(2) Aerobic respiration in plants and fungi - experiments

 As above for animals.

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

C₆H₁₂O_6(aq)  +  6O_2(g)  ===>  6CO_2(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 investigation using peas/beans to investigate respiration CO2 product test 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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Key points - experiment to show aerobic respiration in living organisms

Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology investigation using peas/beans to investigate respiration CO2 product test (~US grades 9-10).

Investigating Aerobic Respiration in Plants and Fungi

This experiment demonstrates that aerobic respiration in organisms like germinating seeds or yeast:

• Releases energy as heat

• Produces carbon dioxide (CO₂)

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Using Germinating Beans or Peas to Show Heat Release

Aim: To show that aerobic respiration releases heat energy.

Apparatus:

• Two vacuum flasks (insulated)

• Thermometers

• Germinating peas/beans

• Boiled peas/beans (dead control)

• Cotton wool (to allow air in but reduce heat loss)

• Stopwatch

Method:

1. Soak two sets of peas/beans in water overnight.

2. Boil one set to kill them (these are the control group).

3. Place equal amounts of germinating peas in one vacuum flask and boiled peas in the other.

4. Insert a thermometer through the cotton wool bung into each flask.

5. Record the starting temperature of each flask.

6. Leave for a few hours and monitor temperature change.

Result:

• The flask with live, respiring seeds shows a rise in temperature.

• The boiled seeds do not, proving the heat comes from respiration.

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Detecting CO₂ from Respiration with Germinating Seeds or Fungi (Yeast)

Aim: To show that carbon dioxide is produced during aerobic respiration.

Apparatus:

• Germinating peas or yeast + sugar solution

• Boiled peas or control

• Conical flasks

• Delivery tubes

• Limewater or hydrogen carbonate indicator

Method:

1. Place germinating peas (or yeast + glucose) in a conical flask.

2. Fit a delivery tube from the flask into a test tube containing limewater or hydrogen carbonate indicator.

3. Observe changes in the indicator after a set time.

Result:

• Limewater turns milky: CO₂ is present.

• Hydrogen carbonate indicator turns yellow: CO₂ level has increased (acidic pH).

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Summary: Aerobic Respiration in Germinating Seeds

Word Equation:

Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP and heat)

This experiment shows:

• Heat is released → respiration is exothermic

• CO₂ is produced → confirms metabolic activity

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Keywords, phrases and learning objectives for this section on respiration

Be able to describe how to investigate aerobic respiration in plants and fungi e.g. using germinating beans or peas.

Be able to describe that the process releases thermal energy ('heat energy') and the release and formation of carbon dioxide in the process.

Know the experimental apparatus required for the investigation and the chemical reagents for test for carbon dioxide gas formed in the anaerobic fermentation of sugar process.

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