Comparison between the three functional plant groups:
Comparison between plants and their adaptations:All three different plant groups, hydrophytes, mesophytes and xerophytes have different adaptations to cope with water loss and maintaining water balance within their habitats.
Comparing the adaptations in each plant group:Stomata adaptationsXerophyte stomata are in sunken pits to prevent water loss and maintain water balance. This is different to mesophytes which have stomata on the underside of the leaves and hydrophytes which have stomata on the topside of leaves. The different adaptations that the stomata have for each plant group is because of their habitats and ecological niches.
Xerophytes live in places where water is very limited, this means that the plants have many adaptations in order to conserve water. By having their stomata in sunken pits it causes wind speed to not affect the rate of transpiration and also creates a microclimate inside the pit which decreases the concentration gradient between the inside of the plant and the outside which causes less water to be lost via osmosis. If they had stomata on the top of leaves it would cause them to lose more water than they probably can get by increasing the rate of transpiration by increasing light intensity, wind speed and temperature. A unique adaptation that only xerophytes have is that the stomata only open at night while they collect light during the day. Thus causing less water to lost and half of the photosynthesis to be done during the day and half done at night, this process is called crassulacean acid metabolism (CAM) photosynthesis. This is different to the mesophyte plant group as they have their stomata on the bottom of the leaves, this is because they live in temperate zones where there is water and light in moderate amounts. By having stomata on the underside of the leaves it causes the stomata to be shaded from the light thus causing less evaporation and transpiration of water out of the leaves. By having the stomata on the underside of the leaf, the transpiration and water vapour that does escape doesn't go straight into the atmosphere, it collects under the leaf which also creates a microclimate which reduces the concentration gradient and less water is lost via osmosis and through the stomata. If mesophytes had stomata on the top of the leaf, the rate of transpiration would increase significantly causing them to lose lots of water. Hydrophytes live in places where water is in abundance but gases such as oxygen and carbon dioxide, used for respiration and photosynthesis are limited, this causes hydrophytes with floating leaves to have stomata on the top of the leaf. By being surrounded by water this causes transpiration to not be a big issue for this plant group and therefore they can afford to lose water. Having stomata on the top of their leaves causes transpiration to occur, but as they live in or by lots of water, more water is absorbed through the roots to replenish the plant and so goes the cycle. This adaptation of having stomata on the top of the leaves allow for hydrophytes to be able to collect gas like oxygen and carbon dioxide easier and faster. Whereas if hydrophytes had stomata on the underside of the leaf like mesophytes it would make it much harder and slower for the plant to collect gases as there is not much gas in water, the stomata would also have to open to allow more gas but by doing this other gases would escape and hopefully collect on the underside of the leaf to be used later. The hydrophytes that are submerged under water usually have stomata on the underside of the leaf but have less stomata and chloroplasts as it is harder for them to get light and gases. (Powell, 2013)(Roberts, 2011)(Class Notes,2015) (Fieldtrip to the Hamilton Gardens) Stem/leaf adaptationsSTEM:
Both xerophytic and mesophytic stems are lignified whereas hydrophyte stems have no lignin and are flexible. This is because xerophytes, and mesophytes live in habitats where there isn't another substance holding them up, which is like hydrophytes which have water which supports them. Xerophytes and mesophytes have lignin because they have a complex vascular system (xylem and phloem) whereas hydrophytes don't as they don't need them because they get their water and minerals via osmosis. This is seen when you compare lily pads to cactus. Cactus’ aren't very flexible compared to lily pads because they have a larger amount of xylem and phloem to hold it upright. This is also because if the hydrophytes were in rough water, and they had a lignified stem, it could easily break whereas in the desert, xerophytes don’t have very much shelter and if their stems weren’t as lignified and were flexible if there was a high wind speed it could damage the plant. This is the same as mesophytes, if the stem wasn’t as lignified it could cause the plant to break which would decrease the plant’s chances of survival. Leaves: Both xerophytic and mesophytic stems are lignified whereas hydrophyte stems have no lignin and are flexible. This is because xerophytes, and mesophytes live in habitats where there isn't another substance holding them up, which is like hydrophytes which have water which supports them. Xerophytes and mesophytes have lignin because they have a complex vascular system (xylem and phloem) whereas hydrophytes don't as they don't need them because they get their water and minerals via osmosis. This is seen when you compare lily pads to cactus. Cactus’ aren't very flexible compared to lily pads because they have a larger amount of xylem and phloem to hold it upright. This is also because if the hydrophytes were in rough water, and they had a lignified stem, it could easily break whereas in the desert, xerophytes don’t have very much shelter and if their stems weren’t as lignified and were flexible if there was a high wind speed it could damage the plant. This is the same as mesophytes, if the stem wasn’t as lignified it could cause the plant to break which would decrease the plant’s chances of survival. Leaves: Xerophyte leaves have a very thick waxy cuticle. This is different to mesophytes which have a waxy cuticle and even more so different to hydrophytes which have a very small waxy cuticle or none if they are submerged. The different adaptations that the leaves have for each plant group is because of their habitats and ecological niches. Xerophytes live in places where water is very limited and the light intensity is usually very high, this means that the plants have many adaptations in order to conserve water. By having a thick waxy cuticle it prevents water from being evaporated out of it and out of the plant. If they had no waxy cuticle at all like submerged hydrophytes,it would cause an increase in the rate of water loss which would not be favourable and thus not help them to maintain water balance. This is different to the mesophyte plant group who have a waxy cuticle, this is because they live in temperate zones where there is water and light are in moderate amounts. By having a waxy cuticle it also causes less water to evaporate and transpire out of the leaves but not as little as xerophytes. If mesophytes had a thicker waxy cuticle like xerophytes, the rate of transpiration would decrease significantly and they could store the water or use it in processes such as photosynthesis. Hydrophytes live in places where water is in abundance but gases such as oxygen and carbon dioxide, used for respiration and photosynthesis are limited, this causes hydrophytes with floating leaves to have a very minimal waxy cuticle if thier leaves float or none if they are submerged. By being surrounded by water this causes transpiration to not be a big issue for this plant group and therefore they can afford to lose water. Having very small waxy cuticle has little protection against evaporation or transpiration but as they live in or by lots of water, more water is absorbed to replenish the plant and so goes the cycle. This adaptation of having a thin or no waxy cuticle allows for easy gas exchange and helps the plant get minerals as it keep having to absorb water to decrease the concentration gradient. Whereas if hydrophytes had a thick waxy cuticle like xerophytes it would make it much harder and slower for the plant to collect gases as there is not much gas in water, it would also limit the concentration gradient between the inside and the outside of the plant causing the plant to not get many minerals. The hydrophytes that are submerged under water usually don’t have a cuticle but if they had a waxy one like mesophytes it would be harder for them to get gases to carry out life processes such as photosynthesis and respiration. (Roberts, 2011)(Class Notes,2015) (Fieldtrip to the Hamilton Gardens)(Powell, 2013) vascular system adaptationsMesophytes have a very complicated vascular system. This is different to hydrophytes which have a very basic system and xerophytes which have more xylem. The different adaptations that the vascular systems have for each plant group is because of their habitats and ecological niches.
Xerophytes live in places where water is very limited and the light intensity is usually very high, this means that the plants have many adaptations in order to conserve water. By having a vascular system which holds lots of water it allows them to store water when water is available and use the water stored when needed. If they had no vascular system like hydrophytes or a very basic one which didn’t conserve water, it would cause an increase in the rate of water loss which would not be favourable and thus not help them to maintain water balance. It would also be a problem when there was a drought and no water had been around. This is different to the mesophyte plant group who have a very complicated vascular system, this is because they live in temperate zones where there is water and light are in moderate amounts. By having a complicated vascular system, it causes water to easily and more efficiently flow through the xylem to the leaves from the roots via water cohesion and the transpiration pull, it also allows for minerals to also flow around the plant via the phloem. If mesophytes had more water conserving xylem and less phloem like xerophytes, the plant in some ways would have an increased chance of survival as it would have plenty of water but it could also increase the rate of osmosis out of the leaf because they do not have a thick enough waxy cuticle to stop lots of water evaporating out of the plant. Hydrophytes live in places where water is in abundance but gases such as oxygen and carbon dioxide, used for respiration and photosynthesis are limited, this causes hydrophytes with floating leaves to have a very large gas pockets and a very basic xylem and phloem structure. This is because they need to float and be buoyant, and it also stores gases which are hard to come by in water, they also get their minerals dissolved in the water which is absorbed into the plants via osmosis. This adaptation of having a basic vascular system or large air pockets allows for easy gas exchange. Whereas if hydrophytes had a complex vascular system like xerophytes it would make it harder for them to hold gases such as carbon dioxide and oxygen and would probably make them less buoyant. The hydrophytes that are submerged under water have much smaller air pockets but still don’t have a very complex vascular system because they get their minerals and water from the water.The different types of vascular systems are shown in the photos below.(Powell, 2013)(Roberts, 2011)(Class Notes,2015)(Jones,2015)
Root adaptationsMesophytes have roots that run deep and spread across. This is different to hydrophytes which have little or no roots and xerophytes which have roots that are either very shallow or very deep. The different adaptations that the vascular systems have for each plant group is because of their habitats and ecological niches.
Xerophytes live in places where water is very limited and the light intensity is usually very high, this means that the plants have many adaptations in order to conserve water. By having root system that travel either really shallow or really deep to get the water reservoirs, it allows them to absorb water quickly and efficiently. If they had roots like mesophytes, in the conditions they live in where water does not come by very often and gets evaporated quickly, if their roots where to deep they would not be able to absorb much water and thus affect their water balance. This is different to the mesophyte plant group who have a very complicated vascular system, this is because they live in temperate zones where there is water and light are in moderate amounts. By having a far spread root system, it causes them to easily be able to absorb water via osmosis through the roots through the xylem to the leaves from the roots via water cohesion and the transpiration pull. If mesophytes had little or no roots like hydrophytes, the plant would not be able to absorb much water and therefore have a hard time carrying out life processes like photosynthesis as it uses water as a reactant. Hydrophytes live in places where water is in abundance but gases such as oxygen and carbon dioxide, used for respiration and photosynthesis are limited, this causes hydrophytes to have very basic or no root system. This is because the some floating hydrophytes need to be able to follow the water and they also get their minerals and water from the water via osmosis. Whereas if hydrophytes had a shallow root system like xerophytes I think the only downside it that they could tear in rough water currents. Some hydrophytes are already are anchored such as the weed eel grass which has a complex root system to survive wave and tidal action. Submerged plants also have little roots but enough to keep them anchored to the ground. (Roberts, 2011)(Class Notes,2015)(Jones,2015) |
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