AQA Biology 3

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Biology 3
Biology 3
Gas and solute exchange
Substances are moved to where they are needed by diffusion, osmosis and active transport.
Diffusion is where a particles move from an area of high concentration to an area of low
concentration. E.g. when a perfume has been sprayed from one side of the room and the
smell eventually reaches to the other side
Osmosis is similar but only refers to water. The water moves across a partially permeable
membrane from a high concentration or a low concentration.
Both diffusion and osmosis need an exchange surface. The exchange surface allows enough
to pass. Exchange surfaces are adapted to maximise effectiveness.
The structure of leaves let gases to diffuse in and out of cells
Carbon dioxide diffuses into the air spaces within the leave and then diffuses into the cells where
photosynthesise happen. The leaf structure is adapted accordingly.
Underneath the leaf there is an exchange surface covered in tiny holes called stomata which
carbon dioxide diffuse through.
Water vapour and oxygen is lost from the stomata
The size of the stomata is controlled by guard's cells. The guard's cell close when lots of
water is being lost. If more water is being lost then gain the plant starts to wilt.
The flatten shape of the leaf increases the surface area
The walls of the cells inside are another surface exchange. Air spaces inside the leaf increase
the area of this surface so there more carbon dioxide getting in
The water vapour escapes by diffusion because there is more in the leaf than outside the
leave. This diffusion is called transpiration. Transpiration happens quicker in hot, dry, windy
The breathing system
Oxygen is need for respiration. Carbon dioxide needs to be removed from the body. This all happens
in the lungs.
Our lungs
The thorax is the top part of the body
It is separated from the lower part of the body by the diaphragm
The lungs are big and pink sponges protected by the ribcage

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Biology 3
The air breathed in goes through trachea. This splits into two tubes called bronchi. They are
continously split into smaller tubes bronchioles that finally end to small bags called alveoli
where gas exchange happens.
Breathing in
Intercostals muscles and diaphragm contract
Thorax volume increases
This decreases the pressure, drawing air in.…read more

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Biology 3
3. This gives a big surface area for absorbing water and minerals. Most of the mineral and
water come from the root hairs
4. They take in mineral using active transport
5. The concentration in the root hair is higher than in the soil. So the mineral are absorbed
against the concentration gradient. This is active transport. Active transport needs energy
from respiration to make it work.
Active transport also happens in the gut and kidney tubules.…read more

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Biology 3
Red blood cells
Red blood cells carry oxygen
Red blood cells have a doughnut shape to give a large surface area for absorbing oxygen
They don't have a nucleus- this allows more oxygen
They contain a substance called haemoglobin. This substance combines with oxygen to make
oxgheamogobin. The body tissues the reverse happens to release oxygen
Plasma is the liquid that carries everything in blood
1. A pale straw liquid which carries:
2. Red and white blood cells and platelets
3.…read more

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Biology 3
Most glucose from food is stored as glycogen. It mainly stored in the liver. During vigorous exercise
more glucose is used up, if the muscles don't get the energy and they keep contracting they get
tired and produce lactic acid...
Anaerobic respiration is used if there's not enough oxygen
When there is no supply of glucose the muscles start doing anaerobic respiration. Anaerobic
respiration just means without oxygen. It is an incomplete breakdown of glucose.…read more

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Biology 3
People with kidney failure are kept alive with dialysis treatment or have a kidney transplant
Dialysis machine filter the blood
In a dialysis machine the person's blood flows alongside a selectively permeable barrier surrounding
by dialysis fluid. It's permeable to things like ions and waste substances but not big molecules like
1. The dialysis fluid has the same concentration of dissolves ions and glucose as healthy blood
2. Useful ions and glucose are not lost from the blood during the dialysis
3.…read more

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Biology 3
A culture of bacteria is added to milk
The bacterium produces solids curds in the milk
The curds were separated from the liquid whey
More bacteria is add to the curds and the whole lot is left to ripen
Mould are added to give colour and taste
Yoghurt is made using bacteria too
Bacteria are used to clot milk during the manufacture of yoghurt
The milk is heated to kill of any bacteria that may be in it
A starter culture of bacteria…read more

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Biology 3
The malted grains are mashed up and water is added to produce a surgery solution with lots
of bits in it.…read more

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Biology 3
Fuels from microorganisms
1. Fuel can be made by fermentation of natural products and lucky enough waste products
2. Fermentation is when bacteria or yeast breaks down sugars by anaerobic respiration
3. Ethanol is made by anaerobic fermentation of sugar
4. Yeast can make ethanol when they break down glucose by anaerobic reparation
5. Sugar canes juices can be used, or glucose can be derived from maize starch by the action of
6.…read more

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Biology 3
3. An outlet for biogas to be piped to where it's needed
Four factors to consider when designing a generator:
Cost: Continuous generators are more expensive as they are continuously fed in waste and
mechanically removed waste
Convinces: batch generator are less convenient as they have to be continually loaded,
emptied and cleaned
Efficiency: gas is produced as 35 degrees.…read more


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