Additional Biology Revision

This is an up-to-date revision guide to help you to pass your additional biology gcse. This is excellent msterial if you want to geet an a* and covers everything you need to know!

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  • Created on: 11-09-11 09:52
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Biology Revision
Animal and Plant Cells
Animal Cells ­ Structure and Function
A nucleus, which controls all the activities of the cell. It also contains the instructions for
making new cells and or new organisms.
The cytoplasm, a water-based liquid gel in which most of the chemical reactions needed for
life take place. One of the most important of these is respiration, where oxygen and sugar
react to release the energy the cell needs.
The cell membrane, which controls the passage of substances in and out of the cell.
The mitochondria, structures in the cytoplasm where most of the energy is released during
Ribosomes, where protein synthesis takes place. All the proteins needed in a cell are made
Plant Cells ­ Structure and Function
They have the same features as animal cells as well as having:
A cell wall made of cellulose which strengthens the cell and gives it support.
Many (but not all) plant cells also have these other features:
Chloroplasts, found in all the green parts of the plant. They are green because they contain
the green substance chlorophyll which gives the plant its colour. They absorb light energy to
make food by photosynthesis.
A permanent vacuole (a space in the cytoplasm filled with cell sap), which is important for
keeping the cells rigid to support the plant.
Chemical reactions in cells
Each reaction is controlled by an enzyme. Each enzyme is a protein which controls the rate of a very
specific reaction. It makes sure that the reaction takes place without becoming mixed up with any
other reaction.

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We find enzymes throughout the structure of a cell, but particularly in the mitochondria (and the
chloroplasts in plants).
Enzymes controlling the reaction of:
Respiration are found in the mitochondria
Photosynthesis are found in the chloroplasts
Protein synthesis are found on the surface of the ribosomes
Specialised Cells
When a cell becomes specialised its structure is adapted to suit the particular job it does.
Fat Cell
Fat cells are storage cells.…read more

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Sperm cells are usually released a long way from the egg they are going to fertilise. They contain the
genetic information from the male parent to pass on to the offspring. They need to move through
the female reproductive system to reach an egg. They then have to break into the egg. They have
several adaptations to make all this possible:
Long tail with muscle-like proteins and a streamlined head so they can swim towards the egg.…read more

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Guard cells are therefore adapted to their function of allowing gas exchange and controlling water
loss within the leaf organ.
Palisade Leaf Cells
Packed with chloroplasts for photosynthesis. There are more of them crammed in at the top
so they are nearer the light.
Tall shape means a lot of surface area exposed down the side for absorbing carbon dioxide
from the air in the leaf.
Thin shape means that there is more space at the top for a larger number of palisade cells.…read more

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When a substance is moving from a high concentration to one which is just a bit lower, the rate of
diffusion will appear to be quite slow. This is because although some particles move into the area of
lower concentration by random movement, at the same time other identical particles are leaving that
area by random movement.
The overall or net movement = particles moving in ­ particles moving out
The difference between two areas of concentration is called the concentration gradient.…read more

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This swollen state keeps the leaves and stems of the plant rigid and firm. So for plants it is important
that the fluid surrounding the cells always has a higher concentration of water than the cytoplasm of
the cells. This keeps osmosis working in the right direction.
But sometimes plants and animals need to move substances such as glucose against a concentration
gradient. For this there is another method of transport known as active transport which uses energy
from respiration.…read more

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Palisade Leaf Cell
Upper epidermis:
Waxy cuticle ­ waterproof layer which stops water loss
Palisade Layer:
Palisade cells at top of leaf, close to light, tightly packed together and full of chloroplasts
Air spaces ­ gas exchange
Spongy Layer:
Cells not tightly packed ­ have a large surface area available for gas exchange and some chloroplasts
Lower epidermis:
Guard cells open and close the stomata to control water loss
Limiting Factors
Plants need certain things such as light, warmth and carbon dioxide if they are…read more

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Carbon dioxide is a raw material. You could dissolve sodium hydrogencarbonate in the water which
gives off carbon dioxide, to control the amount of carbon dioxide.
The atmosphere only contains about 0.04% of carbon and is needed to make glucose.
The carbon dioxide levels around a plant tend to rise in the night as the plant respires but does not
As carbon dioxide levels increase, the rate of photosynthesis also increases.
Temperature Levels
Temperature affects all chemical reactions.…read more

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Glucose is converted into cellulose for making cell walls, especially in a rapidly growing plant.
Making Proteins
Glucose is combined with nitrates to make amino acids, which are then made into proteins.
Stored in Seeds
Glucose is turned into lipids (fats and oils) for storing in seeds. For example, sunflower seeds contain
a lot of oil. Seeds also store starch.
Stored as Starch
Glucose is stored as starch in roots, stems and leaves, ready for use when photosynthesis is not
happening, like in the winter.…read more

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These nitrates, dissolved in water, are taken up from the soil by the plant roots. If a plant is deficient
in nitrates it does not grow properly. It is small and stunted. So nitrates are necessary for healthy
Why do plants need magnesium?
It is not only nitrates that plants need to grow well. There is a whole range of mineral ions they need.
For example, plants need magnesium to make chlorophyll.
Chlorophyll is vital to plants.…read more


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