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B3 Revision ­ Exchange of materials

Define active transport

Active transport is the movement of particles against a concentration gradient using energy

Explain how the body breathes in.

When you breathe in, the ribs move up and out.
The diaphragm contracts and flattens out.
There is a larger volume in…

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Water is lost by diffusion when the stomata opens but is controlled by the guard
Water and minerals are drawn up through the roots (which have a large surface area
due to root hairs and a short distance) via active transport to replace water lost by

Define transpiration…

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Urea, made by the liver, to the kidneys where it is excreted

Describe the effect of exercise on the body and why those changes occur

The heart rate increases and the blood vessels supplying the capillaries dilate to let
more blood containing oxygen and glucose to reach the muscles

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In a dialysis machine a person's blood flows between partially permeable membranes.
The dialysis fluid contains the same concentration of useful substances as the blood.
This ensures that glucose and useful mineral ions are not lost. Urea passes out from
the blood into dialysis fluid.
Treatment by dialysis restores the…

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The inoculating loops (to transfer the microorganisms) must be sterilised by passing
it through a flame
The lid of the Petri dish should be held in place with adhesive tape to prevent any
microorganisms getting in or out

Explain why cultures are incubated at 25C in schools but not in…

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There is a stirrer used to keep the microorganisms spread out and to make sure that
the temperature is the same in all parts of the vessel
There is a water-cooled jacket around the outside as the respiring microorganisms
release heat and a constant temperature needs to be maintained

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Describe the factors to consider when designing a biogas generator

Cost - continuous generators are more expensive than batch generators (waste is
mechanically pumped and digest materially constantly removed)
Convenience - batch generators are less convenient (they have to be continually
loaded, emptied and cleaned)
Efficiency ­ Gas is produced…


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