UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 22/05/2023 [SEARCH]

Respiration: 2. Investigating aerobic respiration in plants and fungi using germinating beans or peas to show heat energy release with the formation of carbon dioxide

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INDEX of biology notes on respiration

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(2) Aerobic respiration in plants and fungi - experiments

 As above for animals.

glucose  + oxygen ===>  carbon dioxide  +  water  + energy

C6H12O6(aq)  +  6O2(g)  ===>  6CO2(g)  +  6H2O(l)  +  energy

In green plants, in daylight, the rate of photosynthesis will exceed that of respiration, but at night or very low light levels, the rate of respiration will exceed that of photosynthesis which falls to virtually zero, otherwise the plant would die!

At dusk or dawn, in poor light, the rates of photosynthesis and respiration are similar.

You can use a plant example to show heat energy is released in respiration (aerobic or anaerobic in living organisms). (Diagram on right)

Such an experiment to show germinating peas or beans ( germinating seeds) release energy using aerobic respiration is illustrated (right diagram).

One lot of peas/beans is soaked for at least 24 hours to get them germinating - look for little shoots/sprouts. Another lot are boiled to kill the enzymes that catalyse respiration - effectively killing the peas/beans. (the 'control' for a fair test).

Each lot is placed in a thermos flask (vacuum flask) on top of some moist cotton wool - space ifs left for an air supply to the peas/beans.

A thermometer is placed in each flask and the neck sealed with a cotton wool plug - both flasks should be kept under the same laboratory conditions of temperature for a week..

Any heat released will produce a temperature rise. If you record the temperature every day you should find that the flask of germinating peas/beans will show an increase in temperature - from heat energy release by respiration.

The control flask of boiled peas/beans should not show a temperature rise.

You can do a similar experiment with the boiled (dead) and unboiled (germinated by soaking for 24 hours) peas or beans to show the formation of carbon dioxide (aerobic respiration) in respiring living organisms). - the simple experiment is illustrated below using germinating peas or beans and dead peas/beans.

The uptake of oxygen in respiration produces carbon dioxide. (Diagram below)

Carbon dioxide is a slightly acidic gas. If carbon dioxide dissolves in the red hydrogencarbonate indicator solution, it turns it yellow. The indicator solution contains a dissolved salt, sodium hydrogencarbonate, and a coloured pH indicator that you see in your chemistry lessons - the carbon dioxide lowers the pH of water.

The peas/beans are suspended on a gauze or layer of cotton wool above some hydrogencarbonate indicator solution in boiling tubes - the boiling tubes are sealed with bungs to stop carbon dioxide from the air getting in

You leave the pair of boiling tubes for an hour.

Left: The germinating peas/beans are respiring and give off carbon dioxide turning the indicator solution yellow.

Right: In the control boiling tube, the dead peas/beans cannot respire (enzymes dead) and you see no change in the indicator colour because no carbon dioxide was formed.

You can do this experiment with animals like woodlice or maggots, using glass beads in the control tube - NOT dead animals and the living animals should not be kept for too long to run out of oxygen and die - ethical points.

You can compare the rates of respiration for different animals but its a pretty crude experiment - I suppose you could weigh equal masses of the animal into the boiling tubes.


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