CG Board Class 10 Science Chapter 7 Solutions: Life Processes: Nutrition, Transportation, Respiration, Excretion (जैविक प्रक्रियाएँ: पोषण, परिवहन, श्वसन, उत्सर्जन) (2026-27)

(i) The internal wall of the stomach is usually not injured by HCl because of:**

• (a) Pepsin
• (b) Mucous
• (c) Salivary amylase
• (d) None of these

(b) Mucous

Explanation: Mucous is secreted by gastric glands to form a protective layer over the stomach inner lining, shielding it from hydrochloric acid.

Answer: (b) Alveoli of lungs and surrounding capillaries

Explanation: The ultra-thin walls of alveoli and surrounding blood capillaries facilitate simple diffusion of O₂ and CO₂.

Answer: (b) Pulmonary vein

Explanation: Pulmonary veins bring oxygen-rich blood from lungs back into the left auricle of the heart.

Answer: (a) Nephron

Explanation: Nephrons are the structural and functional filtering units of kidneys.

| | (Artery) | (Vein) |

| (Valves) | | |

Producers (Autotrophs): Their primary source of energy is Solar Energy** (sunlight). They use inorganic raw materials (CO₂ and H_2O) to trap radiant light energy via chlorophyll and convert it into stored chemical energy (carbohydrates).

• Consumers (Heterotrophs): Their source of energy is Chemical Energy stored in organic food compounds synthesized by producers or other animals. They cannot utilize solar energy directly.

Plants and animals share an interdependent relationship

1. Plants as Food Suppliers: Plants produce complex organic carbon compounds (glucose, starch) and Oxygen (O₂) during photosynthesis, which serve as food and life-sustaining gas for all animals.
2. Animals as Carbon Dioxide Suppliers: Animals perform respiration, releasing Carbon Dioxide (CO₂) into the atmosphere, which plants absorb as a essential reactant for photosynthesis.

Metabolic activities generate toxic nitrogenous wastes like urea and uric acid. If accumulated, these substances alter internal pH, disturb osmotic fluid balance, damage cells, and prove fatal. The formation and excretion of urine purifies the blood, maintains homeostasis, and regulates body water and salt balance.

Xylem Transport:** Transports water and dissolved mineral salts absorbed from the soil. The transport is strictly unidirectional (upwards from roots to leaves driven by transpiration pull).

• Phloem Transport: Transports organic food products (sucrose, glucose) and amino acids synthesized in leaves. The transport is bidirectional (upward and downward to all living/storage tissues using ATP energy).

1. Activation of Enzymes: Creates an acidic medium (pH 1.5-2.0) required to convert inactive pepsinogen into active pepsin for protein digestion.
2. Germicidal Action: Kills harmful bacteria and pathogens ingested along with food.
3. Softening Food: Softens hard food particles for gastric churning.

Polythene Observation: Water drops condense inside the polythene due to transpiration** from leaves on those tied branches.

• Can we estimate total water loss? No, measuring water from a few covered branches gives only a localized sample. To estimate total plant water loss, we would need to multiply this rate by the ratio of total leaf surface area of the entire plant to the leaf area enclosed in the bag, adjusting for shading, humidity inside the bag, and environmental variables.

(a) Maximum transpiration took place from the lower surface** of the leaf (when upper surface was coated in Leaf 3, weight loss was still 36%, whereas coating lower surface in Leaf 4 reduced weight loss to 4%).

• (b) The lower surface has the maximum number of stomata.
• (c) Excess water loss causes leaves to wilt, cells lose turgidity, photosynthesis stops, and the plant may dry up and die.
• (d) If transpiration stops, upward movement of water and minerals (xylem sap ascent) halts, thermal regulation fails (plant overheats), and nutrient supply to top leaves is blocked.

Human heart circulation consists of two separate pathways called Double Circulation