Developmental biology, a branch of Biology Topics, examines the processes of growth and differentiation.
What is Excretion? And Why is excretion important in living things?
All the living things take food. The living things use this food to obtain energy by the process of respiration. The process of respiration produces carbon dioxide gas as the waste material. Moreover, all the food eaten by a living organism is not used completely. A part of the food taken by a living organism remains unused. The unused part of the food also becomes a waste material. Thus, the living things produce some waste materials in their bodies during the various life processes. Many of these waste materials are poisonous to the living things so they have to be removed. The removal of waste substances from the body of a living organism is called excretion. All the living things excrete. That is, all the living things get rid of wastes from inside themselves (which they do not want).
The important waste substances which are produced in the body of animals are carbon dioxide, urea and faeces. The unwanted water is also considered a waste. The animals give out carbon dioxide when they breathe out used air.
The animals give out urea, unwanted water and other salts in the form of urine. The animals give out solid wastes of their body in faeces. The process of excretion in a cow is shown in Figure.
Some harmful or poisonous waste materials are also produced in plants. So, plants also excrete. Excretion in plants means removal of waste products in plants. The plants remove their waste products by different methods. Some of the important plant wastes and the methods by which they are removed are given below :
(i) The main waste products produced by plants are carbon dioxide (during respiration) and oxygen (during photosynthesis). During the daytime, the waste product carbon dioxide is re-used by plants in making food by photosynthesis. At night time, the plants get rid of waste carbon dioxide through the stomata in leaves. The waste product oxygen is also removed from plants through the stomata in their leaves.
(ii) Some plants store some of their waste products in the body parts (like leaves, bark and fruits) in a way that they do not harm the plant as a whole. The plants get rid of these wastes by the shedding of leaves, peeling of bark and felling of fruits.
(iii) Some plants remove their waste products as secretions. For example, the plants secrete a large number of waste products like gum, resin and latex (rubber solution). These plant wastes are useful to human beings.
Thus, excretion is another characteristic common to all living things. Non-living things do not excrete. For example, a rock is a non-living thing which does not produce and excrete any waste materials.