Biology unit 3 notes

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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 the chest cavity with the same volume of gas
There is a lower pressure so air is drawn in.
Explain how the lungs are adapted to carrying out gas exchange (MoTAG)
The lining of the lungs is moist so diffusion is made easier as the gases can dissolve
in
The walls of the alveoli are thin so diffusion takes place over the shortest possible
distance and the rate of diffusion is maximised.
There are millions of spherical alveoli in the lungs so there is a large surface area for
the diffusion of gases.
The alveoli have a rich blood supply so the concentration gradient is maintained
(oxygen constantly removed into blood; carbon dioxide is constantly delivered to
lungs)
Explain how the gut is adapted to carrying out gas exchange (MoTAG)
The lining of the gut is moist so diffusion is made easier as the gases can dissolve in
The walls of the villi are thin so diffusion takes place over the shortest possible
distance and the rate of diffusion is maximised.
There are millions of finger-like villi in the gut so there is a large surface area for the
diffusion of gases.
The villi have a rich blood supply so a steep concentration gradient is maintained
(food absorbed into blood by diffusion when along concentration gradient; food
absorbed into blood by active transport when against concentration gradient)
Explain how certain animals exchange oxygen
Fish exchange oxygen through their gills
Frogs exchange oxygen through their skin
Insect exchange oxygen through their tracheoles
Describe the exchange processes in a plant
Carbon dioxide diffuses in for photosynthesis during day via the stomata of the
leaves

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Water is lost by diffusion when the stomata opens but is controlled by the guard
cells
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
evaporation
Define transpiration and the transpiration stream
Transpiration is the loss of water vapour from the surfaces of the leaves.…read more

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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
The breathing rate increases and the depth of each breath increases to increase the
take-up of oxygen and the rate of removal of carbon dioxide in the lungs
Glycogen stores in the muscles are used up…read more

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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 concentrations of dissolved substances in the
blood to normal levels and has to be carried out at regular intervals.…read more

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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 industry
If grown at higher temperatures, pathogens are more likely to grow but in industry, the
higher temperatures promote growth.…read more

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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
There are measuring instruments to monitor temperature and pH
Describe how mycoprotein foods are created
The fungus Fusarium is grown in sugar syrup in aerobic conditions to produce mycoprotein
and the biomass is then harvested and…read more

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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 most quickly at 35C.…read more

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