5. Life Processes Class 10 NCERT Exemplar Solutions (CBSE 2026 Guide)

Class 10 Science Chapter 5: Life Processes : NCERT Exemplar Solutions with Detailed Explanation

Chapter 6: Life Processes

Multiple Choice Questions

1. Which of the following statements about the autotrophs is incorrect?

(a) They synthesise carbohydrates from carbon dioxide and water in the presence of sunlight and chlorophyll

(b) They store carbohydrates in the form of starch

(c) They convert carbon dioxide and water into carbohydrates in the absence of sunlight

(d) They constitute the first trophic level in food chains

Answer: (c) They convert carbon dioxide and water into carbohydrates in the absence of sunlight .

[ Autotrophs (like green plants) perform photosynthesis to synthesise carbohydrates from carbon dioxide and water in the presence of sunlight and chlorophyll. This process does not occur in the absence of sunlight.]

2. In which of the following groups of organisms, food material is broken down outside the body and absorbed?

(a) Mushroom, green plants, Amoeba

(b) Yeast, mushroom, bread mould

(c) Paramecium, Amoeba, Cuscuta

(d) Cuscuta, lice, tapeworm

Answer: (b) Yeast, mushroom, bread mould

[ Organisms like yeast, mushroom, and bread mould are saprophytes. They secrete digestive enzymes onto the food material to break it down outside their bodies and then absorb the nutrients. This is known as extracellular digestion.]

3. Select the correct statement

(a) Heterotrophs do not synthesise their own food

(b) Heterotrophs utilise solar energy for photosynthesis

(c) Heterotrophs synthesise their own food

(d) Heterotrophs are capable of converting carbon dioxide and water into carbohydrates

Answer: (a) Heterotrophs do not synthesise their own food

[ Heterotrophs (e.g., animals, fungi) cannot produce their own food. They depend on autotrophs directly or indirectly for nutrition.]

4. Which is the correct sequence of parts in human alimentary canal?

(a) Mouth → stomach → small intestine → oesophagus → large intestine

(b) Mouth →oesophagus → stomach → large intestine → small intestine

(c) Mouth → stomach → oesophagus → small intestine → large intestine

(d) Mouth → oesophagus → stomach → small intestine→ large intestine

Answer: (d) Mouth → esophagus → stomach → small intestine → large intestine

[ The correct sequence of parts in the human alimentary canal is as follows:

(i) Mouth (ingestion and initial digestion) → (ii) Oesophagus (passage of food to stomach) → (iii) Stomach (protein digestion and mixing of food) → (iv) Small intestine (major digestion and absorption) → (v) Large intestine (absorption of water and elimination of waste) ]

5. If salivary amylase is lacking in the saliva, which of the following events in the mouth cavity will be affected?

(a) Proteins breaking down into amino acids

(b) Starch breaking down into sugars

(c) Fats breaking down into fatty acids and glycerol

(d) Absorption of vitamins

Answer: (b) Starch breaking down into sugars

[ Salivary amylase (ptyalin) breaks down starch into simple sugars like maltose. If lacking, starch digestion in the mouth is affected. Protein and fat digestion do not occur in the mouth.]

6. The inner lining of stomach is protected by one of the following from hydrochloric acid. Choose the correct one

(a) Pepsin (b) Mucus (c) Salivary amylase (d) Bile

Answer: (b) Mucus

[ Mucus serves as a protective layer on the inner lining of the stomach, preventing it from being damaged by the acidic gastric juices, including hydrochloric acid. ]

7. Which part of alimentary canal receives bile from the liver?

(a) Stomach (b) Small intestine (c) Large intestine (d) Oesophagus

Answer: (b) Small intestine

[ Bile is secreted by the liver and stored in the gall bladder. It is released into the small intestine (specifically the duodenum, the first part of the small intestine) to emulsify fats. The other options (stomach, large intestine, oesophagus) do not receive bile directly from the liver.]

8. A few drops of iodine solution were added to rice water. The solution turned blue-black in colour. This indicates that rice water contains

(a) complex proteins (b) simple proteins (c) fats (d) starch

Answer: (d) Starch

[ Iodine solution is a test for starch. When iodine is added to a substance containing starch, it turns blue-black in colour. Rice water contains starch leached out from rice, so it gives a positive iodine test. Proteins and fats do not give this blue-black colour with iodine.]

9. In which part of the alimentary canal food is finally digested?

(a) Stomach (b) Mouth cavity (c) Large intestine (d) Small intestine

Answer: (d) Small intestine

[ Final digestion of food (carbohydrates, proteins, and fats) occurs in the small intestine with the help of intestinal juice, pancreatic juice, and bile. By the end of the small intestine, digestion is complete. The stomach and mouth cavity do only partial digestion, while the large intestine mainly absorbs water and does not digest food.]

10. Choose the function of the pancreatic juice from the following

(a) trypsin digests proteins and lipase carbohydrates

(b) trypsin digests emulsified fats and lipase proteins

(c) trypsin and lipase digest fats

(d) trypsin digests proteins and lipase emulsified fats

Answer: (d) Trypsin digests proteins, and lipase digests emulsified fats.

[ Pancreatic juice contains enzymes like trypsin (digests proteins into peptides) and lipase (breaks down emulsified fats into fatty acids and glycerol).]

11. When air is blown from mouth into a test-tube containing lime water, the lime water turned milky due to the presence of

(a) oxygen (b) carbon dioxide (c) nitrogen (d) water vapour

Answer: (b) Carbon dioxide

[ Carbon dioxide reacts with lime water to form calcium carbonate, which is insoluble and gives the milky appearance.]

12. The correct sequence of anaerobic reactions in yeast is

(a) Glucose cytoplasm Pyruvate mitochondria Ethanol + Carbondioxide

(b) Glucose cytoplasm Pyruvate cytoplasm Lactic acid

(c) Glucose cytoplasm Pyruvate mitochondria Lactic acid

(d) Glucose cytoplasm Pyruvate cytoplasm Ethanol + Carbondioxide

Answer : (d) Glucose cytoplasm Pyruvate cytoplasm Ethanol + Carbondioxide

[ In yeast, anaerobic respiration (fermentation) occurs entirely in the cytoplasm. Glucose is first broken down into pyruvate during glycolysis, and then pyruvate is converted into ethanol and carbon dioxide in the cytoplasm itself, not in the mitochondria.]

13. Which of the following is most appropriate for aerobic respiration?

(a) Glucose mitochondria Pyruvate cytoplasm + Energy

(b) Glucose cytoplasm Pyruvate mitochondria + Energy

(c) Glucose cytoplasm Pyruvate + Energy mitochondria

(d) Glucose cytoplasm Pyruvate + Energy mitochondria + Energy

Answer: (b) Glucose cytoplasm Pyruvate mitochondria + Energy

[ In aerobic respiration: (i) Glucose is first broken down into pyruvate in the cytoplasm .

(ii) Pyruvate is then converted into CO₂ + H₂O + energy inside the mitochondria .]

14. Which of the following statement(s) is (are) true about respiration?

(i) During inhalation, ribs move inward and diaphragm is raised

(ii) In the alveoli, exchange of gases takes place i.e., oxygen from alveolar air diffuses into blood and carbon dioxide from blood into alveolar air

(iii) Haemoglobin has greater affinity for carbon dioxide than oxygen

(iv) Alveoli increase surface area for exchange of gases

(a) (i) and (iv) (b) (ii) and (iii) (c) (i) and (iii) (d) (ii) and (iv)

Answer: (d) (ii) and (iv).

[ (ii) In the alveoli, oxygen diffuses from alveolar air into blood, and carbon dioxide diffuses from blood into alveolar air.

(iv) Alveoli greatly increase the surface area for efficient gas exchange. ]

15. Which is the correct sequence of air passage during inhalation?

(a) Nostrils → larynx → pharynx → trachea → lungs

(b) Nasal passage → trachea → pharynx → larynx → alveoli

(c) larynx → nostrils → pharynx → lungs

(d) Nostrils → pharynx → larynx → trachea → alveoli

Answer : (d) Nostrils → pharynx → larynx → trachea → alveoli

[ The correct sequence of air passage during inhalation is: Nostrils → Nasal cavity (implied) → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli (in lungs).]

16. During respiration exchange of gases take place in

(a) trachea and larynx (b) alveoli of lungs (c) alveoli and throat (d) throat and larynx

Answer: (b) Alveoli of lungs.

[ The exchange of gases (oxygen and carbon dioxide) during respiration takes place in the alveoli of the lungs. The alveoli are tiny air sacs with thin walls and rich blood capillaries, which facilitate diffusion of gases. The trachea, larynx, and throat are parts of the passage for air but are not sites of gas exchange.]

17. Which of the following statement (s) is (are) true about heart?

(i) Left atrium receives oxygenated blood from different parts of body while right atrium receives deoxygenated blood from lungs

(ii) Left ventricle pumps oxygenated blood to different body parts while right ventricle pumps deoxygenated blood to lungs

(iii) Left atrium transfers oxygenated blood to right ventricle which sends it to different body parts

(iv) Right atrium receives deoxygenated blood from different parts of the body while left ventricle pumps oxygenated blood to different parts of the body

(a) (i) (b) (ii) (c) (ii) and (iv) (d) (i) and (iii)

Answer: (c) (ii) and (iv)

[ (ii) Left ventricle pumps oxygenated blood to the body; right ventricle pumps deoxygenated blood to the lungs.

(iv) Right atrium receives deoxygenated blood from the body; left ventricle pumps oxygenated blood to the body.]

18. What prevents backflow of blood inside the heart during contraction?

(a) Valves in heart (b) Thick muscular walls of ventricles

(c) Thin walls of atria (d) All of the above

Answer: (a) Valves in the heart

[ Valves in the heart, specifically the atrioventricular (AV) valves and semilunar valves, prevent the backflow of blood during contraction. ]

19. Single circulation i.e., blood flows through the heart only once during one cycle of passage through the body, is exhibited by

(a) Labeo, Chameleon, Salamander

(b) Hippocampus, Exocoetus, Anabas

(c) Hyla, Rana, Draco

(d) Whale, Dolphin, Turtle

Answer: (b) Hippocampus, Exocoetus, Anabas

[ These organisms exhibit single circulation, where blood flows through the heart only once during one cycle of passage through the body. ]

20. In which of the following vertebrate group/groups, heart does not pump oxygenated blood to different parts of the body?

(a) Pisces and amphibians (b) Amphibians and reptiles

(c) Amphibians only (d) Pisces only

Answer: (d) Pisces only

[ In fishes (Pisces), the heart pumps oxygenated blood only to the gills for oxygenation, and then the oxygenated blood is distributed to the rest of the body.]

21. Choose the correct statement that describes arteries.

(a) They have thick elastic walls, blood flows under high pressure; collect blood from different organs and bring it back to the heart

(b) They have thin walls with valves inside, blood flows under low pressure and carry blood away from the heart to various organs of the body

(c) They have thick elastic walls, blood flows under low pressure ; carry blood from the heart to various organs of the body

(d) They have thick elastic walls without valves inside, blood flows under high pressure and carry blood away from the heart to different parts of the body.

Answer : (d) They have thick elastic walls without valves inside, blood flows under high pressure, and carry blood away from the heart to different parts of the body.

[ Arteries are vessels that carry oxygenated blood away from the heart to various parts of the body. They have thick and elastic walls, and they operate under high pressure due to the force generated by the heart's pumping action. Arteries do not have valves. ]

22. The filtration units of kidneys are called

(a) ureter (b) urethra (c) neurons (d) nephrons

Answer : (d) Nephrons

[ The filtration units of the kidneys are called nephrons ]

23. Oxygen liberated during photosynthesis comes from

(a) water (b) chlorophyll (c) carbon dioxide (d) glucose

Answer : (a) Water

[ During photosynthesis, oxygen is liberated as a byproduct, and it comes from the splitting of water molecules. ]

24. The blood leaving the tissues becomes richer in

(a) carbon dioxide (b) water (c) heamoglobin (d) oxygen

Answer: (a) Carbon dioxide

[ The blood leaving the tissues becomes richer in carbon dioxide. This carbon dioxide is produced as a waste product of cellular respiration in the tissues.]

25. Which of the following is an incorrect statement?

(a) Organisms grow with time

(b) Organisms must repair and maintain their structure

(c) Movement of molecules does not take place among cells

(d) Energy is essential for life processes

Answer: (c) Movement of molecules does not take place among cells

[ Cells require the movement of various molecules, such as nutrients and signaling molecules, to carry out their functions and maintain cellular processes.]

26. The internal (cellular) energy reserve in autotrophic is

(a) glycogen (b) protein (c) starch (d) fatty acid

Answer : (c) Starch

[ Starch is the primary internal (cellular) energy reserve in autotrophic . ]

27. Which of the following equations is the summary of photosynthesis?

(a)

(b)

(c)

(d)

Answer : (c)

[ This equation represents the process of photosynthesis, where carbon dioxide and water, in the presence of chlorophyll and sunlight, are converted into glucose and oxygen.]

28. Choose the event that does not occur in photosynthesis

(a) Absorption of light energy by chlorophyll

(b) Reduction of carbon dioxide to carbohydrates

(c) Oxidation of carbon to carbon dioxide

(d) Conversion of light energy to chemical energy

Answer: c) Oxidation of carbon to carbon dioxide

[ In photosynthesis, carbon dioxide is reduced to carbohydrates, not oxidized to carbon dioxide. ]

29. The opening and closing of the stomatal pore depends upon

(a) oxygen (b) temperature (c) water in guard cells (d) concentration of in stomatal

Answer : (c) Water in guard cells

[ The opening and closing of the stomata pore depend upon the turgor pressure in the guard cells, which is influenced by the uptake or loss of water by these cells.]

30. Choose the forms in which most plants absorb nitrogen

(i) Proteins (ii) Nitrates and Nitrites (iii) Urea (iv) Atmospheric nitrogen

(a) (i) and (ii) (b) (ii) and (iii) (c) (iii) and (iv) (d) (i) and (iv)

Answer : (b) (ii) and (iii)

[ Most plants absorb nitrogen in the form of nitrates and nitrites (ii) from the soil. Urea (iii) can also be a nitrogen source for some plants. ]

31. Which is the first enzyme to mix with food in the digestive tract?

(a) Pepsin (b) Cellulase (c) Amylase (d) Trypsin

Answer : (c) Amylase .

[ Amylase is the first enzyme to mix with food in the digestive tract. It is responsible for the breakdown of carbohydrates into simpler sugars. ]

32. Which of the following statement(s) is (are) correct?

(i) Pyruvate can be converted into ethanol and carbon dioxide by yeast

(ii) Fermentation takes place in aerobic bacteria

(iii) Fermentation takes place in mitochondria

(iv) Fermentation is a form of anaerobic respiration

(a) (i) and (iii) (b) (ii) and (iv) (c) (i) and (iv) (d) (ii) and (iii)

Answer : (c) (i) and (iv)

[ (i) Pyruvate can be converted into ethanol and carbon dioxide by yeast, a process known as alcoholic fermentation. (iv) Fermentation is a form of anaerobic respiration.]

33. Lack of oxygen in muscles often leads to cramps among cricketers. This results due to

(a) conversion of pyruvate to ethanol (b) conversion of pyruvate to glucose

(c) non conversion of glucose to pyruvate (d) conversion of pyruvate to lactic acid

Answer : (d) conversion of pyruvate to lactic acid .

[ Lack of oxygen in muscles often leads to cramps among cricketers due to the conversion of pyruvate to lactic acid. ]

34. Choose the correct path of urine in our body

(a) kidney → ureter → urethra → urinary bladder

(b) kidney → urinary bladder → urethra → ureter

(c) kidney → ureters → urinary bladder → urethra

(d) urinary bladder → kidney → ureter → urethra

Answer : (c) kidney → ureters → urinary bladder → urethra.

[ Urine is produced in the kidneys, travels through the ureters, is stored in the bladder, and exits through the urethra. ]

35. During deficiency of oxygen in tissues of human beings, pyruvic acid is converted into lactic acid in the

(a) cytoplasm (b) chloroplast (c) mitochondria (d) golgi body

Answer : (a) cytoplasm.

[ During the deficiency of oxygen in tissues of human beings, pyruvic acid is converted into lactic acid in the cytoplasm. ]

Short Answer Questions

36. Name the following

(a) The process in plants that links light energy with chemical energy

(b) Organisms that can prepare their own food

(c) The cell organelle where photosynthesis occurs

(d) Cells that surround a stomatal pore

(e) Organisms that cannot prepare their own food

(f) An enzyme secreted from gastric glands in stomach that acts on proteins.

Answer: (a) The process in plants that links light energy with chemical energy → Photosynthesis

(b) Organisms that can prepare their own food → Autotrophs

(d) Cells that surround a stomatal pore → Guard cells

(e) Organisms that cannot prepare their own food → Heterotrophs

(f) An enzyme secreted from gastric glands in stomach that acts on proteins → Pepsin

37. “All plants give out oxygen during day and carbon dioxide during night”. Do you agree with this statement? Give reason.

Answer: Yes, I agree with this statement. During the day, plants perform photosynthesis in the presence of sunlight and release oxygen. At the same time, respiration also occurs, but the amount of oxygen released is greater than the carbon dioxide produced. During the night, photosynthesis stops due to the absence of sunlight, but respiration continues, so plants release carbon dioxide.

38. How do the guard cells regulate opening and closing of stomatal pores?

Answer: Guard cells regulate the opening and closing of stomatal pores by changing their shape. When guard cells absorb water, they become swollen or turgid, causing the stomatal pore to open. When they lose water, they shrink or become flaccid, causing the stomatal pore to close.

39. Two green plants are kept separately in oxygen free containers, one in the dark and the other in continuous light. Which one will live longer? Give reasons.

Answer: The plant kept in continuous light will live longer.
In continuous light, the plant can perform photosynthesis, producing oxygen and food . The oxygen released can be used for its own respiration. In contrast, the plant kept in the dark cannot photosynthesize, so it only respires using stored food. Once the available oxygen in the container is used up, it cannot be replaced, so the plant will die sooner.

40. If a plant is releasing carbon dioxide and taking in oxygen during the day, does it mean that there is no photosynthesis occurring? Justify your answer.

Answer: No, it does not mean photosynthesis is not occurring.
Plants carry out both photosynthesis and respiration simultaneously during the day. If a plant is releasing CO₂ and taking in O₂, it indicates that the rate of respiration is greater than the rate of photosynthesis at that time . Photosynthesis may still be occurring, but its rate is insufficient to consume all the CO₂ released by respiration.

41. Why do fishes die when taken out of water?

Answer: Fishes die when taken out of water because they cannot breathe oxygen from air. Fishes have gills that are adapted to extract dissolved oxygen from water. In air, the gill filaments collapse and stick together, greatly reducing the surface area for gas exchange. As a result, they cannot take in sufficient oxygen for respiration, leading to suffocation and death.

42. Differentiate between an autotroph and a heterotroph.

Answer: The difference between an autotroph and a heterotrophy are :

Autotroph	Heterotrophy
(i) Autotrophs can prepare their own food using simple substances like carbon dioxide and water.	(i) Heterotrophs cannot prepare their own food and depend on other organisms.
(ii) They use sunlight and chlorophyll for photosynthesis.	(ii) They do not use sunlight or chlorophyll to make food.
(iii) Green plants and algae are autotrophs.	(iii) Animals, fungi and most bacteria are heterotrophs.
(iv) They are producers in a food chain.	(iv) They are consumers in a food chain.

43. Is ‘nutrition’ a necessity for an organism? Discuss.

Answer: Yes, nutrition is essential for organisms. It provides the energy and nutrients required for growth, repair, and maintenance of bodily functions. Without adequate nutrition, organisms cannot sustain life processes, resulting in poor health or death. Nutrients support metabolic activities and overall well-being.

44. What would happen if green plants disappear from earth?

Answer: If green plants disappear from Earth, all life would be severely affected. Plants are autotrophs that produce food and release oxygen through photosynthesis. Without them, herbivores would have no food, leading to the death of carnivores as well. Oxygen levels would drop, making respiration impossible for most organisms. Additionally, the carbon dioxide level would rise, disrupting the balance of gases in the atmosphere. Ultimately, life on Earth would cease to exist.

45. Leaves of a healthy potted plant were coated with vaseline. Will this plant remain healthy for long? Give reasons for your answer.

Answer: No, the plant will not remain healthy for long. Coating the leaves with vaseline blocks the stomata present on the leaf surface. As a result, exchange of gases and transpiration cannot take place properly. This affects photosynthesis and respiration, leading to the death of the plant after some time.

46. How does aerobic respiration differ from anaerobic respiration?

Answer: The differences between aerobic respiration and anaerobic respiration are :

Aerobic Respiration	Anaerobic Respiration
Takes place in the presence of oxygen	Takes place in the absence of oxygen
Glucose is completely broken down	Glucose is partially broken down
Produces carbon dioxide and water	Produces ethanol and carbon dioxide (in yeast) or lactic acid (in muscles)
Releases a large amount of energy	Releases a small amount of energy
Occurs mainly in mitochondria	Occurs in the cytoplasm

47. Match the words of Column (A) with that of Column (B)

Column (A)	Column (B)
(a) Phloem	(i) Excretion
(b) Nephron	(ii) Translocation of Food
(c) Veins	(iii) Clotting of Blood
(d) Platelets	(iv) Deoxygenated blood

Answer: (a) Phloem → (ii) Translocation of food

(b) Nephron → (i) Excretion

(d) Platelets → (iii) Clotting of Blood

48. Differentiate between an artery and a vein.

Answer: The difference between an artery and a vein are :

Artery	Vein
Carries blood away from the heart	Carries blood towards the heart
Blood is usually oxygenated (except pulmonary artery)	Blood is usually deoxygenated (except pulmonary vein)
Walls are thick and elastic	Walls are thin and less elastic
Blood flows under high pressure	Blood flows under low pressure
Valves are absent	Valves are present to prevent backflow

49. What are the adaptations of leaf for photosynthesis?

Answer: The adaptations of a leaf for photosynthesis are:

(i) Large surface area to capture more sunlight.

(ii) Thin structure for rapid diffusion of gases.

(iii) Presence of chlorophyll in chloroplasts to absorb light energy.

(iv) Stomata for exchange of CO₂ and O₂.

(v) Network of veins to transport water and minerals to leaf cells and carry away food.

50. Why is small intestine in herbivores longer than in carnivores ?

Answer: Herbivores eat grass and plant material containing cellulose, which is difficult to digest and requires more time. A longer small intestine allows for slow digestion and complete absorption of nutrients. Carnivores eat meat, which is easier to digest, so their small intestine is shorter. The shorter length prevents undigested meat from rotting inside the body.

51. What will happen if mucus is not secreted by the gastric glands ?

Answer: If mucus is not secreted by the gastric glands, the hydrochloric acid present in the stomach may damage the inner lining of the stomach. This can cause irritation, ulcers and pain in the stomach. Mucus protects the stomach lining from the action of acid.

52. What is the significance of emulsification of fats?

Answer: Emulsification of fats is the process of breaking large fat globules into smaller droplets by bile salts. Its significance is that it increases the surface area of fats, allowing the enzyme lipase to act more efficiently. Lipase can then break down fats into fatty acids and glycerol for absorption. Without emulsification, fat digestion would be very slow and incomplete.

53. What causes movement of food inside the alimentary canal?

Answer: The movement of food inside the alimentary canal is caused by peristalsis. It is the rhythmic contraction and relaxation of the muscles present in the walls of the alimentary canal, which pushes the food forward.

54. Why does absorption of digested food occur mainly in the small intestine?

Answer: Absorption of digested food occurs mainly in the small intestine because its inner lining has numerous finger-like projections called villi, which increase the surface area for absorption. The villi are richly supplied with blood capillaries that help in the quick absorption and transport of nutrients to all parts of the body.

55. Match Group (A) with Group (B)

Group (A)	Group(B)
(a) Autotrophic nutrition	(i) Leech
(b) Heterotrophic nutrition	(ii) Paramecium
(c) Parasitic nutrition	(iii) Deer
(d) Digestion in food vacuoles	(iv) Green plant

Answer: (a) Autotrophic nutrition → (iv) Green plant

(b) Heterotrophic nutrition → (iii) Deer

(d) Digestion in food vacuoles → (ii) Paramecium

56. Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms?

Answer: The rate of breathing in aquatic organisms is much faster because water contains less dissolved oxygen compared to air. Therefore, aquatic organisms need to breathe rapidly to obtain sufficient oxygen for respiration.

57. Why is blood circulation in human heart called double circulation?

Answer: Blood circulation in the human heart is called double circulation because blood passes through the heart twice in one complete cycle of the body.

The two circulations are:

(i) Pulmonary circulation: Deoxygenated blood from the right ventricle goes to the lungs for oxygenation and returns to the left atrium.

(ii) Systemic circulation: Oxygenated blood from the left ventricle is pumped to all body parts, and deoxygenated blood returns to the right atrium.

58. What is the advantage of having four chambered heart?

Answer: The four-chambered heart prevents the mixing of oxygenated and deoxygenated blood. This allows efficient supply of oxygen to all parts of the body, which helps in the production of more energy and supports high metabolic activities in the body.

59. Mention the major events during photosynthesis.

Answer: The major events during photosynthesis are :

(i) Absorption of light energy by chlorophyll.

(ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.

(iii) Reduction of carbon dioxide to carbohydrates.

60. In each of the following situations what happens to the rate of photosynthesis?

(a) Cloudy days

(b) No rainfall in the area

(c) Good manuring in the area

(d) Stomata get blocked due to dust.

Answer: (a) Rate of photosynthesis decreases due to low light intensity .

(b) Rate of photosynthesis decreases because water becomes scarce. Water is a raw material for photosynthesis and also maintains leaf turgidity for stomatal opening.

(c) Rate of photosynthesis may increase slightly because manuring provides essential minerals like nitrogen, magnesium, but manuring primarily affects plant growth, not directly photosynthesis rate.

(d) Rate of photosynthesis decreases because carbon dioxide cannot enter the leaf through blocked stomata and oxygen cannot exit, disrupting gas exchange.

61. Name the energy currency in the living organisms. When and where is it produced?

Answer: The energy currency in living organisms is ATP (Adenosine Triphosphate).

It is produced mainly in the mitochondria of the cell during the process of cellular respiration, especially when glucose is broken down in the presence of oxygen.

62. What is common for cuscuta, ticks and leeches?

Answer: Cuscuta, ticks and leeches are all parasites. They depend on a host organism for food and survival, often harming the host in the process.

63. Explain the role of mouth in digestion of food.

Answer: The mouth plays an important role in digestion of food. Teeth help in chewing and breaking food into smaller pieces, making it easier to swallow. Salivary glands produce saliva which moistens the food and makes its passage smooth. Saliva contains an enzyme called salivary amylase which begins the digestion of starch by breaking it into simpler sugars. The tongue mixes the food with saliva and helps in swallowing it.

64. What are the functions of gastric glands present in the wall of the stomach?

Answer: Gastric glands in the stomach wall secrete hydrochloric acid, pepsin enzyme and mucus. HCl makes the stomach acidic, which helps pepsin digest proteins and also kills harmful germs in food. Pepsin breaks down proteins into simpler substances. Mucus protects the stomach lining from the acidic juice and prevents damage.

65. Match the terms in Column (A) with those in Column (B)

Column (A)	Group (B)
(a) Trypsin	(i) Pancreas
(b) Amylase	(ii) Liver
(c) Bile	(iii) Gastric glands
(d) Pepsin	(iv) Saliva

Answer: (a) Trypsin → (i) Pancreas

(b) Amylase → (iv) Saliva

(d) Pepsin → (iii) Gastric glands .

66. Name the correct substrates for the following enzymes

(a) Trypsin (b) Amylase (c) Pepsin (d) Lipase

Answer: (a) Trypsin: Proteins (it breaks down proteins into smaller peptides).

(b) Amylase: Starch (it breaks down starch into simpler sugars like maltose).

(d) Lipase: Lipids (it breaks down fats into fatty acids and glycerol).

67. Why do veins have thin walls as compared to arteries?

Answer: Veins have thin walls as compared to arteries because veins carry blood at low pressure, so they do not need thick, muscular and elastic walls like arteries. Their thin walls also help in the easy flow of blood towards the heart. Valves are present in veins to prevent the backflow of blood.

68. What will happen if platelets were absent in the blood?

Answer: If platelets were absent in the blood, the process of blood clotting would not take place. As a result, even a small injury could lead to continuous bleeding, which may become dangerous and difficult for the body to control.

69. Plants have low energy needs as compared to animals. Explain.

Answer: Plants have low energy needs as compared to animals because most plant parts are stationary and do not move from one place to another. So, they require less energy. Also, plants do not need energy for maintaining body temperature or for searching food, unlike animals.

70. Why and how does water enter continuously into the root xylem?

Answer: Water enters continuously into the root xylem because root cells actively absorb mineral ions, which lowers the water potential inside the roots. Due to this difference, water moves from the soil (higher water potential) into the root cells by osmosis and then into the xylem. This continuous inflow is also helped by transpiration pull from the upper parts of the plant.

71. Why is transpiration important for plants?

Answer: Transpiration is important because it creates a suction force (transpiration pull) that helps in the upward movement of water and minerals through the xylem from roots to leaves. It also helps in cooling the plant. Along with this, the water and food distribution through xylem and phloem gets balanced, supporting proper transport of nutrients in the plant.

72. How do leaves of plants help in excretion?

Answer: Leaves help in excretion by removing excess water and some wastes from the plant. Water is released through stomata during transpiration. Some wastes are also stored in leaves and are removed when the leaves dry up and fall off.

Long Answer Questions

73. Explain the process of nutrition in Amoeba.

Answer: Nutrition in Amoeba is holozoic. It begins with ingestion, where Amoeba surrounds food particles using pseudopodia and engulfs them to form a food vacuole. Inside the vacuole, digestive enzymes break the food into simpler substances. This is called digestion.

The digested food is absorbed and used for energy, growth and repair. This process is known as absorption and assimilation. Finally, the undigested food is expelled out of the cell through the cell membrane in a process called excretion.

74. Describe the alimentary canal of man.

Answer: The human alimentary canal begins at the mouth, where teeth crush food and saliva with salivary amylase breaks down starch. The muscular tongue mixes the food. Peristaltic movements push it through the oesophagus into the stomach. The stomach's gastric glands release hydrochloric acid, pepsin, and mucus. The acid creates a medium for pepsin to digest proteins, while mucus protects the stomach wall. A sphincter regulates food entry into the small intestine, the longest part where complete digestion occurs. The liver's bile juice makes the acidic food alkaline and breaks fats into smaller globules. The pancreas secretes trypsin for proteins and lipase for fats. Intestinal juice converts proteins to amino acids, carbohydrates to glucose and fats to fatty acids and glycerol. Villi absorb digested food. Unabsorbed food enters the large intestine, where water is absorbed, and the remaining waste is removed via the anus.

75. Explain the process of breathing in man.

Answer: The process of breathing in humans, also known as respiration, involves two main phases:

(a) Inhalation (breathing in): The diaphragm contracts and flattens, while the rib cage moves upward and outward. This increases the volume inside the chest cavity. As a result, air pressure inside the lungs decreases below atmospheric pressure. To balance this, air from outside rushes into the lungs through the nostrils, trachea, and bronchi.

(b) Exhalation (breathing out): The diaphragm relaxes and becomes dome-shaped, and the rib cage moves downward and inward. This decreases the volume of the chest cavity, increasing the air pressure inside the lungs above atmospheric pressure. This forces air out of the lungs.

Thus, breathing is a mechanical process that involves the movement of the diaphragm and ribs to create pressure differences, allowing air to move in and out of the lungs.

76. Explain the importance of soil for plant growth.

Answer: Soil is essential for plant growth because it provides a stable anchorage for roots to hold the plant firmly in place. It supplies essential minerals and water, which are absorbed by roots along with dissolved nutrients. Soil also contains humus, which releases nutrients slowly and improves soil texture. It holds air spaces that allow roots to respire and absorb oxygen. Moreover, soil acts as a reservoir for water, protecting plants from drying out. Without healthy soil, plants cannot get the necessary support, water, minerals or oxygen required for growth and survival.

77. Draw the diagram of alimentary canal of man and label the following parts.

Mouth, Oesophagus, Stomach, Intestine

Answer: Photo

78. How do carbohydrates, proteins and fats get digested in human beings?

Answer: The digestion of carbohydrates, proteins, and fats begins at different points in the human digestive system:

(i) Carbohydrates: Digestion starts in the mouth. Salivary amylase breaks down starch into simpler sugars. In the small intestine, pancreatic amylase continues this process, and final breakdown into glucose occurs.

(ii) Proteins: Digestion begins in the stomach. Pepsin breaks proteins into smaller peptides. In the small intestine, trypsin and other proteases complete the breakdown into amino acids.

(iii) Fats: Digestion occurs mainly in the small intestine. Bile juice emulsifies fats into tiny droplets. Then, pancreatic lipase breaks them down into fatty acids and glycerol.

79. Explain the mechanism of photosynthesis.

Answer: Photosynthesis is the process by which green plants prepare their own food using carbon dioxide, water, and sunlight, with the help of chlorophyll. The mechanism takes place mainly in the leaves. Sunlight is absorbed by chlorophyll present in chloroplasts. This light energy is converted into chemical energy, which is used to split water molecules into hydrogen and oxygen. The oxygen is released as a byproduct. Hydrogen then combines with carbon dioxide to form glucose.

The chemical equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Glucose is later converted into starch and stored in different plant parts. Thus, light energy is transformed into chemical energy stored in food.

80. Explain the three pathways of breakdown in living organisms.

Answer: The three pathways of breakdown in living organisms are :

(i) Aerobic Respiration – This occurs in the mitochondria and requires oxygen. Glucose is completely broken down into carbon dioxide and water, releasing a large amount of energy.

i.e. , Glucose (6-carbon molecules) Pyruvate (3-carbon molecules) + Energy Carbon dioxide + Water + Energy .

(ii) Anaerobic Respiration – This occurs without oxygen, usually in microorganisms like yeast. Glucose is partially broken down into ethanol and carbon dioxide, releasing less energy.

i.e. , Glucose (6-carbon molecules) Pyruvate (3-carbon molecules) + Energy Ethanol + Carbon dioxide + Energy .

(iii) Lactic Acid Fermentation – This also occurs without oxygen, mainly in muscle cells during intense exercise. Glucose is converted into lactic acid, releasing a small amount of energy.

i.e. , Glucose (6-carbon molecules) Pyruvate (3-carbon molecules) + Energy Lactic acid + Energy .

81. Describe the flow of blood through the heart of human beings.

Answer: The flow of blood through the human heart begins with deoxygenated blood from the body entering the right atrium. When the atrium contracts, blood moves into the right ventricle, which then pumps it to the lungs for oxygenation. The oxygen-rich blood returns to the left atrium, and on contraction, it enters the left ventricle. The strong left ventricle then pumps this blood to the entire body. Valves in the heart prevent backward flow, and the thicker walls of ventricles help pump blood efficiently to the lungs and body.

82. Describe the process of urine formation in kidneys.

Answer: Urine formation in the kidneys begins when blood enters the nephrons, the functional units of the kidney. In the glomerulus, blood is filtered, and water, salts, glucose, amino acids, and wastes like urea form the initial filtrate. As this filtrate passes through the renal tubule, useful substances such as glucose, certain salts, and most water are selectively reabsorbed back into the blood. The remaining fluid, containing excess water and wastes, becomes urine, which flows into the ureter, is stored in the bladder, and is later excreted through the urethra.