Complete Biology Revision (incomplete-working progress)

I have been putting these notes together recently and they are not finished yet, but I figured that with the GCSE exams so near i may as well put up what i have got... please comment but dont state the obvious that they are incomplete:D... thats just plain silly:P

P.S i made them nice and colourful (yes i actually spent my time changing font colours ...but it does help if you are a visual learner and also doesnt look as daunting when it comes to revising)

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What are enzymes?
Enzymes are biological catalysts.
They speed up chemical reactions in all living things, and allow them to occur
more easily.
They occur in plant cells and animal cells.
Without them we would not be alive.
Enzymes are just chemical molecules, made up of proteins.
Each particular enzyme has a unique, 3dimensional shape shared by all its
molecules. Within this shape there is an area called the active site where the
chemical reactions occur.
What do enzymes do?
Some enzymes help to break down large
Others build up large molecules from small
While many others help turn one molecule into
Probably the fastest enzyme known is called catalase. It breaks the chemical
hydrogen peroxide down to water and oxygen. Catalase is found in all cells and
protects them from this dangerous waste chemical.

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Optimum conditions
Each type of enzyme has its own specific optimum condition under which it works
Enzymes work best when they have a high enough substrate concentration for the
reaction they catalyse. If too little substrate is available the rate of the reaction is
slowed and cannot increase any further.
The pH must be correct for each enzyme. If the conditions are too alkaline or acidic
then the activity of the enzyme is affected.…read more

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Protease and lipase enzymes are used in biological washing powders to remove
those stubborn stains.
Enzymes are also used in making foods and drinks. The enzyme pectinase helps
to break down the cells in fruit to release more of their juice.
Cell structure
Plants and animal cells share the same basic structural features, although plant
cells have a few extra bits.
Animal Cells
Animal cells come in all kinds of shapes and sizes but have the same basic
features.…read more

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Firstly they have a rigid cell wall made of fibres of cellulose (which we use to make
paper!) that gives them shape and strength. The cell wall fits closely just outside the
cell membrane like a plastic box with an inflated balloon stuffed inside.
Secondly they have a vacuole, which stores extra water and gives extra support to
the cell by pressing hard against the cell wall.…read more

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Diffusion: Molecules move from a place of high concentration into a place of low
Osmosis: a special kind of diffusion, which is very important in Biology it keeps us
Key Facts
1. Osmosis only involves water molecules nothing else. Osmosis is water
2. Osmosis occurs across a barrier such as a cell membrane which is 'partially
permeable', which means it only lets through small molecules like water.
What is Respiration?
Respiration is the reason that we need oxygen.…read more

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Oxygen from the air is able to diffuse into the leaves of plants through tiny airholes
called stomata. This is obvious in plants as they take in oxygen at nighttime and
give out the carbon dioxide produced by respiration.
Respiration and Photosynthesis
Photosynthesis formula:
Carbon Dioxide + Water + Energy >
Glucose + Oxygen
Aerobic respiration occurs in the
opposite direction as photosynthesis.
So in plants, photosynthesis is building
up sugars at the same time as
respiration is using them up.…read more

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The air that we breathe out has more carbon dioxide in it (4%) than we breathe in
(0.04%). It has less oxygen too, the air we breathe in has about 21% oxygen
whereas that which we breathe out has 16%.
The lungs
The air enters the lungs down the trachea which branches into the right and left
bronchi. Each bronchus then divides further into bronchioles. After about 20
branchings you reach the air sacs, the alveoli.…read more

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A stoma is just a hole. It is controlled by two guard cells which change shape to
either open or close the hole. Something makes water enter the cells by osmosis
and so they swell up and change shape, but noone is quite sure of the trigger.
Photosynthesis is the way that plants make their food using energy from sunlight.…read more

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Sun: If there is less sun, which usually means it is cooler too, then there is less
energy for photosynthesis and it occurs more slowly. So photosynthesis works best
when it is warm and sunny don't we all!
Photosynthesis and Transpiration
When plants have their stoma open during the day, they can let carbon dioxide and
oxygen diffuse through them. However, water can also diffuse out from the moist
inside of the leaf to the drier air outside. This movement of water is called
'transpiration'.…read more


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