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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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…

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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…

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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…

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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…

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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…

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themselves further by secreting a capsule which is made of slime around there wall. 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.…

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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…


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