Life Processes — Practice

Question 1

Name the green pigment that captures sunlight for photosynthesis.

Accepted Answer

✦ Answer: Chlorophyll (found in chloroplasts).

Question 2

Which enzyme in saliva begins the digestion of starch?

Accepted Answer

Saliva contains salivary amylase (ptyalin), which breaks starch into sugars.

✦ Answer: Salivary amylase (ptyalin).

Question 3

Name the product of anaerobic respiration in human muscles during heavy exercise.

Accepted Answer

✦ Answer: Lactic acid (its build-up causes muscle cramps).

Question 4

Write the balanced equation for photosynthesis and list the raw materials needed.

Accepted Answer

Step 1 — Equation: 6CO₂ + 6H₂O →(sunlight, chlorophyll) C₆H₁₂O₆ + 6O₂.

Step 2 — Raw materials: carbon dioxide (from air via stomata), water (from soil via roots), and sunlight (captured by chlorophyll).

✦ Answer: equation + CO₂, water and sunlight (chlorophyll).

Question 5

Differentiate between aerobic and anaerobic respiration in terms of oxygen, products and energy released.

Accepted Answer

Aerobic: uses O₂, occurs in mitochondria, products CO₂ + H₂O, releases MORE energy.

Anaerobic: no O₂, occurs in cytoplasm, products are ethanol + CO₂ (yeast) or lactic acid (muscle), releases LESS energy.

✦ Answer: aerobic = with O₂, more energy, CO₂+H₂O; anaerobic = without O₂, less energy, ethanol/lactic acid.

Question 6

Why is the wall of the left ventricle thicker than that of the other heart chambers?

Accepted Answer

Step 1 — The left ventricle pumps oxygenated blood to the entire body.

Step 2 — This needs high pressure, so its muscular wall is the thickest to generate that force.

✦ Answer: It pumps blood to the whole body at high pressure, so it needs thick, strong muscular walls.

Question 7

How does water rise from the roots to the top of a tall tree?

Accepted Answer

Step 1 — Water is absorbed by root hairs and moves into the xylem.

Step 2 — Evaporation of water from leaf surfaces (transpiration) creates a suction called the transpiration pull.

Step 3 — This pull draws a continuous column of water up the xylem.

✦ Answer: Xylem carries water up, driven by the transpiration pull created by evaporation from leaves.

Question 8

Describe the role of the small intestine in digestion and absorption. Why is it well suited to this job?

Accepted Answer

Step 1 — The small intestine is the main site where digestion is completed by bile (emulsifies fat), pancreatic juice (trypsin, lipase) and intestinal juice.

Step 2 — Digested food (glucose, amino acids, fatty acids) is absorbed here into the blood.

Step 3 — Its inner surface has millions of finger-like villi that greatly increase the surface area, and a rich blood supply to carry away the absorbed nutrients.

✦ Answer: completes digestion + absorbs nutrients; villi increase surface area and rich blood supply aids absorption.

Question 9

Explain how urine is formed in a nephron.

Accepted Answer

Step 1 — Blood enters the glomerulus, a tuft of capillaries, where it is filtered under pressure into Bowman's capsule.

Step 2 — As the filtrate passes along the tubule, useful substances — glucose, amino acids, salts and most water — are selectively reabsorbed into the blood.

Step 3 — The remaining liquid containing wastes (mainly urea) is urine, which passes to the bladder.

✦ Answer: filtration in glomerulus → selective reabsorption in the tubule → urine collected and sent to the bladder.

Question 10

What is double circulation? Trace the path of blood through the human heart and explain its advantage.

Accepted Answer

Step 1 — Double circulation means blood passes through the heart twice for each complete circuit of the body.

Step 2 — Path: deoxygenated blood from the body → right atrium → right ventricle → lungs (becomes oxygenated) → left atrium → left ventricle → whole body.

Step 3 — Advantage: oxygenated and deoxygenated blood never mix, so the body always receives fully oxygen-rich blood — essential for warm-blooded animals with high energy needs.

✦ Answer: blood crosses the heart twice; correct path; advantage = no mixing → efficient oxygen supply.

Question 11

Describe the structure of alveoli and explain how they are adapted for the exchange of gases.

Accepted Answer

Step 1 — Alveoli are tiny balloon-like air sacs at the ends of the bronchioles in the lungs.

Step 2 — Adaptations: (i) very large total surface area for maximum gas exchange; (ii) extremely thin (one-cell-thick) walls for easy diffusion; (iii) a dense network of capillaries around them.

Step 3 — Oxygen from inhaled air diffuses into the blood (carried by haemoglobin), and CO₂ diffuses out to be exhaled.

✦ Answer: thin-walled sacs with huge surface area + rich blood supply → efficient diffusion of O₂ in and CO₂ out.

Practice — Life Processes

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