It is easy to tell when animals are breathing. Not only can you see their sides moving but you can also hear them. The process of breaking down their food to release energy is, however, less easy to see.
The same is true with plants. How can we tell if respiration is taking place?
Put in the plant into the dark means the Photosynthesis can not take place. But even in the dark, gas is produced by the plant.
In this experiment, we can see that the lime water which is normally clear turns milky after a short period of time. This indicates that the gas being produced by the plant in the dark is carbon dioxide.
Does the plant take up oxygen when you place in the dark?
In this experiment, any carbon dioxide produced will be absorbed by the calcium oxide in this small beaker.
The plant is placed under a bell jar and sealed with water. Any changing water level will therefore show what is happening to the oxygen.
After a period of time, we can see that the water begins to creep slowly up the inside of the jar, which must mean that oxygen is being taken up by the plant.
The release of carbon dioxide and the taking up of oxygen shows that plants respire in the dark. But do plants also respire in the light during Photosynthesis?
There seems little doubt that they do. The proving that is more difficult.
We know that in higher plants, if the available oxygen is severely reduced when it is in the dark, the plant will begin to die within few hours.
But if oxygen was produced during Photosynthesis, the plant can continue its existence for longer. After a period in the dark, unable to Photosynthesize, the plant visibly wilts. While the plant left in the light is still growing normally.
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