Notes I made for AQA B2 exam :P

Notes I made for AQA B2 exam :P

Notes I made for AQA B2 exam :P

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  • Created on: 18-05-11 19:23
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B2 ­ Revision Notes
Most animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. The nucleus controls all
the activities of the cell. The cytoplasm is a liquid gel which is where most of the chemical reactions, which are
controlled by enzymes in the cytoplasm, take place. The cell membrane controls the passage of substances in and out
of the cell. The mitochondria are where aerobic respiration takes place. And the ribosomes are where all the proteins
are made. As well as all these a plant cell also contains a cell wall which supports and strengthens the cell. The cell wall
is made of cellulose. Most plant cells also contain chloroplasts and a permanent vacuole. The chloroplasts absorb
sunlight in order to photosynthesise and they also provide the plant with its green colouring due to the green
chlorophyll inside the chloroplasts. And the permanent vacuole is filled with cell sap and is important to keep the plant
rigid to help support the plant.
Some cells are specialised so they can do particular functions; for example, root hair cells, sperm cells, red blood cells
and nerve cells.
Dissolved substances move in and out of cells by diffusion, osmosis and active transport. Diffusion is the net
movement of particles of a gas or a solute from an area of high concentration to an area of low concentration (along a
concentration gradient). Osmosis is the net movement of water from an area of high concentration (of water) to an
area of low concentration (of water) along a concentration gradient. And active transport is the movement of
substances against a concentration gradient across a cell membrane using energy.
Photosynthesis can be summed up by the equation:-
Carbon dioxide + water (+light energy) glucose + oxygen
During photosynthesis light energy is absorbed by the chlorophyll in the chloroplasts. It is used to convert carbon
dioxide and water into sugar (glucose). Oxygen is released as a by-product. Leaves are well adapted to allow the
maximum photosynthesis to take place. There are three main factors which limit the rate of photosynthesis ­ light,
temperature (heat) and carbon dioxide (CO) levels. We can artificially change the environment in which we grow
plants. We can use this to observe the effect of different factors on the rate of photosynthesis. We can also use it to
control their rate of photosynthesis. Plant cells use some of the glucose they make during photosynthesis for
respiration. Some of the soluble glucose produced during photosynthesis is converted into insoluble starch for
storage. Plant roots absorb mineral salts. Nitrates make protein and without enough of these plants have stunted
growth. Magnesium makes chlorophyll which is found in the chloroplasts in plant cells, without magnesium plants have
pale yellow leaves. These two mineral ions are important in plants. Radiation from the Sun is the main source of
energy for all living things.

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B2 ­ Revision Notes
Energy Flows
The Sun's energy is captured and used
for plants during photosynthesis. The
mass of living material at each stage of
a food chain is less than at the previous
stage. The biomass at each stage can
be drawn to scale and shown as a
pyramid of biomass. The amount of
biomass and energy gets less at each
successive stage in a food chain.…read more

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B2 ­ Revision Notes
atmosphere by photosynthesis. It is returned to the atmosphere through respiration and combustion. The energy
originally captured by green plants is eventually transferred into consumers, into decomposers or as heat into the
enviroment.…read more

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B2 ­ Revision Notes
Catalysts increase the rate of chemical reactions. Enzymes are biological catalysts. Enzymes are protein molecules
made up of long chains of amino acids. The chains are folded to form the active site. This is where the substrate of the
reaction binds with the enzyme. Enzyme activity is affected by temperature and pH. High temperatures and the
wrong pH can affect the shape of the active site of an enzyme and stop it working.…read more


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