1. Trees in a forest, fish in a river, horseflies on a farm, lemurs in the jungle, reeds in a pond, worms in the soil all these plants and animals are made of the building blocks we call cells. Like these examples, many living things consist of vast numbers of cells working in concert with one another.Other forms of life, however, are made of only a single cell, such as the many species of bacteria and protozoa.Cells, whether living on their own or as part of a multicellular organism, are usually too small to be seen without a light microscope. Cells share many common features, yet they can look wildly different. In fact, cells have adapted over billions of years to a wide array of environments and functional roles. Nerve cells, for example, have long, thin extensions that can reach for meters and serve to transmit signals rapidly. Closely fitting, brick-shaped plant cells have a rigid outer layer that helps provide the structural support that trees and other plants require. Still, as different as these cells are, they all rely on the same basic strategies to keep the outside out, allow necessary substances in and permit others to leave, maintain their health, and replicate themselves. In fact, these traits are precisely what make a cell a cell. Long, tapered muscle cells have an intrinsic stretchiness that allows them to change length within contracting and relaxing biceps.

2. Researchers hypothesize that all organisms on Earth today originated from a single cell that existed some 3.5 to 3.8 billion years ago.This original cell was likely little more than a sac of small organic molecules and RNA-like material that had both informational and catalytic functions. Over time, the more stable DNA molecule evolved to take over the information storage function, whereas proteins, with a greater variety of structures than nucleic acids, took over the catalytic functions. As described in the previous section, the absence or presence of a nucleus and indeed, of all membrane-bound organelles is important enough to be a defining feature by which cells are categorized as either prokaryotes or eukaryotes. Scientists believe that the appearance of self-contained nuclei and other organelles represents a major advance in the evolution of cells. But where did these structures come from? More than one billion years ago, some cells "ate" by engulfing objects that floated in the liquid environment in which they existed. Then, according to some theories of cellular evolution, one of the early eukaryotic cells engulfed a prokaryote, and together the two cells formed a symbiotic relationship. In particular, the engulfed cell began to function as an organelle within the larger eukaryotic cell that consumed it. Both chloroplasts and mitochondria, which exist in modern eukaryotic cells and still retain their own genomes, are thought to have arisen in this manner 3. Cells are considered the basic units of life in part because they come in discrete and easily recognizable packages. That's because all cells are surrounded by a structure called the cell membrane which, much like the walls of a house, serves as a clear boundary between the cell's internal and external environments.The cell membrane is sometimes also referred to as the plasma membrane. Cell membranes are based on a framework of fat-based molecules called phospholipids, which physically prevent water-loving, or hydrophilic, substances from entering or escaping the cell.These membranes are also studded with proteins that serve various functions. Some of these proteins act as gatekeepers, determining what substances can and cannot cross the membrane. Others function as markers, identifying the cell as part of the same organism or as foreign. Still others work like fasteners, binding cells together so they can function as a unit.Yet other membrane proteins serve as communicators, sending and receiving signals from neighbouring cells and the environment whether friendly or alarming Within this membrane, a cell's interior environment is water based. Called cytoplasm, this liquid environment is packed full of cellular machinery and structural elements. In fact, the concentrations of proteins inside a cell far outnumber those on the outside whether the outside is ocean water (as in the case of a single-celled alga) or blood serum (as in the case of a red blood cell). Although cell membranes form natural barriers in watery environments, a cell must nonetheless expend quite a bit of energy to maintain the high concentrations of intracellular constituents necessary for its survival. Indeed, cells may use as much as 30 percent of their energy just to maintain the composition of their cytoplasm. 4. Plant cells are eukaryotic cells, or cells with a membrane-bound nucleus. Unlike prokaryotic cells, the DNA in a plant cell is housed within the nucleus. In addition to having a nucleus, plant cells also contain other membrane-bound organelles, or tiny cellular structures, that carry out specific functions necessary for normal cellular operation.Organelles have a wide range of responsibilities that include everything from producing hormones and enzymes to providing energy for a plant cell. 5. There are two main types or categories of cells: prokaryotic cells and eukaryotic cells. Both of these types of cells have several things in common. All cells are surrounded by a plasma membrane, which is made of a double layer (a bilayer) of phospholipids.Within this membrane, is the cytoplasm which is composed of the fluid and organelles of the cell. Bacteria (Kingdom Monera) are prokaryotes.They do have DNA, but it is not organized into a true nucleus with a nuclear envelope around it. Also, they lack many other internal organelles such as mitochondria and chloroplasts. 6. Organisms in the other four kingdoms are eukaryotes.Their DNA is organized into a true nucleus surrounded by a nuclear envelope which consists of two bilayer membranes. The nucleus of eukaryotic cells contains the genetic material which chemically directs all of the cells activities. Usually this is in the form of long strands of chromatin made of DNA and affiliated proteins.When a cell is getting ready to divide, the chromatin coils and condenses into individual, distinguishable chromosomes. Because the nuclear envelope consists of two bilayer membranes, there is a space between these two membranes called a lumen. Branching off from and continuous with the outer membrane of the nuclear envelope is a double walled space which zigzags through the cytoplasm.This is the endoplasmic reticulum (ER for short) and its central space or lumen is a continuation of the lumen between the membranes of the nuclear envelope.There are two kinds of ER: smooth ER and rough ER.Typically ER closer to the nucleus is rough and that farther away is smooth. Smooth ER is a transition area where chemicals like proteins the cell has manufactured are stored in the lumen for transportation elsewhere in the cell. Pieces of the smooth ER called vesicles pinch off from the smooth ER and travel other places in the cell to transfer their contents. Rough ER gets its name because it has other organelles called ribosome's attached, which give it a rough appearance when viewed by an electron microscope. Rough ER and its associated ribosome's are involved in protein synthesis, with the new polypeptide being threaded into the lumen of the ER as it is formed. 7. Branching off from and continuous with the outer membrane of the nuclear envelope is a double walled space which zigzags through the cytoplasm.This is the endoplasmic reticulum (ER for short) and its central space or lumen is a continuation of the lumen between the membranes of the nuclear envelope. There are two kinds of ER: smooth ER and rough ER.Typically ER closer to the nucleus is rough and that farther away is smooth. Smooth ER is a transition area where chemicals like proteins the cell has manufactured are stored in the lumen for transportation elsewhere in the cell. Pieces of the smooth ER called vesicles pinch off from the smooth ER and travel other places in the cell to transfer their contents. Rough ER gets its name because it has other organelles called ribosomes attached, which give it a rough appearance when viewed by an electron microscope. Rough ER and its associated ribosome's are involved in protein synthesis, with the new polypeptide being threaded into the lumen of the ER as it is formed. 8. Vacuoles and vesicles are similar in that both are storage organelles. Generally, vacuoles are larger than vesicles. Plant cells generally have one large central vacuole that takes up most of the space within the cell and is used for storage of all sorts of molecules. Paramecium have a special type called a contractile vacuole that serves to excrete water from the cell, sort of like our kidneys excrete water from our bodies.Vesicles are small enough and mobile enough that they are often used to move chemicals to other locations in the cell where they might be needed. One of the places to which vesicles travel is the Golgi apparatus or Golgi bodies.These look like stacks of water- balloon-pancakes.They are sort of like the shipping and receiving department of the cell. Materials are received as vesicles unite with the Golgi apparatus, and sent elsewhere as other vesicles pinch off. Materials are temporarily stored in the Golgi bodies, and some further chemical reactions do take place there. 9. Mitochondria are found in nearly all eukaryotic cells, usually several or many per cell.They burn sugar for fuel in the process of cellular respiration: theyre the engine of the cell. Mitochondria consist of a smooth outer membrane and a convoluted inner membrane separated by an intermembrane space.The convolutions of the inner membrane are called cristae and the space inside the inner membrane is the mitochondrial matrix.As sugar is burned for fuel, a mitochondrion shunts various chemicals back and forth across the inner membrane (matrix to/from intermembrane space). 10. Plant cells normally contain another type of organelle that is not found in animals: chloroplasts. Chloroplasts convert light energy (from the sun) to chemical energy via the process of photosynthesis.The main pigment (green colour) located in chloroplasts and involved in photosynthesis is chlorophyll. Chloroplasts are surrounded by an outer membrane and inner membrane separated by an intermembrane space.The fluid within the centre of the chloroplast is called stoma.Within this fluid is an interconnected system of stacks of disks, kind of like more water-balloon-pancakes. Each sack is called a thylakoid. and has chlorophyll and other useful pigments built into its membranes. A stack of thylakoids is called a granum. 11. It has been suggested that mitochondria and chloroplasts may have originally arisen from prokaryotic invaders. Evidence for this includes the fact that both of these organelles contain their own DNA (separate from that in the nucleus) and program some, but not all, of their own protein synthesis.They control their own replication within the cell, and often can move around within the cell and change shape.They are both surrounded by two bilayer membranes suggesting one membrane originated from the plasma membrane of the cell and one from the plasma membrane of the hypothetical invader. Interestingly, because of the way human eggs and sperm are formed and unite, while half of the DNA in the nucleus of the newly formed embryo comes from the mother and half comes from the father, since sperm do not pass any of their mitochondria to the offspring, the mitochondrial DNA comes only from the mother.This has enabled some rather interesting studies to be done tracing relationships among various ethnic groups of people around the world based on mitochondrial DNA. The cytoskeleton is made of various types of special proteins. Microtubules are hollow tubes made of globular proteins. Most notably, they are found in cilia, flagella, and centrioles.The arrangement of microtubules in cilia and flagella consists of nine doublets around the edge and two single microtubules in the centre, all running the length of the structure.This is referred to as the nine-plus-two formula. In centrioles, microtubules are arranged in 9 sets of 3 each. Animal cells typically have a pair of centrioles located just outside the nucleus and oriented at right angles to each other.These function in cell division. Microfilaments are also part of the cytoskeleton and are made of solid rods of globular proteins. 12. 9 + 2 Formula 9 Sets Of 3 : Cross Section 9 Sets Of 3 : 3-D 13. In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and it is usually separately enclosed within its own lipid bilayer. The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name organelle, the suffix being a diminutive). Organelles are identified by microscopy, and can also be purified by cell fractionation.There are many types of organelles, particularly in eukaryotic cells.While prokaryotes do not possess organelles per se, some do contain protein-based micro compartments , which are thought to act as primitive organelles. 14. All living things are made up of cells. Cells are the basic structural and functional unit of life All cells come from preexisting cells 15. Protoplasm The term "protoplasm," from proto, first, and plasma, formed substance, was coined by the botanist Hugo von Mohl, in 1846, for the "tough, slimy, granular, semi-fluid It was used 1839 by Czech physiologist Johannes Evangelista Purkinje (1787-1869) to denote the gelatinous fluid found in living cell. Compose of inorganic and organic compounds like carbohydrates, proteins, lipids and nucleic acids 16. Plasma membrane / plasmolemma Bi-lipid layer Semi permeable Serves as boundary between the outside environment and the inside environment Outer membrane of cell that controls movement in and out of the cell 17. Fluid mosaic model -S.J. Singer and Garth Nicolson in 1972 - fluid because of I its hydrophobic components such as lipids and membrane proteins that move laterally or sideways throughout the membrane.That means the membrane is not solid, bu more like a 'fluid'. -mosaic that is made up of many different parts the plasma membrane is composed of different kinds of macromolecules 18. Most commonly found in plant cells & bacteria Supports & protects cells Made of cellulose 19. Control center of the cell Separated from cytoplasm by nuclear membrane/nuclear envelope Contains genetic material DNA arranged in thread like structure called chromatin Also contain RNA and proteins Nucleolus distinct part in the nucleus where ribosome synthesis takes place 20. Surrounds nucleus Made of two layers Openings allow material to enter and leave nucleus 21. In nucleus Made of DNA Contain instructions for traits & characteristics 22. Inside nucleus Contains RNA to build proteins 23. Gel-like mixture Surrounded by nuclear membrane Contains hereditary material 24. Powerhouse of the cell Produces energy through chemical reactions breaking down fats & carbohydrates Double membrane Cristae inner folds Matrix fluid part 25. Chloroplast Site for photosynthesis Contains green pigment called chlorophyll 26. Chromoplast Gives the yellow, orange, red color to fruits and flowers 27. Leucoplast Non pigmented Located in roots Storage for carbohydrates, proteins and lipids 28. Each cell contains thousands Made up of RNA and protein Protein synthesis Attached or free 29. Moves materials around in cell Serves as canal for substances Smooth type: lacks ribosomes Rough type : ribosomes embedded in surface 30. Branching canal No ribosome's Transport for large molecules Stores calcium ions in muscle cells 31. Contains attached ribosomes Transport ribosomes 32. packaging organelle Move materials within the cell Move materials out of the cell 33. Digestive organelle' for proteins, fats, and carbohydrates Transports undigested material to cell membrane for removal Cell breaks down if lysosome explodes 34. Membrane-bound sacs for storage, digestion, and waste removal Contains water solution Help plants maintain shape 35. Cytoskeleton 36. Thin and fibrous Bones and muscles of cells Microfilaments Microtubules Centrioles and spindle fiber Amoeboid movement of amoeba, cilia by paramecium and flagellum by euglena are made possible.