Life Processes: Excretion MCQs Quiz | Class 10
This quiz is for **Class X Science (Code 086)**, covering **Unit II: World of Living** and focusing on **Life Processes: Excretion**. It includes basic concepts and an overview of excretion in plants and animals. Test your knowledge on these topics and download a detailed answer PDF for revision.
Understanding Excretion: A Vital Life Process
Excretion is the biological process by which an organism rids its body of harmful metabolic waste products and excess substances. These waste products, if allowed to accumulate, can become toxic and disrupt normal bodily functions. Therefore, excretion plays a crucial role in maintaining homeostasis, the stable internal environment necessary for survival.
Key Concepts of Excretion:
- Metabolic Wastes: These are byproducts of various biochemical reactions occurring in the body. Primary metabolic wastes include nitrogenous compounds (like urea, ammonia, uric acid), carbon dioxide, water, and salts.
- Importance: Removal of these wastes prevents poisoning of the cells and helps regulate the body’s water and salt balance.
Excretion in Animals (Focus on Humans):
Animals have specialized organs for excretion, reflecting their complex physiological needs. The human excretory system is a prime example:
- Kidneys: A pair of bean-shaped organs that filter blood. They remove nitrogenous wastes (primarily urea), excess salts, and water to form urine.
- Ureters: Tubes that carry urine from the kidneys to the urinary bladder.
- Urinary Bladder: A muscular sac that stores urine until it is excreted.
- Urethra: A tube through which urine is expelled from the body.
The Nephron – Functional Unit of the Kidney:
Each kidney contains millions of tiny filtering units called nephrons. A nephron consists of:
- Glomerulus: A capillary tuft where blood is filtered, forming glomerular filtrate.
- Bowman’s Capsule: Cup-shaped structure enclosing the glomerulus, collecting the filtrate.
- Renal Tubule (PCT, Loop of Henle, DCT): Where essential substances like glucose, amino acids, salts, and most water are reabsorbed back into the blood, and additional wastes are secreted into the tubule.
- Collecting Duct: Collects urine from several nephrons and passes it to the ureter.
Excretion in Plants:
Plants do not have specialized excretory organs like animals, as their metabolic rates are lower, and they re-utilize or store many waste products. Their methods of excretion include:
- Gaseous Wastes:
- Carbon Dioxide: Produced during respiration, released through stomata (leaves) and lenticels (stems).
- Oxygen: Produced during photosynthesis, released through stomata.
- Water Vapour: Released through transpiration from stomata.
- Solid and Liquid Wastes:
- Storage: Many waste products are stored in non-living parts of the plant, such as old xylem, or in specific cells or vacuoles, preventing harm to metabolically active tissues.
- Shedding: Wastes accumulated in leaves are removed when the leaves fall off (e.g., in deciduous trees). Bark peeling also removes stored wastes.
- Exudation: Plants excrete some wastes as gums, resins, latex, and sap, often through specialized ducts or surfaces.
- Secretion into Soil: Some plants excrete waste substances into the soil around their roots.
Comparison of Excretion in Plants and Animals:
| Feature | Plants | Animals (e.g., Humans) |
|---|---|---|
| Specialized Organs | Generally absent | Present (e.g., Kidneys, Lungs, Skin) |
| Main Nitrogenous Waste | Not applicable (no primary nitrogenous waste like urea) | Urea, Uric Acid, Ammonia |
| Gaseous Waste Removal | Stomata, Lenticels | Lungs (CO2), Skin (water vapor) |
| Water Removal | Transpiration | Kidneys (urine), Skin (sweat), Lungs (vapor) |
| Other Methods | Falling leaves, Bark shedding, Gums, Resins | Defecation (undigested food), Sweat glands |
Quick Revision Points:
- Excretion is the removal of harmful metabolic wastes.
- In humans, the kidneys are the primary excretory organs, filtering blood to form urine.
- Nephrons are the functional units of kidneys, performing filtration, reabsorption, and secretion.
- Plants excrete gaseous wastes via stomata and lenticels.
- Plants store solid/liquid wastes in old parts or shed them (leaves, bark) or exudate them (gums, resins).
- Transpiration helps plants remove excess water.
Practice Questions:
- Describe the path of urine formation and excretion in the human body.
- Explain the role of the nephron in maintaining the body’s internal balance.
- List three ways plants get rid of their waste products.
- Why is it essential for organisms to excrete metabolic waste products?
- What are lenticels, and what is their role in plant excretion?
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