Biology Further GCSE Revision Notes - AQA

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Exchange of material - Active Transport
08 April 2012
· Three methods for dissolved substances to move in and out of
o Diffusion ­ net movement of substances from a high to a
low concentration along a concentration gradient.
o Osmosis ­ net movement of water from a high to a low
concentration along a concentration gradient through a
partially permeable membrane
o Active transport ­ movement substance against a
concentration gradient and/or across a cell membrane
using energy, i.e. it allows cells to move substances from
an area of low concentration to an area of high
· Active transport
o Active transport system uses energy to carry a molecule
across the membrane and then return it to its original
position which it gets from respiration.
o Many cells, the rate of respiration and active transport
are closely linked therefore cells involved in active
transport generally have a lot of mitochondria to provide
the energy it needs
· Importance of active transport
o Mineral ions in soil are usually found in very dilute
solutions à this is especially more dilute than inside the
cell so plants need to use active transport to absorb
these mineral ions against the concentration gradient.
o Glucose is always moved out of your gut and kidney
tubules into your blood even when it is against a large
concentration gradient à again it uses active transport
o Many marine birds and reptiles take in large amounts of
salt in sea water they drink, but the kidneys cannot get
rid of this so they have salt glands near their eyes and
nostrils and sodium ions are moved out of the body into
the salt glands which produce a very strong salt solution
à sodium ions need to be moved against a huge
concentration gradient so active transport is vital
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Exchange of gases in the lungs
08 April 2012
· The breathing system
o Breathing brings oxygen into the body and removes carbon dioxide produced
o Lungs bring in oxygen-rich air and removes air containing waste carbon dioxide
o When you breathe in the ribs move up and out and your diaphragm flattens from its normal
dome shape.…read more

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Nitrogen is around 80% when we breathe in and 80% when we breathe out
· Oxygen is around 20% when we breathe in and around 16% when we breathe out
· Carbon dioxide is around 0.04% when we breathe in and 4% when we breathe out
· We can test for carbon dioxide in air we breathe out using lime water which turns cloudy when
CO2 is bubbled through it. The faster it turns cloudy, the greater the concentration of carbon
dioxide.…read more

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Exchange in the guts
08 April 2012
· Digestion is the breakdown of food into small soluble molecules
which can be absorbed
· Food is broken down in your gut and forms simple sugars such as
glucose, amino acids, fatty acids and glycerol which all need to be
absorbed by the body.
· Absorption in the small intestines
o The molecules from food need to be made available to your
body cells so that it can fuel respiration and help build
tissues.…read more

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Exchange of materials in other organisms
08 April 2012
· Gas exchange in fish
o Gills are made up of many thin layers of tissue with a rich blood supply
o Gills are thin so there is only a short distance for the gases to diffuse across
o Gills are always moist because they work in water
o In a bony fish gills are contained in a special gill cavity. Water is pumped over them constantly to
maintain a concentration gradient.…read more

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Exchange in plants
08 April 2012
· Plants need osmosis to take water from soil and active transport to obtain minerals from the
· Gas exchange in plants
o Plants get CO2 for photosynthesis by diffusion through their leaves.
o The flattened shape of the leaves increases the surface area for diffusion.…read more

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08 April 2012
· Water loss from the leaves
o Plants contain stomata which open to allow CO 2 into plant; however, when the stoma is
open water is lost through water vapour.…read more

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Transport of substances around the body - The circulatory system
08 April 2012
Cells need oxygen and food and this can be satisfied only by a transport system which supplies
oxygen and removes waste. We use the blood circulation system
A double circulation
o We have two transport systems:
One carries blood from your heart into your lungs and back again to
exchange oxygen and Carbon Dioxide with the air.…read more


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