Respiration and Excretion in plants
Respiration in Plants
Respiration is the process of releasing energy from food. Like human beings and other animals, plants also need oxygen from the environment and release carbon dioxide. This shows that even plants undergo the process of respiration. So, Oxygen and carbon dioxide are also called respiratory gases.
The respiration is plants differ from human beings and other animals in the following aspects:
- Respiration takes place individually in all parts of the plants like stem, roots, leaves etc. In human beings and animals respiration takes place through one part only.
- In plants, respiratory gases are hardly transported from part to another part. On the other hand, in animals and human beings respiratory gases are transported to all parts of the body.
- The rate of respiration is slow in plants whereas it is faster in humans and animals.
Plants get oxygen by diffusion
Diffusion is the only process through which much needed oxygen is supplied to all the cells of the plants. Diffusion occurs in roots, stems and leaves.
Respiration in roots:
Roots of the plant take oxygen from the air that is present in-between the particles of soil. Root-hair, which is an extension of the epidermal cells of a root, is in direct contact with the soil. Oxygen diffuses in root hair and reaches all the other cells of the roots. It is through root hairs that only carbon dioxide gets diffused into them and is expelled from the roots of a plant. Thus, respiration in roots of the plant occurs by diffusion of oxygen and carbon dioxide through root hairs.
Also, many a times we have noticed that plants die if they are waterlogged for long. This is because due to water logging air is expelled from in-between the particles of soil and thus, oxygen becomes unavailable to the roots of the plants. Under such condition plant respire anaerobically which produces alcohol and kills them.
Respiration in stems
The soft stems of small herbaceous plants have stomata in them and hard stem of big plants and trees have lenticels in them. Lenticels are in the small area of a bark. These cells are loosely placed and therefore allow the gaseous exchange of respiratory gases between air and living cells of the woody stem.
Stomata help in the gaseous exchange of respiratory gases between stems of herbaceous plants and air. It is through stomata that oxygen from air diffuses into the stem and goes to all the cells of a stem for respiration.
Similarly, carbon dioxide produced in the stems diffuses into stomata of herbaceous plants and lenticels of trees or large plants and goes out into the air.
Respiration in leaves
Respiration in leaves takes place through stomata that is present as tiny pores in the leaves of a plant. Oxygen gets diffused in stomata and reaches other cells of the leaves. The carbon dioxide produced in the process of respiration also gets diffused with stomata and moves out of the leaves.
Also, respiration in leaves takes places at both day and night time. But photosynthesis occurs only during day time. Because of this, net gaseous exchange in the leaves of a plant is:
- During day time, oxygen is produced in the leaves. This is because photosynthesis occurs during the day. So leaves use some of this oxygen for respiration and rest of it is diffused out in the air. The carbon dioxide produced during respiration in the leaves is also used up in photosynthesis. Rather more carbon dioxide is required from the air. Therefore, net gaseous exchange during day time is, oxygen diffuses out and carbon dioxide diffuses in.
- During night time no photosynthesis occurs in the leaves. Therefore, in the process of respiration oxygen diffuses into leaves from the air and carbon dioxide diffuses out in the air. So, the net gaseous exchange in leaves at night is oxygen diffuses in and carbon dioxide diffuses out.
Excretion in Plants
Excretion is the removal of waste from the body. Plants also produce waste products but very slowly and in very small amounts. They do not have any special organ for the removal of their waste product.
The waste products of a plant are carbon dioxide, water vapour and oxygen. While carbon dioxide and water vapour are waste products of respiration, oxygen is a waste product of photosynthesis. These waste products are removed through stomata in leaves and lenticels in stems and are released into the air.
Some of the waste products are stored in the leaves, bark and fruits of a plant or a tree. Trees get rid of them when dead leaves bark and ripe fruits fall off from them. Some plants store waste in their fruits in the form of solid bodies called raphides. For example, fruit yam has needle-shaped raphides on its surface. Plants also secrete waste in the form of gum and resins from their stem and branches.
Therefore, various methods used by plants to get rid of their waste products are:
- Gaseous waste through stomata and lenticels.
- Stored solid and liquid waste by shedding leaves, peeling of bark and falling of fruits.
- By secreting waste in the form of gum and resins.
- Excrete waste into the soil around them.
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