Chapter 5 · Life Processes

NCERT Class 10 Science Chapter 5 Intext Questions (Page 87)

All 5 questions of NCERT Class 10 Science Chapter 5 Intext Questions (Page 87) — Life Processes — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   What ​are ​the ​differences between ​autotrophic ​nutrition ​and heterotrophic ​nutrition?
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   Autotrophs make their own food from carbon dioxide and water using sunlight; heterotrophs depend on ready-made food from other organisms.

   (1) Source of food: in autotrophic nutrition the organism makes its own food from simple inorganic substances, carbon dioxide and water; in heterotrophic nutrition the organism takes in ready-made complex organic food produced by other organisms. (2) Requirements: autotrophic nutrition needs sunlight and chlorophyll (photosynthesis); heterotrophic nutrition needs neither, but needs enzymes to break the complex food down into simpler substances before it can be used. (3) Chemistry: autotrophs build up carbohydrate from ${\text{CO}}_2$ and water and store the surplus as starch; heterotrophs break food down into simpler molecules such as glucose, amino acids and fatty acids and, in animals, store the surplus as glycogen. (4) Dependence: autotrophs are independent producers; heterotrophs depend directly or indirectly on autotrophs for food. (5) Examples: autotrophs are green plants and some bacteria; heterotrophs are animals, fungi (bread moulds, yeast, mushrooms) and parasites (cuscuta, ticks, lice, leeches, tape-worms).

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2. Q2
   Where ​do plants ​get each ​of the ​raw ​materials ​required for ​photosynthesis?
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   Carbon dioxide comes from the air through stomata, water and minerals from the soil through roots, and light from the sun.

   Carbon dioxide is taken from the atmosphere through the stomata, tiny pores on the surface of the leaves whose opening and closing is controlled by the guard cells (some gaseous exchange also occurs across the surface of stems and roots). Water is absorbed from the soil by the roots of terrestrial plants and carried up to the leaves through the xylem. Sunlight, the source of energy, comes from the sun and is absorbed by chlorophyll held in the chloroplasts of the leaf cells. The other materials the plant needs to build its body, nitrogen, phosphorus, iron and magnesium, are also taken up from the soil by the roots; nitrogen is taken in the form of inorganic nitrates or nitrites, or as organic compounds prepared by bacteria from atmospheric nitrogen.

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3. Q3
   What is ​the role ​of the ​acid ​in our stomach?
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   Hydrochloric acid gives the acidic medium pepsin needs to act and kills germs that enter with the food.

   The acid in our stomach is hydrochloric acid, secreted by the gastric glands in the stomach wall. Its roles are: (1) it creates a strongly acidic medium in the stomach, which is necessary for the action of the protein-digesting enzyme pepsin, since pepsin is active only in an acidic medium; and (2) it kills most of the bacteria and other germs that enter the stomach along with the food, protecting the body from infection. The inner lining of the stomach is protected from the acid by the mucus that the gastric glands also secrete; when this protection fails, we feel 'acidity'.

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4. Q4
   What is the ​function ​of ​digestive enzymes?
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   Digestive enzymes are biological catalysts that break large, insoluble food molecules into small, soluble ones that can be absorbed into the blood.

   Digestive enzymes are biological catalysts that break down the large, complex, insoluble molecules of the food we eat into small, simple, soluble molecules that can be absorbed through the wall of the alimentary canal into the blood. Each enzyme acts on one class of food: salivary amylase (in saliva) breaks starch into simple sugar; pepsin (in the stomach, in an acidic medium) and trypsin (from the pancreas) break down proteins; lipase (from the pancreas) breaks down emulsified fats; and the enzymes of the intestinal juice complete the process, converting proteins to amino acids, complex carbohydrates to glucose, and fats to fatty acids and glycerol. Without these enzymes the food could not be absorbed or used by the cells for energy, growth and repair.

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5. Q5
   How is the ​small ​intestine ​designed to ​absorb ​digested ​food?
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   The small intestine's length, villi, thin walls and rich blood supply give a large surface, a short path and rapid removal of absorbed food.

   The small intestine is designed for absorption in three ways. (1) It is the longest part of the alimentary canal, fitted into a compact space by extensive coiling, so the digested food stays in contact with a very long absorbing tube (herbivores, which must digest cellulose, have an even longer one). (2) Its inner lining is thrown into numerous finger-like projections called villi, which increase the surface area for absorption enormously; the wall of each villus is thin, so the digested food has only a short distance to cross. (3) The villi are richly supplied with blood vessels, which take up the absorbed food (glucose, amino acids, fatty acids and glycerol) and carry it to each and every cell of the body, where it is used for energy, building new tissues and repairing old ones; this constant removal keeps absorption going.

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