Compact Edexcel SNAB Biology Revision Guide made by me

Note: The bolded and underlined starred info is previous mark scheme answers on those particular topics. Good luck to everyone who's resitting this unit and those who are doing it in the future!

P.S. Apologies for the random typos, just leave me a message if you cant figure out what it is meant to read!

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  • Created by: NR
  • Created on: 08-12-12 14:51

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Page 1

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Surface Area: Volume ratio
Big organisms - much smaller surface to volume ratio so there is not enough surface to serve the needs of
the large volume inside by diffusion
Lungs to increase surface area for exchange
Mass transport system (e.g. heart and circulation) to move exchanged materials around the…

Page 2

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Left ventricle is thicker because it has to pump blood all around the body, whereas the right
ventricles only need to pump blood to the lungs, which are nearby
Ventricles have thicker wall than the atria, because they have to pump blood out of the heart,
whereas the atria just…

Page 3

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Risk - the probability of the occurrence of an unwanted event or outcome
We underestimate or overestimate the risk (perceived risk), due to interest or approval of the activity

Risk factors of CVDs and CHDs

Factors Examples
Genetic Tendency to high blood pressure and poor
cholesterol metabolism
Arteries that are…

Page 4

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3. Cholesterol builds up, leading to the formation of atheroma
4. Build-up of calcium salts and fibres leading to plaque formation
5. Narrowing of artery / loss of elasticity of artery
6. Raised blood pressure
7. More damage to the endothelial lining of artery
8. Increased risk of blood clotting…

Page 5

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Reduce total cholesterol levels Rarely:
inhibit cholesterol synthesis Inflammation
More LDL receptors on liver Liver failure*
cells, so more LDLs will be
cleared from the blood
Anticoagulants e.g. warfarin Reduces risk of clot formation Uncontrolled bleeding
Dosage control - essential
Platelet inhibitory drugs e.g. Makes platelets less sticky Aspirin irritates…

Page 6

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Polysaccharides unbranched
Amylose - 1-4 glycosidic bonds
Found in starch - energy storage molecule in plants
glucose molecules in tight spirals (compact) and good for storage, as you can fit more
into a small space
Straight chain
Insoluble, no osmotic effect
Starch - 25% amylose and 75% amylopectin…

Page 7

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Saturated (fats) Monounsaturated (one Polyunsaturated (more
double bond) (oil) than one double bond)
Strong intermolecular bonds Weaker bonds weaker because of Weaker bonds weaker because of
kinked shape kinked shape
Solid at room temp Liquid at room temp Liquid at room temp
Straight chain molecule Molecule with one kink…

Page 8

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Structure of amino acids and protein
Proteins- polymers made of many similar molecules (amino acids) joined together in long chains
Globular protein: complex tertiary, and sometimes quaternary structure (e.g. enzymes, membrane
proteins, antibiotics)
Fibrous protein: little or no tertiary structure and parallel polypeptide chains are cross-linked to form
fibres (e.g.…

Page 9

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Enzymes (globular proteins): biological catalysts that speed up reactions both intracellular, which include
those involved in protein synthesis, such as: peptide bond formation and extracellular, which include:
digestion, and decomposition by bacteria

Each enzyme has a specific 3-D shape including an active site
Only molecules with a specific shape (the…

Page 10

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Phospholipids have a phosphate head, two fatty acids and ester bonds

Fact to explain Implications for the model
Phospholipids have a hydrophilic head and a Creates two different response to water
hydrophobic tail (like triglycerides)
Phospholipids, when suspended in water, Suggests a phospholipid bilayer
naturally form bilayers, which consists of…


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