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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…

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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…

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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…

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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…

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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…

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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…

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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…

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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…

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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…

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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…


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