Q.2 Describe homeostasis in plants. What different mechanisms are adopted for homeostasis in plants? OR How plants remove metabolic wastes?
Answer:
Homeostasis in plants
Plants respond to environmental changes and keep their internal conditions constant i.e. homeostasis. They apply different mechanisms for the homeostasis of water and other chemicals (oxygen, carbon dioxide, nitrogenous materials etc).
Removal of extra Carbon dioxide .
In daytime, the carbon dioxide produced during cellular respiration is utilized in photosynthesis and hence it is not a waste product. At night, it is surplus because there is no utilization of carbon dioxide. It is removed from the tissue cells by diffusion. In leaves and young stems, carbon dioxide escapes out through stomata. In young roots, carbon dioxide diffuses through the general root surface, especially through root hairs.
Removal of extra oxygen
Oxygen is produced in mesophyll cells only during daytime, as a by-product of photosynthesis. After its utilization in cellular respiration the mesophyll cells remove the extra amount of oxygen through stomata.
Removal of extra water
1. Transpiration
(a) Definition
Transpiration is the loss of water from plants surface in the form of vapours e.g; conifers and most of plants.
(b) Explanation.
Plants obtain water from soil and it is also produced in the body during cellular respiration. Plants store large amount of water in their cells for turgidity. Extra water is removed from plant body by transpiration.
At night, transpiration usually does not occur because most plants have their stomata closed. If there is a high water content in soil, water enters the roots and is accumulated in xylem vessels.
2. Guttation
(a) Definition
The appearance of drops of water on the tips or edges of leaves is called guttation. Guttation is not to be confused with dew, which condenses from the atmosphere on to the plant surface.
(b) Explanation
Some plants such as grasses and strawberry force this water through special pores, present at leaf tips or edges, and form drops. Removal of Other Metabolic Wastes Plants deposit many metabolic wastes in their bodies as harmless insoluble materials.
Example
1. Calcium oxalate crystals
Calcium oxalate is deposited in the form of crystals in the leaves and stems of many plants e.g. in tomato.
2. Shedding of leaves
In trees, which shed their leaves yearly, the excretory products are removed from body during leaf fall.
3. Resins
ยท Resins are removed by coniferous trees.
4. Gums
leaf cell Gums are removed by keekar.
5. Latex
Latex are removed by rubber plants.
6. Mucilage
Mucilage are removed by carnivorous plants and lady finger.
