October 24, 2013

Excretion in Plants- General Knowledge

Excretion in plants: The main excretory products include water and oxygen. These wastes diffuse out of the plant through the stomata and lenticels of stems as they are formed. Other plant wastes include; tannins, alkaloids, anthocyanins which are converted into insoluble compounds like granules and oil droplets which remain in the cells and are got rid of when certain parts of the plants e.g fruits, leaves and flowers fall off from the plants.
Excretion in Higher Plants:

Green plants utilize carbon dioxide for photosynthesis which is a metabolic waste product of respiration. Some of the methods of excretion in plants are As follows.
1. Resins, latex, rubber and gums are exuded from various parts of the plant body.
2. In some deciduous plants, the excretory matter is thrown out when the leaves fall.
3. In some plants, tannin is stored in the bark and woody part of the trunk. Due to this the wood appears dark.
4. In the different parts of the plant body, crystals of some chemical substances are set aside, for example calcium carbonate crystals in the leaf of fig, calcium oxalate crystals in the leaf of colocasia. These excretory materials do not harm the plant. Saprophytic plants such as Mucor, Rhizopus and Penictllium excrete their wastes through diffusion. These products maybe poisonous, however many have found use in everyday life of humans, such as latex which is used to produce gloves and clothing.

Excretion in plants differs from that in animals because of the following reasons
  1. Plants have got a lower metabolic rate compared to animals therefore the rate of accumulation of metabolic waste is very low
  2. Plants are autotrophs and therefore synthesize their own organic requirements according to the demand for them. There are never excess proteins in plants therefore very little excretion of nitrogenous wastes
  3. Plants have a capacity to store excretory products in some structures where they can be lost at a later stage e.g. fruits, flowers, leaves, barks etc.
  4. Much of the plant structure is based on carbohydrate and not protein. The products of carbohydrates carbon dioxide and oxygen can be used in photosynthesis as raw materials. The oxygen given out as a byproduct of photosynthesis can be used in respiration
Osmoregulation in plants: Plants are divided into four main groups depending on the amount of water available to them. They are; halophytes, mesophytes and hydrophytes, xerophytes.
Hydrophytes: These are plants which live partially or completely submerged in water. They have thin or no cuticle at all, no vascular tissue and reduced root systems because water is readily available to them, they also have many stomata on the upper surface.
Halophytes: These are plants that live in salty waters; they have special cells which have a higher concentration of solute than those of the ordinary plants. As a result they are able to take up water in the normal way
Mesophytes: These are plants which grow in normal water well watered soils and water lost by transpiration is replaced by absorption. They have no special means of conserving water although most of them have a well developed root system.
Xerophytes: These are plants which live in arid conditions such as deserts, and have a problem of dehydration. They have the following adaptations for their survival
  1. Some xerophytes have thick waxy cuticle impermeable to water  e.g. cactus
  2. Some have leaves modified into thorns or spines to reduce the surface area which minimizes on the rate of transpiration
  3. Some shed off their leaves  (deciduous) to reduce on the transpiration through the leaves
  4. Some roll their leaves to trap still and damp air that reduces transpiration.
  5. Some have sunken stomata which are guarded by hairs, the hair traps moisture which reduces on the rate of transpiration
  6. Some have succulent tissues like stems which store water
  7. They have a well developed tap root system for absorbing water from deep areas


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