Life Processes in Living Organisms
Transportation of Water and Minerals in Plants (Group B)
Excretion and Its Importance
Excretory system consists of groups of organs that are responsible for excreting waste materials such as, harmful chemicals and other impurities from the body. The major excretory organ is kidney. However, there are some other organs also that perform the function of excretion.
Let us understand the function of the following organs as excretory organs.
Respiration is a necessary process that provides energy for cellular activities. During respiration, carbon dioxide gets accumulated in the cells, from where it diffuses into the bloodstream and is finally transported to the lungs. From lungs, this carbon dioxide leaves the body every time we exhale.
Liver helps in the excretion of various unneeded substances in the body. It converts toxic ammonia into urea, a harmless fluid, by the process of deamination. This urea is then filtered by the kidney into urine. It does not directly eliminate excretory substances.
Skin also acts as an excretory organ. It possesses glands, namely, sweat glands and sebaceous glands. Sweat is a watery fluid that consists of metabolic wastes like water, sodium chloride, lactic acid, amino acids, urea, glucose, etc. Besides excreting metabolic wastes from the body, sweat also has a cooling effect on the body. On the other hand, sebaceous glands help in excretion of sebum which consists of lipids, fatty acids, etc.
How the other kinds of waste materials removed from the body? Is there a particular organ system that functions to remove waste materials from the body?
The organ system that performs the function of excretion is known as the excretory system. The excretory system removes the waste materials present in the blood.
Which organs are involved in this process? What mechanism is required for filtering blood?
The primary components of the excretory system are the kidneys, the ureter, the urinary bladder, and the urethra.
When blood reaches the kidneys, useful substances are absorbed back into blood, while the waste materials are dissolved in water and removed from the body in the form of urine.
The urine enters a long tube-like structure called the ureter. The ureter then passes the urine into the urinary bladder, which stores it until it is passed out of the body. Urine is passed out of the body through a muscular tube-like structure called the urethra.
Waste materials are also removed from the body through sweat. During sweating, water and salts are removed from the body.
In animals, control and coordination is governed by the nervous system. However, plants do not have a nervous system.
Then, how do plants respond to stimuli?
Plants respond to stimuli by showing movement.
Have you ever seen any movement in plants?
- When you touch a sensitive plant such as touch- me- not (Mimosa pudica), the plant folds its leaves and droops.
- When a seed germinates, the root grows down in the soil and the stem grows up in the air.
In the first example, touch is the stimulus and the plant responds by folding its leaves. Therefore, the plant shows movement by folding its leaves.
In the second example, the seed germinates and shows directional movement.
In the first example, movement is independent of growth i.e. there is no growth involved. However, in the second example, the movement of the seedling is caused by growth. If the seedling is prevented from growing, then it will not show any movement.
Thus, plants exhibit both growth-dependent and growth-independent movements.
In plants (like animals), the information is carried from cells by electro-chemical means. However, there is no specialized tissue for the conduction of information. In fact, plants change their shape by changing the amount of water in them. This results in swelling and shrinking. This change of shape results in movement.
You must have seen plants such as peas and grapes with tendrils. Movement in these plants occurs in the growing stem of the tendrils. When the tendrils come in contact with a supporting object, they coil and cling around it. Plants respond to stimuli slowly by growing in a particular direction. This type of growth is directional.
Nastic movements in plants
Nastic movements are the movements in plants that take place in response to the environment stimulus. One of the main feature of the nastic movement is that the direction of the movement is independent of the direction of stimulus.
For example, the movement of organs like leaves and petals that are directed by the touch as in the leaflets of to…
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