Edexcel AS Biology Revision Notes Unit 1

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  • Created on: 20-05-13 06:53
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AS Biology Revision Notes ­ Unit 1
Topic 1: Lifestyle, Health, and Risk
* Water molecules are non-linear and polar molecules because the H
and O atoms are different in size and electronegativity.
* They form hydrogen bonds with other water molecules.
* Some properties include...
Property Explanation
Excellent solvent Essential role in transport of
molecules in biological systems.
Less dense as a solid Ice insulates water beneath it, protecting marine life from freezing.
High SHC Cells do not heat up or cool down easily, thus has a homeostatic/stable
Transparent Allows marine life to exist as photosynthesis can occur underwater as
well as gas exchange.
* They have a general formula: Cx(H2O)n
* Saccharides are made from sugar molecules that are made from combinations of the elements carbon,
hydrogen, and oxygen only.
* They are used for:
1. Fuels for respiration (glucose).
2. Energy storage molecules (starch and glycogen).
3. Structural molecules (cellulose).
Monosaccharides - Single sugar units - glucose - Used in respiration
(Monomers) NB: there are 2 types of glucose:
alpha and beta
- Fructose - Found in fruit & honey
- Galactose - Found in lactose
(All the above are hexose sugars:
Disaccharides - 2 single sugar units - Maltose - Found in germinating
joined by a glycosidic (2 glucose molecules) seeds e.g. barley
- Sucrose - Crystals used in cooking
(Glucose and fructose)
- Lactose - Sugar found in milk

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AS Biology Revision Notes ­ Unit 1
(Glucose and galactose)
Oligosaccharides - 3-10 sugar units. Found in vegetables e.g.…read more

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AS Biology Revision Notes ­ Unit 1
Polysaccharides (polymers) are long chains of glucose molecules.
Found in muscle and liver cells for energy storage.
Made of poly alpha glucose linked together.
Insoluble because it has 1,4 and some 1,6 links, which form branches in the chain.
Very compacted, thus good for storage.
Found in amyloplasts (starch grains) inside plant cells for energy storage.
Made of 2 types of molecules: amylose and amylopectin.…read more

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AS Biology Revision Notes ­ Unit 1
* Saturated fatty acids contain the maximum number of hydrogen atoms and no carbon-carbon double
bonds. They are found in animal fats and dairy products.
* Monounsaturated fats contain 1 double bond, for example olive oil.
* Polyunsaturated fats contain a larger number of double bonds, for example, vegetables and fish oils.
* If one of the fatty acids in a triglyceride is replaced with a phosphate group, a phospholipid is formed.…read more

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AS Biology Revision Notes ­ Unit 1
returning from the veins.
Increased pressure opens the atrioventricular valves allowing blood to enter the
The atria contract to force remaining blood into ventricles.
Ventricular systole Ventricles contract from the base up, increasing the pressure and closing the
atrioventricular valves.
The semilunar valves open and blood is forced into the arteries.
Diastole As the atria and ventricles relax, pressure falls.
In the ventricle, this causes closure of the semilunar valves.…read more

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AS Biology Revision Notes ­ Unit 1
- Large lumen (decreases effect of friction).
Capillaries - Walls are one cell thick (cells are called
Adapted for exchange of endothelial cells).
substances. - Lumen is the same width as one RBC
(therefore more of RBC in contact with wall,
therefore smaller diffusion distance).
- No muscle or elastic tissue.
- They are very small.
* Atherosclerosis:
A disease where fatty deposits block an artery or increase its chances of being blocked by a blood
clot (thrombosis).…read more

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AS Biology Revision Notes ­ Unit 1
- Nicotine stimulates adrenaline release, increasing heart rate and blood pressure.
- Chemicals damage endothelium, triggering atherosclerosis.
- Decreased levels of HDLs.
Inactivity - Most common risk factor.
- Exercise can halve the risk of developing CHD.
- Reduces blood pressure.
Stress Leads to increased blood pressure, poor diet and increased alcohol consumption.
Alcohol - Heavy drinkers have an increased risk of CHD as alcohol raises blood pressure,
contributes to obesity, and causes irregular heartbeat.…read more

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AS Biology Revision Notes ­ Unit 1
* Determining Risks:
Risk is the probability of occurrence of some unwanted event or outcome.
A time period is always quoted.
Not all individuals are at risk to the same degree.
Risk factors increase the chance of the harmful outcome.
Factors that contribute to health risks include:
Physical environment
Social environment
Lifestyle and behaviour choices
Two factors are positively correlated if an increase in one is accompanied by an increase in the other.…read more

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AS Biology Revision Notes ­ Unit 1
Topic 2: Genes and Health
Cell Membrane:
* Cell membrane is made up of a phospholipid bilayer.
* The phosphate head of the phospholipid is a polar molecule and
attracts water ­ it is hydrophilic.
* The fatty acid tails are non-polar and hydrophobic.
* In the cell membrane, the hydrophobic tails face inwards to avoid water,
while the hydrophilic heads point outwards.…read more

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AS Biology Revision Notes ­ Unit 1
Secondary structure: the shape the molecule folds because of hydrogen bonding between the C=O
of one amino acid and the N-H of the amine group of another ­ an helix or a pleated sheet.
Tertiary structure: the final 3D shape of the molecule, held together by ionic bonds, interactions
between hydrophilic R groups and strong disulphide bridges between R groups containing sulphur.
Quaternary structure: if the protein contains more than one polypeptide chain.…read more



Brilliant resource very detailed. 


Pretty well oriented...Thanks alot IIwellyne!

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