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 on: 08-12-12 14:51
Preview of Compact Edexcel SNAB Biology Revision Guide made by me

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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 body
In smaller unicellular organisms, substances move around slowly by diffusion (open circulatory
Diffusion is too slow to move substances around the larger bodies of multicellular organisms
Circulatory system: the substances are carried in blood pumped by a heart
Closed circulatory system: blood is enclosed in narrow blood vessels, which increases efficiency, as
blood travels faster as a higher pressure is generated
Single circulatory system (e.g. fish): heart pumps blood to gills for gas exchange and then, to tissues
and back to the heart
Double circulatory system (e.g. birds and mammals) allows blood to travel around the bodies faster,
delivering nutrients faster, so animals have a higher metabolic rate
Overcomes the limitations of diffusion
Blood needs to be pumped a long way around the body at high pressure
Blood is pumped at lower pressure to the lungs, as it reduces risk of damage to lungs and allows
more efficient exchange of gases
Circulation provides oxygen and removes carbon dioxide
Circulation helps the regulation of body temperature
The Flow of the Blood
1. Blood returns to the heart through the pulmonary vein from lungs and it drains into the left atrium
2. Raising of the blood pressure in the left atrium forces the left atrio-ventricular valve open
3. Contraction of the left atrial muscle (left atrial systole) forces more blood through the valve
4. As soon as left atrial systole is over, the left ventricular muscles start to contract (left ventricular
systole). This forces the left atrio-ventricular valve closed and opens the semilunar valve, which is
the valve in the mouth of the aorta.
5. Blood then leaves the left ventricle along the aorta, which goes around the body.
6. Blood returns to the heart through the vena cava
7. Raising of the blood pressure in the right atrium forces the right atrio-ventricular valve open
8. Contraction of the right atrial muscle (right atrial systole) forces more blood through the valve
9. As soon as right atrial systole is over, the right ventricular muscles start to contract (right
ventricular systole). This forces the right atrial-ventricular valve closed and opens the semilunar
valve, which is the valve in the mouth of the pulmonary artery
10. Blood then leaves the right ventricle along the pulmonary artery, which goes to the lungs
Cardiac Cycle
1. Right ventricular diastole / Left atrial systole
2. Left atrial diastole/ Left ventricular systole
3. Left ventricular diastole / Right atrial systole
4. Right atrial diastole/ Right ventricular systole
In diastole/atrial systole, the AV valves are open and the SL valves are closed
During atrial systole, the atria are contracting and the ventricles are relaxed
During ventricular systole, the ventricles are contracting and the atria are relaxed
During diastole, both are relaxed
Structure of the Heart

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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 need to pump blood a short distance into the ventricle
The atrio-ventricular valves link the atria to the ventricles and stop blood flowing back into the atria
when the ventricles contract
The semi-lunar valves link…read more

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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 easily damaged
Mutations in gene that affect relative HDL:LDL
levels in blood
Gender * male Oestrogen gives women some protection
before menopause
Afterwards, the risk is about the same
Ageing * increasing age Elasticity of…read more

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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.…read more

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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.…read more

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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
A mixture of two polysaccharides of glucose: amylose and amylopectin
Energy storage molecule in plants
Easily hydrolysed
Compact structure
More glucose in a smaller space
Polysaccharides branched
Amylopectin - 1-4 and 1-6 glycosidic bonds…read more

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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 in chain Molecule with x kinks in chain
BMI Status
<20 underweight
20-25 correct
25.…read more

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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.…read more

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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 substrate) fit into the active site
This is known as lock and key hypothesis, the alternative is the induced fit theory, where the
substrate may induce the enzyme into the right shape
Globular proteins have…read more

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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 the
hydrophobic tails on the inside and the
hydrophilic heads on the outside
Experiment on total area of a monolayer film Supports the bilayer model
of phospholipids which are extracted from
cells is twice as…read more


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