Chapter 6: Life Processes
NCERT Class 10 Science Exercise Solutions
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The kidneys in human beings are a part of the system for
(a) nutrition.
(b) respiration.
(c) excretion.
(d) transportation.
Explanation: Kidneys are the primary excretory organs in humans. They filter blood to remove nitrogenous wastes like urea and excess salts, producing urine. This is a vital part of the excretory system, which also includes ureters, urinary bladder, and urethra.
The xylem in plants are responsible for
(a) transport of water.
(b) transport of food.
(c) transport of amino acids.
(d) transport of oxygen.
Explanation: Xylem is the vascular tissue in plants that transports water and dissolved minerals from roots to all aerial parts. It consists of tracheids, vessels, xylem parenchyma, and fibers. Phloem, on the other hand, transports food (sucrose, amino acids).
The autotrophic mode of nutrition requires
(a) carbon dioxide and water.
(b) chlorophyll.
(c) sunlight.
(d) all of the above.
Explanation: Autotrophic nutrition (photosynthesis) requires carbon dioxide, water, chlorophyll, and sunlight to synthesize organic compounds (glucose). Chlorophyll captures light energy, CO₂ and H₂O are raw materials, and sunlight provides the energy.
The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
(a) cytoplasm.
(b) mitochondria.
(c) chloroplast.
(d) nucleus.
Explanation: Pyruvate, produced in the cytoplasm during glycolysis, enters mitochondria. Here, it undergoes aerobic respiration (Krebs cycle and electron transport chain) to release CO₂, H₂O, and a large amount of energy in the form of ATP.
How are fats digested in our bodies? Where does this process take place?
Digestion of Fats: Fats are large insoluble molecules that need to be broken down into fatty acids and glycerol for absorption.
Process:
1. Bile juice (from liver) emulsifies fats into smaller droplets in the small intestine, increasing surface area for enzyme action.
2. Pancreatic lipase (from pancreas) breaks down emulsified fats into fatty acids and glycerol.
3. Intestinal lipase completes the digestion.
Site: Mainly in the small intestine (duodenum).
What is the role of saliva in the digestion of food?
Saliva, secreted by salivary glands, plays multiple roles:
1. Moistening and Lubrication: It moistens food, making it easier to chew and swallow.
2. Chemical Digestion: Contains enzyme salivary amylase (ptyalin) which breaks down starch into maltose (a simpler sugar).
3. Cleaning and Protection: Washes away food particles, maintains oral pH, and has antibacterial properties.
4. Solubilization: Helps dissolve food particles so they can be tasted by taste buds.
What are the necessary conditions for autotrophic nutrition and what are its by-products?
Necessary Conditions for Autotrophic Nutrition (Photosynthesis):
1. Carbon dioxide (from air)
2. Water (from soil)
3. Chlorophyll (in chloroplasts)
4. Sunlight (source of energy)
5. Suitable temperature and other environmental factors.
By-products:
1. Oxygen (released into atmosphere)
2. Water vapor (through transpiration)
The main product is glucose, which is stored as starch.
What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.
Differences:
| Aerobic Respiration | Anaerobic Respiration |
|---|---|
| Occurs in presence of oxygen | Occurs in absence of oxygen |
| End products: CO₂, H₂O | End products: Ethanol + CO₂ (in yeast) or Lactic acid (in muscles) |
| High ATP yield (36–38 ATP per glucose) | Low ATP yield (2 ATP per glucose) |
| Occurs in mitochondria | Occurs in cytoplasm |
| Complete oxidation of glucose | Incomplete oxidation of glucose |
How are the alveoli designed to maximise the exchange of gases?
Alveoli are tiny, balloon-like structures in lungs optimized for gas exchange:
1. Large Surface Area: Millions of alveoli provide ~80 m² surface area.
2. Thin Walls: Single-cell thick epithelium reduces diffusion distance.
3. Rich Blood Supply: Surrounded by dense capillary network for efficient O₂/CO₂ exchange.
4. Moist Surface: Lining fluid helps dissolve gases for diffusion.
5. Elasticity: Expand and recoil during breathing to maintain airflow.
6. Close Contact: Alveolar and capillary walls are in close proximity (0.5–1 μm).
What would be the consequences of a deficiency of haemoglobin in our bodies?
Haemoglobin deficiency (anaemia) leads to:
1. Reduced Oxygen Transport: Haemoglobin carries O₂; deficiency causes hypoxia in tissues.
2. Fatigue and Weakness: Cells don’t get enough O₂ for energy production.
3. Pale Skin and Nails: Due to less red colour from haemoglobin.
4. Shortness of Breath: Especially during physical activity.
5. Dizziness and Headaches: Brain receives less oxygen.
6. Poor Immunity: Increased susceptibility to infections.
7. Impaired Growth in Children: Due to reduced cellular respiration.
Describe double circulation in human beings. Why is it necessary?
Double Circulation: Blood passes through the heart twice in one complete cycle:
1. Pulmonary Circulation: Deoxygenated blood → right atrium → right ventricle → lungs (oxygenation) → left atrium.
2. Systemic Circulation: Oxygenated blood → left atrium → left ventricle → aorta → body tissues → deoxygenated blood returns to right atrium.
Why necessary:
- Maintains high pressure for systemic circulation to efficiently supply O₂ to all body parts.
- Separates oxygenated and deoxygenated blood, preventing mixing and ensuring highly oxygenated blood reaches tissues.
- Essential for endotherms (birds, mammals) with high metabolic and energy demands.
What are the differences between the transport of materials in xylem and phloem?
| Xylem | Phloem |
|---|---|
| Transports water and minerals | Transports organic nutrients (sucrose, amino acids) |
| Unidirectional (roots → aerial parts) | Bidirectional (source to sink) |
| Driven by transpiration pull, root pressure | Driven by osmotic pressure (ATP required) |
| Consists of dead cells (tracheids, vessels) | Consists of living cells (sieve tubes, companion cells) |
| No energy expenditure (passive process) | Energy expenditure (active process) |
Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.
| Alveoli (Lungs) | Nephrons (Kidneys) |
|---|---|
| Function: Gas exchange (O₂ in, CO₂ out) | Function: Filtration of blood, urine formation |
| Structure: Tiny air sacs with thin walls, surrounded by capillaries | Structure: Bowman’s capsule, glomerulus, tubules (PCT, loop of Henle, DCT) |
| Mechanism: Diffusion across partial pressure gradient | Mechanism: Ultrafiltration, reabsorption, secretion |
| Surface area: Very large (~80 m²) for diffusion | Surface area: Large due to microvilli in tubules |
| Exchange: O₂ and CO₂ between air and blood | Exchange: Wastes (urea), water, ions between blood and filtrate |
| End product: Oxygenated blood | End product: Urine |
Both are microscopic structural units designed for exchange: alveoli for gases, nephrons for wastes.