MOD.

TOPIC

NOTES

1

CELL STRUCTURE

CELL THEORY:

1. All living things are made of cells.

2. Cells are the basic structural and functional units of organisms.

3. All cells come from pre-existing cells.

TYPES OF CELLS:

Cells are often divided into certain groups based on major characteristics. One such grouping divides cells into prokaryotes and eukaryotes.

· PROKARYOTES

· Primitive cells.

· Much smaller and simpler than eukaryotic cells.

· More of them than eukaryotic cells.

· Four main structures

· Cell membrane

· Cytoplasm

· Ribosomes

· Genetic material.

· Pro = before, karyon = nucleus.

· No membrane surrounding genetic material i.e. no nucleus.

· Genetic material is found in a large loop (the bacterial chromosome) and as small circular structures (plasmids).

· This may be referred to as the nucleoid.

· Other structures found in a prokaryote include the cell wall, pili (hair like structures on the cell surface that allow the cell to adhere to surfaces), fimbriae (hair-like structures, often shorter than pili), flagella (whip-like tail to provide locomotion), and a capsule (layer of complex carbohydrates outside the cell wall, protects the cell).

· Most organisms composed of prokaryotic cells are usually unicellular.

· Prokaryotic organisms can be divided into two main groups – bacteria and archaea.

· Bacteria are widespread and can either be harmful or beneficial.

· Archaea live in harsh environments, subjected to extreme conditions such as hydrothermal vents and hot springs.

· EUKARYOTES

· Approx. 10-100µm.

· More complex than prokaryotic cells.

· Characterised by membrane bound organelles.

· Each organelle has a specific function within the cell.

· Together the organelles carry out all the biochemical processes and reactions of the cell such as respiration and photosynthesis.

· Can be multicellular or unicellular.

· Examples of unicellular eukaryotes include paramecium, amoeba and euglena.

· Multicellular plants and animals are composed of a variety of different types of eukaryotic cells.

· Possible origin of eukaryotic cells is the endosymbiotic theory:

· That some cells ate smaller cells but failed to digest them.

· The small cells (mitochondria from bacteria and chloroplasts from cyanobacteria) lived on inside their ‘host’ in a relationship that soon became mutualism (both organisms benefit), and later the ingested cells evolved to become organelles.

EARLY MICROSCOPES:

· The first compound microscope had two convex lenses at either end of a barrel and was invented by Hans and Zacharias Janssen.

· This led to Robert Hooke’s discovery of the cell.

MODERN MICROSCOPES – LIGHT MICROSCOPES:

· A light source passes through a condenser lens then through the specimen.

· The beam of light passes through the convex objective lens, the image is magnified and viewed through the ocular lens.

· Magnification of up to 1500x and maximum resolution of 200nm.

FLUORESCENCE MICROSCOPES:

· Better resolution than light microscopes.

· Sample is labelled with a fluorescent dye that attaches to particular structures.

· Sample is illuminated with a high-intensity source of light that causes the fluorescent substance to emit light.

ELECTRON MICROSCOPES:

· Revolutionised the study of microscopic organisms.

· Uses an electron beam instead of light and electromagnets instead of glass lenses.

· Greater resolution due to shorter wavelength.

· Many cell parts seen for the first time after the invention of the electron microscope.

· Two types:

· Transmission Electron Microscope (TEM)

· Electrons pass through the specimen.

· Produces 2D images.

· Most common form of electron microscope.

· Maximum magnification = 1 500 000x

· Resolution = 2nm

· Scanning Electron Microscope (SEM)

· Bombards solid specimens with a beam of electrons.

· Resolution = 10nm

· Produces 3D images.

COMPUTER-ENHANCED TECHNOLOGY:

· Microscope images can be digitally processed to allow cells to be viewed in different ways.

· Cell scan software can provide 3D images of cell structures.

DRAWING BIOLOGICAL DIAGRAMS:

1. Clear and simple drawing.

2. Sharp pencil.

3. Suitable size: large enough to allow detail to be easily drawn.

4. Size of parts should be in proportion to observed size.

5. Accurate drawing of significant feature of specimen; not an artistic impression, not shaded, not 3D (nucleus may be shaded if stained).

6. No unbroken lines for cell membranes or outside boundary of specimen.

7. Label structures – labelling lines drawn with a ruler and pencil, horizontal where possible and not crossing

8. Include a title, magnification and stain used.

9. If specimen is living, indicate movements made during observations.

ORGANELLES IN CELLS:

· Found in eukaryotic cells.

· Have internal structures enclosed by a membrane.

· Work together to enable the cell to work efficiently.

· Many organelles have maximised their surface area.

· Vary in size; some can be seen with the light microscope (nucleus, chloroplasts, vacuole in plant cells) whereas others can only be seen using an electron microscope (e.g. mitochondria).

CELL STRUCTURE:

ANIMAL

PLANT

ORGANELLES:

· Cell Membrane

· Surrounds cell contents and separates it from its surroundings.

· Controls the passage of water and other chemicals into and out of cells.

· Selectively permeable barrier (semi-permeable).

· Found in plant and animal cells.

· Cytoplasm

· Fluid part of cell.

· Incorporates cytosol (watery liquid) and the organelles (excluding the nucleus).

· The cytosol is the watery medium containing dissolved solutes (not organelles).

· Nucleus and Nucleolus

· Large oval or spherical, generally in the centre of the cell.

· Contains genetic material (found as DNA and proteins).

· Acts as control centre of cell.

· Nuclear membrane is made up of two membranes.

· Inner membrane attaches to proteins to provide support for chromosomes.

· Outer membrane is continuous with endoplasmic reticulum.

· Nucleolus is a small structure within the nucleus where ribosomes are assembled.

· Some eukaryotic cells do not have a nucleus e.g. mature red blood cells and xylem cells.

· Ribosomes

· Only visible under an electron microscope.

· Composed of proteins and ribosomal RNA (rRNA).

· Site of protein synthesis.

· Do not have a membrane surrounding them.

· Found free in the cytosol or bound to endoplasmic reticulum (forming rough endoplasmic reticulum, RER).

· Endoplasmic Reticulum

· A network of parallel membranes forming connecting tunnels throughout the cytoplasm connecting the cell membrane and nuclear membrane.

· Forms a communication system (important for transport of proteins, steroids and lipids) that is central to many chemical reactions).

· Rough ER

· Has ribosomes attached.

· Proteins such as hormones are synthesised, distributed to the Golgi apparatus and then secreted outside the cell.

· Smooth ER

· Produces lipids, steroids and hormones such as cholesterol and testosterone.

· Small vesicles containing products of SER are transported to the cell membrane or Golgi.

· Golgi Apparatus

· Consists of stacks of flattened membranous vesicles formed from the ER.

· Transport vesicles containing products and lipids bud off from RER and SER and fuse with the Golgi where their contents are modified and repackaged for later use.

· Lysosomes

· Single membrane bound organelles formed by the Golgi apparatus.

· Contains a variety of enzymes.

· Fuses with food vacuoles, release their enzymes and digest food.

· White blood cells contain many lysosomes to enable them to digest engulfed bacteria.

· Involved in autolysis (self-digestion), which occurs during human development.

· Rarely found in plant cells.

· Mitochondria

· Once were separate prokaryotes before becoming organelles.

· Double membrane; smooth outer membrane and folded inner membrane.

· Highly folded structure of the inner membrane increases surface area for chemical reactions.

· Central matrix contains enzymes for cellular respiration.

· Also contains double stranded DNA.

· Plastids

· Found in plant cells and algal cells.

· Responsible for manufacturing and storing complex chemical compounds.

· Contains DNA, chloroplasts and leucoplasts.

· Chloroplasts

· Elliptical shape with a double membrane.

· Contains chlorophyll, found on the thylakoid membrane.

· Chlorophyll absorbs light energy and converts it into chemical energy through various reactions.

· Contains interconnecting stacked discs of thylakoid membrane called grana, which is where the light dependent reactions of photosynthesis occur.

· Vacuoles

· Large, permanent, fluid-filled sacs in the cytoplasm of mature cells.

· Consist of watery solution called cell sap surrounded by a single membrane.

· Important for support as when filled with water the vacuole pushes outwards with the cytoplasm, exerting a pressure on the cell wall, keeping it firm.

· Small temporary vacuoles may be found in animal cells but are not for support.

· Cytoskeleton

· The distribution and arrangement of organelles inside a cell is due to a network of tiny microtubules, microfilaments and intermediate filaments.

· These make up the cytoskeleton.

· Provides a framework for the shape of the cell, cell movement, cell division and organelle movement.

· Cell Wall

· A rigid structure that surrounds the cell membrane of plant cells, fungal cells and some prokaryotic cells.

· Fungal cell walls are made of chitin.

· In plants, cell walls are made of cellulose.

· Provides support, prevents expansion of the cell and allows water and dissolved substances to pass freely through it.

· Lignin can also be found in cell walls of woody plants, especially the xylem, where it adds strength.

REGULATING THE INTERNAL ENVIRONMENT OF CELL MEMBRANES:

· Commonly regulated aspects of the internal environment include:

· Temperature

· Oxygen concentration

· Carbon dioxide concentration

· Nitrogenous waste concentration

· pH

· Osmotic pressure

· Glucose concentration

PHOSPHOLIPIDS:

· Molecules are made up of hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

· The bilayer has 2 layers of phospholipids.

· Hydrophilic heads form the outside and inside lining of the cell membrane and hydrophobic tails meet in the middle.

· Due to their structure, phospholipids react to the presence of water.

FLUID STRUCTURES:

· Cell membranes are fluid structures.

· Individual phospholipids are free to move about within layers.

· They rarely cross from one side of the membrane to the other.

· The level of membrane fluidity depends on the percentage of unsaturated fatty acids in the phospholipids; the greater the percentage, the more fluid the membrane.

FACTORS AFFECTING THE MEMBRANE:

· Temperature

· As temperature increases, fluidity increases.

· Phospholipids become less tightly packed and move more freely.

· As temperature decreases, cell membranes with a high percentage of saturated fatty acid chains may solidify.

· Cholesterol

· More cholesterol leads to more fluidity.

· Reduces the permeability of the cell membrane to small, water soluble molecules.

· Proteins

· Carbohydrates

· Play a role in recognition of antibodies, hormones and viruses by cells.

CELL FUNCTION

MOVEMENT ACROSS THE MEMBRANE DEPENDS ON:

· Chemical properties of the material being moved.

· Physical properties of the molecules such as size and shape.

· Permeability of the cell membrane to the material.

· Concentration gradient across the membrane – the higher the gradient, the faster the movement.

· Surface-area-to-volume ratio.

CELL MEMBRANE PERMEABILITY:

· This is the ability of a cell membrane to allow the exchange of liquids and materials between the internal and external environment of a cell.

· The cell membrane is semi-permeable; it is selective.

· Many different types of molecules can pass across the membrane.

· The way in which this happens depends on the type of molecule.

DIFFUSION:

· Particles in a solution move from an area of high concentration to an area of low concentration, along a concentration gradient.

· Many particles collide with each other during the process, so overall movement is very slow.

· Observed when a drop of ink is placed in a jar of still water, as the dye particles move randomly throughout the water until the colour is homogeneous.

· Diffusion is a passive process as it does not require energy.

· Factors affecting rate of diffusion.

· Concentration

· Temperature

· Particle size

· Diffusion across membranes (simple diffusion)

· Solute membranes diffuse across a membrane if the membrane is permeable to them.

· Movement is constant, back and forth, across the membrane.

· If the concentration of solute is equal on both sides, there is no net movement.

· If concentration of solute is higher on one side than the other, the net movement of solute particles will be from high to lower concentration.

· If the membrane is semipermeable then there will be no movement of solute down the concentration gradient.

· Facilitated Diffusion

· Membrane transport proteins are specific for particular particles, so transport is selective.

· Transport is more rapid than simple diffusion.

· Transport proteins can become saturated as the concentration of the transported substance increases.

· Transport of a particle may be inhibited by the presence of another particle.

· No energy is required, movement is down a concentration gradient.

CARRIER PROTEINS AND CHANNEL PROTEINS:

· Channel proteins

· Proteins may provide a channel for the water-soluble particles and ions to travel through.

· The channel is specific for a particular substance.

· Channel proteins do not bind to the particle being transported.

· They function like pores; they open and close.

· Carrier proteins

· Undergoes a shape change allowing the specific molecule to be transported across the membrane.

· They bind the molecules being transported.

· After transport, the carrier protein returns to its original shape.

OSMOSIS:

· The net movement of water molecules across a semipermeable membrane.

· If a dilute and concentrated solution are separated by a semipermeable membrane which allows the movement of free water molecules, the water molecules will move from the dilute solution to the concentrated solution.

· This movement is along a water concentration gradient, known as the osmotic gradient.

· The pressure causing water to move is called osmotic pressure.

· Osmosis in animal cells

· The cell membrane is permeable to water so if cells are placed in freshwater, an osmotic gradient will draw water into cells.

· This is because the cytosol is a concentrated solution containing many dissolved substances.

· Osmosis in plant cells

· If a plant cell is placed in freshwater, it will take in water by osmosis and swell to some extent, however the cell wall prevents it from bursting.

· Plant cells with a high internal pressure are said to be turgid.

ACTIVE TRANSPORT:

· Cells using energy to transport particles across the cell membrane.

ENDOCYTOSIS:

· Occurs by active transport.

· Cells take in materials in bulk, forming vesicles in the cell membrane.

· A small area of the membrane sinks inwards forming a pocket.

· Materials near the membrane are enclosed by the membrane as it pinches off to form a vesicle.

· 3 Types:

· Phagocytosis

· Pinocytosis

· Receptor-mediated endocytosis

EXOCYTOSIS:

· The movement of secretory vesicles towards the cell membrane and the release of its contents.

· Occurs due to the dynamic and fluid nature of the membranes.

· Used for secreting proteins, release of cellular waste and breakdown products from lysosomes.

SURFACE-AREA-TO-VOLUME RATIO:

· SAVR =

· This affects the movement of substances into and out of cells through the cell membrane.

· Surface area of a cell is the total area of the cell membrane.

· The volume of a cell is the space taken up by the internal contents.

· A cell must have sufficient surface area to supply its volume with requirements and remove waste.

· Small cell = large surface area in comparison to its volume, hence a high SA:V ratio.

· As the cell size continues to grow it reaches a point where diffusion is not fast enough to sustain the cell, so the cell divides if it’s possible.

· This is why individual cells remain small.

INCREASING THE SA:V RATIO

· Cell Compartmentalisation

· Reduces the amount of exchange that needs to occur across the cell membrane to maintain an environment suitable for all cell functions.

· Creates more space for membrane-bound enzymes, allowing increased activity in the cell.

· Flattened Shape

· Flattening a shape keeps the volume constant but increases surface area.

· For example, red blood cells and lung epithelium.

· Cell Membrane Extensions

· Works well for cells involved in absorbing nutrients or secreting wastes.

· For example, microvilli and root hair cells.

SUITABLE FORMS OF ENERGY

· Autotrophs (“self-feeders”)

· Make organic compounds from inorganic compounds in the soil and atmosphere.

· Conversion is called carbon fixation.

· Called producers.

· Includes all green plants that carry out photosynthesis.

· Carry out both photosynthesis and cellular respiration.

· Heterotrophs (“other feeders”)

· Obtain organic compounds by consuming other organisms.

· Called consumers.

· Includes all animals and fungi.

· Only use cellular respiration.

· Both autotrophs and heterotrophs use matter to produce energy required for biological processes.

· Photosynthesis and cellular respiration are reactions that transform matter into energy.

CELL REQUIREMENTS – MATTER

· Inorganic Compounds

· Water (H2O)

· Important solvent and transport medium.

· Oxygen (O2)

· Needed for efficient energy supply from cellular respiration.

· Taken in as gas or in solution.

· Carbon Dioxide (CO2)

· Ultimate source of carbon atoms for organic molecules.

· Nitrogen (N2)

· Key atom in the acids that make up proteins.

· Minerals

· Important for building enzymes and vitamins.

MOD.

TOPIC

CONTENT

2

ORGANISATION OF CELLS

COLONIAL, UNICELLULAR AND MULTICELLULAR ORGANISMS:

· UNICELLULAR ORGANISMS

· First life forms – arose more than 3.8 billion years ago.

· A single cell carries out all life processes, including obtaining nutrients, exchanging gases, removing waste and reproducing.

· May live together in groups, however each cell is still capable of breaking away and living independently.

· EXAMPLES: Prokaryotes such as Escherichia coli and eukaryotes such as euglena.

· COLONIAL ORGANISMS

· A group of cells or organisms working collectively is called a colony.

· Colonial organisms may be unicellular or multicellular.

· Cells of unicellular colonial organisms can exist independently; however, the cells of multicellular colonial organisms cannot exist alone (but the multicellular organism itself can).

· EXAMPLES: Volvox, coral and jellyfish.

· MULTICELLULAR ORGANISMS

· A community of cells working together to enable the organism to carry out life processes, including reproduction.

· Consists of eukaryotic cells.

· Large organisms made up of smaller cells increases SA:V ratio.

· Each specialised cell type is structurally suited to a particular function.

· FORMATION OF SPECIALISED CELLS

· When cells become specialised they differentiate – they develop structures enabling them to carry out their function, making them different to other cells.

· Specialised cells originate from stem cells, which are undifferentiated cells with the ability to divide repeatedly.

· Cell specialisation refers to the role/function of the cell, while differentiation is the process of a stem cell goes through to become specialised.

· Enables organisms to grow larger while still efficiently carrying out processes.

· Specialised cells cannot survive independently – they rely on other cells in the organisms to carry out functions they cannot.

· Communication between cells is vital.

· In animals this is via the blood stream and nervous system whereas in the plants it is brought about by chemical and physical contact between cells.

ORGANS, TISSUES + SYSTEMS

· Organelle Cell Tissue Organ Organ System Organism

· EXAMPLE: Mitochondria Cardiac Muscle Cell Cardiac Muscle Tissue Heart Cardiovascular System Human

· ANIMAL CELLS

· TISSUES

· Epithelial Tissue

· Covers body surfaces, protects organs and forms glands.

· Densely packed cells in single sheets or layers.

· Doesn’t contain blood vessels.

· 2 distinct surfaces – exposed to the exterior body cavity or exposed to adjacent tissue.

· Some are specialised for absorption or secretion.

· Connective Tissue

· Varies greatly in form and function.

· Comprises extracellular matrix with cells scattered through it.

· Matrix made up of collagen fibres (strength) and elastin (flexibility) and a substance that fills the space.

· Nervous Tissue

· Comprises brain, spinal cord, peripheral nerves.

· Nervous tissue is highly specialised for communication between all parts of the body.

· Neurons are highly specialised and consist of multi-branched dendrites and axons extending from the cell body.

· Branches increase the surface area to receive messages.

· Muscle Tissue

· Contain muscle cells called muscle fibres, which are highly specialised.

· 3 types of muscle cells – skeletal, cardiac and smooth.

· All contain proteins actin and myosin which interact to cause cells to lengthen and shorten.

· SKELETAL: Long fibres with striations. Attached to bone, contractions lead to movement. Require conscious thought to function.

· CARDIAC: Present in the heart, also have striations. Connection junctions between cells for coordinated heartbeat. Function automatically.

· SMOOTH: No striations. Their contractions move substances through specialised organs e.g. through intestines. Functions automatically.

· PLANT CELLS

· TISSUES

· Meristematic Tissue

· Tips of roots and shoots.

· Cells divide leading to growth.

· Cells are small and cube-shaped.

· Site of cell differentiation.

· Dermal Tissue

· Protects plant tissues, found on outer layers of stem, roots and leaves.

· Epidermal layer is outermost, secreting a waxy layer called the cuticle, vital to reduce water loss.

· Most epidermal cells lack chloroplasts.

· Some can produce fine hairs to trap air, reducing water loss.

· Epidermal cells in the root have hairs to increase surface area for water uptake.

· Vascular Tissue

· Responsible for transport of systems.

· Xylem transports water and minerals from roots to leaves, phloem transports products of photosynthesis from leaves to the rest of the plant.

· Ground Tissue

· Internal cells of a plant other than vascular tissue.

· Makes up the bulk of plant tissue.

· Consists of a variety of cells for storage, support and photosynthesis.

NUTRIENT AND GAS REQUIREMENTS

AUTOTROPHS AND HETEROTROPHS

AUTOTROPHS:

· Produce their own organic compounds and energy from inorganic compounds from their environment, such as carbon dioxide and water.

· Can be divided into two groups:

· Photoautotrophs – use light energy (e.g. green plants).

· Chemoautotrophs – use chemical energy (e.g. nitrifying bacteria in the soil)

HETEROTRROPHS:

· Obtain organic compounds by consuming other organisms.

· Heterotrophs include all animals and fungi.

VASCULAR AND NON-VASCULAR PLANTS

· Majority of autotrophic organisms are plants.

· Vascular plants possess a transport system to move substances from one part of the plant to another.

· A small number of plants are called non-vascular because they do not possess this transport system (e.g. mosses and liverworts).

· Have a very simple structure.

· All nutrients are absorbed, and wastes are removed by diffusion and osmosis through the surfaces of the plant.

CELLS, TISSUES, ORGANS AND ORGAN SYSTEMS

· Plants have specialised cells grouped into tissues.

· These tissues form organs that carry out particular functions to support the effective and efficient functioning of the plant e.g. transport, photosynthesis, gas exchange.

· These organs are part of the organ systems:

· THE ROOT SYSTEM

· Usually underground.

· The main function of anchoring the plant and absorbing water and inorganic nutrients from the soil.

· Very large surface area.

· Absorption occurs through specialised epidermal cells in the outermost layer of the root.

· Increased surface area achieved in the following ways:

· Extensive branching (also provides good anchorage)

· Root hair zone located in the younger part of each root – epidermal cells protrude outwards into the surrounding soil, as microscopic extensions called root hairs.

· Flattened epidermal cells increase the exposed surface.

· Water moves via osmosis.

· Mineral ions usually move via diffusion – if diffusion is too slow, facilitated diffusion and active transport may be involved.

· Root cells have no chloroplasts and thus cannot photosynthesise, but they can carry out respiration,

· THE SHOOT SYSTEM (Stems)

· Located above ground

· Main function is to provide structural support and a transport pathway between the roots and leaves.

· Contains three types of tissue:

· Dermal Tissue: Outer layer of the stem and provides waterproofing, protection and control of gas exchange.

· Vascular Tissue: Composed of xylem and phloem tissue arranged in structures called vascular bundles.

· Provide structural support and enable transport of materials.

· Arrangement of vascular tissues vary between different plant species.

· Ground Tissue: Fills in around the vascular tissue.

· THE SHOOT SYSTEM (Leaves)

· Located above ground

· Main function is to absorb sunlight and carbon dioxide and produce glucose through the process of photosynthesis.

· Leaves are adapted to absorb the maximum amount of sunlight possible to provide the energy needed to break bonds in water during the first stage of photosynthesis.

· Thin, flat structure of leaves is well suited to this function – no internal cell is too far from the light.

· Large SA allows maximum absorption.

· Transparent epidermis allows sunlight to penetrate the photosynthetic cells beneath.

· Mesophyll is responsible for most of the plants photosynthesis.

· Palisade Cells: Dense with chloroplasts and are main photosynthetic cells, situated vertically, large number ensures maximum rate of photosynthesis.

· Spongy Mesophyll Cells: Irregular in shape and distribution, situated between palisade cells and lower epidermis, fewer chloroplasts.

· Leaves are also the site of transpiration, which is a process by which water evaporates from the leaf and aids the movement of water from the roots to the leaves and cools the plant.

· The structure of a leaf allows it to carry out these functions in an efficient and effective manner.

· Sizes and shapes of leaves vary immensely.

· Plants in hot, dry habitats have:

· Waxy Cuticles – reduce the amount of water lost through evaporation.

· Small Leaves – minimal surface area to reduce water loss.

· Rainforest Plants have:

· Large, Thin, Flat Leaves – absorb as much sunlight as possible.

· Less concern about water loss due to high humidity.

· Gaseous Exchange:

· Epidermis covers the surface of leaves.

· Epidermal cells protect the inner tissues and are able to secrete a waterproof cuticle to prevent evaporation of water.

· Epidermal cells are transparent to allow light to pass to the cell layers beneath.

· Guard Cells – control exchange of gases and the loss of water through leaves, occur in pairs surrounding the stoma (plural = stomata).

TRANSPORT:

· Main transport tissues are in the vascular tissue (xylem and phloem) in the centre of the root.

· The main vein in the leaf is the midrib and many smaller veins branch out from it.

· Distribution of vascular tissue throughout the leaf ensures no leaf cells are too far away from a source of transport.

· Vascular tissue also plays an important role in supporting the thin leaf blade.

CELLULAR RESPIRATION IN PLANTS:

· Plants carry out cellular respiration as well as photosynthesis.

· Occurs during the day and night.

· During the day:

· O2 for cellular respiration comes produced as a by-product of photosynthesis.

· Any O2 not used is released by the plant to outside environment.

· CO2 released is used as reactant in photosynthesis.

· When the rate of photosynthesis is high, this CO2 supply is usually insufficient, so the plants absorb it from the air instead.

NUTRIENT REQUIREMENTS IN PLANTS:

· Carbon Dioxide

· The opening and closing of the stomata has the greatest effect on carbon dioxide concentration in the leaf.

· If the stomata is closed, available carbon dioxide is used up and the rate of photosynthesis is reduced.

· Water

· Amount of water needed for photosynthesis is small compared to that needed for survival.

· When water availability level is low, stomata close and reduce amount of carbon dioxide entering the leaf, reducing the rate of photosynthesis.

· Light Energy

· The greater the light intensity the faster the rate of photosynthesis until a plateau is reached.

· The plateau is where all photosynthesis systems and enzymes are working at optimum rate.

PHOTOSYNTHETIC OUTPUTS:

· Oxygen

· Used as a measure of the rate of photosynthesis.

· Influenced by both the rate of photosynthesis and the amount of oxygen used in respiration.

· Glucose

· Measured directly using biomass

· Can be indirectly measured using starch levels.

EXPERIMENTS:

· Joseph Priestly (1733 – 1804)

· Jar Experiment – one jar with a mouse and a candle, the flame goes out and the mouse dies.

· Another jar with a mouse, candle and mint plant – the flame stays lit and the mouse lives.

· Proved that plants emit oxygen.

· Jan Ingenhousz (1730 – 1799)

· Similar to Priestly except included the concept of light.

· Concluded that light was needed for photosynthesis to occur.

HUMAN DIGESTIVE SYSTEM:

· Digestion is the breakdown of large complex molecules into smaller simpler particles which can be absorbed.

· Mechanical Digestion is the physical breakdown of food into smaller pieces.

· Starts with the teeth, churns in the stomach.

· Increases surface area of food for the action of enzymes.

· Chemical Digestion is the process of using digestive enzymes to chemically breakdown large, complex food molecules into smaller, simpler forms.

· Obtains:

· Glucose from complex carbohydrates

· Amino acids from proteins

· Fatty acids and glycerol from lipids

· Nucleotides from nucleic acids

· Pathway through the digestive system:

· Mouth

· Digestion begins as teeth break up food into smaller pieces with a greater surface area.

· Salivary amylase is released and is mixed with food by the tongue.

· Complex carbohydrate starch sugar maltose

· Tongue forms a bolus which is swallowed and enters the oesophagus.

· Oesophagus

· Bolus travels along the oesophagus to the stomach.

· Entrance of trachea is covered by epiglottis.

· Muscular contractions (peristalsis) move the food towards the stomach.

· Stomach

· Narrow openers = sphincters control the movement of substances into and out of the stomach.

· Relaxation and contractions of muscles continue mechanical digestion.

· Bolus breaks up and combines with gastric juices forms chyme.

· Gastric juices contain water, hydrochloric acid, pepsinogen and pepsin.

· Interior of the stomach = pH2.0-3.0

· Pepsinogen is converted into active pepsin, which breaks down long chain proteins into shorter peptide chains and breaks down nucleic acids in food.

· Small Intestine

· Approx. 7m long divided into three sections – duodenum, jejunum and ileum.

· Chyme enters via pyloric sphincter.

· Release of pancreatic juices.

· Contains amylase, trypsin, lipase and bicarbonate ions.

· Bile is released into the duodenum.

· Produced in the liver and stored in the gall bladder.

· Emulsifies fats into smaller droplets.

· Food enters the jejunum where most of the absorption takes place.

· Amino acids, glucose, fatty acids and glycerol move into transport systems in the small intestine.

· Move by diffusion and active transport.

· Villi greatly increase the surface area for absorption.

· Lacteals are connected to the lymph system.

· Glucose and amino acids are absorbed into capillaries while fatty acids and glycerol are absorbed into the lacteal.

· Liver

· Once absorbed, digested food is transported to the liver.

· Important for metabolism.

· Keeps sugars, glycogen and protein levels balanced.

· Detoxifies the blood.

· Large Intestine

· Undigested material moves to the large intestine.

· Colon

· Site of water and salt absorption.

· Undigested material compacts.

· Bacteria produces vitamins A and K, which are absorbed into the bloodstream.

· Rectum

· Remaining undigested material (faeces) moves into the rectum by peristalsis and is eliminated through the anus.

GAS EXCHANGE IN PLANTS

· Leaves are adapted for gas exchange.

· Large and flat – large SAV ratio.

· Spongy mesophyll layer increases surface area and allow gases to move freely within the leaf.

· Surface of cell is moist

· Occurs through stomata and the lenticels.

· Stomata:

· Found on the underside of the leaf.

· Occasionally found on the upper epidermis.

· Either side of stomata are the guard cells.

· These bean-shaped cells contain chloroplasts (unlike other epidermal cells)

· The inner wall of each guard cell is thicker than the outer wall.

· Stomata open and close when the guard cells gain or lose water.

· Lenticels:

· Pores through which gaseous exchange happens in woody plants

· Found on trunks and branches of trees and woody shrubs

· Appear as small dots, but under the microscope they are seen as clusters of loose cells in the cork layer

· Diffusion through lenticels is relatively slow

GAS EXCHANGE IN ANIMALS

· Oxygen is essential for cellular respiration.

· Carbon dioxide must be removed as it is toxic in high concentration.

· Mammals have lungs, fish have gills and insects have tracheal systems.

· Large surface area enhanced by folding, branching or flattening.

· Moist, thin surfaces so that gasses can dissolve and diffuse.

· Close proximity to transport system so gases can move easily.

· Maintenance of a concentration gradient.

· LUNGS:

· Gas exchange structures = alveoli

· Increased surface area – folded

· Thin lining – flattened single layer of cells

· Moist surfaces – saturated with water vapour and mucus

· Maintenance of concentration gradient – refreshed through breathing, blood supply removes and delivers gases.

· Each alveolus is connected to the outside and is surrounded by capillaries.

· GILLS:

· Concentration of gases in water are lower than their concentrations in the air.

· Fish possess gills which allow them to extract the maximum amount of oxygen.

· Require water to flow constantly over the gills.

· TRACHEAL SYSTEMS:

· Insects take in and expel air through spiracles.

· Do not have lungs or blood capillaries.

· Branching air tubes called tracheal tubes.

· Number of open spiracles determines the rate of respiration.

· Muscular movements of the thorax and abdomen help ventilate the tracheal system.

TRANSPORT

TRANSPORT SYSTEMS IN PLANTS

· Involves vascular tissue arranged in vascular bundles made up of phloem and xylem tissue.

· XYLEM:

· Movement upwards from the root.

· Consists of xylem tracheids and xylem vessels.

· Tracheids: long structures with tapered end walls in contact with each other.

· Xylem vessels are continuous tubes for the transport of water.

· Walls of vessels and tracheids are lined with lignin – helps prevent the collapse of the vessel and easy movement of water.

· Fibres provide support.

· PHLOEM:

· Sieve tube cells and companion cells.

· Sieve tube cells are long thin phloem cells with large pores through their end cell walls.

· These perforated cell walls are called sieve plates

· Sieve tube cells possess mitochondria and endoplasmic reticulum, but no nuclei or other organelles

· They are arranged end to end forming sieve tubes

· Sieve tube cells share cytoplasm, their sieve tubes form channels through which sugars and other plant products can flow

· Companion cells are found alongside sieve tubes.

· They have a nucleus and other organelles that are lacking in sieve tubes.

· Companion cell function is uncertain, but they are thought to assist effectiveness of sieve tube elements by providing ATP.

· They also help with loading and unloading of sugars into sieve tubes

THE TRANSPIRATION-COHESION-TENSION THEORY

· Concentration of water outside the leaf is lower than inside the leaf

· Water diffuses out of the leaf (transpiration)

· The water lost is replaced by water from the surface of mesophyll cells

· This increases the surface tension of water on the outside of the mesophyll cells

· Water is drawn in from the xylem tissue in the veins to replace lost water

· This increases the tension on the column of water in the xylem, drawing more water up from the roots (like a drinking straw)

THE SOURCE-SINK THEORY:

· Glucose produced in the leaf during photosynthesis is either stored as starch or converted to sucrose and distributed to all parts of the plant

· Distribution is called translocation and occurs in the phloem

· Substances in the phloem move in whichever direction is required.

· The phloem also carries amino acids and some mineral nutrients

· Sucrose makes up approx. 90% of phloem sap.

· Once it reaches cells is it converted to glucose for respiration or stored as starch

· The movement is driven by the formation of high- and low-pressure regions within the phloem

· Movement occurs from high to low pressure

· High-pressure occurs where the sucrose is produced (the source) and low-pressure occurs where the sucrose is required (the sink)

TRANSPORT SYSTEMS IN ANIMALS:

· Cardiovascular System:

· Made up of blood, heart and blood vessels.

· Lymphatic System:

· Transports excess fluid back into the cardiovascular system and is made up of lymph vessels and lymph.

· Open Circulatory Systems:

· Heart/s and open-ended blood vessels.

· Blood is pumped into cavities which surround organs.

· Blood is returned to heart.

· Not as efficient as closed systems.

· Transport fluid = haemolymph

· Closed Circulatory Systems:

· Found in all vertebrate animals.

· Made up of blood vessels and a heart in a sealed system.

· Transports nutrients and oxygen to cells while transporting waste and carbon dioxide away from cells.

THE HEART

· Mammals have a four chambered heart.

· Top chambers = atria (atrium).

· Bottom chambers = ventricles.

· Left and right sides of the heart are separated by a muscular wall (septum).

· Each side beats simultaneously.

· One-way direction of blood flow.

· Composed of cardiac muscle tissue – produces heartbeat when it contracts.

· Left ventricle pumps blood to all areas of the body and therefore has much thicker muscular walls.

· Right ventricle only pumps deoxygenated blood to lungs.

· Deoxygenated blood returns from the body to the right atrium via two large veins, the superior vena cava and the inferior vena cava.

· In the pulmonary artery carbon dioxide diffuses into the alveoli and oxygen diffuses from the alveoli into the blood.

· Oxygenated blood then moves to left atrium of the heart via the pulmonary vein.

· Then moves to left ventricle where it’s pumped via the major artery, the aorta, to all areas of the body.

· The pumping of oxygenated blood to all parts of the body and return of deoxygenated blood to the heart is called systemic circulation

· The pathway of blood from the heart to the lungs and back to the heart is called pulmonary circulation.

STRUCTURE OF BLOOD VESSELS

· All share similar structure, but layers of tissue and the size of the lumen differ.

· Each vessel is modified to best carry out its specific function.

· ARTERY: Thicker walls and narrow lumen as blood enters under high pressure, and thicker walls minimise the chance of the artery tearing. Walls also are more elastic, so it can expand and contract.

· Carries blood from the heart.

· Contraction squeezes blood forward and propels it along.

· VEIN: Thinner walls and wider lumen as the blood is not as high pressure. The walls are not as elastic as the veins do not need to contract and expand as much as the arteries.

· Returns blood to the heart.

· Lumen is wider to allow easy flow of blood.

· Blood is propelled by the contracting of muscles surrounding the veins.

· Valves situated at regular intervals to stop the reverse flow of blood.

· CAPILLARIES: Walls are one cell layer thick so that substances can be diffused efficiently.

· Brings blood into close contact with the tissues, enabling exchange of chemical substances between cells and the bloodstream.

· Red blood cells pass through in single file, increasing their exposed surface area for the exchange of gases, nutrients and waste.

BLOOD AS A TRANSPORT MEDIUM

· Blood distributes nutrients and gases around the body, wastes to be excreted from the body, carries hormones, antibodies, clotting factors and other substances required for efficient functioning.

· Red Blood Cells:

· Transport oxygen.

· Form in bone marrow.

· Haemoglobin (oxygen carrier) is developed within the cell.

· Round, biconcave and slightly flattened towards the centre – more pliable and elastic in order to squeeze through capillaries.

· White Blood Cells:

· Also produced in bone marrow.

· Part of the immune system.

· Role is to defend the body against foreign bodies.

· Found in tissues as well as the blood.

· Can pass through capillaries by squeezing between the cells that make up the wall of the capillary.

· Larger than red blood cells.

· Not as abundant as red blood cells.

· All white blood cells have a nucleus.

· Platelets:

· Function in the clotting of blood.

· Contact between fibres and platelets causes platelets to break open and release an enzyme, thromboplastin, which sets in progress a sequence of steps to seal the blood vessels and cause blood to clot.

· Crescent shaped.

· Half the size of red blood cells.

· Plasma:

· Yellow, watery fluid.

· 90% water, 10% protein

· Makes up the majority of the volume of blood and carries many substances throughout the body:

· Proteins

· Nutrients

· Gases

· Excretory Waste Products

· Ions

· Hormones

· Vitamins

CHANGES IN COMPOSITION OF TRANSPORT MEDIUM:

· Lungs:

· As blood moves through the lungs it gains oxygen and loses carbon dioxide.

· Digestive System:

· Increase in digestive end products.

· Lymphatic System:

· Gain fatty acids that have been emptied into the bloodstream.

· Heart:

· High lipid content.

· Stomach:

· Water and other substances (e.g. alcohol) are diffused into the blood.

· Liver:

· Decrease in digestive end products.

· Glucose may be added or removed.

· Urea is added to the blood.

· Toxins such as alcohol are removed.

· Some vitamins and iron are removed.

· Kidneys:

· Urea is decreased.

· Excess water and salts are removed.

· Large Intestines:

· Water, salts and vitamins are absorbed into the blood.

· Endocrine Glands:

· Hormones are added.

LYMPHATIC SYSTEM:

· Forms part of the transport system in mammals.

· To prevent this interstitial fluid from building up in the tissues, lymph vessels in the tissues absorb it.

· This fluid, along with other substances present in the lymph vessels, such as white blood cells and the end products of lipid digestion, is known as lymph

· Lymph flows in the lymph vessels in one direction, from the tissues to the heart

· Movement of lymph is assisted by the contraction of muscles in close proximity to the vessels

· Valves are present in lymph vessels to prevent lymph going backwards

· Lymphatic vessels from all regions of body eventually join up to form two main lymphatic channels.

· In the region of the shoulders, the lymphatic vessels drain into the veins, allowing lymph fluid to re-join the blood

· This helps maintain the volume of blood and therefore blood pressure

· Lymphatic system also plays an important role in the defence of the body.

MOD.

TOPIC

CONTENT

3

EFFECTS OF THE ENVIRONMENT ON ORGANISMS

ECOSYSTEMS:

· Species have characteristics that suit them to the area they live in.

· Diversity that is seen is developed over time due to survival of the fittest and reproduction.

· Combination of abiotic and biotic factors.

· Diversity and distribution is due to the variation in abiotic and biotic factors.

TYPES OF ECOSYSTEMS:

· Aquatic Environments

· Salt concentration

· Light availability

· Pressure

· Saltwater, marine (reefs) or freshwater.

· E.g. wetlands, mangrove swamps, rock platforms, estuaries, rivers, lakes, oceans and coral reefs.

· Terrestrial Environments

· Desert

· Grasslands

· Shrubland

· Woodland

· Temperate Forest

· Tropical Rainforest

· Abiotic factors create selection pressures for organisms – which affects the biotic factors.

· Ecosystems provide nutrients, shelter and opportunities to mate.

· Competition – some organisms can survive and reproduce, and others cannot.

· Successful species have a range of favourable characteristics – adaptations.

SELECTION PRESSURES IN AN ECOSYSTEM:

· Natural Selection

· Changes in environment – changes in resource availability.

· EXAMPLES:

· Abiotic Factors:

· Temperature

· Light Intensity

· Soil Types

· Water Availability

· Gas Concentration

· Biotic Factors:

· Competition

· Predators

· Prey Availability

ABUNDANCE AND DISTRIBUTION:

· Distribution: where a species is found.

· Abundance: how many individuals of that species live throughout the ecosystem.

· Both abiotic and biotic factors affect these.

ENVIRONMENTAL PRESSURES IN TERRESTRIAL AUSTRALIAN ECOSYSTEMS:

· Rainfall, temperature and landform patterns affect distribution and abundance.

· High temperature and high rainfall along the east coast creates suitable tropical environment for rainforest ecosystem.

· High temperature and low rainfall in the centre of Australia creates a suitable environment for desert ecosystems.

ECOLOGY:

· Ecology is the study of the interrelationships between different types of organisms and between organisms in their environments.

· Determines distribution and abundance of flora and fauna.

· Determines measures of population in different areas.

MEASURING PLANT ABUNDANCE:

· Measuring is easy as plants are not mobile.

· Use sampling techniques.

· Quadrats – 1m x 1m

MEASURING ANIMAL ABUNDANCE:

· Slow moving animals are easily counted.

· Quick animals are harder to count.

· Abundance =

· Mark-release method

· Assumes that there is no migration, births or deaths between sampling periods.

TRAPPING TECHNIQUES:

· Traps, nets, small pits

· Radio tracking

POPULATION TRENDS:

· Examining population trends leads to inferences about species and what environment they are most suited.

· In large areas, transects are used.

· Transects are narrow strips that cross the entire area being studied.

· Provide an accurate and easy method of representing an area.

· Transect line from the sea to inland is used to look at the abundance of mangroves.

CHANGES IN POPULATIONS OVER TIME:

·

ADAPTATIONS

ADAPTATIONS:

· Organisms are adapted to survive in their natural environment as a result of evolutionary change by natural selection.

· An adaptation is a characteristic that an organism has inherited and that makes it suited to its environment.

· Adaptations are not intentional.

· They occur as a result of a change or variation that arises.

· New organisms possess a changed feature that may benefit the organism by making it more suited to the environment it lives in.

· May be passed on to offspring.

· In Australian environments, the main abiotic selection pressures are lack of water, high temperature and high sun exposure.

· There are three types of adaptations:

· Structural – how an organism is built.

· Physiological – how an organism functions.

· Behavioural – how an organism acts or behaves.

STRUCTURAL ADAPTATIONS – PLANTS:

· Plants that live in hot/dry environments must achieve a balance between photosynthesis and how much water the plant can afford to lose for cooling purposes without risking dehydration.

· XENOPHYTES – Structural adaptations to maximise absorption and storage of water and minimise the loss of water.

· Succulents:

· Fleshy stem/leaves

· Ability to swell to retain moisture.

· Eucalypts/Banksia

· Leathery leaves

· Thick wax cuticle

· Protects from excessive sunlight.

· Provides insulation

· Provide reflective properties

· Reduce amount of evaporation

· Leaf shape is important in retaining water.

· Cypress Pines:

· Tiny cylindrical leaves – small SAV ratio

· Reduces water loss through transpiration.

· Spinifex:

· Tough, pointed leaves for reducing water loss.

· Porcupine Grasses:

· Roll their leaves during the hottest part of the day.

· Stomata are on inside of roll so not exposed to dry atmosphere.

· Hard leaves minimise water loss with a waxy or hairy surface.

· Sunken stomata are lower than the surface of the leaf, allowing moist air to be trapped in the pit.

· Hairs in the pit trap water vapour.

· Epidermal hairs on the surface of the leaf also trap a moist layer of air.

STRUCTURAL ADAPTATIONS OF ANIMALS

· Main survival issues for animals are gaining enough water and food, keeping cool or warm, finding space to live, reproducing and deterring predators.

· The Thorny Devil:

· Body covered with large prickly spikes, making it look ferocious and hard to swallow.

· Layered scales that capture water from rain and dew, funnel it back into the mouth and then use its tongue to draw water into its mouth.

· False head – makes it look larger and thus deters predators.

· Gold and brown colour camouflages it with the desert soil.

· Wombat

· Large muscular shoulders and long claws for extensive digging.

· Pouch to protect joey from dirt while digging.

· Herbivorous

· 24 rootless teeth that continuously grow to replace those that are worn down from gnawing hard materials.

PHYSIOLOGICAL ADAPTATIONS

· All the processes involved in an organism carrying out its function.

· EXAMPLES:

· Intertidal marsh crabs – have gills and kidneys that function to concentrate and excrete excess salt.

· Flamingos – can tolerate the alkaline waters of soda lakes which would kill other birds.

· Plant Stem Cells – sensitive to the hormone auxin, which causes them to grow towards light.

ABIOTIC FACTORS - PLANTS

· TEMPERATURE

· Low temperature – strategies to reduce the risk of ice forming in cells.

· Some alpine plants produce organic compounds that act as an ‘antifreeze’ substance.

· Deciduous trees lose their leaves and undergo a period of dormancy.

· SALT

· Can be damaging to cell structure and metabolism.

· Salt-tolerant plants – can increase water content in vacuoles to maintain metabolism.

· Salt-avoidant plants – minimise salt concentration using structural and physiological adaptations to be able to excrete excess salts.

ABIOTIC FACTORS – ANIMALS

· WATER

· Spinifex hopping mouse – reduce water loss by excreting highly concentrated urine, reabsorbing most of the water produced as a by-product from cellular respiration.

· Freshwater Fish – concentration of ions in their cells higher than their surrounding water, fish rarely drink and have a high kidney filtration rate.

· TEMPERATURE

· Penguins – counter current heat exchanger system to keep their extremities warm, large insulating layer (blubber) – also in polar bears.

· Land Snails – move into the shade and seal up their shell.

· Cane toad – burrows underground and sealing itself in a water tight mucus cocoon.

BEHAVIORAL ADAPTATIONS

· Refers to actions performed by organisms in response to a stimulus.

· EXAMPLES:

· Puffer fish – pump air into their stomachs and blow up twice their size to frighten predators.

· Antarctic penguins – huddle during winter and rotate through the huddle to reduce their time exposed on the outside of the huddle.

· Tropical Houseplant (Mimosa Pudica) – leaves respond to touch and fold inwards to protect itself from harm.

· Venus flytrap – adapted to live in nitrogen poor soils, gain nitrogen from digesting insects.

· Eastern Brown snake – move into the shade when hot or into sun when cold, less active in cold weather.

· Bilby – hide in burrow during day to avoid heat and reduce water loss.

· Sugar Gliders – produce a pungent aroma from glands on head, chest or genitals to allow members of a group to locate each other.

· Meerkats – live in large social communities, one meerkat is posted as a sentry and alert others of imminent danger.

DARWIN IN THE GALAPAGOS ISLANDS

· The Galapagos Islands are a group of volcanic islands, off the coast

· of Ecuador, that span the equator.

· Made up of 18 main islands, three smaller islands and a number of

· smaller rocky islands and islets.

· They are home to a large number of species, including fur seals, sea lions, tortoises, sea turtles, marine iguanas and the now famous Galapagos od Darwin’s finches

· It was his visit to the Galapagos Islands that provided Darwin with further evidence to strengthen his ideas.

· FINCHES:

· Darwin observed small finches in the Galapagos Islands and collected specimens

· On his arrival back to England, he presented these specimens to the Royal Society and then to John Gould, a famous English ornithologist, who classified them as 14 different species, 12 of which were new.

· Gould commented that the birds were like those found in South America.

· Darwin reasoned that the different finches he found from island to island could be explained as follows

· A few South American finches must have arrived on one

· of the remote islands of the Galapagos

· These finches had naturally occurring variations in, for example, their colour, beak size and leg length

· The descendants of these birds gradually populated the other islands, each of which had different environmental conditions

· Depending on which island they lived on, and the

· conditions they found themselves in, some birds thrived

· and reproduced

· Those finches that were not adapted to the conditions on the island died out

SURVIVAL OF THE FITTEST:

1. Variation exists within populations

2. More offspring are produced than can survive

3. Those offspring better adapted to their environment will survive and reproduce

4. The favourable adaptations are passed on to the next generation

5. Over time the favourable adaptations will increase in the population (if the environment does not change)

THEORY OF EVOLUTION BY NATURAL SELECTION

· Evolution - a change in living organisms over a long period of time

· Ideas have been around since the mid-1700s. At the beginning of the 19th Century Jean Baptiste Lamarck put forward his theory, which was later rejected, but it led the way for further ideas, which have resulted in the currently accepted Theory of Evolution by Natural Selection

· All theories of evolution share the same common basic premises:

· Living organisms arose from common ancestors or a common life form and have changed over time

· Differences that occur among groups of living organisms imply that living things change over time

· Similarities occur in living things and suggest a common ancestry the basic chemistry, inherited from a common life form, has remained relatively unchanged and has been passed down through generations.

INTRODUCTION

· Theory of evolution proposed over 250 years ago.

· 1800’s – scientists started to propose mechanisms to explain evolution.

· Approximately 8.7million species have been discovered that are now extinct.

· Species that exist today have developed over billions of years.

BIOLOGICAL DIVERSITY

· BIODIVERSITY: The variety of all forms of life on Earth, the diversity of the characteristics of living organisms and the variety of their ecosystems.

· Diversity allows for adaptations.

· Three levels of biodiversity:

1. Genetic Diversity

2. Species Diversity

3. Ecosystem Diversity

· BAW BAW FROG

· Endangered species found in central highlands of Victoria.

· Ancestors were distributed along the Great Dividing Range.

· Low genetic diversity

· Past climate change placed great pressure on the species.

· Population has had a 98% decline

· Disease – chytrid fungus

· Threatened by Greenhouse Effect

BIODIVERSITY AND EVOLUTION

· Evolution relies on biodiversity.

· New field of study called ecoevolution (the effect of global changes on biodiversity) and evolutionary ecology.

GENETIC DIVERSITY

· Important for a population to be able to adapt.

· Environments are constantly changing and thus provide selection pressures enabling some organisms with favourable characteristics to survive.

· Reduced genetic diversity can lead to extinction.

CALICIVIRUS

· A virus that affects rabbits was used as biological control for a number of years.

· Some rabbits do not die as they have inherited resistance.

· This is gradually inherited through reproduction and eventually the entire rabbit population will be resistant to the calicivirus.

NEO-DARWINISM:

· Scientists have applied concepts of Mendelian genetics to support and explain Darwin and Wallace’s ideas on random genetic variation leading to gradualism and the formation of new species

· It was only after Mendel’s experimental results were confirmed and accepted, that the Darwinian theory of evolution was extended to include genetic processes involved in natural selection,

· Therefore, the explanation of Darwinian evolution based on modern genetics is what we term ‘Neo-Darwinism’.

· Many variations arise from the interaction of an organisms with its environment

· This type of variation affects the individual organisms

· Variations that can be passed on from one generation to the next - heritable characteristics - affect evolution

· Heredity and variation are essential for evolution to occur

· Variations that pass from one generation to another are often produced in a population because of mutations

TYPES OF SPECIATION:

· Speciation is the formation of new and distinct species during evolution

· Allopatric speciation: speciation that occurs when populations become isolated. Involves several stages:

1. In a parent population that has a large range within a common gene pool, there is a regular flow of genes due to mating events between individuals

2. Part of the population becomes separated due to physical barriers. This prevents the flow of genes between the parent population and the isolated population

3. The two populations experience different selection pressures that favour some individuals with specific genotypes over others. This alters the frequency of specific genes. The isolated population will become a subspecies

4. If the populations are separated long enough, the gene pool of each population will change in isolation. Gene flow will not occur, as the populations are not in breeding contact. They may become so different that they will no longer interbreed if brought together

· Closely related species whose distribution overlaps are called sympatric species. Species that are geographically isolated are called allopatric species.

ORIGIN OF LIFE ON EARTH:

· Environment on early Earth provided conditions for inorganic molecules to form organic molecules.

· First prokaryotic cells.

· Further advances happened when cells began to specialise.

· Endosymbiont Theory

· Formed first eukaryotic cells.

MICROEVOLUTIONARY CHANGES AND SPECIATION:

· Change in the environment is the primary cause for change in living organisms.

· Abiotic factors include:

· Physical Conditions (temperature, light, water, wind and tides etc.)

· Chemical Conditions (gases, pH, concentration of salt etc.)

· Environmental change can lead to resources becoming limited gives rise to competition between organisms for resources.

SELECTION PRESSURES:

· Selection pressures include:

· Environmental Change

· Disease

· Predation

· Competition

· Diversity of individuals makes the population better able to survive changes in the environment.

MICROEVOLUTION AND MACROEVOLUTION

· MACROEVOLUTION:

· Takes place over millions of years.

· Measured as geological time.

· Results in new species (e.g. evolution of humans)

· MICROEVOLUTION:

· Takes place over shorter periods of time resulting in changes in a population.

· Generally, does not produce a new species.

· New varieties or races (e.g. breeds of dog).

· Can lead to speciation (e.g. small changes in a dog sized ancestor lead to evolution of the horse).

EVOLUTION OF THE HORSE:

· Has a complete fossil record

· Mammal belonging to the family Equidae

· Evolved over 50 million years from a dog-sized, forest-dwelling animal Hyracotherium

· Shares a common ancestor with tapirs and rhinoceroses

· Horse evolution has a branching nature (rather than a linear evolution)

· The fossil record showed there were several different migrations, changes in trends from smaller to larger sizes as well as reduction in size. The rate of evolutionary change did not appear to be constant.

· Fossils have shown changes in body size, number of toes and dentition (teeth - development of grinding surfaces)

· Genetic variation caused by mutations, natural selection, genetic drift and speciation have all contributed to the evolution of the horse

· Microevolution can occur when a series of mutations leads to a change in gene frequency in a population. This change in the gene pool is due to chance and is called genetic drift. If a population becomes isolated speciation might occur.

· A small population with a mutated gene may become separated from the main population, causing the mutated gene to increase in the population as interbreeding occurs. If the change is favourable it is selected for (it increases chance of survival)

· The isolated population evolves to become significantly different from the original population and eventually if brought back together they would not be able to interbreed, resulting in the formation of a new species.

EVOLUTION OF THE PLATYPUS

· Australian mammals include an abundance of marsupials (pouched mammals) and monotremes (egg-laying mammals), but few placental mammals.

· Fossil record is poor. Monotremes were present in Mesozoic era, when Australia was part of Gondwana

· Platypus has features like birds (bill, webbed feet), reptiles (venom glands, egg laying) and mammals (hair on back, suckle their young)

· Their species name changed from Platypus anatinus to Ornithorhyncus anatinus

· Cynodonts are thought to be earliest ancestor of mammals. Monotremes thought to have split off first (150 mya), followed by marsupials (130 mya) and placental lines of mammals (110 mya)

· COMMON GENES:

· Studies of fossil evidence and the genome of the platypus show that it is not directly related to birds. It is a descendent of reptiles, split approx. 166 mya.

· Evidence suggests therian mammals gave rise to marsupials and the placentals, which branched off 148 mya.

· Fossil analysis shows platypus and echidna share a common ancestor. This split occurred about 19-48 mya.

· Comparing genomes of platypus, marsupial and placental mammals show approx. 82% genes are common

· Platypus lays eggs with yolk, humans do not produce yolks. A gene (for production of yolk) is present in the platypus and absent from humans.

· All three groups have 2 genes related to tooth production, which together with a third gene for production of milk protein, seem necessary for lactation (milk production). This shows the ability to produce milk arose before the Jurassic period.

EVOLUTION – THE EVIDENCE

BIOCHEMICAL EVIDENCE:

· Evidence has shown that all living organisms share the same macromolecules such as proteins and DNA as well as biochemical processes such as respiration.

· It is predicted that biochemical comparison of these organisms would show that more closely related organisms would show more similar proteins or DNA.

· Predictions were tested using new technologies.

AMINO ACID SEQUENCING:

· Proteins are a component of all living cells in membranes and as enzymes.

· Made up of amino acids.

· Proteins are made from a combination of approx. 29 amino acids.

· The sequence of amino acids in the protein is analysed and similarities and differences between organisms are identified.

· Differences imply the organism has evolved.

· Number of differences is proportional to the length of time since the organism separated.

DNA HYBRIDISATION:

· Samples of DNA are removed from the two species to be compared

· The DNA is split lengthwise by heating to 90-94oC (dissociation) to expose nucleotide bases on each strand

· The separated strands of the species to be compared are then mixed.

· The two strands combine (reassociation) and form a ‘hybrid’ DNA molecule

· The more closely matched the DNA, the tighter the binding.

· Heat is applied to determine how tightly the DNA strands have combined. More closely related species have more similar sequence of bases and therefore the strands bind tightly.

DNA SEQUENCING:

· The exact order of bases in DNA of one species is compared with a similar fragment of another species.

· A piece of DNA is isolated from each organism.

· Multiple copies are made, and dye is used to label the bases.

· A DNA sequencer is used to graph and print out the sequence of bases, which are then compared.

· Organisms that share a common ancestor share fewer differences.

· Provides more detailed information than other biochemical methods.

COMPARATIVE ANATOMY:

· Study of similarities and differences in the structure of living organisms.

· Imply common ancestors.

· HOMOLOGOUS STRUCTURES (Divergent Evolution)

· Differences in structure represent modification.

· Organisms that have the same basic plan to their structure but show modifications are called homologous – they have the same evolutionary origins.

· ANALOGOUS STRUCTURES (Convergent Evolution)

· Structures that look similar but are very different (e.g. wings of bird and wings of grasshopper)

· May have started off differently but over time evolve to look similar.

· E.g. Australian Echidna and European Hedgehog

· Do not show evolutionary relatedness – shows the evolution of structures for a common purpose.

· VESIGIAL STRUCTURES

· Evolutionary remnants of body parts that no longer serve a useful function.

· Provides evidence of common ancestry.

· E.g. presence of coccyx and appendix in humans.

COMPARATIVE EMBRYOLOGY:

· Comparison of developmental stages of different species.

· Related species show similarities in their embryonic development.

· E.g. fish, amphibians, birds and mammals all have gill slits.

BIOGEOGRAPHY:

· Study of geographical distribution of organisms.

· For a new species to arise, it must be genetically isolated.

· E.g. Galapagos Finches, birds in Bali and Lombok (Wallace’s Line)

· Distribution of Flightless Birds

· Originated from a common ancestor on Gondwana

· Resulted in distribution of emus in Australia, ostriches in South Africa, kiwis in New Zealand and rheas in South America.

· No similar birds in Northern Continents.

· Evidence for adaptive radiation.

FOSSIL EVIDENCE:

· Palaeontology – study of fossils

· Provide direct evidence of the existence of an organism preserved in rock, ice, amber, tar, peat or ash.

· Law of superposition.

MOD

TOPIC

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POPULATION DYNAMICS

RECENT EXTINCTION – AUSTRALIAN MEGAFAUNA

· Scientists are able to apply their knowledge of population dynamics to unexplained extinctions.

· The type and number of species on the planet are constantly changing.

· During the Pleistocene Epoch there were a number of megafaunas in Australia.

· Extinction of megafauna is thought to have been due to human impact along with climate change.

THEORY 1: CLIMATE CHANGE

· Continent dried out

· Rainforests were contracting – stored moisture and returned moisture to the atmosphere.

· Eucalypt forests replaced these, and water was not as efficiently retained.

· Became hotter and drier, fires broke out due to lightning.

· Plants and animals that survived the drought and fire reproduced changing the flora and fauna.

THEORY 2: ARRIVAL OF HUMANS

· Aboriginal people arrived successful predators.

· Used ‘fire stick’ farming techniques.

· Introduction of dingoes may have reduced the diversity of carnivore predators.

THEORY 3: LEVEL OF NUTRIENTS

· Low level of nutrients in the soil dry

· Led to smaller animals can be sustained on less

· Evidence for this can be seen in the smaller size of mammals in Australia compared to counterparts across the world.

EVIDENCE OF HUMAN AND MEGAFAUNA CO-EXISTING

· Cuddie Springs – fossil site in Central NSW discovery of bones and tools made by humans.

· Kangaroo Leg Bone

· Stone Tools

· Mixtures of megafauna bones

· Charcoal from camp fires

· Sandstone grinding stone

· Additional evidence found at a site north of Melbourne.

PAST ECOSYSTEMS

PAST ECOSYSTEMS:

· It is unclear when humans first became interested in fossils.

· Philosophers hinted that fossils were evidence of previous life.

· Law of superposition oldest layer at bottom and newest at top.

· Law of original horizontality all sedimentary strata are originally horizontal

· Law of lateral continuity

· Law of cross-cutting relationships

SLOW CHANGES:

· Changes in the Earth’s crust happened because of slow, progressive causes such as long cycles of erosion and deposition.

· Known as gradualism.

· First geological time scale constructed in 1841.

· Discovery of radioactivity in 1896 by Henri Becquerel led to absolute dating technique to age rocks – age of earth estimated 4.5 billion years.

· Geology and palaeontology are valuable in combination to produce evidence of the past.

· Evidence used to reconstruct past ecosystems is referred to as proxy data.

ABORIGINAL ROCK PAINTINGS

· Represents the longest unbroken art tradition in the world.

· Humans are driven by nature to record details of their existence.

· West Kimberley rock paintings

· Wandjina paintings – 50,000 – 60,000 years old – provide clues about the past.

· Studied scientifically from 2007.

· Radiometric dating is used to date the paintings.

· Uranium/thorium dating can be applied to underlying calcite formations to show when they were formed.

· Evidence of a symbiotic relationship between fungi and bacteria that colonised pigment.

THE GREAT OXYGENATION EVENT

· Approx. 2 billion years ago.

· There was probably limited aerobic respiration prior to this.

· Increased oxygen in the atmosphere had 2 effects

· It created a selection pressure for organisms that could overcome the harmful effects of oxygen.

· Some oxygen metabolites (hydrogen peroxide and hydroxide radicals) are toxic and only organisms with specific new metabolic pathways could take advantage of the benefits of oxygen without it being toxic. These pathways were selected for and allowed the rise of aerobic respiration, leading to development of larger more complex organisms

PALAEONTOLOGICAL EVIDENCE – FOSSILS

· ‘Fossil’ from the Latin word fossus - ‘to be mined, dug up, buried or quarried’.

· Fossils are remains of living things or evidence of their past existence.

· They provide clues linking changes in selection pressure to evolution.

· They need to be distinguished from naturally occurring patterns in rocks

· Fossils are generally found in sedimentary rocks due to the way the rocks are formed, preserving evidence from the past

· Classifying fossils

· Mineralised remains (moulds and casts, petrified wood, opalized remains)

· Organic remains (in ice, amber, bogs and dry caves)

· Impressions (shape of external organism recorded in sediment)

· Trace fossils (remnants of organic molecules associated only with life). ‘Geochemical remains’

MICROFOSSILS

· Discovery of Precambrian fossils from Marble Bar, WA (3400-3500 million years old) in silica-rich apex chert (microcrystalline quartz) provided first evidence of past ecosystems on Earth

· Microfossils of single-celled, filamentous anaerobic prokaryotes found, closely resembling modern examples living in hydrothermal vents and volcanic hot springs.

· Infers that these organisms lived in hydrothermal environment

· They are anaerobic and sulfur-metabolising (chemosynthetic) microorganisms

· Scientists infer that chemosynthesis was earliest way for organisms to build organic molecules

CHEMOSYNTHESIS

· Organisms use inorganic compounds available from the environment to manufacture organic compounds

· Does not require sunlight

· Can happen in deep oceans

· Absence of light is a selection pressure

STROMATOLITIC FOSSILS

· Unusually shaped fossils found in Archaean chert at Bitter Springs, NT.

· Dated to around 3.5 billion years old

· Provide valuable information about structure of early organisms and their environment

· In water, colonies of photosynthetic cyanobacteria trap layers of calcium carbonate and ‘grow’ upwards in columns towards the sun.

· Living stromatolites can be found in WA at Hamelin pool, Shark Bay, growing by 1mm per year, individual domes reaching diameter of 200cm and height of 50cm.

· Many selection pressures affected the evolution of stromatolites.

· Modern stromatolites are found in sheltered bays - unique combination of abiotic conditions

· Shallow waters - increased light intensity for photosynthesis, warm still waters allowing growth without disturbance.

· Water is mineral rich and hypersaline (high salinity).

· Modern examples in Turkey and Canada, as well as Jenolan Caves (Nettle Cave) where stromatolites grow near the light, open ends of the cave.

· Stromatolites became more common 2.5 billion years ago having a profound effect on the Earth’s hydrosphere and atmosphere.

· One of the selection pressures in a pre-oxygen atmosphere was high level UV radiation. Living in water provided some protection from this, while life on land was virtually impossible (DNA mutations).

· As oxygen levels rose, concentration of ozone in stratosphere also rose and life could now exist on land.

PALAEOSOLS

· ‘Fossilised soils’.

· Soils that contain unusually large concentrations of carbon usually indicate presence of life

· Some of these soils have been found in South Africa

· There are also palaeosols that have formed under environmental conditions no longer present.

· For example, they may indicate tropical environments but be found in arid conditions, so they are useful in reconstructing a timeline of past environments.

· They have also been used to reconstruct a timeline for the development of the oxic atmosphere.

GEOLOGICAL TIMESCALE

· Fossil evidence has helped with the construction of geological timescale

· The timescale is divided into eons, eras, periods and epochs (in decreasing duration).

· Lines are drawn across the scale where significant events took place which led to species extinction

· The division between Cretaceous and Tertiary periods represents a mass extinction approx. 65mya - the Cretaceous-Tertiary (KT) extinction - resulting in disappearance of 65% of organisms in the fossil record and the appearance of many new species

ICE CORE DRILLING

· Claude Lorius (French glaciologist) discovered and developed palaeo atmospherics - interpretation of past environments from the study of gases and other materials trapped in ice

· He noticed bubbles escaping from ice at it melted in his drink which led him to believe that these bubbles could hold important information about composition of the air when the ice formed

· Antarctic snow forms as layers like sedimentary rock - deeper layers represent more ancient depositions. As snow falls year after year, gases and atmospheric particles get trapped.

· Scientists could drill through the layers, extract the gases and reconstruct the climate record (temperature and chemical profiles for thousands of years)

· The best place for sampling must be where temperatures never rise above 0oC, such as Greenland, Antarctica and high mountain ranges. If the ice melted, water would disrupt the ice profile and make it useless

RADIOMETRIC DATING/GEOCHRONOLOGY

· A technique used to determine the age in years of a fossil, rock or mineral

· Based on the content of radioactive isotopes

· Dates igneous and metamorphic rock

· Many elements have unstable isotopes (Parent isotope) which undergo radioactive decay and release energy and/or particles to become a more stable daughter atom.

· Rate of decay is calculated using the age equation that compares the abundance of the naturally occurring isotope with the abundance of the decay product.

TECHNOLOGY USED TO MEASURE RADIOACTIVITY

· Radioactivity is measured using a combination of technologies, including nuclear reactors, mass spectrometers, laser beams and special microscopes

· In 1980s, significant advancement in radiometric dating - development of SHRIMP (Sensitive High-Resolution Ion Microprobe) technique which dates very resilient grains of mineral known as zircon - allowed scientists to identify the oldest rocks on Earth (approx. 4.4 billion years old).

· Fission track dating - Electron microscopes see ‘tracks’ left by

· Decaying Uranium atoms that leave marks on the surface of grains

· as they release particles and energy. Density is analysed

· and age can be estimated.

· Luminescence dating - measures the amount of natural radiation trapped in mineral crystals using heat (thermoluminescence) or laser light.

· The longer the crystal has been buried, the brighter the luminescence

GAS ANALYSIS

· Scientists can use data in ice cores to reconstruct atmospheric concentrations of certain gases, particularly CO2 and O2.

· CO2 is a normal part of Earth’s atmosphere along with nitrogen, oxygen, argon and other trace gases

· But CO2 is also considered a ‘greenhouse gas’ that traps solar radiation keeping the Earth warm enough to sustain life

· However, increasing CO2 in atmosphere is likely to increase Earth’s atmospheric temperature, known as the ‘enhanced greenhouse effect’ or ‘global warming’

· Scientists use ancient CO2 levels to infer past climates - warming or cooling would have a direct effect on the types of plants and animals that are suited to survive in such a climate

· Oxygen has three naturally occurring isotopes: 16O, 17O and 18O which are incorporated into water molecules. The ratio of 18O/16O in analysed ice core samples indicates ancient water temperatures which scientists can use to reconstruct water temperatures on Earth

EVOLUTION OF AUSTRALIAN BIOTA

· Scientists analyse evidence of organisms from the past to determine if present-day organisms may have evolved from them

· Due to Australia's long history of isolation, Australian ecosystems consist of a unique array of flora and fauna

· Fossil evidence provides clues to the slow, progressive changes in Australian species over roughly 30 million years (since it moved away from Antarctica)

· Australia’s climate has alternated between warm/wet cycles and cold/dry cycles which has influenced the pattern of vegetation - gone from tropical rainforests with broad-leafed plants to predominantly open grassland and desert with sclerophyll plants as the dominant plant life

ORIGINS OF PRESENT DAY PLANTS AND ANIMALS

· Distribution and abundance of present day plants in Australia reflect three main origins:

· Those already on the continent when it split from Gondwana

· Those that dispersed from South-east Asia to Australia

· Introduced species

· Origins of animals that led to present-day fauna:

· ‘Original residents’ - those already on continent when it split from Gondwana (e.g. frogs, reptiles, monotremes, marsupials, emus and lyrebirds)

· Asian ‘immigrants’ that arrived when sea levels were low - 15 mya and again 40,000-30,000 mya (e.g. poisonous snakes, back-fanged snakes, rats, mice and bats)

· Those introduced by immigrant traders or late arrival Aboriginals - 4,000 year ago (e.g. dingoes)

· Those introduced by European immigrants - beginning 200 years ago

CHANGING FLORA AND FAUNA

· Many hypotheses have been put forward to account for the changes in Australia’s flora and fauna

· Changes are intimately linked with the movement of continents and the subsequent effects on climate

· Australia was originally part of the great southern continent of Gondwana

· In the early Cretaceous period, Australia lay much further south that its present location

· Climate was cool and wet

· Conifers, cycads and dinosaurs were abundant

· Australia's first mammals had already appeared and later developed into the familiar Australian mammals we know today

FUTURE ECOSYSTEMS

MINING

· Mining represents a rich source of income for Australia

· Ores such as lead, iron ore, silver, aluminium, gold, copper, uranium and zinc are extracted from the ground.

· Some ores are processed and refined in Australia before exportation, while others are exported for processing and manufacturing purposes.

· Mining is carried out in all states and territories in Australia.

· It contributes to land degradation in the following ways:

· Extraction and refining of ores leaves behind chemical pollutants, which accumulate in soil and local waterways

· Acid wastes are produced, which change the acidity of waterways

· The topography of the land is altered by removal of topsoil and vegetation, leading to soil erosion and siltation of local waterways

· Old buildings and machinery may be left behind once mining operations cease

· Air pollution with oxides of sulfur and nitrogen may lead to the production of acid rain which destroys vegetation and soil invertebrates

EXTINCTION

· Habitat loss is the leading cause of extinction around the world

· Island populations are often relatively small, and thus particularly vulnerable to extinction (73% of the 90 species of extinct mammals over the last 500 yrs. lived on islands)

· Another 19% of these lived in Australia

·