Stomata Adaptations
Stomata are pores, usually found on the underside of a leaf that are formed by guard cells opening and closing. Stomata are used for transpiration of water from the plant. From the diagram, when the guard cells are swollen with water, the pressure pushes the guard cells apart and hence forms the stoma. All of the different plant groups generally have their stomata located in different places. Mesophytes have most of their stomata at the bottom of the leaf whereas hydrophytes have the majority of theirs at the top of the leaf. Xerophytes have stomata underneath the leaf, however much fewer stomata are usually present.
Mesophytes have the majority of their stomata at the bottom or underside of their leaves. This is because when the water evaporates out, it rises again and causes condensation on the bottom of the leaf, which then drips back down for the roots to then absorb again. This isn't totally necessary for mesophytes as they generally live in conditions where they get enough water, however in an environment with lots of plants all fighting for water, this adaptation could be very useful for the plant.
Xerophytes have very small amounts of stomata on their leaves so to prevent excess water loss. Also, xerophytes restrict when they open their stomata, according to sunlight, because photosynthesis which requires sunlight also requires water. "Cacti can close stomata during the day to reduce water loss, and open them at night to let in CO2; the CO2 combines with an organic acid to be stored until daytime when it is released and enters the chloroplasts to make glucose in the Calvin Cycl phase of photosynthesis."1
As read in leaf adaptations, some xerophytes have curled leaves, that forms a pit of stomata in the centre. This adaptation is so that when the leaf loses water through transpiration it can absorb it right back after it has left the leaf.
Quite oppositely, hydrophytes have stomata on the top of their leaves so that they can lose more water if they need to via transpiration. The stomata on the top of the leaf lets the water more easily evaporate because of the more extreme concentration gradient of water between the air and the leaf. It's also easier for the water to evaporate because water naturally evaporates up so won't be getting trapped on the underside of the leaf like it does for the mesophytes.
Mesophytes have the majority of their stomata at the bottom or underside of their leaves. This is because when the water evaporates out, it rises again and causes condensation on the bottom of the leaf, which then drips back down for the roots to then absorb again. This isn't totally necessary for mesophytes as they generally live in conditions where they get enough water, however in an environment with lots of plants all fighting for water, this adaptation could be very useful for the plant.
Xerophytes have very small amounts of stomata on their leaves so to prevent excess water loss. Also, xerophytes restrict when they open their stomata, according to sunlight, because photosynthesis which requires sunlight also requires water. "Cacti can close stomata during the day to reduce water loss, and open them at night to let in CO2; the CO2 combines with an organic acid to be stored until daytime when it is released and enters the chloroplasts to make glucose in the Calvin Cycl phase of photosynthesis."1
As read in leaf adaptations, some xerophytes have curled leaves, that forms a pit of stomata in the centre. This adaptation is so that when the leaf loses water through transpiration it can absorb it right back after it has left the leaf.
Quite oppositely, hydrophytes have stomata on the top of their leaves so that they can lose more water if they need to via transpiration. The stomata on the top of the leaf lets the water more easily evaporate because of the more extreme concentration gradient of water between the air and the leaf. It's also easier for the water to evaporate because water naturally evaporates up so won't be getting trapped on the underside of the leaf like it does for the mesophytes.
References:
1. ESA Study Guide, chapter 26 transpiration, page 259
1. ESA Study Guide, chapter 26 transpiration, page 259