Biology Chapter 2: Cells 18/02/12 1:09 PM

Eukaryotie: True-Kernal (Reffering to membrane bound nucleus)DNA: Deoxyribonucleic Acid. Genetic material that is the blueprint of all life.Amoeba: Singe celled organism (Unicellular)Biogenesis: Living-Creation, or creation from living things. (Pre-existing cells) Creation of life from pre-existing live matter.Platelets: Fragments or remains of dead cells found in blood and used to coagulate (clog up) wounds to stop bleeding.ATP: Adenosine Tri Phosphate (Molecule used for energy)ADP: Adenosine Di Phosphate (Used energy molecule)Equilibrium: Equal concentration on both sides of cell (Equal)Passive transport is always along the concentration gradient until equilibrium is reached. Facilitated diffusion is passive transport through protein pathways to allow larger molecules throughOsmosis is passage of water from high concentration to low concentration.Active transport moves against a concentration gradient and therefore requires energy (ATP) to do so. H+=ProtonPolysaccharide: Poly-Many Saccharide-Sugars or Carbohydrates.Prokaryotic: Pro-Before Karyon-Kernel (Pre-Kernel referring to the fact that the DNA is unbound, not held together by a membrane) Simpler than Eukaryotic cells.Organelles: Little Organs -elles: LittleMitochondrion: Generates energy in animal cellsEnzyme: Catalyzes/ Speeds up or slows down a chemical reactionStarch: Molecule of glucose

Amylase: Enzyme that breaks down starch into glucose, is present in saliva.Cell Cycle:Growth: Longest Period – Involves cell enlargement and synthesis (combination of two or more entities that together form something new; alternately, it refers to the creating of something by artificial means) of organelles and moleculesReplication: Cell Division (Mitosis) – Daughter cells identical to parent cells form.Cell Death: Enzymes dismantle cell’s molecules for reuse and recycling.Microscopes: Top to Bottom:Eye Piece: Device looked through to see specimenBody Tube: Holds eyepiece and connects it to the objective lensNosepiece: Rotating section that contains objective lensObjective Lens: Lenses attached to microscopes of varying magnificationArm: Part of microscope used to carry itCoarse Adjustment Knob (Large Knob): Used to focus specimen. Moves either stage or lens.Fine Adjustment Knob (Smaller Knob): Fine tunes focus after using coarse knob.Stage: Large flat area, that has an aperture in it to allow light through. Is found under the objective lens.Stage Clips: Used to hold specimen slide in place on stage.Aperture: Hole in stage that allows light through the to illuminate the specimenDiaphragm: Controls amount of light going through apertureLight/Mirror: Source of light usually found near the base of the microscope. The light source makes the specimen easier to see.Using A Microscope: Use lowest power objective lens. Fasten specimen to slide. Using coarse adjustment knob, lower lens as far as it will go without touching the slide. Look through eyepiece and adjust light source for greatest amount of light. Turn coarse adjustment knob so that lens moves away from slide until image is in focus. Focus further using fine adjustment knob. Centre image in field of view by moving slide around.

Cell Wall Structure:

Cell Outermost StructureBacteria Cell Wall of peptidoglycan/murein

(Mesh like polymer of sugars and amino acids)

Fungi Cell Wall of Chitin (Fibrous substance of polysaccharides)

Yeasts Cell Wall of Glucan (D-Glucose linked by glycosidic (sugar-nonsugar) bonds) and Mannan (Polymer of mannose (natural polysaccharide))

Algae Cell Wall Of Cellulose (Insoluble carbohydrate)

Plants Cell Wall of Cellulose (Insoluble Carbohydrate)

Animals No Cell Wall, Plasma Membrane secretes a mixture of glycoproteins that form extracellular matrix.

2.1 Cell Theory 18/02/12 1:09 PM

2.1.1 Outline Cell TheoryThree Main Principles:All organisms are composed of one or more cellsCells are the smallest units of lifeAll cells come from pre-existing cells2.1.2 Discuss evidence for cell theoryUse of microscope has enabled observation of small scale units of life referred to as independent, separate beings called cells.No single organism found that contains less than one cell.Experiments show sterilized broth unable to spontaneously grow life without exposure to pre-existing life.The cell theory has amassed tremendous credibility through the use of the microscope in the following:Robert Hooke- studied cork and found little tiny compartments that he called cellsAntonie van Leeuwenhoek- observed the first living cells, called them 'animalcules' meaning little animalsSchleiden- stated that plants are made of 'independent, separate beings' called cellsSchwann- made a similar statement to Schleiden about animals.2.1.3 State that unicellular organisms carry out all the functions of life.All organisms exist in a uni- or multi cellular form. Carry out all functions including: Metabolism (The chemical processes that occur within a living organism in order to maintain life.), Growth (May be limited but still evident), Reproduction (Passing off of hereditary molecules to offspring),Response (Imperative for survival of organism to respond to environmental change),Homeostasis (Maintenance of internal chemical and biological balance ie. Temperature or ph)

Nutrition (The process of providing or obtaining the food necessary for health and growth.)2.1.4 Compare relative sizes of organisms using SI unit.Cells are relatively large, and then in decreasing size order are organelles, bacteria, viruses, membranes and molecules.Decreasing Order Cells (Largest single unit) 100 micrometres μmOrganelles 10 micrometresBacteria 1 micrometre (1x10-6 of a metre, one millionth of a metre)Viruses 100 nanometres nmMembranes 10 nanometresMolecules 1 nanometres (one billionth of a metre, 1/1000000000)

metre

m 1

centi c 0.01cmmilli m 0.001mmmicro μ 0.000001 μmnano n 0.000000001 nm

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification.Magnification = Measured length of the image/ Measured length of the specimenLength Of The Actual Specimen = Length of the image/ Magnification2.1.6 Limiting Cell SizeAs the size of the structure increases, surface to volume ratio decreases. As exchange of substances depends on the organisms surface area that is in contact with its surroundings, the decreases in surface to volume ratio decreases the amount of exchange, limiting a cells growth and size.Surface area to volume ration effectively limits the size or growth of a cell. In a cell, rate of heat and waste production and resource consumption are factors (depend on) its volume. Cell size also affect rate of chemical reaction within its interior. Surface area affects rate of movement of materials in and out of cell. This effectively inhibits larger cells abilities to function, and places limits their growth.Larger cells have relatively less surface area to work with, inhibiting their function. Therefore, organisms tend to have many small cells rather than few large ones (To maintain efficiency). Volume of a cell determines requirements while surface area determines supply.Cells that are naturally large in size are modified to allow efficient function (ie. Long and thin rather than spherical and inclusion of in/out foldings to increase surface area)Surface area of a sphere: (4)(pi)(radius squared)Volume of a sphere: (4/3)(pi)(radius cubed)2.1.7 State that multicellular organisms show emergent propertiesEmergent properties refers to the phenomenon of properties/functions of a large unit occur and are unrelated to any single smaller unit of the substance. I.e. individual heart cells cannot pump blood but the heart as a unit experiences this property.Multicellular organisms show emergent properties because they retain the ability to reproduce themselves. This allows the possibility of growth and replacement of dead or damaged cells. Multicellular organisms usually start out as a single cell after some type of sexual reproduction. This single cell has the ability to reproduce at a very rapid rate, forming a multicellular organism.

2.1.8 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.Cells that reproduce in multicellular organisms go through a process called differentiation to produce all the required cell types that are necessary for the wellbeing of the organism. The number of the different cell types from the original one is staggering. This differentiation process is the result of the expression of certain specific genes but not others. Genes, segments of DNA on a chromosome, allow for the production of all the different cells in the organism. Therefore, each cell contains all the genetic information for the production of the complete organism. However, each cell becomes a specific type of cell dependent on which DNA segment becomes active.2.1.9 State that stem cells retain the capacity to differentiate.Stem cells are cells within organisms that retain their ability to divide and differentiate into various cell types. Stem cells divide to form specific types of tissue, but also produce cells that remain as stem cells. Under the right conditions stem cells can be induced to express particular genes and differentiate into a particular type of cell. The stem cells that remain after division retain the ability to form any type of cell in an organism and can even form a complete organism, allowing for continual production of a particular type of tissue. 2.1.10 Outline the therapeutic use of stem cells.The use of embryonic or pluripotent stem cells allows for the ability of doctors to replace differentiated cells that have been lost in a patient due to injury or disease. This involves therapeutic cloning, where stem cells are implanted in area’s affected by disease, replacing damaged cells and relieving disease symptoms. Tissue-specific stem cells, or stem cells that reside only in certain types of tissue and can only produce new cells of that particular tissue can be introduced in to humans to replace damaged tissue cells, like the bone marrow of leukaemia patients.

2.2 Prokaryotic Cells 18/02/12 1:09 PM

2.2.1 Draw and label a Diagram of E.Coli as an example of a Prokaryotic Cell

2.2.2 Annotate the diagram with the functions of each named structureCell Wall: Semi-Rigid structure. Privdes anchor for Flagella, Protects cell and maintains its shape. (Composed of peptidoglycan/murein in most prokaryotic cells). Murein is a polymer mesh of sugars and amino acids.Capsule: (Also Slime Capsule, Polysaccharide layer (Many-Sugars) Thick layer outside cell wall. Used to stick cells together and for adhering to surfaces like teeth, skin and food. Also used as a food reserve and protection against chemicals and phagocytosis (consumption by white blood cells). Also prevents desiccation (Drying out)Plasma Membrane: Is found just inside the cell wall. Controls movement of materials in and out of the cell (Semi-permeable). Plays a role in binary fission of Prokaryotic Cells. Semi-permeable lipids regulating movement of materials in and out of cell.Cytoplasm: (Cell Plasma) Aqueous medium/solution containing dissolved solutes, food storage particles, enzymes and organelles (Ribosomes).Nucleoid of DNA: Irregularly shaped Region of cytoplasm containing/housing DNA (Genetic Material). Not enclosed within a nucleus. A single, long, continuous circular thread of DNA. Controls cell and reproduction. (Also called bacterial chromosome).

Plasmid: Small, circular, DNA molecules which are not connected to the Nucleoid or Bacterial Chromosome. Replicate independently of chromosomal DNA. Not required under normal conditions but aid in cell adaption through plasmid transfer (Donation of genetic material between cells allows for genetic resistance for viruses, antibiotics and also causes mutations).Ribosomes: Spherical structures/organelles scattered, unattached to membrane in the cytoplasm whose main function is protein synthesis and gene expression.Pili: Hair like structures used for cell attachment. Main function is in joining together bacterial cells in preparation for the transfer of DNA from one cell to another (Reproduction) and to form tissue. Flagella: Whip like tail (Flagellum) or tails (Flagella) used for locomotion/ motility/movement of the cell. Longer than pili. Thread-Like appendage.Not Shown: Mesosome:Invagination (fold) within plasma membrane of cell caused by preparation for electron microscopy as well as to increase surface to area ratio.2.2.3 Identify structures from 2.2.1 in Electron Micrographs of E.Coli

2.2.4 State that Prokaryotic cells divide by Binary Fission:

Prokaryotic cells divide by a very simple process called Binary Fission, in which DNA is copied, two daughter chromosomes become attached to different regions on the plasma membrane, and the cell divides into two genetically identical daughter cells. This divisional process includes an elongation of the cell and a partitioning of the newly produced DNA by microtubule-like fibres made of protein called FTsZ. Each new cells contains about half the original amount of cytoplasm. Growth restores cells to original size

1.

2. DNA is Cloned (Replicates itself)

3. DNA attaches to opposite sides of the membrane

4. Cytokinesis (Cell Motion/Movement). Division or splitting of enlarged cell in to two genetically identical daughter cells

Summary:Prokaryotes do not have a membrane bound DNA, making them prove to outside stimuli like viruses and pathogens. Their DNA is a nucleoid of one circular chromosome.DNA is free, unattached to proteins.Lack membrane bound organelles. Ribosomes are complex structures within the plasma membrane that lack their own exterior membraneCell wall is made up of peptidoglycan/Murein. Murein is a polymer mesh of sugars and amino acids.Divide by Binary Fission, a simple form of Cell DivisionCharacteristically small in size, 1-10 micrometres.

2.3 Eukaryotic Cells 18/02/12 1:09 PM

2.3.1 Draw and label a diagram of the ultrastructure of a liver cell as an example of an animal cell.

2.3.2 Annotate the diagram with the functions of each named structure.Found in Animal Cells:Plasma Membrane: Is found just inside the cell wall. Controls movement of materials in and out of the cell (Semi-permeable). Plays a role in binary fission of Prokaryotic Cells. Semi-permeable lipids regulating movement of materials in and out of cell.Cytoplasm: Jelly-like substance. (Cell Plasma) Aqueous medium/solution containing dissolved solutes, food storage particles, enzymes and organelles (Ribosomes). Fluid portion referred to as Cytosol.Nucleus: An isolated region where the DNA resides. It is bordered by a double membrane referred to as the nuclear envelope/membrane.Nucleolus: A Dense, solid structure involved in ribosome synthesis.Nuclear Membrane: This membrane allows compartmentalization of the Eukaryotic DNA, therefore providing an area where DNA can carry out its functions and not be affected by processes occurring in other parts of the cell.Nuclear Pore: Allows communication between the Nucleus and the rest of the cell.Golgi Apparatus: Stores, Modifies and Packages proteins.

Endoplasmic Reticulum: Transports materials through out the internal region of the cell. Network of tubes and flattened sacs. ER connects with the plasma membrane and the nuclear membrane and may be smooth or have attached ribosomes (rough ER). Production of membrane phospholipids and cellular lipids, sex hormones like testosterone and estrogen. Detoxifies drugs in liver. Stores calcium ions needed for contraction of muscle cells. Transports lipid based compounds. Aids liver in releasing glucose in to bloodstream when necessaryRough ER: Has ribosomes attached to it and is a site of protein synthesisSmooth ER: Has no ribosomes.Ribosomes: Small (20nm) structures, free in the cytoplasm or associated with the ER, they are responsible for protein synthesis. Lack exterior membrane. Carry out protein synthesis. Composed of RNA and protein. Larger and Denser in Eukaryotes when compared with Prokaryotes. Mitochondria: Rod Shaped. Mitochondria carry out respiration. They have their own DNA, allowing them some autonomy in the cell. They have a double-membrane, the outer membrane is smooth but the inner membrane is folded into cristae (internal compartments). The mitochondria provides the cell with usable cellular energy called ATP and is referred to as the cell powerhouse.Centrioles: Are associated with nuclear division. They are composed of microtubules. The area in which centrioles are found is called the centrosome. It is present in all eukaryotic cells, but centrioles are absent from higher plant cells.Lysosome: Sacs bounded by a single membrane. They contain and transport enzymes. Lysosomes show little internal structure. Lysosomes are usually absent from plant cells. Arise from G.A. Enzymes contained are hydrolytic (Decompose in water). Used to catalyze the breakdown of proteins, acids, lipids and carbs. Fuse with old or damaged organelles to recycle them. Also break down materials brought into cell using phagocytosis. Interior of lysosome is acidic, which is necessary for enzymes to hydrolyze large molecules.Vacuoles: Smaller in animal cells than plant cells. Storage organelles that usually form from the Golgi Apparatus. They are membrane bound and have many possible functions.Found in Plant Cells:Central Vacuole: Has storage and hydrolytic functions (decomposes chemical compounds by reactions with water).

Chloroplasts: Specialized plastids (manufacture and store important chemical compounds used by the cell) containing green pigment of chlorophyll. Sites for Photosynthesis.Cell Wall: Semi-Rigid structure composed mainly of cellulose.Plasma Membrane: Is found just inside the cell wall. Controls movement of materials in and out of the cell (Semi-permeable). Plays a role in binary fission of Prokaryotic Cells. Semi-permeable lipids regulating movement of materials in and out of cell.Mitochondria: Mitochondria carry out respiration. They have their own DNA, allowing them some autonomy in the cell. They have a double-membrane, the outer membrane is smooth but the inner membrane is folded into cristae (internal compartments). The mitochondria provides the cell with usable cellular energy called ATP and is referred to as the cell powerhouse.Starch Granula: Carbohydrates (Complex Sugars) stored in amyloplasts (non-pigmented organelles).

Golgi Apparatus: Stores, Modifies and Packages proteins.Ribosomes: Small (20nm) structures which manufacture proteins. Free in cytoplasm and/or associated with the surface of the Endoplasmic Reticulum. Lack exterior membrane. Carry out protein synthesis. Composed of RNA and protein. Larger and Denser in Eukaryotes when compared with Prokaryotes.Nuclear Membrane: Double-layered Membrane. This membrane allows compartmentalization of the Eukaryotic DNA, therefore providing an area where DNA can carry out its functions and not be affected by processes occurring in other parts of the cell. Nucleolus: A Dense, solid structure involved in ribosome synthesis.Nuclear Pore: Allows communication between the Nucleus and the rest of the cell.Nucleus: An isolated region where the DNA resides. It is bordered by a double membrane referred to as the nuclear envelope/membrane.Cytoplasm: contains dissolved substances, enzymes and the cell organelles. Jelly-like substance. (Cell Plasma) Aqueous medium/solution containing dissolved solutes, food storage particles, enzymes and organelles (Ribosomes). Fluid portion referred to as Cytosol.Endoplasmic Reticulum: Network of tubes and flattened sacs. ER connects with the plasma membrane and the nuclear membrane and may be smooth or have attached ribosomes (rough ER). Transports materials through out the internal region of the cell. Production of membrane phospholipids and cellular lipids, sex hormones like testosterone and estrogen. Detoxifies drugs in liver. Stores calcium ions needed for contraction of muscle cells. Transports lipid based compounds. Aids liver in releasing glucose in to bloodstream when necessary

2.3.3 Identify Structures from 2.3.1 in Electron Micrographs of Liver Cells.

2.3.4 Compare Prokaryotic and Eukaryotic Cells.Differences:

Prokaryotic Cells Eukaryotic CellsDNA in a ring form without protein DNA with proteins as

Chromosomes/ ChromatinDNA free in the cytoplasm (Nucleoid Region)

DNA enclosed within a nuclear envelope (Nucleus)

No Mitochondria Mitochondria Present70S Ribosomes 80S RibosomesNo Internal Compartmentalization to form Organelles

Internal Compartmentalization present to form many types of Organelles.

Size Less Than 10 Micrometres Size More Than 10 MicrometresSimilarities:Both types of cell have some sort of outside boundary between that always involves a plasma membrane.Both types of cells carry out all the functions of life.DNA is present in both cell types.2.3.5 State three differences between plant and animal cells.Plant Cells Animal CellsExterior of cell includes an outer cell wall with a plasma membrane just inside.

Exterior of Cell includes only a plasma membrane. There is no cell wall.

Chloroplasts are present in the cytoplasm

There are no chloroplasts

Possess large centrally located vacuoles

Vacuoles are usually not present or are small.

Store carbohydrates as starch Store Carbohydrates as glycogenDo not contain centrioles within a centrosome area.

Contain centrioles within a centrosome area.

Presence of Cell wall allows for a fixed, often angular shape

Lack of cell wall means cell is flexible and likely to be a rounded shape

Similarities:Most cellular organelles are present in both plant and animal cells.

2.3.6 Outline two roles of Extracellular ComponentsCell Walls in plant cells maintain shape, prevent excess water uptake and support plants upright position against gravity.Secretion of glycoproteins by animal cells forms extracellular matrix of proteins and fibres that strengthen plasma membrane, allow attachment between cells, and aid cell to cell interaction. Research point towards involvement of ECM in directing stem cells to differentiate. ECM aids in cell migration and movement.

2.4 Membranes 18/02/12 1:09 PM

2.4.1 Draw and label a diagram to show the structure of a membrane.

2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.The hydrophobic and hydrophilic regions cause phospholipids to always align as a bilayer if there is water present and there is a large number of phospholipid molecules. As the fatty acid tails do not strongly attract one another, the membrane can retain its shape whilst still remaining fluid and flexible. Hydrophilic molecules are attracted to water. Hydrophobic molecules are not attracted to water, but are attracted to each other. The phosphate head is hydrophilic and the two hydrocarbon tails are hydrophobic. In water, phospholipids form double layers with the hydrophilic heads in contact with water on both sides and the hydrophobic tails away from the centre. The attraction between the heads and the surrounding water makes membranes very stable, whilst the lack of attraction between the tails allow them to remain fluid and move.

The hydrophilic and hydrophobic properties of the different regions of the phospholipid molecules cause them to form a stable bilayer in an aqueous environment.

2.4.3 List the functions of membrane proteins.Six General Functions:Hormone binding sites: Specific shape exposed to exterior that fits shape of specific hormones. Attachment cause change in shape of the protein, resulting in message being relayed to interior of cellEnzymatic Action: Enzymes attached to membranes catalyze (Speed up or slow down) chemical reactions. May be placed on interior or exterior of cell. Often grouped so a sequence of metabolic reactions (metabolic pathway) can occur.Cell Adhesion: Provided by proteins that hook together in various ways to provide permanent or temporary connections. Connections, referred to as junctions, may include gap junctions or tight junctions.Cell to Cell Communication: Proteins attached with molecules of carbohydrate. This provides an identification label representing cells of different types or species.Channels for passive transport: Proteins that span membrane provide passageways for substances to pass through. When this transport is passive, a material moves through the channel from an area of high concentration to an area of low concentration.Pumps for active transport: Proteins shuttle substances from one side of membrane to another by changing shape. This process requires the expenditure of energy in the form of ATP. It does not require a difference in concentration to occur.2.4.4 Define Diffusion and OsmosisDiffusion is the passive movement of particles from a region of higher concentration to a region of lower concentration. Diffusion is movement along a concentration gradient. Facilitated diffusion occurs when particles travel across a membrane using carrier proteins without expending any energy to do so.

Osmosis is the passive movement of water molecules across a partially permeable membrane, from a region of lower solute concentration (Hypo-osmotic) to a region of higher solute concentration (Hyper-osmotic). Osmosis is also movement along a concentration gradient as the low solute concentration would have a higher concentration of water than the high solute concentration. Isosmotic or balanced/equal solutions result in equilibrium, where no net movement on either side of the semi permeable membrane is evident.

Passive transport continues until there is an equal concentration of substances in both areas involved. This is called equilibrium.Size and polarity (charge) of molecules determine the ease with which various substances can cross membranes. Small and non-polar molecules cross membranes easily whilst large polar molecules cross membranes with difficulty.

2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion

Simple Diffusion Substances other than water move between phospholipid molecules or through proteins which possess channels. Stops at equilibrium.

Facilitated Diffusion Non-channel protein carriers change shape to allow movement of substances other than water. Levels off when total saturation of available carriers occurs.

Osmosis Only water moves through the membrane using aquaporins which are proteins with specialized channels for water movement. Stops when a isosmotic (same osmotic pressure) solution occurs on either side of the membrane.

2.4.6 Explain the role of protein pumps and ATP in active transport across membranes.Active transports requires energy, which is found in the form of Adenosine Tri-Phosphate in cells. Active transport occurs when substances move against a concentration gradient. This process allows cells to maintain interior concentrations of molecules that are different from exterior concentrations. Along with energy, a membrane protein must be involved for this active transport to occur, allowing molecules to cross the membrane against the concentration gradient.

Protein pumps work by binding intracellular ions/molecules to a membrane protein. A phosphate group from ATP then binds with the membrane protein, creating ADP or Adenosine Di Phosphate and causing the membrane protein to change shape, expelling the ions/molecules to the exterior. Two extracellular ions/molecules bind to a different region of the protein, causing the phosphate group to release. Loss of the phosphate group restores the membrane protein to its original shape, releasing ions/molecules in to the intracellular space. The cycle can now begin again as necessary.

2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.Vesicles are small, membrane bound sacks that can store or transport substances. They are usually made up of lipid membranes (phospholipid bilayer), allowing them to fuse with the plasma membrane. Proteins produced by the ribosomes of the rough endoplasmic reticulum enter the lumen of the ER (Inner Area of the E.R).Protein exits the ER and enters the cis side of face of the Golgi Apparatus that is attached/near the ER using a vesicle.Protein moves through the Golgi Apparatus, is modified and exits on the trans or face further from ER inside a vesicle.The vesicle with the modified protein inside moves to and fuses with the plasma membrane. This results in the secretion of the contents from the cell. At this point the vesicle has become part of the plasma membrane.

Vesicle is made by pinching off a piece of membrane.

Fluidity of membrane allows this.Vesicles can be used to transport material around inside cells.Proteins are transported in vesicles from the rough endoplasmic reticulum to the Golgi apparatus and from the Golgi apparatus to the plasma membrane.Formation of vesicle from plasma membrane allows material to be taken in.Endocytosis/pinocytosis (Liquids)/phagocytosis (Solids) is absorption of material using a vesicle.Fusion of vesicle with plasma membrane allows material to be secreted / passed out.Exocytosis is secretion of material using a vesicle.

2.4.8 Explain how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.

Due to its fluid yet rigid structure, the membrane is able to alter its shape. In Endocytosis, this allows for the membrane to be pulled inwards, then pinched in at the top, enclosing the necessary molecules. It then breaks off the membrane, which snaps together and takes its usual shape as the newly formed vesicle travels through the cytoplasm with its contents. In Exocytosis, it allows for the vesicle to fuse with the plasma membrane, keeping the cell sealed whilst allowing an opening for the contents of the vesicle to be expelled. Once it has finished, the membrane spreads apart, flattening out into its usual shape and incorporating the vesicle within.

Examples of Exocytosis include:The production and secretion of insulin by the pancreas into the blood stream to regulate blood glucose levelsNeurotransmitters that are released at synapse in the nervous system.Examples of Endocytosis include:Phagocytosis or the intake of large particulate matterPinocytosis or the intake of extracellular fluids

2.5 Cell Division 18/02/12 1:09 PM

2.5.1 Outline the stages in the cell cycle, including interphase (G1, S, G2), Mitosis and Cytokinesis

New cells are produced by the division of an existing cell, beginning with Interphase, then mitosis and then cytokinesis.Interphase: DNA replication and transcription occurs.Mitosis: The division of the nucleus to form two genetically identical nuclei is termed mitosis.Cytokinesis: Division of the cytoplasm to form two new cells is called cytokinesis.

Interphase is a very active time in a cells life. It involves metabolic reactions, DNA replication and an increase in the number of organelles. Because interphase involves growth, it is essential that protein synthesis occurs at a rapid rate during this phase.

The largest part of the cell cycle in most cells is interphase. It includes within it three separate phases, G1,S and G2. During G1, the major event is growth of the cell. At the beginning of G1, the cell is at its smallest. S phase occurs after G1 and DNA replication becomes the main activity of the cell. This phase is also known as synthesis phase. After its chromosomes have been replicated, the cell begins G2 and beings to grow again, making preparations for mitosis or M phase. During G2, organelles may increase in number whilst DNA begins to condense in from chromatin in to chromosomes, and microtubules may begin to form. Condensation is accomplished via a process called supercoiling. The DNA wraps around histones (stone like proteins) to produce nucleosomes. These nucleosomes are further wrapped in to a solenoid. Solenoids group together in looped domains and then a final coiling occurs to produce the chromosome.

Mitosis or M Phase involves the separation of chromosomes, which move to opposite poles of the cell, thus providing identical genetic material to each of these locations. When the chromosomes are at the poles of the cell, the cytoplasm divides to form two distinct cells from the larger parent. These two cells have the same genetic material and are referred to as daughter cells.

M Phase involves four phases which are prophase, metaphase, anaphase and telophase.In Prophase, the chromatin fibres beome more tightly coiled to form chromosomes. The nuclear envelope then disintegrates and the nucleoli disappear. The miotic spindle begins to form and is complete at the end of prophase. The centromere of each chromosome has a region called the kinetochore that attaches to the spindle. The centrosomes move toward opposite poles of the cell due to lengthening microtubules. In Metaphase, the chromosomes are moved to the middle or equator of the cell. This is reffered to as the metaphase plate. The chromosomes centromeres lie on the plate. The movement of chromosomes is due to the action of the spindle which is made of microtubules. The centrosomes are now at the opposite poles.In Anaphase, the shortest stage of mitosis, the two sister chromatids of each chromosome are split. These chromatids, now chromosomes, move towards the opposite poles of the cell. The chromatid movement is due to shortening of the microtubules of the spindle. Because the centromeres are attached to the microtubules, they move towards the poles first. At the end of this phase, each pole of the cell has a complete, identical set of chromosomes.In Telophase, the chromosomes are at each pole. A nuclear membrane (envelope) begins to re-form around each set of chromosomes. The chromosomes start to elongate to form chromatin. Nucleoli reappear and the spindle apparatus disappears. The cell is elongated and ready for cytokinesis. Nuclear division is now complete.

All the stages of Mitosis are occur in continuum. They are not discrete or separate stages. Once nuclear division has occurred, the cell undergoes cytokinesis, which means it splits in to two separate cells. Animal cells have a fluid plasma membrane and therefore pinch inward to form cleavage furrows. Plant cells have firm cell walls and therefore form cell plates, which occur midway between the two poles of the cell and move outward towards the sides of the cell from a central region. Both processes result in two separate daughter cells that have genetically identical nuclei.

2.5.2 State that tumours (Cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue.

When cells multiply rapidly, or in other words when mitosis gets out of control and a cell begins to divide, the new daughter cell begins to divide as well. This overflow of cells can form a solid mass called a tumor. This is a diseased state of a cell which can result in cancer. Tumors can occur in any organ or tissue that undergoes an unusual or disorderly pattern of division/reproduction.

2.5.3 State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.

The largest part of the cell cycle in most cells is interphase. It includes within it three separate phases, G1,S and G2. Interphase is a very active time in a cells life. It involves metabolic reactions, DNA replication/Protein synthesis and an increase in the number of organelles like mitochondria and chloroplasts, as a result in increased energy demand. Because interphase involves growth, it is essential that protein synthesis occurs at a rapid rate during this phase.

2.5.4 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).

Mitosis or M Phase involves the separation of chromosomes, which move to opposite poles of the cell, thus providing identical genetic material to each of these locations. When the chromosomes are at the poles of the cell, the cytoplasm divides to form two distinct cells from the larger parent. These two cells have the same genetic material and are referred to as daughter cells.

M Phase involves four phases which are prophase, metaphase, anaphase and telophase.In Prophase, the chromatin fibres beome more tightly coiled to form chromosomes. The nuclear envelope then disintegrates and the nucleoli disappear. The miotic spindle begins to form and is complete at the end of prophase. The centromere of each chromosome has a region called the kinetochore that attaches to the spindle. The centrosomes move toward opposite poles of the cell due to lengthening microtubules.

In Metaphase, the chromosomes are moved to the middle or equator of the cell. This is reffered to as the metaphase plate. The chromosomes centromeres lie on the plate. The movement of chromosomes is due to the action of the spindle which is made of microtubules. The centrosomes are now at the opposite poles.In Anaphase, the shortest stage of mitosis, the two sister chromatids of each chromosome are split. These chromatids, now chromosomes, move towards the opposite poles of the cell. The chromatid movement is due to shortening of the microtubules of the spindle. Because the centromeres are attached to the microtubules, they move towards the poles first. At the end of this phase, each pole of the cell has a complete, identical set of chromosomes.In Telophase, the chromosomes are at each pole. A nuclear membrane (envelope) begins to re-form around each set of chromosomes. The chromosomes start to elongate to form chromatin. Nucleoli reappear and the spindle apparatus disappears. The cell is elongated and ready for cytokinesis. Nuclear division is now complete.

All the stages of Mitosis are occur in continuum. They are not discrete or separate stages. Once nuclear division has occurred, the cell undergoes cytokinesis, which means it splits in to two separate cells. Animal cells have a fluid plasma membrane and therefore pinch inward to form cleavage furrows. Plant cells have firm cell walls and therefore form cell plates, which occur midway between the two poles of the cell and move outward towards the sides of the cell from a central region. Both processes result in two separate daughter cells that have genetically identical nuclei.

2.5.5 Explain how mitosis produces two genetically identical nuclei.The result of the process of mitosis is two nuclei. During S phase, each chromosome replicates (forms an exact copy of itself). These copies are called sister chromatids. These identical sister chromatids are separated during Anaphase, and are moved to each pole. When they are separated they are referred to as chromosomes. The result is two nuclei, identical to each other and to the original nucleus.

2.5.6 State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis.

Growth of organisms, development of embryos, repair of damaged tissues and asexual reproduction all involve mitosis. Mitosis does not occur randomly or happen by itself, it is a part of the cell cycle.