AQA (HIGHER) B3- Exchange of Materials

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Exchange of materials
Osmosis: the diffusion of water across a partially permeable
The water moves from a region of high concentration to a region of low
concentration. ( a dilute solution to a concentrated solution)
It moves down the concentration gradient.
Active Transport: the absorption of substances across a partially
permeable membrane against the concentration gradient
Active transport requires the use of energy( ATP) released from respiration
because it moves against the concentration gradient.
Happens when cells need things that are in
short supply
Cells are able to absorb ions from dilute solutions e.g root hair cells absorb mineral
ions from the dilute solution in the soil by active transport & glucose can be
reabsorbed in the kidney tubules by active transport
1. Molecules enter the transport protein
2. ATP causes protein to rotate and release the molecule inside the cell
3. The transport protein rotates back again so the process an start again.
The sports drink dilemma:
When you exercise, your muscles respire and release energy which requires
After a while your body needs to cool down and you begin to sweat to do this.
Sweat contains water and mineral ions.
So when you sweat a lot our body cells become dehydrated, and it becomes
essential for the body to replace lost water, minerals and glucose .
Sports drinks contain water, sugar and mineral ions to help rehydrate body cells.

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These drinks are designed to help balance the concentration of fluids in and
outside of your cells. If the sports drink matches your body fluids it is called isotonic.
Some say water is just as good as sports drinks for short periods of exercise
however the sports drinks help replace minerals and sugars as well as water.
Exchange of materials in the lungs:
Large organisms contain special exchange surfaces to be able to get all the food
and oxygen they need.…read more

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Ventilating the lungs:
o The lungs contain the exchange surface of the breathing system.
o They are situated in the thorax, inside the ribcage and above the diaphragm.
When we breathe in: When we breathe out:
The intercostal muscles between the ribs The intercostal muscles and the
and the diaphragm contract. diaphragm relax.
The ribcage moves up and out and the The ribcage moves down and in and the
diaphragm flattens. diaphragm becomes domed.
The volume of the thorax increases.…read more

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Artificial breathing aids:
There are many reasons why someone cannot get enough oxygen into their
o The alveoli may be damaged: the surface area for gas exchange is reduced.
o The tubes leading to the lungs may be narrowed: less air can move easily through
o The person may be paralysed: their muscles will not pull the ribcage up and out.
Several breathing aids have been developed:
o The `iron lung'- used for people with Polio who were paralysed.…read more

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Food we eat gets digested in the gut into small,
soluble amounts that can be easily absorbed into the blood
in the small intestine.
o The villi line the inner surface of the small intestine
and are the exchange surface for food molecules.
o They are long finger-like projections which
increase the surface area for absorption.
o The walls of the villi are thin and there are
many capillaries close to the wall.…read more

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Transpiration: the passage of gases through fine tubes because
of differences in pressure or temperature.
o Plants take up water through the roots and the water passes through the
plant to the leaves. In the leaves the water evaporates from the leave cells
and the water vapour diffuses out through the stomata.
o The movement of water through a plant is called- the transpiration stream.
o The rate of evaporation increases in hot, dry, windy and bright conditions.…read more


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