The roots of all three plants (mesophyte, hydrophyte and xerophyte) have all adapted in different ways to enable the plant to flourish in its given environment. The roots of the Oak tree are well developed and grow deep into the ground in search of water. Compared to the roots of the Water Lilly, which are undeveloped, as they do not need to absorb water as the plant lives in water meaning water can enter any part of the plant via osmosis. The roots of a barrel cactus are well developed like the oak tree but differ as they only grow close to the surface. The roots of an oak tree grow deep and stretch long distances as they live in an environment where although water is not scarce is not abundant meaning a larger surface area of roots enables the plant to absorb more water (1). The roots of an oak tree also have tiny root hairs that also increase the surface area of the roots allowing the plant to absorb more water. The roots of the oak tree differ from the roots of the Water Lilly due the fact that they live in different environments. The roots of a Water Lilly are undeveloped, as the plant does not need to waste energy growing and developing its roots when the plant is surrounded by water. Because the plant is surrounded by water it is able to intake water anywhere for example the water can just enter the leaves via osmosis instead of only entering the roots and having to be transported up to the leaves via xylem and a transpiration pull. The only purpose of the Water Lilly's roots is to anchor the plant as they are embedded in the mud bellow the water line, the roots also help a absorb oxygen from the water to keep the plant buoyant and afloat (2). The roots of a Water Lilly are extremely different to the roots of a barrel cactus due to the fact that the Water Lilly lives in an environment where there is an abundance of compared to the barrel cactus which lives in an environment where there is a shortage of water and there are large periods of time where it doesn't rain, this is means the roots of a barrel cactus have adapted in order to conserve water. The roots of the barrel cactus are well developed and succulent in order to store large amounts of water as when it does rain the plant needs to absorb as much water as possible and store it for latter use when there is no longer water available. The roots of barrel cactus grow shallow and are large net-like units which have been structured in a way that allow the plant to absorb as much water as it can during dessert rains. The roots grow close to the surface as when it does rain due to the in intense heat water evaporates fast so there would be no point having roots deep in the ground as the water never get absorbed that deep as its evaporated by the intense heat (3). All the plants roots have adapted in different ways to allow the plant to keep water balance the roots of an oak tree grow deep into the ground in search of sufficient water and minerals that the plant needs in order to keep water balance the roots of a water Lilly are undeveloped as they are not needed in order to keep water balance in the plant as water enters the plant via osmosis at any place e.g. stem and leaves. And the roots of the barrel cactus are succulent and grow close to the surface in order to absorb water before it evaporates and then store this water for later use in order to keep water balance within the plant (4). All three of these plants need water in order to carry out processes such as photosynthesis as water is a raw material in this process. They also need water in order for their cells to stay turgid as plants do not have skeletons like animals do so they relay on their vacuoles being fill of water to keep the upright structure of the plant, this is important as the plant needs to stay upright in order for them to absorb sunlight. This is why it is so important for water balance to be controlled in the plant, as all these plants will fail to survive if water balance in the plant was not controlled.
(1)http://plantwaterbalance.blogspot.co.nz/2013/06/mesophytes-adaptations.html
(2)http://www.everything-ponds.com/hydrophytes.html
(3)http://www.conservancy.co.uk/learn/downloads/fieldtrips/xerophytes.pdf
(4)http://www.thestudentroom.co.uk/wiki/Revision:Xerophytes_and_Hydrophytes
(1)http://plantwaterbalance.blogspot.co.nz/2013/06/mesophytes-adaptations.html
(2)http://www.everything-ponds.com/hydrophytes.html
(3)http://www.conservancy.co.uk/learn/downloads/fieldtrips/xerophytes.pdf
(4)http://www.thestudentroom.co.uk/wiki/Revision:Xerophytes_and_Hydrophytes