In-text Questions — Respiration — Life Processes

1. 12 marksNCERT Cl-10 Science, In-text Qs after §5.3/§5.4.1 intro, Q1

   What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

   Hint. Compare how much oxygen is present in air versus how much is dissolved in the same volume of water.

   Step 1 — Compare oxygen availability. The concentration of oxygen in air is far higher than the amount of oxygen dissolved in water.

   Step 2 — Draw out the consequence. Because air is so oxygen-rich, a terrestrial organism doesn't need to work nearly as hard to obtain enough oxygen, whereas an aquatic organism must extract oxygen from water where it is much more dilute — which is why fish, for instance, must pass water over their gills continuously and at a much faster rate than terrestrial animals breathe.

   ✦ Answer: Terrestrial organisms breathe air, which has a much higher oxygen concentration than the oxygen dissolved in water, so they can obtain sufficient oxygen far more easily than aquatic organisms can.

   Where students slip. Assuming aquatic organisms have it easier because they're 'surrounded by oxygen-containing water' — the concentration of oxygen actually dissolved in water is much lower than in air, which is precisely the terrestrial advantage.

2. 23 marksNCERT Cl-10 Science, In-text Qs after §5.3/§5.4.1 intro, Q2

   What are the different ways in which glucose is oxidised to provide energy in various organisms?

   Hint. All paths start the same way — glucose to pyruvate — and then split depending on whether oxygen is available.

   Step 1 — Common first step. In every case, glucose (6-carbon) is first broken down in the cytoplasm into pyruvate (3-carbon), since this initial step is shared by all the pathways that follow.

   Step 2 — With oxygen (aerobic). Pyruvate is broken down further in the mitochondria, using oxygen, into carbon dioxide and water — releasing a large amount of energy.

   Step 3 — Without oxygen, in yeast (anaerobic/fermentation). Pyruvate is converted into ethanol and carbon dioxide, releasing less energy.

   Step 4 — Without oxygen, in our muscles (anaerobic). Pyruvate is converted into lactic acid, also releasing less energy — the build-up of lactic acid during sudden vigorous activity is what causes muscle cramps.

   ✦ Answer: Glucose always breaks down to pyruvate first. With oxygen, pyruvate is fully oxidised in the mitochondria to CO₂ and water (lots of energy). Without oxygen, it becomes ethanol and CO₂ in yeast, or lactic acid in our muscles — both releasing much less energy.

   Where students slip. Treating the yeast and muscle pathways as identical just because both are 'anaerobic' — they produce different end products (ethanol+CO₂ versus lactic acid), even though both skip the oxygen-using mitochondrial step.

3. 32 marksNCERT Cl-10 Science, In-text Qs after §5.3/§5.4.1 intro, Q3

   How is oxygen and carbon dioxide transported in human beings?

   Hint. One of these two gases needs a special carrier pigment; the other dissolves well enough on its own.

   Step 1 — Oxygen. Oxygen is carried mainly by haemoglobin, a pigment present in red blood corpuscles that has a very high affinity for oxygen.

   Step 2 — Carbon dioxide. Carbon dioxide is more soluble in water than oxygen is, so it is mostly transported simply dissolved in the blood plasma, without needing a dedicated carrier pigment.

   ✦ Answer: Oxygen is transported bound to haemoglobin in red blood corpuscles; carbon dioxide, being more water-soluble, travels mostly dissolved directly in the blood plasma.

   Where students slip. Saying both gases are carried by haemoglobin — only oxygen relies on haemoglobin for transport; CO₂ doesn't need it because it dissolves well enough in plasma on its own.

4. 42 marksNCERT Cl-10 Science, In-text Qs after §5.3/§5.4.1 intro, Q4

   How are the lungs designed in human beings to maximise the area for exchange of gases?

   Hint. Think about what happens once air enters the lungs and keeps dividing into smaller and smaller passages.

   Step 1 — Describe the branching structure. Within the lungs, the air passage divides into smaller and smaller tubes, finally ending in enormous numbers of tiny balloon-like structures called alveoli.

   Step 2 — Explain why this maximises area. Having so many tiny alveoli, rather than one large sac, gives a vastly greater total surface area for gas exchange than a simple large chamber would.

   Step 3 — Add the capillary detail. Each alveolus is surrounded by an extensive network of blood capillaries, so gases can diffuse across a huge combined surface directly into and out of the blood.

   ✦ Answer: The air passage branches into smaller and smaller tubes ending in millions of tiny alveoli, each wrapped in blood capillaries — this gives an enormous total surface area (roughly 80 m²) for efficient gas exchange.

   Where students slip. Describing the lungs as 'big' as the reason for efficient exchange — it's specifically the huge number of tiny alveoli, not overall lung size, that produces such a large exchange surface.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc105.pdf) — five in-text question sets (21 questions total) plus one end-of-chapter Exercise (13 questions, not 20 as some older manifests claim). Unchanged by rationalisation; the chapter describes the breathing passage and the nephron's tubule in generic functional terms rather than naming every intermediate structure.. Questions are referenced from the NCERT textbook for identification.