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Biology Unit 2
2.1 Animal and Plant Cells

Cell membrane ­ has tiny pores. These allow small molecules
like water and gases to diffuse through, but keep large
molecules inside the cell.
Cytoplasm ­ where many of the chemical reactions in the cell
occur. These reactions are catalysed by enzymes.…

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Cells may be specialised for a particular function. Their structure will
allow them to carry this function out.

Leaf cell ­ absorbs light energy for photosynthesis ­ packed with
chloroplasts. Regular shaped, closely packed cells form a
continuous layer for efficient absorption of sunlight.
Root hair cell - Absorbs water…

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Osmosis is the movement of water from a less concentrated
solution to a more concentrated solution through a partially
permeable membrane.

Eventually the level on the more concentrated side of the
membrane rises, while the one on the less concentrated side falls.
When the concentration is the same on both…

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Plants get hydrogen and oxygen from water in the soil, and carbon
and oxygen from the atmosphere. Water and carbon dioxide are
used to synthesise food during photosynthesis. Oxygen is used to
release energy from food during respiration.

In addition to these three elements, plants need a number of

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Most food chains are pretty short. There are rarely more than four
stages, because a lot of energy is lost at each stage.

Biomass means the mass of living material at a stage in a food
chain. A pyramid of biomass is a chart, drawn to scale, showing the…

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When an animal eats a plant, carbon from the plant becomes part of
the fats and proteins in the animal. Microorganisms and some
animals feed on waste material from animals, and the remains of
dead animals and plants. The carbon then becomes part of these

2.6 Enzymes
Enzymes are…

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Making proteins ­ in plants

Enzymes in digestion
Digestion is the breakdown of large molecules into smaller,
soluble molecules that can be absorbed into the body. Digestion
happens inside the gut, and relies on enzymes.

enzym reaction catalysed where produced Where used
amylas Starch sugars salivary glands, in the…

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After the stomach, food travels to the small intestine. The enzymes
in the small intestine work best in alkaline conditions, but the food is
acidic after being in the stomach. Bile is produced in the liver and
neutralises the acid to provide the alkaline conditions needed in the
small intestine.…

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Soluble, so may be difficult
to reclaim from liquid

2.7 Homeostasis
Waste products
Waste products must be removed from the body. If they are not,
they will increase in concentration and may interfere with chemical
reactions or damage cells.
Waste product Why is it produced? How is it removed?

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Too cold
When we get too cold:
· Muscles contract rapidly - we shiver. These contractions need
energy from respiration, and some of this is released as heat.
· Blood vessels leading to the skin capillaries become narrower
- they constrict - letting less blood flow through the skin and…


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