In plants, gas exchange occurs through small pores in the leaf surface called st
ID: 10788 • Letter: I
Question
In plants, gas exchange occurs through small pores in the leaf surface called stomata. Stomata can open to allow the exchange of gases and close to reduce water loss from the plant. In a regenerative chamber, the
transpiration of water via the stomata represents a major source of clean water. The fossil record suggests that the density of stomata is influenced by the concentration of atmospheric CO2 Stomatal density was found to be high in fossilised ginkgo leaves .during the late Permian and again in the Pleistocene, periods when the geological record suggests the levels of atmospheric CO2 were low. Conversely, stomatal densities were low during the Cretaceous; a time when CO2 levels were high and the climate was considerably warmer than it is today.
(i)
Suggest two possible reasons why stomatal density is linked to the concentration of atmospheric CO2
(ii)
Some scientists claim that plants have the capacity to ameliorate the excesses of climate change by removing more carbon from the atmosphere; based on what the fossil record tells us about stomatal density is this a justifiable view?
Explanation / Answer
(i) Stomatal density controls the amount of CO2 taken up for glucose synthesis and the the amount of H2O released as a byproduct of synthesis. In periods where atmospheric CO2 levels were low, plant stomatal density was high to maximize glucose synthesis. Conversely, in the Cretaceous period when CO2 levels were high and the atmosphere was much warmer plant stomatal density was low, as in there was more retention of water in plants that prevented them from drying out. (ii) In light of the fact that stomatal density is also influenced by the heat of the climate, plants cannot necessarily ameliorate excess climate change by removing excess CO2 if the heat of the climate has the counter effect of decreasing stomatal density causing plants to retain more water and take up less CO2. Thus, there is a tradeoff in plants for CO2 uptake and water retention such that CO2 uptake is minimized in exceedingly warm environments.