AQA Unit 1 -Lipids, Diffusion, Osmosis, Active transport, Cholera and Oral Rehydration Therapy

Just some notes from the Nelson Thorne AQA AS Biology book.. (the fish one).
Hope it helps, good luck for retakers !! =D

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  • Created on: 13-05-12 14:10
Preview of AQA Unit 1 -Lipids, Diffusion, Osmosis, Active transport, Cholera and Oral Rehydration Therapy

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3.4 Lipids
- Contain carbon, hydrogen and oxygen,
- The proportion of carbon to hydrogen is smaller.
- They are in soluble in water.
- They are soluble in organic solvents like alcohol.
Role of lipids
Their main role is in the plasma membrane. Phospholipids provide flexibility in the membrane and allow the
transport of lipids soluble.
Energy store, when oxidised when lipids give more energy than carbohydrates,
Waterproofing, lipids are insoluble so they are good for waterproofing, plants, and insects
have waxy cuticle layers. Humans have an oily secretion in their skin glands.
Insulation, fats are slow conductors of heat. So when it is stored it helps to retain body heat.
Protection, fat is stored around the delicate organs, like kidneys.
Fats are solid at room temperature, but oils are liquid. Triglycerides are called this as they
have three (tri) fatty acids and a glycerol. Each glycerol forms a bond with the glycerol
through condensation reaction.
There are over 70 fatty acids and they all have a carboxyl group (-COOH) with a
hydrocarbon group on the end. If the chain has no ©-© double bonds then it is saturated as all the carbons are
liked to all the possible hydrogen. If there are a few double bonds in carbon (C=C), it is called unsaturated.
Phospholipids
Phospholipids are similar to triglycerides but they do not have three fatty acid heads but two with a
phosphate group.
- They have a hydrophilic head which is attracted to water.
- They have a hydrophilic tail which is not attracted to water, it moves away from it.
The molecules have said to be polar, this means when in water they arrange themselves so that the
head is in the water and the tail is away from it.
Test for lipids
1. Take a grease free tube, take 2cm3 of sample and add 5cm3 of ethanol.
2. Shake the tube to dissolve the sample.
3. Add 5cm3 of water and shake gently.
4. If a lipid is present, a cloudy white colour appears in the sample.
3.5 The cell-surface membrane
All membranes in the have the basic cell membrane the plasma membrane.
It surrounds the cell and creates a boundary from the cell cytoplasm and movement of
substances.

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Phospholipids
One layer of phospholipids with the heads outwards and tails pointing in, then the tails of another
phospholipid facing the other way (Picture).
Only lipid soluble can move through the membrane, the function of the membrane:
-Allows lipid-soluble substances to enter and leave the cell.
-Prevents water-soluble substances entering or leaving the cell.
-Makes the membrane in flexible.
Proteins
Are arranged randomly, they occur in two ways:
- Extrinsic proteins, these are on the surface or partly inside.…read more

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When the particles are all evenly places it is called dynamic equilibrium.
Rate of diffusion
Concentration gradient as the greater the distance of concentration between ions and the exchange surface
the bigger the faster the diffusion rate.
Area over which diffusion takes place, the larger the area of an exchange surfaces the faster the rate of
diffusion.
Thickness of exchange surface, the thinner the exchange surfaces the faster the rate of diffusion.…read more

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The more solute which is added the more negative the solution goes to.
- Water will move from a region of higher (less negative) to a water potential of a lower of (more negative).
To find the water potential of cells, is to put them in a series of different water potentials. When there is no
net movement the external water potential is the same as the internal water potential.…read more

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Villi and microvilli
Glucose is absorbed by the small intestine by the finger-like projections villi, they have their walls and they lined
with epithelial cells, on the other side is a rich network of blood capillaries. They increase the surface area and
therefore increase the rate of absorption.
Villi are situates in between the lumen and the intestines, they are part of a specialised exchange surface. Villi
increase the levels of absorption by:
- Increasing the surface area for diffusion.…read more

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A flagella is a rigid
corkscrew which is rotating to make it move through fluids
Inside the cell the cell surface membrane, contains 70s type ribosomes, these are larger in eukaryotes, but
they still synthesis proteins. Bacteria stores glycogens in granules and oil droplets. The genetic material is in
circular plasmids, but the main part it DNA which are just in stands and not membrane bound. They can
reproduce to give bacteria resistance to chemicals (like antibiotics).…read more

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Water can be replaced by using a drip, but this requires a trained person to do this. A solution is to have a fluid
which can trigger normal water balance.
- Water, to rehydrate the tissues.
- Sodium, to replace the lost sodium ions but also to make use of the sodium-glucose carrier protein.
- Glucose, to stimulate the uptake of sodium ions in to the intestine and to provide energy.
- Potassium, to replace the lost ones and to make more an appetite.…read more

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