Adaptations of Aquatic and Tertiary Organism.

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Sam Hall        Page  of         06/05/2007

Adaptations of Aquatic and Tertiary Organism.

Within plants water is transported up the stem via the process of transpiration. The stomata, as well as permitting entry of carbon dioxide, allow evaporation of water from the plant this is the process of transpiration. Transpiration occurs all over the plant through stomata in the stem and epidermis as well as in the leaves, however the adaptation of the leaf is its large surface are this means the main source of water loss is from the leaves. There is also “cuticular transpiration” which is water loss through the cuticles of the epidermis cells, these accounts for around 5% of water loss within the plant. The rate of transpiration is specific to the environment.

Experiments with the potometer and an atmometer the rate of transpiration is dependent on a wide variety of internal and external factors.

The opening between the stoma creates a chamber underneath the lower epidermis lined with spongy mesophyll cells, known as the “sub-stomatal air chamber”.

The number of stomata, their distribution, structural features and how open they are at the time. Externally many things effect transpiration, such as;

  1. Temperature High temperatures encourages evaporation of water from the mesophyll cells
  2.  Relative Humidity, the degree to which the atmosphere is saturated with water vapour. This is important because it determines the saturation deficit, the humidity difference between the inside and outside of the leaf. As evaporation precedes from the mesophyll cells the air within the sub-stomatal air chambers develops greater saturation. There will be a concentration gradient dependent on the humidity of the surrounding atmosphere.  This will dictate the rate water transpires out through the stomata.
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Plant species have adapted to suit their environment via natural selection. Plants in dry/arid habitats such as Cacti have cut down the number of stomata, and lowering their evaporating surface areas. In the other direction plants in a rain forest have developed far larger surface areas and greater number of stomata to allow far greater water potential to develop within the plant.    

  1. Air Movement, water vapour will be concentrated around the outside of the stomata. This is known as diffusion shells. The movement of air around the plant will blow away the diffusion shells increasing ...

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