Biology unit2 (aqa)

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  • Created by: rakhi
  • Created on: 01-01-11 15:51
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All animals and plants are made of cells. Animal cells and plant cells have features in common,
such as a nucleus, cytoplasm, cell membrane, mitochondria and ribosome's. Plant cells also have
a cell wall, and often have chloroplasts and a permanent vacuole. Cells may be specialised to carry
out a particular function. Dissolved substances pass into and out of cells by diffusion. Water
passes into and out of cells by osmosis.
Animal and plant cells:
Plant and animal cells have similar features. All parts of the cell have a specific function.

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Specialised cells:
Cells may be specialised for a particular function. Their structure will allow them to carry this
function out.
Cell Function Adaption
Absorbs light energy Packed with chloroplasts. Regular
for photosynthesis shaped, closely packed cells form a
continuous layer for efficient
absorption of sunlight.
Leaf cell
Absorbs water and Long 'fingerlike' process with very
mineral ions from thin wall, which gives a large surface
the soil area.…read more

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Dissolved substances have to pass through the cell membrane to get into or out of a cell.
Diffusion is one of the processes that allows this to happen. Diffusion occurs when particles
spread. They move from a region where they are in high concentration to a region where they are in
low concentration. Diffusion happens when the particles are free to move. This is true in gases and
for particles dissolved in solutions.…read more

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Water can move across cell membranes because of osmosis. For osmosis to happen you need:
Two solutions with different concentrations
A partially permeable membrane to separate them
Partially permeable membranes let some substances pass through them, but not others.
Osmosis is the net 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.…read more

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Green plants absorb light energy using chlorophyll in their leaves. They use it to react carbon
dioxide with water to make a sugar called glucose. The glucose is used in respiration, or converted
into starch and stored. Oxygen is produced as a byproduct. This process is called
photosynthesis. Temperature, carbon dioxide concentration and light intensity are factors that can
limit the rate of photosynthesis. Plants also need mineral ions, including nitrate and magnesium, for
healthy growth.…read more

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The equation for photosynthesis:
Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is
used for respiration, while some is converted into insoluble starch for storage. The stored starch
can later be turned back into glucose and used in respiration. Oxygen is released as a byproduct
of photosynthesis.
Factors limiting photosynthesis:
Three factors can limit the speed of photosynthesis, light intensity, carbon dioxide concentration
and temperature.…read more

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Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses.
They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a
higherthannormal light intensity. The use of paraffin lamps inside a greenhouse increases the rate
of photosynthesis because the burning paraffin produces carbon dioxide and heat too.
Plants and minerals:
Plants need to take in a number of elements to stay alive.…read more

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The Sun is the ultimate source of energy for most communities of living things. Green plants
absorb some of the Sun's light energy to make their own food by photosynthesis. The other
organisms in a food chain are consumers, because they all get their energy and biomass by
consuming other organisms.
Word Meaning
Producers Green plants make food by photosynthesis.…read more

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Primary consumers Usually eat plant material. They are herbivores. For example rabbits,
caterpillars, cows and sheep.
Secondary Usually eat animal material. They are carnivores. For example cats, dogs
consumers and lions.
Predators Kill for food. They are either secondary or tertiary consumers
Prey The animals that predators feed on.
Scavengers Feed on dead animals. For example, crows, vultures and hyenas are
Decomposers Feed on dead and decaying organisms, and on the undigested parts of plant
and animal matter in faeces.…read more


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