Chapter 5 · Life Processes

NCERT Class 10 Science Chapter 5 Exercises

All 13 questions of NCERT Class 10 Science Chapter 5 Exercises (Life Processes), in the book's order, each with its answer and a step-by-step solution.

1. Q1
   The ​kidneys in human beings ​are ​a ​part ​of the ​system ​for

   1. (a)nutrition.
   2. (b)respiration.
   3. (c)excretion.
   4. (d)transportation.
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   (c) excretion.

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2. Q2
   The xylem in ​plants ​are ​responsible for

   1. (a)transport of water.
   2. (b)transport of food.
   3. (c)transport of amino acids.
   4. (d)transport of oxygen.
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   (a) transport of water.

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3. Q3
   The autotrophic ​mode ​of ​nutrition ​requires

   1. (a)carbon dioxide and water.
   2. (b)chlorophyll.
   3. (c)sunlight.
   4. (d)all of the above.
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   (d) all of the above.

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4. Q4
   The breakdown of ​pyruvate ​to give ​carbon dioxide, ​water ​and energy ​takes place ​in

   1. (a)cytoplasm.
   2. (b)mitochondria.
   3. (c)chloroplast.
   4. (d)nucleus.
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   (b) mitochondria.

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5. Q5
   How are fats digested in our ​bodies? ​Where does ​this ​process take ​place?
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   Bile emulsifies fat, then pancreatic lipase splits it into fatty acids and glycerol; all of this happens in the small intestine.

   Fat is digested in two stages, both of them in the small intestine. Fat reaches the small intestine as large globules, in food that is still acidic from the stomach. Bile juice, secreted by the liver and stored in the gall bladder, first makes the food alkaline and then emulsifies the fat: its bile salts break the large globules into many small droplets. This is a physical change that greatly increases the surface available to the enzyme. Lipase, the fat-digesting enzyme of the pancreatic juice secreted by the pancreas, then acts on the emulsified fat and breaks it down into fatty acids and glycerol, and the intestinal juice secreted by the glands in the wall of the small intestine completes the digestion. The products are absorbed by the villi. So the process takes place entirely in the small intestine, which is where both the bile duct and the pancreatic duct open.

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6. Q6
   What is ​the ​role of saliva ​in ​the ​digestion ​of food?
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   Saliva begins starch digestion with salivary amylase, and moistens, softens and lubricates the food so it can be chewed and swallowed easily.

   Saliva is secreted by the salivary glands in the mouth and has two roles. Chemically, it contains the enzyme salivary amylase, also called ptyalin, which begins the digestion of starch by breaking this complex carbohydrate down into maltose, a simpler sugar; this is the first chemical digestion that food undergoes anywhere in the alimentary canal. Physically, saliva wets and softens the food so that the teeth can grind it thoroughly, and its mucus lubricates the chewed mass so that it is swallowed easily and slides down the food pipe, while the tongue mixes the food with saliva so that the enzyme reaches all of it. Saliva only begins the digestion of starch, because food stays in the mouth for a few seconds and salivary amylase is inactivated by the acid of the stomach; the digestion of starch is completed in the small intestine.

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7. Q7
   What ​are ​the necessary ​conditions for ​autotrophic nutrition ​and what are its ​by-products?
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   Carbon dioxide, water, sunlight and chlorophyll are needed; carbohydrate is the product and oxygen, from splitting of water, is the by-product.

   The necessary conditions for autotrophic nutrition, that is for photosynthesis, are four. Carbon dioxide, which diffuses into the leaf through the stomata; water, absorbed from the soil by the roots and carried up to the leaf in the xylem; sunlight, which supplies the energy; and chlorophyll, the green pigment of the chloroplasts, which absorbs that light. Carbon dioxide and water are the raw materials and are used up, while sunlight and chlorophyll are not consumed but are indispensable — remove any one of the four and the plant makes no food. The overall change is $6{\text{CO}}_2+6{\text{H}}_2\text{O}\stackrel{\text{sunlight, chlorophyll}}{\to }{\text{C}}_6{\text{H}}_{12}{\text{O}}_6+6{\text{O}}_2$. Of the two substances produced, the carbohydrate is the product: it is used for energy and the surplus is stored in the leaf as starch. Oxygen is the by-product — it is formed when water molecules are split during photosynthesis, and it is released into the air through the stomata.

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8. Q8
   What ​are ​the differences ​between aerobic and anaerobic respiration? Name some organisms that ​use ​the anaerobic mode ​of ​respiration.
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   Aerobic respiration uses oxygen and releases much energy; anaerobic respiration, as in yeast and some bacteria, occurs without oxygen and releases little.

   Both kinds of respiration begin alike: in the cytoplasm, glucose (a $6$-carbon molecule) is broken down into two molecules of pyruvate (a $3$-carbon molecule). They differ in what happens to that pyruvate. (i) Oxygen: aerobic respiration takes place in the presence of oxygen; anaerobic respiration takes place in its absence. (ii) Site: aerobic respiration is completed in the mitochondria; anaerobic respiration takes place entirely in the cytoplasm. (iii) End products: aerobic respiration gives carbon dioxide and water, while anaerobic respiration gives ethanol and carbon dioxide in yeast, or lactic acid in our muscle cells. (iv) Energy released: aerobic respiration releases a large amount of energy from each glucose molecule; anaerobic respiration releases only a small amount, because the glucose is not broken down completely. Organisms that use the anaerobic mode: yeast, which ferments sugar to ethanol and carbon dioxide; many bacteria, such as the lactic acid bacteria that turn milk into curd; and internal parasites such as Ascaris (roundworm) and tapeworm, which live in the gut where there is very little oxygen. Our own muscle cells use this mode temporarily during vigorous exercise, and the lactic acid that collects is what causes cramps.

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9. Q9
   How ​are ​the ​alveoli ​designed to maximise the ​exchange of gases?
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   Alveoli have a huge surface area, one-cell-thick walls, a dense capillary network and a moist lining, so diffusion of gases is fastest.

   Gases are not pumped across the wall of the lung — they move by diffusion, which is faster when the surface is larger, the barrier thinner and the difference in concentration greater. The alveoli are built to make all three as favourable as possible. (i) Huge surface area: the lungs end not in one cavity but in about $300$ million balloon-like sacs, whose walls spread out flat would cover about $80{\text{m}}^2$ — roughly forty times the area of the whole of your skin — all packed inside the chest. (ii) Extremely thin barrier: the wall of an alveolus is one cell thick and the wall of the capillary against it is also one cell thick, so a gas crosses only two thin layers. (iii) A rich supply of blood: each alveolus is wrapped in a dense network of blood capillaries, and the blood arriving is poor in oxygen and rich in carbon dioxide. Because the blood is continually carried away and the air is continually renewed by breathing, the difference in concentration across the wall never disappears. (iv) A moist surface: the lining is covered by a film of moisture in which the gases dissolve before they diffuse across. Together these give the lungs a very large, very thin, well-supplied and moist surface — exactly the conditions for the fastest possible exchange of gases.

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10. Q10
    What would be the ​consequences ​of a ​deficiency ​of ​haemoglobin ​in ​our ​bodies?
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    Less haemoglobin means less oxygen reaches the cells, causing anaemia: weakness, tiredness, breathlessness and paleness.

    Haemoglobin is the red pigment in the red blood cells that binds oxygen at the lungs and releases it to the cells all over the body, and almost all the oxygen the body receives travels this way. If haemoglobin is deficient, the blood can carry much less oxygen even though its volume and the working of the lungs are normal; this condition is called anaemia. Less oxygen reaching the cells means aerobic respiration cannot release energy at the usual rate, so the person tires quickly, feels weak, and becomes breathless on slight exertion; the heart beats faster and the breathing quickens as the body tries to compensate. The skin, the tongue and the nail beds turn pale, because it is haemoglobin that colours the blood, and there may be headache, giddiness and poor concentration. In children the deficiency slows growth and lowers resistance to infection. The usual cause is too little iron in the diet, since it is the iron in haemoglobin that holds the oxygen, and the remedy is iron-rich food such as green leafy vegetables, dates and jaggery.

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11. Q11
    Describe double ​circulation of blood in human ​beings. Why ​is ​it ​necessary?
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    Blood passes twice through the heart per round, via lungs then body, which keeps oxygenated blood unmixed and at sufficient pressure.

    Double circulation means that in completing one full round of the body the blood passes through the heart **twice**, on two joined circuits. First loop (pulmonary circulation): deoxygenated blood from all the organs enters the right atrium through the vena cava, passes into the right ventricle, and is pumped through the pulmonary artery to the lungs; there it gives up carbon dioxide and takes up oxygen, and returns through the pulmonary veins to the left atrium. Second loop (systemic circulation): from the left atrium the oxygenated blood passes into the left ventricle, which pumps it through the aorta to every part of the body; after delivering oxygen and collecting carbon dioxide it returns through the vena cava to the right atrium, completing the circuit. The left ventricle has the thickest wall because it must drive blood the whole length of the body, and valves ensure the blood moves in one direction only. It is necessary for two reasons. First, the septum divides the heart completely, so oxygenated and deoxygenated blood never mix and the blood sent to the organs carries the maximum possible oxygen. This matters because human beings, like all birds and mammals, are warm-blooded and use energy continuously to keep the body temperature constant, so their need for oxygen is high and unbroken. Second, blood loses most of its pressure in passing through the fine capillaries of the lungs, so it must be returned to the heart and pumped again by the left ventricle to reach the whole body at sufficient pressure.

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12. Q12
    What are the ​differences ​between the ​transport ​of ​materials in xylem and ​phloem?
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    Xylem carries water and minerals upward in dead cells, pulled by transpiration; phloem carries food both ways in living cells, pushed by pressure.

    (i) Material carried: the xylem carries water and the mineral salts dissolved in it, absorbed from the soil by the roots; the phloem carries the soluble food made in photosynthesis, chiefly sucrose, along with amino acids and other substances. The movement of food in the phloem is called translocation. (ii) Direction: xylem transport is one-way, upward only, from the roots to the stem, leaves and other parts; phloem transport goes in both directions — downward from the leaves to the roots, fruits and seeds for storage, and upward from the storage organs to the buds in spring. (iii) Kind of cells: xylem is made of tracheids and vessels, which are **dead** cells whose end walls have broken down to leave continuous hollow tubes; phloem is made of sieve tubes and companion cells, which are **living**. (iv) Driving force: in the xylem, root pressure moves water up at night, and during the day the evaporation of water from the leaves creates a transpiration pull that draws the water column upward — the energy comes from the sun, not from the plant. In the phloem, food is loaded into the sieve tube using energy from ATP; this draws water in from the xylem by osmosis, and the pressure so created pushes the material to the parts of the plant where it is needed. So the xylem is pulled from the top without the plant spending energy, while the phloem is pushed from the source at the cost of ATP.

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13. Q13
    Compare the functioning of alveoli in the ​lungs ​and nephrons ​in ​the kidneys with ​respect to ​their ​structure and functioning.
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    Both are thin, numerous, capillary-covered exchange units, but the alveolus works by passive diffusion while the nephron filters under pressure and reabsorbs selectively.

    Similarities in structure: the alveolus is the functional unit of the lung and the nephron is the functional unit of the kidney, and each organ is built by repeating that unit an enormous number of times — about $300$ million alveoli in a pair of lungs and about a million nephrons in each kidney. Both therefore provide a very large total surface for exchange inside a small organ; both are extremely thin-walled, only one cell thick, so that the distance to be crossed is short; and both are wrapped in a dense network of blood capillaries that brings blood into intimate contact with the exchange surface. Differences in structure: an alveolus is a simple blind-ended sac, so air enters and leaves by the same passage, whereas a nephron is a long tube open at the far end — it begins as the cup-shaped Bowman's capsule around a knot of capillaries called the glomerulus and continues as a coiled tubule leading to a collecting duct. Functioning: at the alveolus the exchange is by **diffusion** alone, oxygen passing from the air into the blood and carbon dioxide from the blood into the air, each moving down its own concentration difference; the process is passive, needs no energy and requires no selection. At the nephron the work is done in two stages: blood is first **filtered under pressure** at the glomerulus, so that water, salts, glucose, amino acids and urea all pass into the capsule; then, as the filtrate moves along the tubule, **selective reabsorption** returns the glucose, the amino acids, most of the salts and most of the water to the blood, part of this by active transport using energy. What remains is urine, which leaves the body. In short, both are thin, numerous, capillary-covered exchange surfaces, but the alveolus removes a gaseous waste in a single passive step while the nephron removes a dissolved waste by filtering everything out and then taking the useful part back.

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