B I O L O G Y // AQA // Revision Cards

• Carbohydrates contain: carbon (C), hydrogen (H), and oxygen (O).
• There are several types of carbohydrates: sugars, starch and cellulose.

S U G A R S

• Small, water-soluble, sweet molecules that are in two groups; monosaccharides and disaccharides.
• Monosaccharides are simple sugars (e.g. glucose, fructose, and galactose).
• Glucose has two forms; alpha and beta.
• Disaccharides form when two monosaccharides bond through a condensation reaction (forming a glycosidic bond).
• Glucose + Fructose = Sucrose
• Glucose + Galactose = Lactose
• Alpha Glucose + Alpha Glucose = Maltose
• Chemical test: Benedict's solution (take sample, add Benedict's, boil sample, colour change from blue to red).

I M P O R T A N C E

• Immediate energy source
• Energy transport
• Chemical energy (efficient source)

S T A R C H

• A polysaccharide made up of amylose and amylopectin.
• It is insoluble, compact and stores glucose.
• It has (alpha) 1-4 glycosidic bonds which have a bond angle-this lead to the molecule spiralling.
• Chemical test: Iodine test (take sample, add drops of iodine, solution goes from brown to blue/black).

I M P O R T A N C E

• Compact energy store
• Insoluble (little effect on osmotic balance).
• Large surface area (more branches, increases attachment of glucose).

C E L L U L O S E

• It has (beta) 1-4 glycosidic bonds (the molecule is long and straight).
• Several celluloses lie side by side to make microfibrils (these are held together by hydrogen bonds).
• Chemical test: HCl test (take sample, add HCl, boil. Neutralise. Add Benedict's and boil. Colour change blue to red).

L I P I D S

• Lipids contain: carbon (C), hydrogen (H), and oxygen (O).
• They are hydrophobic and there are three main types: triglycerides, phospholipids, and cholesterol.
• Chemical test: Emulsion test (take sample, dissolve in alcohol, tip into water, cloudy white emulsion produced).
• Cholesterol: a hydrophobic, ring-like structured lipid which, in excess, can lead to coronary heart disease.

T R I G L Y C E R I D E S

• A triglyceride (a glycerol and three fatty acids)-these undergo a condensation reaction and form an ester bond.
• A fatty acid is a chain of carbon atoms that has an acid group (all fatty acids have double bonds).
• Saturated fatty acids have the maximum amount of hydrogen.
• Unsaturated fatty acids have less hydrogen because they contain certain C=C double bonds.

P H O S P H O L I P I D S

• Phospholipids are like triglycerides, except they have only two fatty acids and a phosphate group.
• They consist of hydrophilic heads and hydrophobic tails.

I M P O R T A N C E

• Protection (e.g. fat under the skin, kidneys at the back of the abdomen).
• Insulation (for reduction in heat loss-for core body temperature).
• Energy source (34hJg-1).
• Energy store (unlimited storage).
• Water-proofing (skin produces oils etc).
• Structural (make up cell membranes).
• Steroids (hormones like testosterone, progesterone etc).

P R O T E I N S

• Proteins contain the elements; carbon (C), hydrogen (H), oxygen (O), nitrogen (N).
• Proteins are very large molecules composed of amino acid chains which are unbranched.
• They all have the same structure, but the R group can be one of twenty chemical groups.
• Essential amino acids cannot be made by interconnecting others.
• 1st Class Protein: contain essential amino acids // 2nd Class Protein: made up of plant protein.
• Proteins are held together by peptide bonds.
• The order of the sequence of amino acids determines its structure and how it works.
• Chemical Test: Biuret's reagent (take a sample, add Biruret's, colour changes from blue to violet).

I M P O R T A N C E

• Growth and repair (the cytoplasm is 10% protein).
• Enzymes (these are proteins) // Antibodies (made of proteins) // Receptors.
• Cell Recognition (antigens).
• Energy (especially for carnivores).
• Structual (e.g. muscle, bones, hair, skin).

S T R U C T U R E

• Primary: this is simply the sequence of amino acids along the chain.
• Secondary: certain sequences of amino acids fold up into short regions of the 3D structure (e.g. alpha helix/beta pleated sheet).
• Tertiary: an overall 3D shape molecular structure-either globular or fibrous.
• Quarternary: some proteins require two or more polypeptide chains and form a functional protein molecule (e.g. haemoglobin, collagen, antibodies).

B O N D I N G

• Primary: peptide bonds.
• Secondary: hydrogen bonds (formed between certain atoms within the protein chains).
• Tertiary: hydrogen bonds and disulphide bridges (they form strong cross-links).
• Quarternary: hydrogen bonds, disulphide bridges, ionic bonds, hydrophobic interactions.
• Ionic Bonds: some amino acids have charged (R) groups (where the + and - form a bond).
• Hydrophobic Interactions: hydrophobic (R) groups fold into the molecule away from water- these interact.

N U C L E I C  A C I D S

• Nucleic acids are all polymers with unbranched chains. They are made up of nucleotides.
• Nucleotides are made up of a phosphate, a nitrogenous base and a five-carbon sugar (phosphate bonded to sugar by an ester bond).
• It can react with an (OH) group on another sugar to form a phosphodiester bond.
• Bases-based on the two families of chemicals: Purines (2 ring structure) and Pyrimidines (1 ring structure).
• Bases; Adenine; Guanine; Thymine; Cytosine; and Uracil (corresponds as Thymine).

T Y P E S

• [Name // Sugar // Bases // Structure // Where it's found]
• DNA (deoxyribonucleic acid) // [Deoxyribose // ATCG // Double Helix //Nucleus]
• RNA (ribonucleic acid).
• mRNA (messenger) [Ribose // AUCG // Simple Chain // Cytoplasm, Nucleus]
• tRNA (transfer). [Ribose // AUCG // 'Clover leaf' // Cytoplasm]
• rRNA (ribosomal). [Ribose // AUCG // Ribosome // Cytoplasm]

• Codes are stored in DNA in the nucleus and ribosomes produce proteins in the cytoplasm (DNA stays in the nucleus). A copy is produced which can move, mRNA, can leave the nucleus and more to the cytoplasm.
• At the ribosomes, it is used as a template to move the protein.
• Transcription: copy from DNA to mRNA // Translation: reading the mRNA.

T R A N S C R I P T I O N

• Enzyme (polymerase) attaches to promoter region and moves down the DNA, breaking the hydrogen bonds, linkinng the base pairs.
• The nucleus contains the free nucleotides, they come into the unzipped DNA and bond to their complementary base. The enzymes joins them together. 
• Then enzyme moves down DNA strand, mRNA strand detaches (DNA zips up).
• Enzyme continues until it reaches 'stop' codon, it then detaches and releases mRNA strand.

S P L I C I N G

• Genes contain non-coding regions of DNA called introns in between the coding sections (exons). mRNA strand made is known as pre-mRNA because it also contains introns between the exons. Splicing enzymes cut out the inhibitor and join all the exons together.

G E N E T I C  C O D E

• Genetic code is an non-overlapping code (where it is read in triplets so there are no overlapping of the bases).
• The code is also universal (whatever triplet code it is, it is the same for all species-acts as evidence for evolution).
• It is also degenerate (there are several ways to code for an amino acid-each one can have one or more).
• Decoding: make an mRNA strand of a known sequence, add it to a bacterial culture and see what protein is made.

T R A N S L A T I O N

• mRNA enters the cytoplasm and the small subunit of the ribosome attaches next to the start codon.
• tRNA has anticodons and has different amino acids attached (AUG-start codon-binds to the mRNA).
• The large subunit now completes the ribosome structure (it has 2 binding sites one with tRNA and the other empty).
• The next tRNA enters the second site, a peptide bond is formed between the two amino acids (holds both to tRNA).
• The first tRNA leaves the ribosome and the whole structure moves three bases along the mRNA and process repeats.
• When the stop codon is reached, a release factor binds to the stop codon.
• The polypeptide is released and the ribosome disassembles.

D N A  R E P L I C A T I O N

• In theory, there a three possible ways to copy DNA: conservative, disruptive and semi-conservative.
• Meselson & Stahl grew bacteria in a medium with heavy nitrogen (15N)-all the DNA made was heavier.
• They took another sample after 20 minutes and transferred it to another medium but with lighter nitrogen (14N).
• 20 minutes after, a sample was taken of DNA and span in a centrafuge.

E X P L A N A T I O N

• Parents were grown in heavy nitrogen (15N) and both DNA strands are made of 15N compounds and spin to the bottom.
• 1st Generation: parents DNA splits to form two templates, new strands formed from 14N compounds.
• Each DNA molecule consists of one 15N and one 14N- so overall, an intermediate mass that spins to the middle of tube.
• 2nd Generation: the hybrid strands now seperate, the heavy strands have a new light one added.
• The light strand has another light strand, there are two bands; one hybrid (15N and 14N) and one light (14N and 14N) which stays towards the top of the tube.

M E C H A N I S M

• The mechanism involves two enzymes; Helicase (breaks hydrogen bonds between base pairs) and DNA polymerase (which makes new strands).
• The chain is said to have a 3" and a 5" end.
• This denotes the carbon atom the phosphate is attached to.
• 3" to 5" run in opposite directions on the two strands.
• DNA polymerase recognises the 3" end and makes a new strand on the 5" to 3" direction.
• This works for one of the strands- the leading strand due to the strands being anti-parallel.
• DNA polymerase joins the strand as far as it has been opened by helicase and builds the new chain 'backwards'.
• This is the lagging strand- it is built in short sections which are then joined together.

• Most enzymes are proteins they speed up reactions as they are biological catalysts.
• They take part in reactions but are regenerated, so far, most enzymes are only required in small amounts (intracellular).
• Extracellular are produced in large amounts and 'exported' out of cells (e.g. digestive enzymes).
• The prefix is determined by substrate it chemically reacts with. The suffix is the phrase (-ase).

S T R U C T U R E

• Enzymes are usually globular proteins with a tertiary or quarternary structure.
• The surface has one or more pockets/grooves/holes-one will be the catalytic site (the active site).
• This site gives enzymes their specifity, only the correctly shaped molecule can fit well enough to have the reaction occur.
• Other sites bind together/bind other molecules what can control enzyme activity.
• Lock and Key Theory: the correct shape of substrate fits perfectly and allows reactions to occur.
• Induced Fit Theory: the substrate fits closely into the site at first.
• A conformational change occurs and the active site changes shape to become a perfect fit for the substrate.
• The substrate molecule fits as it has been induced and is now called an enzyme substrate complex. The reaction occurs and products are released.

• Activation Energy: the energy required to initiate a reaction (it is lowered due to the substrate being held in the correct orientation for the reaction to occur).
• There are four main factors affecting enzymes; temperature; pH; enzyme concentration; & substrate concentration.
• Temperature: the rise in temperature makes the enzymes molecules vibrate more. If the temperature goes above a certain level, the vibrations break the bonds that hold its shape. The active site changes and the enzyme and substrate no longer fit together (the enzyme is denatured).
• pH: all enzymes have an optimum pH value (most human enzymes work best at pH7). H+ and OH- ions in acids/alkalis can affect the ionic bonds and hydrogen bonds in the enzymes' tertiary structure. This makes the active site change shape, so the enzyme is denatured.
• Enzyme Concentration: the more enzyme molecules, the more likely a substrate will collide and form an enzyme-substrate complex. Increasing the concentration of enzymes consequently increases rate of reaction. A limited amount of substrate means there's more than enough enzyme molecules for existing substrate (adding more than capacity would have no affect).
• Substrate Concentration: the higher the substrate concentration, the faster the reaction. More substrate molecules, more collisions, more active sites used until 'saturation'. Full active sites can be reached, adding more substrate has no affect. Substrate concentration decreases with time, so will rate of reaction.

C O M P E T I T I V E  I N H I B I T O R S

• A non-substrate (competitive inhibitor) molecule has a very similar structure to the substrate.
• The inhibitor will compete with the substrate molecules to bind to the active site and so, prevent the substrate from entering. No reaction takes place. Thus, reducing rate.
• The effect on rate is determined by the ratio of substrate : inhibitor.
• If there's a high concentration of the inhibitor, it will take up nearly all the active sites and hardly any of the substrate will get to the enzyme.
• A higher concentration of substrate, will increase the rate of reaction.

N O N - C O M P E T I T I V E  I N H I B I T O R S

• Non-competitve inhibitor molecules bind to the enzyme away from its active site.
• This causes the active site to change shape so the substrate molecules can no longer bind to it.
• They don't 'compete' with the substrate molecules to bind to the active site because they are a different shape.
• Increasing the concentration of substrate won't make any difference to the reaction rate-enzyme activity will still be inhibited.

W A T E R

• Water is polar (hydrogen bonds are individually weak, but collectively very strong).
• Water is cohesive (cohesion is the attraction between molecules of the same type). Water has strong cohesion as the molecules are polar. Strong cohesion helps water to flow (e.g. how water travels up columns in the xylem). Strong cohesion = high surface tension (when in contact with the air). This can be how pond skaters 'walk' on water.
• Water is adhesive('sticks' to something else other than itself).
• Water is a metabolite (metabolic reactions such as condensation/hydrolysis).
• Water has high latent heat(takes a lot of energy to break hydrogen bonds between water molecules).
• Water-when cooled-can become dense (it is at its most dense at 4 degrees). Thus, when its colder than 4 degrees, it floats. Water freezes from the top down, therefore, allowing aquatic life to survive in winter.
• Water has a specific heat capacity(the amount of heat required to raise temperature by 1 degree). To increase the temperature, the hydrogen bonds have to vibrate-water has lots of hydrogen bonds. Water doesn't experience rapid temperature changes. Temperature is relatively stable so it enables lifeforms to flourish.
• Water is a good solvent (because water is polar, the positive end of a water molecule will be attracted to the negative ion, and the negative attracts the positive-this means ions will get totally surrounded by water molecules and dissolve).

• Cells --> Tissue --> Organ --> Organ System --> Organism
• 4 tissue classes; epithelia; muscular; nervous; connective.
• Epithelia: covering tissues, single layers, multiple laters, glandular, flat/cuboidal/elongated.
• Muscular: contractable, three types; skeletal/straited/voluntary; cardiac; non-striated/involuntary/smooth.
• Nervous: generates/transmits electrical impulses (generally doesn't divide or reproduce).
• Connective: extracellular material makes up more than half the tissue (e.g. blood, bone, cartilage, cartilage, ligaments, tendons, areolar connective tissue).
• Organelles: intracellular structures with specific functions.
• Eukaryotes have membrane bound structures.
• Nucleus: largest organelle // contains genetic information // double membrane.
• Chloroplast: handles photosynthesis // double membrane // can engulf bacteria.
• Mitochondria: site of aerobic respiration // acitivty of organelle can be determined by no. // double membrane //cristae.
• Lysosomes: single membrane // densely stained interior // contains digestive enzymes // involved in cell death.
• Endoplasmic Reticulum: system of membranes // smooth: protein synthesis // rough: proteins made at ribosomes.
• Golgi Apparatus: fluid filled membrane bound flattened sacs // processes & packages new lipids & proteins.
• Ribosomes: appear as black dots on micrograph (e.g. on RER) // free in cytoplasm // site of protein synthesis.

S E P A R A T I O N  O F  O R G A N E L L E S

• The method involves ultracentrafugation (where the samples are spun at increasing speeds).
• Sample is ground up (macerated) or liquidised in; ice cold (slows enzymes); isotonic (prevents osmotic bursting); buffer (keeps pH constant).
• Filter the liquid to remove large unbroken cells and other debris.
• Take liquid and pour into centrifuge tubes.
• Spin at a few thousand revs per minute for a few minutes.
• Nuclei collect at the bottom of the tube as a pellet.
• Pour the supernatant into a new tube and leave the pellet in the old one.
• Nuclei can be resuspend in the buffer and spin again to wash them.
• Spin the second tube at a higher speed for about 30 minutes.
• This will produce a pellet of either mitochondria in animal tissues or chloroplasts in plant tissue.
• (If its plant tissue it does not have to be spun as fast otherwise chloroplasts will be contaminated with mitochondria).
• By increasing the speed and length of spin all the other organelles can be separated out.
• The fastest, largest spin gurantees ribosomes as the outcome.

• Magnification: how much bigger an image is (magnification = size of image / size of real object).
• Resolution: the ability to distinguish two close objects as individual structures.
• If magnification > 1 = image size is bigger than the actual object (it is magnified).
• If magnification < 1 = image size is small than the actual object.

M I C R O S C O P E S

• Light microscopes use light to form an image:
• (+) magnifies up to x1500, easy to use, portable (most likely to be used in schools etc), relatively cheap, can view living organisms without harming them, coloured micrographs due to different variety of stains.
• (-) limited magnification due to resolution (0.2 micrometers), depth of field (not everything is in focus).
• Electron microscopes blast a stream of electrons at the specimen to form a 3D image.
• (+) greater magnification (x500 000), greater resolution (x1000 better than light = 0.0002 micrometers)
• (-) expensive (used in research facilities), very large (has its own room), not easy to use (have to be trained), difficult specimen preparation (specimen has to be dead), black and white image produced.
• Two types of electron microscopes: transmission and scanning.
• Transmission: beams of electrons goes through the specimen.
• Scanning: electron beams knocks off the specimen.

• Prokaryotic cells are smaller and simpler than Eukaryotic cells.
• Prokaryotes have: plasma membrane, flagellum, no DNA in nucleus (free floating), slime capsule, plasmids, cells walls, ribosomes, pilus, and cytoplasm.
• About the 1/10 the size of mammalian cells.
• Plasmids: small loops of DNA that contain genes for antibiotic resistance and can be passed between prokaryotes.
• Flagellum: a long, hair-like structure that rotates to make the cell move.
• Slime Capsule: helps protect bacteria from attack by cells of the immune system.
• DNA: prokaryotes don't have a nucleus- they have free floating DNA in the cytoplasm (circular DNA).
• Cytoplasm: this has no membrane bound organelles-they have ribosomes.
• Cell Wall: supports the cell and prevents it from changing shape (made of polymer murein).
• Plasma Membrane: mainly made of lipids and proteins, controls the movement of substances into and out of the cell.
• Life History: free living (soil, water and air); topical (on the surface of organisms); pathogens (live in & parasite organisms).
• Reproduction via binary fission.

• Viruses are non-living (obligate parasites e.g. they all have to infect a cell to complete their life cycle).
• They are nucleic acids surrounded by protein (they are not alive).
• Unlike bacteria, viruses have no plasma membrane, no cytoplasm, and no ribosomes.
• Viruses don't undergo cell division-they inject their DNA/RNA into the host cell which then replicates the viral particles for them.
• Viruses contain a core of genetic material (either DNA/RNA).
• The protein coat around the core is called the capsid, attachement proteins stick out from the edge of the capsid (these let the virus cling on to a suitable host cell).
• Viruses use their attachment proteins to bind to complementary receptor proteins on the surface of host cells.
• Different viruses have different attachment proteins and therefore, require different receptor proteins on host cells (this means viruses can only infect one type of cell).
• They inject their DNA/RNA into the host cell (this hijacks the cells and then uses its own machinery to do the viruses work and replicate the viral particles).

• The basic structure is a phospholipid bilayer (7-9 nanometers).
• It contains; proteins; cholesterol; and modified molecules.
• Proteins: these can be just in the surface (extrinsic) or in the core of the membrane & hydrophilic surface (intrinsic).
• Large proteins span the entire membrane and these are called transmembrane proteins (often have channels or gates). Cholesterol (a lipid): found inside the hydrophobic core which increases stability of cell by restricting movement of phospholipids-making the membrane less fluid and more rigid).
• Modified molecules: these are things such as glycoproteins (proteins with short sugar chains) and glycolipids (lipids with branched sugar chains).
• The uper and lower surfaces can move relative to one another (alongside molecules inside can move also).
• This is called the Fluid Mosaic Model.

F U N C T I O N S

• Controls what can and can't enter or leave the cell (outer limit of cell keeps contents in).
• Cell Adhesion (helps cells stick together and form tissues).
• Antigens (antibody has complementary fit to antigen etc).
• Carriers/Channels (allow substances in and out of the cell).
• Recognition (various receptors detect chemicals).

S I M P L E  D  I F F U S I O N

• The net movement of particles from an area of high concentration to an area of low concentration.
• Molecules will diffuse both ways, but the net movement will be to the area of lower concentration.
• This continues until particles are evenly distributed throughout the liquid or gas.
• The concentration gradient is the path from high concentration to low concentration.
• Diffusion is a passive process- no energy is needed for it to happen.
• Particles can diffuse across cell membranes as long as they can move freely through the membrane.
• When molecules diffuse directly through a cell membrane, it's also known as simple diffusion.
• Polar molecules have partial positive and negative charges. Non-polar molecules don't.
• Simple diffusion depends on...
• 1) The concentration gradient- the higher it is, the faster the rate of diffusion. The difference in concentration between the two sides of the membrane decreases until it reaches an equillibrium, which means that diffusion slows down over time.
• 2) The thickness of the exchange surface- the thinner the exchange surface, the faster the rate of diffusion.
• 3) The surface area- the larger the surface area, the faster the rate of diffusion.

F A C I L I T A T E D   D I F F U S I O N

• Some large molecules would diffuse extremely slowly through the phospholipid bilayer because they're so big.
• Charged particles (ions and polar molecules) would also diffuse slowly-that's becuase they're water soluble, and the centre of the bilayer is hydrophobic.
• So to speed things up, large or charged particles diffuse through carrier proteins or channel proteins in the membrane.
• Carrier proteins move large molecules down the gradient, large molecules attach to carrier proteins in the membrane. The protein changes shape, and releases molecules on the other side of the membrane.
• Channel proteins allow the passage of larger molecules. They form pores in the membrane for charged molecules to diffuse through.
• Facilitated diffusion depends on...
• 1) The concentration gradient- the higher the concentration gradient, the faster the rate of facilitated diffusion. As equilibrum is reached, the rate of facilitated diffusion will level off.
• 2) The number of channel or carrier proteins- once all the proteins in a membrane are in use, facilitated diffusion can't happen any faster, even if you increase the concentration gradient. The greater the number of channel or carrier proteins in the cell membrane, the faster the rate of facilitated diffusion.

A C T I V E  T R A N S P O R T

• Active transport is the net movement of particles against a concentration gradient (uses energy).
• It usually transports solutes from a low to a high concentration.
• Transmembrane carrier proteins move molecules against the concentration gradient (requires ATP).
• ATP is a common source of energy in the cell (produced by respiration).
• ATP undergoes a hydrolysis reaction, splitting into ADP and Pi (inorganic phosphate). This releases energy.
• A molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side.
• Carriers are specific as they recognise a particular molecule and move that through.
• Co-transporters are a type of carrier protein which bind molecules at a time.
• The concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient.
• Active transport depends on...
• 1) The speed of individual carrier proteins.
• 2) The number of carrier proteins present.
• 3) Rate of respiration.

Endocytosis: The taking in of matter by a living cell by invagination of its membrane to form a vacuole.

Exocytosis: A process by which a cell transports secretory products through the cytoplasm to the plasma membrane.

P H A G O C Y T O S I S

• Refers to the engulfing of the larger, solid particles.
• E.G. White blood cell and bacterium:
• A cell that engages in phagocytosis is called a phagocyte.
• The white blood cell recognises the invader and realises it needs to be destroyed (signal molecules released by the bacterium and is drawn toward it).
• The white blood cell then has to attach its membrane to the membrane of the bacterium (surface receptors).
• Once attached, the membrane of the WBC (white blood cell) swells outward & around the bacterium and engulfs it.
• This results in a phagosome, containing the offending bacterium.
• The white blood cell brings digestive enzymes into the phagosome-these break up the bacterium, and resulting harmless particles are either used by the cell or released out of the cell.

O S M O S I S

• The movement of water across a partially permeable membrane, from an area of high water potential to an area of low water potential.
• All cell membranes are selectively permeable, all cell walls are completely permeable.
• Water potential is the potential (likelihood) of water molecules to diffuse out of or into a solution.
• Pure water has the highest water potential, all solutions have a lower water potential than pure water,
• If two solutions have the same water potential, they're said to be isotonic.
• Osmosis depends on several factors...
• 1) The water potential gradient- the higher the water potential gradient, the faster the rate of osmosis. As osmosis takes place, the difference in water potential on either side of the membrane decreases, so the rate of osmosis levels off over time.
• 2) The thickness of exchange surface- the thinner the exchange surface, the faster the rate of osmosis.
• 3) The surface area of the exchange surface- the larger the surface area, the faster the rate of osmosis.

• Pure water has a potential of 0.
• If a solute dissolves in the water, the value becomes negative (the more dissolved, the more negative).
• Water potential is measured in kPA.
• Saline and glucose drips are both isotonic with the blood (so they are the same potential).
• Water moves from a low potential to a high potential until it reaches an equillibrum.
• SA: length x width x no. of faces
• Volume: length x width x height

B I O L O G I C A L   I M P L I C A T I O N S

• Volume of an organism is made of cells (all cells produce heat).
• Heat is lost to the environment through a surface for small mammals.
• Birds who maintain their body temperature, lose heat regularly, have a high metabolic feed all the time.
• Very large mammals have huge volume of cells and relatively small surface area to lose it through.
• Elephants ears add SA and act as radiators for large amounts of blood flowing through it.
• In colder climates the largest member of the family is usually found there.
• Small, cold-blooded organisms heat up quickly but cool down quickly at night.
• Large organisms heat up slowly but cool down slowly at night.

• Barriers- skin, mucus membrane (effective unless damaged).
• Secretions- tears, HCl in the stomach (tears rid of unwanted things in the eye, HCl acts as an antibac).
• If pathogens do bypass a barrier then the body responds with inflammation.
• Damage causes the release of histamine causes blood capillaries to leak, swell and the area becomes hot and itchy.
• Attracts a general type of white blood cells to the area.
• This will deal with minor infections engulfs pathogens and increased blood flow which brings generalised antibodies that will link the bacteria together and stop them spreading reactions occur with any pathogen, non-specific defences.

S P E C I F I C   D E F E N C E S

• If a pathogen evades the non-specific defences it can spread through the body.
• Viruses infect are particular type of cell. Symptoms are caused by loss of function and cell death.
• Bacteria infect tissues and release toxins that cause the symptoms. Symptoms occur because the second line of defence takes a a few days to establish.
• The defence system involves two types of response: (1) Humoural Response-provides a response against bacterial infections; (2) Cellular Response- provides a defence against virally infected cells and cancer cells.

H U M O U R A L   R E S P O N S E

(1) Antigen Presentation- White blood cells engulf bacteria and have the ability to recycle the bacterial antigen onto their own surface.

(2) Clonal Selection- The presenting white blood cells move through the blood and lymphatic systems. Here there are a huge number of unique cells each of which has a differently shaped receptor on their surface. These are B cells and T cells. The B cell and T cell bind to the surface of the presenting cell. The T cell is specifically a T Helper cell.

(3) Clonal Expansion- The Th cell releases a hormone that causes the B cell to divide. Hundreds of exact copies or clones are made.

(4) Differentiation- The B cells now differentiate. Plasma cells produce thousands of antibodies. The antibodies remain in the blood for a few weeks but are eventually removed by the liver. Memory cells remain in lymph nodes and 'remember' the infection. If the same disease comes around again, they respond immediately. Antibodies are produced in even more numbers and the bacteria are removed before symptoms have appeared. This gives the impression that you haven't had the disease.

C E L L U L A R   R E S P O N S E

This works in the same way as the humoural response except cytoxic T cells are selected instead of B cells. Differentiation of the T cells produce killer T cells. Kill infected cells or cancer cells directly.

• Antibodies are quarternary proteins.
• Functions:
  • Cross-link pathogens (which stops infection spreading).
  • Opsonisation (coats pathogen and makes it more likely to be engulfed).
  • Neutralise toxins (antibody + antigen --> antibody-antigen complex --> removed by liver).
  • (The removal of toxins reduces symptoms).

• A vaccination is where a small quanitity of the pathogen's antigen is introduced.The body responds as if it is an infection, the crucial part is the production of memory cells.
  • (i) Dead pathogen.
  • (ii) Broken up pathogen.
  • (iii) Live but weakened strain of pathogen.
• These will instantly respond if the real disease comes around. (Immunity: the ability to resist infection). Herd Immunity: if enough people in a population are vaccinated (80-90%) then those who aren't will also be protected. i.e. the chance of 'bumping' into someone with the disease will be very small.Monoclonal Antibodies are provided by a single activated plasma cell (used medically or scientifically).
  • (i) Passive Immunity: antibobodies introduced directly from an external source (e.g. breat milk/placenta/anti-venom). Provides protection for the few weeks the antibodies circulate but once gone, any protection is lost.
  • (ii) Active Immunity: the natural response the body has to an infection. Artificial response to a vaccine.
• Magic Bullets- used to target certain cells.
  • Direct treatment- the antibody is complementary to the antigen on the cell, blocks the signals and lets the cells (most likely cancer) dissolve.
  • Indirect treatment- an antibody is made that is complementary to a cancer cell antigen. The antibody has a cytotoxic drug or radioactive source bounded to it. The treatment goes straight to the cells (less damage, less side effects, lower doses).

D I A G N O S T I C   T O O L S

• These can be used to detect certain diseases and cancers because of their specificity.
• e.g. Influenza, chlamydia, hepatitus, and certain cancers.
• e.g. Prostate cancer- detects raised levels of a protein called prostate specific antigen.
• e.g. Pregnancy testing- pregnant women produce human chorianic gonadotrophin (HCG): This sticks to the second band and the dye colour builds (usually blue).If a man has testicular cancer, their body releases HCG. Therefore, if a man used a pregnancy test, it can test for that type of cancer.
  • If you're not pregnant, no HCG, no complex.
  • If you are pregnant, a HCG complex is formed. 

E T H I C S

• Mice tumour cells are the source of the antibodies.
• They have been successful but have also caused a few deaths (patients must be aware of the risks).
• Testing antibodies are risky-it can lead to organ failure.

• HIV: Human Immunodeficiency Virus (disease causing virus) // AIDS: (disease caused by HIV).
• If you are exposed to the virus you will make antibodies against it. If these antibodies are found in the blood then you are HIV+.
• HIV is a retrovirus- it contains RNA as its genetic material. It also contains the enzyme reverse transcriptase.
• This makes a single strand DNA copy from the RNA, which is made into a double stranded DNA by DNA polymerase.
• Once the DNA double strand is formed, the cells' own RNA polymerase will transcribe all the viral genes to make the viral proteins.
• Its host cell is a T helper cell (Th). An increased infection of Th cells prevents them from initiating clonal expansion.
• i.e. B cells and cytoxic cells are not made to divide so no plasma cells or cytoxic killer cells can be produced.
• This is the point at which the infected person goes from HIV+ to being an AIDS sufferer.
• AIDS kills due to infections that would normally be dealt with by the immune system. Since it can no longer response to these infections, they can become life threatening.
• AIDS victims can die of pheumonia, other 'controlled' problems can be cytomegalavirus and cancers like kaposis sarcoma.
• There is no cure and/or vaccine for either. Drugs can be used to target some stages in its 'life history'.
• e.g. prevent the virus from binding to the host cell, inhibit reverse transciptase & target virus assembly.
• None are 100% effective.

E L I S A   T E S T   F O R   H I V

• There are two types of testing to do for HIV: direct (1) and indirect (2):
  • (1) A petri dish is used and a HIV antibody is stuck to the bottom of it.
  • A blood sample is added. If there is HIV, it will bind to the antibody.
  • The dish is the washed which removes any virus antigen that isn't attached.
  • A second antibody is added (which has an enzyme attached to it).
  • It is washed again to remove the unbound antibody enzyme.
  • A chemical is added that the enzyme breaks down to a coloured dye.
  • The container/dish turns blue if the virus or virus antigen is present.
• The test is semi-quantitative-the darker the colour, the more viral antigen present.
  • (2) A dish is used and HIV antigens are stuck to the bottom of it.
  • A blood sample is added. Patients exposed to HIV will have antibodies-these will bind to the antigens.
  • The dish is washed which removes any antibodies not attached.
  • An antibody is added and the enzyme complementary to the HIV antibody.
  • The dish is washed again, which removes unbound enzyme.
  • Add a yellow dye (if the dye turns blue, it has reacted with the enzyme). Therefore, blue = HIV+.

• Breathing: exchange of gases with the environment can be done through organisms surface or through a sepcialised organ. (Mechanism of exchange in either case is diffusion).
• Fick's Law: rate of diffusion x surface area x conc difference / thickness of exchange surface
• For efficient gas exchange, a respiratory organ must have; large SA; minimum seperation of air, and body fluids (or water); extensive blood supply; moist absorbing surface.
• (Also-ventilation air of water in contact with the exchange surface is renewed).

G A S  E X C H A N G E  ( M A M M A L I A N )

• The gas exchange surface of a mammal is the alveolus.
• There are numerous alveoli - air sacs, supplied with gases via a system of tubes (trachea, splitting into two bronchi - one for each lung - and numerous bronchioles) connected to the outside by the mouth and nose.
• These alveoli provide a massive surface area through which gases can diffuse.
• These gases diffuse a very short distance between the alveolus and the blood because the lining of the lung and the capillary are both only one cell thick.
• The blood supply is extensive, which means that oxygen is carried away to the cells as soon as it has diffused into the blood. Ventilation movements also maintain the concentration gradients because air is regularly moving in and out of the lungs.

• Mammals have lungs, with thin elastic sacs in the thorax. Communication via the bronchi and trachea with the atmosphere.
• Airways are lined with mucus secreting cells and ciliated cells.
• Mucus traps dust, pollen, spores and pathogens. Cilia moves mucus up and out of the lungs.
• Major airways are held open by carbon or oxygen rings of cartilage. Carbon rings in trachea allows adjacent oesophagus to expand when swallowing.
• Minor bronchioles end in a mass of thin walled sacs called alveoli.
• Alveoli have a single cell layer made of flattened cells, surface is covered by a dense capillary network.

V E N T I L A T I O N  / (Exchange of the air in the lungs)

• (1) Diaphragm contracts [Inhalation]; (2) Pressure increases; (3) Atmospheric pressure is greater; (4) Air moves out [Exhalation].
• Tidal Volume: volume of a resting breath.
• Inspiratory Reserve Volume: maximum volume that can be inhaled after a normal inhale.
• Expiratory Reserve Volume: maximum volume that can be exhaled after a normal exhale.
• Residual Volume: air left in the lungs after exhaling completely.
• Dead Space: air inhaled during breathing that stays in the conducting zone.

P E A K   F L O W   M E T E R S

• Measures how fast air can enter and leave the lungs. (Used for asthma control where you establish a base line value and use meter to see how effective various drugs are in controlling attacks).
• Asthmatics have no difference in key volumes to anyone else. 
• FEV 1: common measurement in lung studies-measures amount of air that can be breathed out in one minute.
• Reasons for reduced FEV 1; fibrosis; any damage to the lungs will be "repaired" by producing scar tissue.
• Effects: increases diffusion pathways; reduces elasticity of lungs (so they do not inflate as much and do not recoil as much); thus, lung volume decreases.
• Caused by: pathogens (e.g. TB); pneumonia; repeated lung infections; exposure to dust/chemicals; coal miners/smokers; disease processes (e.g. cancer, bronchitis, emphysema).

• There are two groups of fish (bony and cartilagenous). Both exchange gases with water via their gills.
• Most fish have small gills on each side of the pharynx.
• The gills are supported by the gill arch-in the gill arch, run the bronchial artery and vein.
• Branching off the gill arches are the gill filaments-a branch of the artery runs down one side of each filament while a branch of the bein runs down the other.
• The two connect via capillaries that run across the filament in gill lammellae.
• In bony fish, the gills are protected behind a bony plate called the operculum.
• In cartilagenous fish, each gill opens into an individual gill slit.
• Sharks cannot easily ventilate and tend to swin with their mouths open maintining a flow of water over the gills.
• Bony fish can ventilate in a similar way to mammals-volume and pressure changes in the mouth and throar, more water in through the mouth, over the gills and out via the operculum.
• Bony fish are very efficient due to coutner current flow. Blood and water flow in opposite directions. So, exchange occurs across the entire width of the gill lamellae.
• Blood can become 80% saturated.
• Sharks- blood and water flow in the same directions. Uptake of O2 occurs across only half of the gill. As soon as blood and water levels of O2 are the same, there is no further uptake.

• Insects don't use a circulatory system to carry oxygen. Instead, air is moved to every organ in a series of internal tubes.
• These communicate with the atmosphere via openings called spiracles. These usually have flaps that stay closed then occasionally to let air in.
• The tubes are called tracheoles. They are supported by rings of chitin that prevent collapsing.
• The tracheoles branch when they reach the tissues and end in small, blind ending tubes which we find filled.
• More advanced insects have tracheae that run the length of the body.
• Air diffuses in and down tubes, directly into the tissues.
• Uptake of O2; (1) Diffusion down tracheoles; (2) Ventilation movements refreshes air in tracheae; (3) Uptake of fluid from ends of tracheoles.
• When an insects active, it takes part in anaerobic respiration and produces 'lactate'- this lowers the water potential and so, water moves out of the tracheole by osmosis. Moving air deeper into tissues. reducing diffusion pathways.
• Problems: (1) Diffusion pathway limits size of insects; (2) Have to shed tube lining when moulting; (3) Water loss- surfaces designed to exchange gases also lose water vapour. For non-aquatic insects this is a big problem.
• Adaptations for water loss: (a) Waxy cuticle waterproofs the exoskeleton; (b) Small SA:V ratio (lose less water-minimises area through which water is lost); (c) Keep spiracles shut for as long as possible.
• CO2 rises until critical point, spiracle opens, ventilations and CO2 drops. The time its open, is shorter than when it is shut-reducing water loss.

E X C H A N G E   I N   A   L E A F

• Photosynthesis is the dominant reaction in the light (takes in CO2 and gives out O2).
• In the dark, respiration is the dominant reaction (takes in O2 and gives out CO2).

L I G H T

• Chloroplasts in the palisade cells use up CO2 very rapidly. This sets up a diffusion gradient. CO2 diffuses from the air spaces of the spongy mesophyll into the palisade cells.
• This is replaced by CO2 diffusing in through the stomata on the lower surface of the leaf from the atmosphere. O2 does the opposite. It is produced in the chloroplasts and diffuses out, through the spongy mesophyll and stomata into the atmosphere.

D A R K

• No photosynthesis so cells are only respiring. O2 now used up by all the cells, and are replaced by O2 diffusing into the leaf via the stomata.
  
• Cells release CO2 which diffuses out into the atmosphere.

• Adaptations for diffusion: (1) Large SA; (2) Thin; (3) Rapid uptake of gases; (4) Prevention of water loss.
• Normally, photosynthesis 'wins' and the stomata opens in the light so water vapour is lost. However at night, the stomata shuts
• A waxy cuticle waterproofs the surfaces (this is adequate for most plants that have water available in the soil).
• Plants that grow in dry areas are known as xerophytes.
• For plants where water is not always available for them, adaptations are necessary:
• (1) Reduced surface area (e.g. needles, spines, no leaves whatsoever).
• (2) Increase in diffusion pathways (e.g. fewer stomata, thicker cuticle).
• (3) Store water (e.g. cacti).

• Mammals are heterotrophic (eat complex mixtures of large insoluble molecules).
• Small soluble molecules are the only ones that can be absorbed-so digestion is necessary. The process requires enzymes that can hydrolyse the bonds.

M E C H A N I C A L   D I G E S T I O N

• Various teeth break up the food into a size that can be swallowed (mouth).
• Saliva is released which helps soften and lubricate the food (produced due to sensory reactions to food).
• Food comes together as a bolus (what is going to be swallowed)-this involves complex coordination muscles.
• It enters the oesophagus, a muscular tube that moves the bolus down to the stomach via peristalils (squeezing).
• Food enters the stomach and builds up in layers, food triggers the release of stomach secretions.
• (i) HCl - this kills pathogens. (ii) Enzymes - proteases break down proteins. These are precursor molecules activated in the lumen (prevents self-digestion). (iii) Mucus - a thick layer forms a protective coating.
• There is very little absorption in the stomach, except for small molecules (e.g. alcohol). Food remains for 2/3 hours.
• The stomach has three layers of muscle and thoroughly mixes the food and secretions (chemical digestions occurs and this is now called chyme).
• The pyloric sphincter opens for short intervals, allowing small quantities of chyme into the duodenum.
• Acid triggers release of pancreatic secretion and bile (pancreas: neutralising salts, mucus, amy/prote/lip-ase).

• Ileum- adapted for absorption due to; large surface area (long and villi); thin walls (single epithelial layer); extensive blood supply (maintains concentration gradient).

A B S O R P T I O N

• Chemical digestion produces a variety of small, soluble molecules.
• These are absorbed in a variety of ways.
• Glucose: if concentration is high, it is done by simple diffusion.
• Co-transport: blood takes absorbed glucose to the liver (stored as glycogen).
• Amino acids: absorbed by diffusion or active transport, co-transport (mechanism with Na+).
• Lipids: breakdown products include glycerol, monoglycerides and fatty acids.
• Micelles are formed, a hydrophobic core of fatty acid tails enclosed by the hydrophillic acid and glycerol parts.
• Micelles dissolve through the membrane, and reform into triglycerides.
• Na+ = co-transported with Glucose and Amino acids (diffusion & active transport).
• Fe = has a complex system of chemicals that enable its absorption.
• Vitamins absorbed directly via diffusion/active transport (they are absorbed as intact molecules).
• Colon: what remains is passed here; mucus; dead cells; enzymes; undigested food; unabsorbable food; water; bacteria. This leaves semi-solid cylinders of waste, they move to the rectum where they are then egested via anus.

P R O B L E M S

• Cholera - toxins inhibit water uptake (diarrhoea).
• Lactose intolerance - lactase stops being produced. So, any dairy products leave lactose in the gut.
• In the colon, bacteria ferment the lactose = gases which cause bloating.
• Lactose also lowers water potential of the guts contents.
• Water leaves cells by osmosis- causing diarrhoea.

E N Z Y M E S  &  D I G E S T I O N

• (1) Carbohydrates: Salivary Amylase has little effect as it has too short a time to break down any starch (deactivated by the pH of the stomach). Pancreatic Amylase: (amylose --> maltose). Maltase: attached to epithelial membranes-completes breakdown and products are immediately absorbed.
  
• (2) Lipids: broken down by lipase, requires bile to emulsify lipids to allow better mixing due to lipid insolubility.
• (3) Proteins: pepsin breaks (every break creates two new ends-the more breaks, digestion is quicker) bonds between certain pairs of amino acids to produce chains of variable lengths (e.g. endopeptidase).
• Trypsin also breaks internal peptide bonds so even more smaller peptides are produced.

• Exopeptidases break amino acids off from the end. 
• There are now lots of free ends that can be attached.
• Carboxypeptidase attacks from the acid end.
• Aminopeptidase attacks from the amino end (these release free amino acids).

O T H E R   D I G E S T I V E   S Y S T E M S

• Herbivore systems are more complex. Cellulose cannot be digested by most animals (they lack B glycosidase).
• Digestive systems are adapted to hold organisms that can produce cellulase (micro-organisms).
• These are housed in part of the digestive system and break down cellulose that is eaten (ruminants).
• (1) Ruminants: (sheep/cows/deer) have a fermentation chamber [rumen]. Food is chewed and swallowed and enters the rumen. Bacterial fermentation occurs and food is then rechewed before passing on to the duodenum.
• (2) Rabbits: fermentation occurs in the caecum and appendix. This is after the ileum where absorption occurs. Food is passed through the digestive system twice. All sugars are absorbed on 2nd passage.
• (3) Carnivores: protein is easier to digest so digestive system is simple and gut may be quite short. 
• Except = Giant Panda (very poorly adapted to deal with the bamboo it eats).

• Most organisms begin as a single fertilised egg (zygote).
• An adult human has 37.2 trillion cells.
• So the zygote needs to divide to produce all these cells.
• There are also approximately 200 different cell types so cells also need to differentiate. 
• All daughter cells must have a complete set of the genetic code if they and their daughters are to function.

M I T O S I S // (A process that produces new cells).

• Once tissues are formed, their rate of division varies (e.g. lining of gut is replaced every five days).
• Liver cells only divide to repair damage (nerve cells don't divide).
• Even rapidly dividing cells have to 'rest' (known as Interphase).
• Interphase: during this stage, the cell does its 'normal' function but also prepares for the next division.
• DNA replication occurs (checked before division).
• Once the process starts, it takes an hour to complete.
• This results in the division of the nucleus.
• The cytoplasm (alongside organelles) may or may not be shared between the two daughter cells (cytokinesis).
• Although it is a continuous process, mitosis is split into 4 stages; Prophase; Metaphase; Anaphase; Telophase.

1) Prophase

• Long thin chromosomes are coiled up due to condensation-visible with a light microscope (coiling prevents damage).
• At the same time, protein fibres are being organised, these radiate across the cell and form the spindle.
• Chromosomes exist as a pair of sister chromatids held together by the centromere.
• Nuclear membrane dissolves.

2) Metaphase

• Chromosomes move to the cell equator. Spindle fibres attach to the centromeres.

3) Anaphase

• Spindle fibres contract and pull chromatids.

4) Telophase

• Nuclear membrane reforms, the spindle dissolves and the chromosomes uncoil.

• A group of about 200 different diseases caused by an abnormal cell cycle.
• Mutations to the genes that control mitosis and other stages of the cell cycle lead to uncontrolled division & growth.
• This results in a lump of cells called a tumour. These can occur in any tissue but are more common (lungs/breast/ovary/prostate/digestive system). Two types of tumours: Benign and Malignant.

(1) Benign: These simply increase in size and only cause problems if it puts pressure on other structures e.g. nerves & blood vessels. They can be surgically removed and usually don't come back.

(2) Malignant: These usually invade other tissues and disrupt their function. Some are fragile and clumps of cells break off and travel in the blood or lymph to other tissues (these can form secondary tumours-metastasis). To ensure all cells have been removed radiotherapy or chemotherapy may be required.

T R E A T M E N T

• Chemotherapy: (i) prevents DNA replication (ii) prevent spindle formation e.g. vinblastin.
• Radiotherapy: X rays damage chromosomes beyond repair. Both of these rely on the increased mitotic activity of cancer cells (high mitotic index). 
• However, they also effect other rapidly dividing tissues. Magic bullets and monoclonal antibodies.

• This only occurs in gametogenesis. (Mitosis: all body cells. // Meiosis: limited to production of gametes).
• Results in production of eggs (Ova), sperm, pollen. Consists of two sets of divisions-meiosis I and meiosis II.
• The point is to halve the number of chromosomes so that at fertilization the normal number is restored. If not- chromosome numbers would double each generation.
• Most organisms have 2 sets of chromosomes and are DIPLOID.
• So, their gametes have 1 set (2n) so they are HAPLOID (n).
• Meiosis I: Prophase I // Metaphase I // Anaphase I // Telophase I
• Meiosis II: Prophase II // Metaphase II // Anaphase II // Telophase II
• Telophase II: cells nucleus reforms but cells are now haploid. 4 daughter cells with haploid chromosomes.
• Cells may stick together (tetrad) (e.g. sperm).
• In women all Ova are produced utero, they are held at prophase I until puberty.
• At puberty, hormones start some ova which then continue meiosis up to metaphase II.
• Cytokinesis is uneven, it produces one cell (future ovum) which has all the cytoplasm & organelles while the other is basically a nucleus. This is called a polar body and soon degenerates. If the ovum is fertilized, it very quickly completes meiosis and produces another polar body.
• In humans = 1 sperm mother cell --> 4 equal sperm. 1 egg mother cell --> 1 ovum and 2/3 polar bodies.
• Some organisms show alternation of generations e.g. jellyfish and fern.

• Mammals have a double circulation. Fish have a single circulation.
• Blood passes through the heart twice for one complete circuit of the body. 
  
• Double Circulation: (+) heart gets oxygenated blood first. It can pump harder for longer due to supply of oxygen.          (+) high blood pressure can be used to move blood to the body organs-a lower blood pressure can be used to move blood to the lungs (prevents lung capillaries bursting, more flexible). (+) reduces overall pressure as lung capillaries are on a separate circuit.
• Blood vessels: Arteries // Veins // Capillaries.
• Artery= elastic tissue & smooth muscle / Veins= lumen & connective tissues / Capillaries= no SM or ET
• Arteries: carry blood away from the heart under high pressure. Smooth endothelium to help blood flow reduces friction & prevents clotting. Thick muscle & elastic tissue layers to withstand pressure. Connective tissue prevents overexpansion.
• Veins: take blood back towards the heart, lowers blood pressure, smooth endothelium, thinner layers of muscle & elastic tissue. Lume  appears larger due to less elastic recoil. Has valves.
• Capillaries: single layer of cells, tend to be 'leaky', blood pressure at its lowest, some have a diameter less than the RBCs flowing through there. They form a huge network in tissues capillary beds.

P R O B L E M S

• Aneurysms, weakness in artery walls (blood pressure causes wall to bulge out), can cause pressure in skull and cause strokes, varicose veins, pressure on valves causes them to expand.
• Blood flows quickly through single vessels much more slowly through capillaries- gives time for exchange.

F L O W  O F  B L O O D

• (1) Heart - pumps blood to organs. Pressure is lost so heart doesn't pump blood back as well.
• (2) Anything above the heart - gravity causes blood to go back.
• (3) Effect of body muscles - large veins tend to run through large muscles. As the muscle contracts it squeezes the vein and the blood is pushed out the way. It cannot go in the wrong direction too far because of the valves.
• (4) Inspiration - reduced pressure in the thorax 'sucks' blood up the inferior vena cava.

C A R D I A C   C Y C L E

• (a) Atrial Systole - the atria contract and force blood through the atrioventricular valves into the ventricles. This expands and fills the ventricles, taking approximately 0.1 seconds at rest.
• (b) Ventricular Systole - ventricle walls contract, producing a rapid rise in pressure. This pressure rapidly exceeds that in the atria so the AV valve closes ('lubb sound'). Pressure continues to rise and now exceeds that in the artery. So, semi-lunar valves open and blood enters the arteries, taking approximately 0.3 seconds.
• (c) Diastole - muscles relax, ventricular pressure rapidly falls and so is now less than in the artery, so the semi-lunar valves close ('dupp' sound). Relaxation of atrial muscle allows blood to flow in and fill atrial chamber, taking approximately 0.4 seconds.
• This process REPEATS and takes 0.8 seconds each time.
• Pressure changes in the heart: over the course of the cardiac cycle, the pressure in the atria and ventricles rises and falls relative to each other and the arteries.
• There are 4 key events: (1) Atrio-ventricular valve closes (preventsback flow) // (2) Semi-lunar valves opens (blood forces open) // (3) Semi-lunar valves shut (prevents backflow into valves) // (4) Atrio-ventricular valve opens (pressure falls below atrial pressure).

• At rest the normal or ideal blood pressure is [ 120 (i) / 70-80 (ii) ].
• (i) systolic pressure produced by ventricular  contraction.
• (ii) diastolic pressure - how much pressure is in the system when the heart is at rest.

P U L S E   R A T E

• At rest the pulse is between 70-80 beats per minute. Blood flow to tissues is controlled by both pulse rate and blood pressure.
• [ Cardiac output = stroke volume x pulse rate ]
• At rest, the stroke volume (amount pumped out by ventricles in one beat) for a man is about 75cm3.

H E A L T H   I S S U E S

• Blood pressure (above 160) - hypertension; risk of heart disease; (a) heart works harder than normal; (b) weaknesses in artery walls; (c) arteries become thicker (arteriosclerosis).
• Causes: stress, salt, obesity, lack of exercise, genetics.
• Low blood pressure = fainting etc.

S M O K I N G

• Smokers are 2-6x more likely to get heart disease,
• (a) CO - combines irreversibly with Hb (forms carboxichaemoglobin).
• O2 carriage reduced so heart has to pump harder to make up for short, increases risk of CHD and strokes.
• (b) Nicotine - binds to adrenaline receptors. Adrenaline itself raises blood pressure and pulse rate. So, nicotine increases risk of CHD and strokes. Nicotine makes platelets, which makes blood 'stickier' (more likely to clot).

C H O L E S T E R O L

• Carried in the blood associated with protein: HDL - good // LDL - bad.
• Too much LDL causes deposition of cholesterol in artery walls (atheroma); statins reduce cholesterol.

• Exchange occurs in the capillaries: thin 'leakyl epithelial wall, high blood pressure in arterioles, end of capillary bed, narrow lumen which increased pressure and slows down flow.
• This results in liquid being forced out of the capillaries, this liquid contains everything found in blood except (RBCs and protein remain in capillaries).
• The fluid formed is Tissue Fluid.
• Cells obtain everything they need from the tissue fluid and pass their wastes into it.
• The water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid.
• Lymphatic Capillary: responsible for taking away last bits of water.

T R A N S P O R T   O F   G A S E S

• Measurement of gases- these can be done as simple percentages (but for accuracy, partial pressures- P).
• P = fraction of gas in mixture x pressure.
• So, for atmospheric O2: P = 0.2 x 100 kPA --> P = 20 kPA.
• It can also be measured in mm of Mercury.
• Atmospheric pressure = 760mm.

• Measurement of gases - these can be done as simple percentages (a more accurate way is to use partial pressures [ P ] ). P = fraction of gas in mixture x pressure.
• So, for atmospheric  O2: P = 0.2 x 100 // P = 20 kPA. 
• It can also be measured in mm of Mercury (atmospheric pressure = 760mm).
• Haemoglobin is a quarternary protein (2 alpha and 2 beta globin chains with each chain with a haem group).
• Hb + 4O2 <--> HbO8
• Oxygenated blood is bright red due to oxyhaemoglobin, deoxygenated blood is a dull purple colour.

I N   T H E   L U N G S

• O2 diffuses into the RBC where the first O2 molecule combinees with a haem group.
• This causes a confrontational change so the next 3 O2 molecules are added more easily.

I N   T H E   T I S S U E S

• Here, the oxygen is released to the tissues. However, the relationship is not linear.
• The PO2 in the lungs is 13kPA. PO2 in tissues at rest is about 5kPA.
• The PO2 in active tissues is about 2.5kPA.

• Blood from the lungs flow through living tissue, these are well oxygenated and only remove a small quantity of O2 from the blood.
• This leaves most of the oxygen for the respiratory tissues, the 1st O2 molecule is difficult to detach. i.e. Hb has a high affinity for the O2 molecule and 'hangs' onto it until the PO2 falls to much lower levels.
• Once the 1st O2 is given up a conformational change occurs again and the remaining O2 is given up very quickly.
• So, a drop in PO2 from 13kPA in the lungs to 5kPA in resting tissue releases 28% of the O2.
• But, a drop from 5-2.5kPa in active tissues releases a further 40%.
• i.e. tissues that need the most O2 get the most of O2.

E F F E C T S   O F   C O 2

• Active tissues have a low PO2 but also have a high PCO2. [ CO2 + H20 --> H2CO3 (carbonic acid). ]
• This reduces the pH (more acidic). Hb shows less affinity for O2 at low pH levels.
• So, it will now give up O2 at higher PO2 levels than it would in the absence of CO2. (Bohr Shift/Effect).
• Lugworms: live in organic rich, deoxygenated sand at the coast. The PO2 in their U shaped burrow is very low.
• Myoglobin - an oxygen storage compound found in muscle (very high affinity for O2, only gives it up at very low PO2).

F O E T A L   H A E M O G L O B I N

• This is different to adult blood. From the 2nd month, foetal Hb is produced up to birth.
• After birth, adult Hb is produced. It differs in that it has 2 alpha chains but instead of beta chains it has 2 gamma chains.
• Foetal Hb has a higher affinity for O2 than adult Hb. i.e. it can take O2 off the mothersblood for its own use.

• If the plant is cut at the stem, it is arranged in a circle for structure and transport.
• In herbaceous plants, vascular bundles provide support. 
• As well as acting as the transport system.
• Xylem is a one-way transport system for water and minerals (doesn't require energy, it is a non-biological process).
• Xylem tissue: packing cells and xylem vessels - dead columns of cells.
• Xylem vessels: additional lignin wrapped around columns of dead cells.
• Phloem tissue: a living tissue, transport system which transports organic substances (in either direction).
• Transport of water from roots to xylem (common question):

C O H E S I V E   T E N S I O N   T H E O R Y

• 1) Water taken up via osmosis and water moves across root cortex via symplast/apoplast pathway.
• 2) Water enters cells in vascular bundle via osmosis (This creates root pressure).
• 3) Photosynthesising leaves have a negative water potential. So water is taken in via osmosis and cells become turgid.
• 4) Pressure forces water out of cell and into cell wall- where it evaporates via mesophyll or escapes through stomata.
• 5) This water is replaced with water from xylem vessels in the stem/trunk.

• Factors that affect transpiration:(a) Temperature; (b) Air movement; (c) Humidity; (d) Light; (e) Water availability.
• (a) Temperature increases evaporation. Molecules have more kinetic energy and thus, move faster. The more humid, the more water vapour in atmosphere (increasing the conc gradient).
• (b) Air current increase water loss-meaning that, less water vapour held next to leaf surface.
• (c) As humidity increases, transpiration decreases (therefore, less conc difference).
• (d) The stomata opens in the daylight, and closes at nighttime.
• (e) If the roots cannot absorb enough water to replace what is lost.
• Source: cells in a plant that make sugars. 
• Sink: cells that rapidly use and store sugars like glucose.
• Material flow from regions of high pressure to those of low pressure (in phloem sieve tubes).
• The source has a negative water potential so the cells are turgid.
• The sink is has a less negative water potential.
• Experiments for evidence:
• (1) Tree Ringing- ring of bark removed, becomes swollen with graphic substances.
• (2) Steam Treatment- steam jet kills cells, the radioactive sugars don't move due to dead phloem.
• (3) Aphid Stylet- cut stylet off green fly, stylet in sieve tube when the stem is cut.

• Karl Linnaeus proposed the Binaurial System (each organism has a unique name).
• The first name is Genus (always has a capital letter, and in either Greek or Latin).
• The second name is species (in lowercase).
• If the name is printed (like so) it will be in italics. But if written it will be underlined.
• If organisms are similar enough, they will be placed in the same genus.
• To identify organisms, the dichotomous key was created.
• Species: populations of organisms that closely resemble each other (appearance/biochemical processes/behaviour/ecological niche).
• Problems with that definition: (1) some species have castes that don't look alike (e.g. worker/soldier ants). (2) some don't sexually reproduce. (3) some are isolated in different areas.
• Five kingdoms: Animal; Plants; Fungi; Bacteria; Protoctista.

• Keep / Ponds / Clean / Or / Frogs / Get / Sick

• Kingdom / Phylum / Class / Order / Family / Genus / Species

• Courtship allows organisms to recognise and mate with members of their own species.
• Reasons for Courting: (a) recognise own species, sex and reproductive status; (b) identify receptive fertile partners; (c) pair bonds are formed for successful mating and parenting; (d) synchronising mating to give best chance of reproduction.
• Courtship displays must be specific to the species but may share similarities to similar species.
• It is usually started by the male-if a female responds, she is fertile and receptive.
• Displays follow a stimulus response chain (something that triggers a set response in the other).
• The longer the display, the more likely it will end in mating.

R E L A T E D   S P E C I E S

• DNA Analysis: Genome Sequencing- this is done using modern machinery where it gives base sequence of all an organisms DNA.
• Protein Sequencing- e.g. cytochrome C found in mitochondria of nearly all organisms.
• Immunological Comparisons- a serum from species A is added to species B, species B will make antibodies against antigens in other serum. They will react to make a precipitate or complex. Therefore, the more precipitate, the more similar the serum, the more related they are.
  

D N A   H Y B R I D I S A T I O N

• DNA samples are heated so the hydrogen bonds break and the two strands separate. 
• Then add DNA from another species that has been labelled radioactively or with a fluorescent marker.
• The labelled DNA separates due to the temperature. This is then cooled so either the original DNA strands reform or a hybrid DNA is formed.
• This is then purified (to get rid of non-hybrid DNA)-and the process is repeated for other species.
• The hybrid DNA is slowly warmed again-the temperature determined for each species at which the strands separate again.
• The fewer base pairs, the lower the separation temperature, the less related the species are.

I N D E X  O F   B I O D I V E R S I T Y

• Diversity = N (N-1) / [n (n-1)
• N = number of organisms overall.
• n = number of a specific species in the population.

• Monocultures: growing a single variety of crop over a large area (reduces biodiversity enormously; leaves plants susceptible to disease; removes wildlife sanctuaries and wind protection).
• Zero Grazing: animals kept in pens and food supplied via a conveyer belt (a limited number of varieties which reduces genetic diversity-there has to be a balance between farming and conservation).
• Conservation: there is a moral obligation to not let organisms go extinct-a lot of drugs are plant based. They could potentially go extinct before their pharmaceutical potential has been looked at.

G E N E T I C    B I O D I V E R S I T Y

• All organisms are unique unless they are identical twins, clones or offspring of asexual reproduction.
• Sources of variation; (1) Independant Assortment; (2) Metaphase I; (3) Random Fertilization; (4) Mutations; (5) Environmental Effects; (6) Combination of Environment and Genetics.
• (1) Chromosomes in meiosis, because eggs and sperm must have 1 of each chromosome but it could come from either parents. // (2) Crossing over increases variation as new unique combinations of parental DNA occur.
• (3) Any sperm could fertilise any egg. // (4) These affect genes randomly in gamete producing cells.
• (5) e.g. himalayan rabbit changes colour at lower temperatures. // (6) e.g. height, weight, shoe size.

E F F E C T S   O N   O R G A N I S M S

• Organisms are always competing for resources, any variation that makes one individual 'better' in some way will put them at an advantage-allowing them to survive at the expense of others.
  
• This can be likely to then pass onto the offspring.
• Selection pressures work on variations within a population. Variations that may appear to be harmful, may be beneficial if conditions change.
• e.g. Antibiotic resistance in bacteria: the bacteria is put in growing conditions where it can flourish, the more resistant bacteria grows more slowly, the antibiotic is introduced and kills the bacteria off and the resistant bacteria remains and flourishes.
• Stabalising: maintains that variation and makes the population 'move in' towards the mean value.
• Directional: where a new distribution is created due to selection pressure focused on the lower sides of data.
• Disruptive: where the selection pressure is at the mean values and two new populations are formed.
  
• Genetic Drift: variations may disappear from small populations due to low numbers and limited number of crosses.
• Bottleneck Effect: large numbers rapidly reduced to a few individuals, and the new population is descended from the small population left over.
• Founder Effect: small number of individuals colonize a completely new area/island. Variation is limited due to this.