Chapter 5 · Life Processes

NCERT Class 10 Science Chapter 5 Intext Questions (Page 81)

All 4 questions of NCERT Class 10 Science Chapter 5 Intext Questions (Page 81) — Life Processes — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   Why is ​diffusion insufficient to ​meet ​the oxygen requirements ​of multi-cellular organisms like ​humans?
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   Most cells lie far from the surroundings and diffusion is too slow over such distances, so the lungs and blood (haemoglobin) carry oxygen.

   In a multi-cellular organism like a human the body is large and most of its cells are not in direct contact with the surrounding environment. Diffusion is fast only over very short distances; over the distances inside a human body it is far too slow. By diffusion alone an oxygen molecule would take about three years to reach the toes from the lungs, while every cell needs oxygen continuously. So diffusion cannot meet the oxygen requirement of all the cells. Instead, oxygen is taken in by a specialised organ, the lungs, and carried to every cell by the blood, with haemoglobin as the respiratory pigment; diffusion serves only for the last short step across the alveolar wall and into each cell.

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2. Q2
   What ​criteria do we ​use ​to ​decide ​whether ​something ​is alive?
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   Visible movement is not enough; something is alive if its life processes, the molecular movements that maintain it, are going on.

   The common, everyday criterion is visible movement: an animal running, chewing or breathing, a plant growing. But it is not enough, because a plant that is not visibly growing is still alive, and some animals breathe without any visible movement. The real criterion is that the organism carries on the life processes, the invisible movements of molecules by which it constantly repairs and maintains its organised structure: nutrition, respiration, transportation of substances within the body and excretion of wastes. Anything in which these maintenance processes are going on, even while it is asleep or apparently doing nothing, is alive. (Viruses, which show no molecular movement of their own until they infect a cell, are the controversial borderline case.)

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3. Q3
   What ​are ​outside ​raw materials used ​for by ​an organism?
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   Food from outside gives energy and building material for growth and repair; oxygen from outside oxidises food in respiration.

   An organism takes in raw materials from outside for three main purposes. (1) Energy: the maintenance processes that keep the body's organised structure from breaking down need energy, and this comes from outside in the form of food, which is broken down in the body into a uniform source of energy for the molecular movements of life. (2) Growth and repair: additional raw material from the food (carbon-based molecules, and for plants also water, nitrogen and other minerals from the soil) is used to build new cells and tissues, to grow and develop, and to synthesise proteins and other substances the body needs. (3) Oxidation of food: oxygen taken in from outside is used in respiration to break down the food and release its energy. Water, also taken in from outside, is the medium in which all these reactions take place.

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4. Q4
   What ​processes would ​you ​consider ​essential for ​maintaining life?
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   The life processes are nutrition, respiration, transportation and excretion, and they go on all the time, even at rest.

   The processes essential for maintaining life, the life processes, are: (1) Nutrition, the taking in of food, a source of energy and of raw material, from outside the body; (2) Respiration, the taking in of oxygen from outside and its use to break down the food and release energy for the cell; (3) Transportation, the carrying of food and oxygen from where they are taken up to every part of the body, and of wastes away from the cells; and (4) Excretion, the removal from the body of the harmful by-products formed in these reactions. These maintenance processes must go on all the time, even when the organism is at rest or asleep.

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