Transcript
JULIA COOKE
Plants make food through photosynthesis, by converting carbon dioxide and water into sugars and other carbohydrates, using sunlight as energy. The first part of the process is to allow carbon dioxide into the leaves through little pores on the leaf surfaces. On this oak leaf, there are roughly 500 pores in each one millimetre by one millimetre square of leaf on the lower side, and 100 pores in each square millimetre of leaf on the upper side.
The pores are called stomata, or stomates. As well as the entry of carbon dioxide into the leaf, water also evaporates from the plant through these pores, known as transpiration, and oxygen is released, which is critical to our own survival. Plants take up carbon dioxide and release oxygen and water vapour. We call this gas exchange. Plants carefully balance gas exchange to maximise photosynthesis but avoid too much water loss by opening and closing the stomata.
To open the pores, water is pumped into the two guard cells that border each stomate, and water is pumped out of the cells to close them. Opening and closing pores isn’t instantaneous. It takes time and occurs in response to environmental cues. In oak leaves, stomata respond to light levels, because light is needed as the energy source for photosynthesis. They can also respond to water availability in the air and soil.