA node (sinoatrial node) – known as the heart’s natural pacemakerThe impulse starts in a small bundle of specialized cells located in the right atrium, called the SA node. The electrical activity spreads through the walls of the atria and causes them to contract. This forces blood into the ventricles.The SA node sets the rate and rhythm of your heartbeat. Normal heart rhythm is often called normal sinus rhythm because the SA (sinus) node fires regularly.

AV node (atrioventricular node)The AV node is a cluster of cells in the center of the heart between the atria and ventricles, and acts like a gate that slows the electrical signal before it enters the ventricles. This delay gives the atria time to contract before the ventricles do.

His-Purkinje NetworkThis pathway of fibers sends the impulse to the muscular walls of the ventricles and causes them to contract. This forces blood out of the heart to the lungs and body. The SA node fires another impulse and the cycle begins again. At rest, a normal heart beats around 50 to 99 times a minute. Exercise, emotions, fever and some medications can cause your heart to beat faster, sometimes to well over 100 beats per minute.

4. What is blood pressure?

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Blood pressure (BP), sometimes referred to as arterial blood pressure, is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure. The blood pressure in the circulation is principally due to the pumping action of the heart. Differences in mean blood pressure are responsible for blood flow from one location to another in the circulation. The rate of mean blood flow depends on the resistance to flow presented by the blood vessels. Mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy. Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles. Gravity affects blood pressure via hydrostatic forces (e.g., during standing) and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure in veins.

QUESTIONS FOR NUTRITION1. Why is it necessary for food to be digested?

Food must be digested because the body cannot use food in the state that it is eaten to provide itself with nutrition and energy. Without the mechanical and biochemical process of digestion, foodstuffs would be removed from the digestive system unchanged, failing to provide cells and organs with substances necessary for survival. Digestion is a relatively complex process, and if any of the necessary enzymes or processes are missing or defunct, the body is at risk for malnutrition and digestive disease. The digestive system is equipped to utilize all nutrients of foods, like protein, carbohydrate and fat, in similar yet differing ways to obtain sustenance from each.

2. Describe some simple sugars and explain their nutritional value.

Synthetic SugarsCorn syrup and high fructose corn syrup are manufactured simple sugars. They are formed in chemical laboratories and food plants. These molecules are similar to simple sugars but are designed for additional shelf life and lower costs. These chemicals do not have any dietary benefits, and long term risks have not yet been completely established.

HoneyHoney is a natural sweetener. Honey does often have additional simple sugars added to it in order to make it sweeter. Honey is not hydrogenated, and there may be bacteria or other contaminates in the honey because of the lack of purification. Honey should not be given to children under 1 and should not be consumed by people with a compromised immune system.

FruitFruits taste naturally sweet because they are full of natural simple sugars. These simple carbohydrates are what make the fruit sweet and provide people with the natural burst of energy so common after eating fruit. Natural simple sugars are considered healthy because they also include natural plant and fruit fibers, provided the fruit is eaten and not just the juice.

3. Why are proteins important in a diet?Protein are compounds that help the body repair cells and grow. Each cell in the body incorporates protein, and it is also located in almost every body fluid. Protein is essential in a healthy diet.

4. What is the role of lipids in one’s diet?There are three different functions for lipids in our bodies: Energy storage Forming the membranes around our cells.

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Hormones and vitamins

5. What are vitamins and why are they important?Vitamins are organic substances. They are activating enzymes, which are proteins that act as catalysts to speed up biological reactions that take place in the body.

IMPORTANCE OF VITAMINSThe body needs a minimum amount of vitamins and minerals each day to remain healthy and function properly. A balanced diet normally supplies sufficient vitamins. However, serious disorders can still develop if the diet does not meet your body's needs. Symptoms of a deficiency in vitamins and minerals usually appear when the lack is already in a relatively advanced level. For instance, people who do not have enough of the vitamins A, B1 and B2 suffer from recurring tiredness, mental or emotional disturbances, loss of appetite and chapped lips, among others.The common causes of these vitamin deficiencies include poor eating habits, alcoholism, emotional stress, the improper absorption of vitamins and minerals (usually due to liver or intestinal disorders), the intake of medicines that interfere with the ingestion of vitamins and lack of exposure to sunlight. If you constantly feel sluggish and suffer from chronic health-related inconveniences, you might be short of the vitamins your body needs to function properly. Doctors will usually prescribe supplements that address the lack of vitamins and minerals in the body. However, also keep in mind not to overdo it, as an excess of vitamins can also be harmful. Do you still need to take vitamins even if you maintain a healthy diet? The answer is yes.Proper food consumption should be accompanied by the right vitamins and minerals. Vitamins serve as buffers in the event that your diet does not meet your daily requirements fully. Surely you can't calculate how much vitamins and minerals your body takes in with every meal you consume. And while most people take vitamins to avoid common deficiency-related diseases, not all products available cater to what your body requires. There are those that still lack what you need.The key components you must look for in a supplement are the vitamins B6, B12, D, E and folic acid. Aside from being dietary supplements, these so-called B vitamins have been known to help combat certain types of cancer and heart ailments. While there remains no hard-lined link between cancer and a daily intake of B vitamins, studies that suggest their preventive powers have helped raise the importance of daily doses of vitamins and minerals into our system.

6. What is the difference between a vitamin and a mineral?Vitamins are organic compounds and Minerals are inorganic. While Vitamins come from plants and animals, minerals are from soil and water. In chemical form, the minerals are much simpler than the vitamins. While all vitamins are needed for the body, all minerals are not needed.

7. What is thought to be the value of fiber in one’s diet? Relieves constipation/diarrhea. Fiber holds water; softens stool to prevent constipation; forms

gels to thicken stool to prevent diarrhea.

Hemorrhoid control. Softer stools ease elimination to prevent weakening of rectal muscles and protruding of swollen veins.

Weight control. Creates feeling of fullness that promotes weight loss; can be used as replacement for fats and sweets.

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Reduces colon cancer. Speeds movement through intestinal tract reducing exposure time of cancer-causing agents; does same for bile (associated with cancer risk).

Reduces blood lipids/cardiovascular disease. Binds bile, cholesterol, and other lipids to carry them out of the body.

Benefits blood glucose/insulin controls diabetes. Mildly stimulates insulin production and causes a gradual increase in blood glucose.

Controls appendicitis. Loosens stool to prevent packing in the appendix and possible infection.

Controls diverticulosis. Exercises digestive-tract muscles so that they retain their tone, resists bulging of the wall of the intestinal tract into pouches, called diverticula, that could be infected.

References

Books:

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Allen, Robert D. (1995). Biology a Critical Thinking Approach. Dubuque, IA: Wm. C. Brown Publishers

Campbell, Mitchell, Reece, Addison. (1997). Biology: Concepts and Connections. Canada. Wesley Longman Inc

Campbell, Neil A. Biology (Fourth Edition). California: The Benjamin/ Cummings Publishing Company, Inc.

Essenfeld, Gontang, Moore. (2004). Biology. Adison-Wesley Publishing Company

Hadsall, A. (2009). High School Science Today. Makati City: Diwa Learning Systems, Inc.

MacKever, S., Foote, M., et.al. (1997). Science Encyclopedia. London & Newyork: Dorling Kindersley

Miller, K., & Levine, J. (1998). Biology the Living Science. New Jersey: Prentice Hall Inc.

Padua, A. and Crisostomo, R. (2007). Year II: Functional Biology. Araneta Avenue, Quezon City: Vibal Publishing House, Inc.

Payawal, R., Alvarez, L & Coronado, A. et. al. (2012). Practical Biology: A Modular Approach 2nd edition.

Manila

Electronic Sources:

http://bioweb.wku.edu/courses/biol115/wyatt/biochem/lipid/lipid1.htm

http://www.healthguidance.org/entry/4588/1/The-Importance-Of-Vitamins-To-Your-Body.html

http://www.medphys.ucl.ac

http://www.stevenlewis.info/gs/loeb.htm