AQA Further Biology B3 Revision

All you need to know for the B3 unit in a brief and easy to read document.

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Further Biology Revision Notes
Further Biology B3
Transporting Substances
There are two main ways substances are moved into and out of cells:
Diffusion ­ the net movement of particles along a concentration gradient;
Osmosis ­ the movement of water along a concentration gradient, involving a partially
permeable membrane.
However, sometimes substances need to be transported against a concentration gradient; this is
where active transport becomes useful. Active Transport is the movement of particles from an area
of lower concentration to an area of higher concentration.
Active transport requires energy. Therefore, cells which make a lot of energy can carry out lots of
active transport. To make lots of energy, they need to have lots of mitochondria.
Active transport is widely used in cells. For example, mineral ions in soil and usually found in very
dilute solutions (more dilute than the solution in the plant cells). Using active transport, plants can
absorb the mineral ions from the soil, even though it's against a concentration gradient.
Exchange of gases in the lungs (The breathing system)
Your body needs a constant supply of oxygen for cellular respiration. The job of the breathing
system is to move air in and out of your lungs. Breathing brings oxygen into your body and removes
waste carbon dioxide produced by your cells.
When you breathe in:
Your ribs move up and out;
Your diaphragm flattens;
Air is pulled into the lungs.
When you breathe out:
Your ribs move down and in;
Your diaphragm returns to its domed shape;
Air is forced out of the lungs.
The lungs are adapted to improve the efficiency of gaseous exchange. They are made up of clusters
of alveoli which are tiny air sacs with large, moist surface areas (which is effective in terms of
diffusion). They have a rich blood supply and therefore a good concentration gradient is maintained ­
oxygen is constantly removed into the blood and carbon dioxide is constantly delivered to the lungs.
The layer of cells between the air in the lungs and the blood is also very thin to allow diffusion to take
place over the shortest possible distance.

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Further Biology Revision Notes
Exchange in the gut
The molecules from food need to be made available to your body cells; to provide fuel for
respiration and the building blocks for all the tissues of your body. Subsequently, they have to move
from the inside of the small intestine to the bloodstream and they do this via a combination of
diffusion and active transport.…read more

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Further Biology Revision Notes
When the stomata on the leaves of plants open to allow carbon dioxide to come in, some water
vapour is lost. This loss of water vapour is known as transpiration.
As water evaporates from the surface of the leaves, water is pulled up through the xylem from the
roots of the plant to the leaves to replace it; this is called the transpiration stream.
Conditions which increase the rate of photosynthesis increase the rate of transpiration.…read more

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Further Biology Revision Notes
Because of the double circulation, the heart has two pumps, which beat together about 70 times
each minute. The walls of the heart are almost entirely muscle, supplied with oxygen by the coronary
blood vessel.
Transport in the blood
Blood is a complex mixture of cells and liquid; the liquid part of the blood is called the plasma. Plasma
carries red blood cells, white blood cells and platelets.…read more

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Further Biology Revision Notes
Muscle fibres need energy to contract. They contain many mitochondria to supply the energy they
need by aerobic respiration. Muscles contain glycogen stores, which can be rapidly converted to
glucose to supply the fuel needed for cellular respiration when your muscles contract.
Cellular respiration:
Glucose + Oxygen Carbon dioxide + water (+Energy)
Muscle fibres usually occur in big blocks or groups known as muscles. Your muscles contract to cause
movement.…read more

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If you have been exercising hard, your heart rate and breathing rate remain high for a period of time
(the length of time depends on how fit you are).
Waste lactic acid from anaerobic respiration cannot be removed just by breathing as with carbon
dioxide. The lactic acid must be broken down into water and carbon dioxide which requires oxygen.
The amount of oxygen needed to break down the lactic acid is known as the oxygen debt.…read more

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Further Biology Revision Notes
fluid contains no urea so there is a strong concentration gradient from the blood to the fluid, and all
the urea leaves the blood.
Disadvantages of using a dialysis machine: has to be used at regular intervals; sessions are long;
patients must follow a carefully controlled diet.
Kidney transplants
Instead of dialysis, there is another option of treatment for those suffering from kidney failure: a
kidney transplant. A kidney transplant is when a recipient receives one healthy kidney from a donor.…read more

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Further Biology Revision Notes
The nutrients are often contained in an agar medium (agar is a substance which dissolves in hot water
and sets to form a jelly). Your pour hot agar containing the nutrients into a petri dish, leave it to cool
and then add the microorganisms.
The other way to provide the nutrients to grow microorganisms is as a broth in a culture flask.
You need to keep the pure strains of bacteria you are growing free from other microorganisms.…read more

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Producing microbes on a much larger scale can bring with it many problems:
The metabolism of all the millions of microorganisms cause the temperature to rise
The carbon dioxide waste from respiration can alter the pH of the culture (changes in pH can
affect the activity of the enzymes in the culture and so it may stop growing or die)
Other waste products can build up and poison the culture
When microbes are grown on an industrial scale, large vessels known…read more


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