CLASS X | SCIENCE | LIFE PROCESSES
Notes prepared by Subhankar Karmakar
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The process of removal of toxic wastes from our body of an organism is called excretion. Excretion takes place in plants as well as in animals.
Biochemical reactions that takes place inside the cells of an organism may produce toxic wastes which are removed by the process of excretion.
• The main waste products produced by plants are carbon dioxide, water vapour and oxygen.
• The gaseous wastes of respiration and photosynthesis in plants (carbon dioxide, water vapour and oxygen) are removed through the "stomata" in leaves and "lenticels" in stems and released to the air.
• The plants excrete carbon dioxide produced as a waste during respiration only at night time.
• The plants excrete oxygen as a waste only during day time.
• Water vapour produced during respiration is excreted by plants during day time as well as night time by the process of Transpiration.
• The plants also store some of the waste products in their body parts like in the leaves, bark and fruits of the plants. Plants get rid of them by shedding of leaves, peeling of bark and felling of fruits.
• Some of the plant wastes get stored in the fruits of the plant in the form of solid raphides. Plants secrete their wastes in the form of gum and resins from their stems and branches.
1. AMOEBA: In Amoeba carbon dioxide is removed by diffusion through the cell membrane but nitrogeneous wastes like ammonia and excess water are removed by Conractile Vacuole.
2. EARTHWORM: In Earthworm, the tubular structures called nephredia are the excretory organs. But it also uses its moist skin as an additional excretory organ.
Excretion is the process by which the body eliminates waste products and excess substances to maintain homeostasis, or balance, in the body. In human beings, excretion primarily involves the elimination of metabolic waste products and excess water and salts.
There are several organs involved in excretion in human beings:
Kidneys: The kidneys are the primary excretory organs in the body, responsible for filtering waste products from the blood and excreting them in the form of urine.
Skin: The skin plays a role in excretion by eliminating excess water, salts, and urea through sweat.
Lungs: The lungs excrete carbon dioxide and small amounts of water vapor during exhalation.
Liver: The liver plays a role in excretion by eliminating toxins and waste products from the body.
The process of excretion in human beings involves several steps. First, waste products are filtered from the blood by the kidneys and transported to the bladder. The bladder then stores the urine until it is eliminated from the body through the urethra. Meanwhile, excess water, salts, and urea are eliminated through sweat and the lungs.
Overall, the process of excretion is essential for maintaining the proper balance of fluids and chemicals in the body and for removing waste products that can be harmful if they build up in the bloodstream.
1. The major wastes produced by the human body are : Carbon dioxide and Urea.
2. Carbon dioxide is producedas a waste by the oxidation of food during the process of respiration and Urea is produced as a waste by the decomposition of unused proteins in the liver.
3. While Lungs excrete carbon dioxide, our Kidneys excrete urea.
4. The excretory system of human beings consists of (i) two kidneys, (ii) two ureters, (iii) Bladder and (iv) Urethra.
5. The function of kidneys is to remove the poisonous substance urea, other waste salts, and excess water from the blood and excrete them in the form of a yellowish liquid called urine.
6. The dirty blood enters the kidneys through the renal artery and cleaned blood is carried away from the kidneys by the renal vein.
7. Each kidneys are connected to the urinary bladder by excretory tubes called ureters. Urine is stored in the bladder. Urethra is a tube and the urine collected in the bladder is expelled from our body through the urethra.
8. Each kidney is made up of a large number of excretory units called nephrons. The nephron has a cup shaped bag at its upper end which is called Bowman's Capsule. The lower end of Bowman's capsule is tube shaped and it is called a tubule. The Bowman's capsule and tubule taken together make a nephron.
9. One end of the tubule is connected to the Bowman's capsule and the other end is connected to a urine collecting duct of the kidney.
10. The Bowman's capsule contains a bundle of blood capillaries which is called glomerulus. One end of the glomerulus is attached to the renal artery which brings the dirty blood containing urea waste to it. The other end of glomerulus comes out the Bowman's capsule as a blood capillary, surrounds the tubule of nephron and finally joins a renal vein carrying clean blood.
11. The function of glomerulus is to filter the blood passing through it. Only the small molecules of substances like glucose, amino acids, salts, urea and water present in blood can pass through the glomerulus and collect as filtrate in the Bowman's capsule.
The large molecules like oroteins and blood cells can not pass out through the glomerulus capillaries and hence remain behind in the blood.
12. The function of the tubules of nephron is to allow the selective reabsorption of the useful substances like glucose, amino acids, salts and water into the blood capillaries. But the waste material like urea remains behind in the tubule. It does not get reabsorbed into blood capillaries.
