GCSE Biology 4411 AQA Unit 2

GCSE biology 4411 AQA Unit 2 revision notes

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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.
Nucleus ­ controls the activities of the cell. It contains genetic
information for making proteins. This has a membrane
extending from it onto which ribosomes are attached.
Mitochrondrion ­ where energy stored in sugars is released by
respiration in the cell.
Ribosomes ­ where protein synthesis occurs. A copy of the
genetic information needed to produce a protein is made from
the DNA in the nucleus. This copy becomes attached to a
ribosome. Enzymes then use this information to join amino acids
in the correct sequence to produce the protein.
Chloroplasts ­ contain a green pigment called chlorophyll. This
absorbs light energy. Chloroplasts convert this light energy into
chemical energy into carbohydrates.
Vacuole ­ is filled with a solution of ions called cell sap. When it
is full the vacuole supports the cell.
Cell wall ­ made up of tiny fibres. Together these are very
strong, so the cell wall supports the cell.

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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 and mineral ions from the soil -
Long 'finger-like' process with very thin wall, which gives a large
surface area.…read more

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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 sides of the membrane,
the movement of water molecules will be the same in both
directions.…read more

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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
minerals for healthy growth. These are absorbed through the roots
as mineral ions dissolved in the soil water.…read more

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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
biomass at each stage in a food chain. It is always pyramid
Efficiency of food production
The efficiency of food production can be improved by reducing the
amount of energy lost to the surroundings.…read more

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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 biological catalysts. Enzymes are also proteins that
are folded into complex shapes that allow smaller molecules to fit
into them. The place where these substrate molecules fit is called
the active site.…read more

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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 mouth
e pancreas, small intestine and small
protea Proteins amino stomach, pancreas, in the stomach
se acids small intestine and small
intestine.…read more

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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. It also emulsifies fat droplets to produce a larger
surface area for enzymes to work.…read more

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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.…read more

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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
conserving heat in the body.
The hairs on the skin also help to control body temperature. They lie
flat when we are warm, and rise when we are cold.…read more


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