NCERT Exemplar Class 10 Science Chapter 6 Life Processes

NCERT Exemplar Class 10 Science Chapter 6 Life Processes are part of NCERT Exemplar Class 10 Science. Here we have given NCERT Exemplar Class 10 Science Chapter 6 Life Processes.

NCERT Exemplar Class 10 Science Chapter 6 Life Processes
Short Answer Type Questions

Multiple Choice Questions (MCQs)

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

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

(b) They store carbohydrates in the form of starch

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

Answer. (c)

Explanation:

Autotrophs obtain the required carbon and energy requirements from carbon dioxide and Sunlight. They combine carbon dioxide and water to form carbohydrates. The main photosynthetic pigment is chlorophyll, which helps to trap the Sunlight to carry out the light reaction of photosynthesis to synthesise carbohydrates.

Since autotrophs are the only organisms that can fix the atmospheric carbon dioxide into organic compounds, these organisms occupy first trophic level in food chain and serve as a source of food and energy for organisms of higher trophic levels.

Question. 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

(d) Cuscuta, lice, tapeworm

Answer. (b)

Explanation: Yeast, mushroom and bread mould are saprophytes which derive their nutrition from dead organisms. For the purpose, these organisms secrete digestive enzymes on their substratum to break down the complex food material into the simpler ones. These digested food materials are then absorbed by them.

Question. 3 Select the correct statement

(a) Heterotrophs do not synthesize their own food

(b) Heterotrophs utilize solar energy for photosynthesis

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

Answer. (a)

Explanation: Heterotrophs are the organisms that cannot synthesize their own food and depend on available organic/inorganic compounds to fulfil their energy requirements. Examples: All animals.

Question. 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

(d) Mouth → Oesophagus → Stomach → Small intestine → Large intestine

Answer. (d)

Explanation: Human alimentary canal consists of organs of digestion which are namely, in sequence, mouth, oesophagus, stomach, small intestine, large intestine and anus.

Question. 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

(d) Absorption of vitamins

Answer. (b)

Explanation: Amylase is the enzyme which helps in primary digestion of starch only. Digestion of starch by salivary amylase into maltose starts in mouth. Oesophagus then pushes the food into stomach. It does not carry out digestion at all. Pancreatic amylase also digests remaining starch into maltose sugars. Intestinal maltase carries out final chemical digestion of maltose into glucose molecules.

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

(a) Pepsin

(b) Mucus

(d) Bile

Answer. (b)

Explanation: The gastric glands of stomach produce gastric juice, which contains pepsinogen, HCl, and mucus. HCl impart highly acidic pH to stomach which help in the further digestion of food. The mucus in gastric juice helps protect the stomach wall from corrosive effect of hydrochloric acid.

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

(a) Stomach

(b) Small intestine

(d) Oesophagus

Answer. (b)

Explanation: Bile is secreted by liver and is stored in gall bladder from where it enters the small intestine via common duct.

Question. 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

(d) Starch

Answer. (d)

Explanation: Presence of starch in a solution turns added iodine drops in blue black color. Hence, the blue-black colour of rice water confirms presence of starch.

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

(a) Stomach

(b) Mouth cavity

(d) Small intestine

Answer. (d)

Explanation: Digestion of food starts in mouth by salivary amylase. From here it enters into the stomach via oesophagus. Gastric juice of stomach digests the protein part of food. Pancreatic amylase, trypsin and lipase as well as intestinal peptidases and maltase carry out the final chemical digestion of food in small intestine. The simpler substances formed by chemical digestion are then absorbed by small intestinal villi.

Question. 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

(d) Trypsin digests proteins and lipase digests emulsified fats droplets

Answer. (d)

Explanation: Pancreatic juice contains sodium bicarbonate and digestive enzymes amylase, trypsin, lipase and nucleases. Pancreatic amylase carries out digestion of starch, trypsin digests protein, and lipase breaks down fat droplets already emulsified by bile salts.

Question. 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

(d) Water vapour

Answer. (b)

Explanation: Carbon dioxide gas turns lime water milky. Since the exhaled air is carbon dioxide rich, when air is blown from mouth into test tube, the lime water turned milky.

Question. 12 The correct sequence of anaerobic reactions in yeast is

Answer. (d)

Explanation: Yeast is unicellular eukaryote which carries out ethanol fermentation. The first phase is break down of one molecule of glucose into two molecules of pyruvate in the presence of cytoplasm. Due to limited oxygen availability, pyruvate remains in cytoplasm where pyruvate decarboxylase and alcohol dehydrogenase enzymes carry out the second phase of anaerobic respiration and produce ethanol and carbon dioxide..

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

Answer. (b)

Explanation: Aerobic respiration is complete breakdown of glucose into carbon dioxide and water with release of large amount of energy. It occurs in three steps, glycolysis , citric acid cycle and ETC. Glycolysis is breakdown of glucose into pyruvate. It is oxygen independent pathway that occurs in cytoplasm. Aerobic respiration takes place in the mitochondria, using the pyruvate produced via glycolysis. It produces large amounts of energy in the form of ATP along with carbon dioxide gas and water.

Question.14 Which of the following statements (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 form 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 increases surface area for exchange of gases

(a) (i) and (iv)

(b) (ii) and (iii)

(d) (ii) and (iv)

Answer. (d)

Explanation: During inhalation, diaphragm contracts and lowers while the rib cage moves upward and outward.

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

(a) Nostrils → Larynx Pharynx → Trachea → Lungs

(b) Nasal passage → Trachea → Pharynx → Larynx → Alveoli

(d) Nostrils → Pharynx → Larynx → Trachea → Alveoli

Answer. (d)

Explanation: During inhalation, the air is drawn through the nostrils into nasal passage. From there, air enters into pharynx, larynx, trachea (windpipe), bronchi, lungs and finally to the alveoli.

Question. 16 During respiration exchange of gases take place in

(a) Trachea and larynx

(b) Alveoli of lungs

(d) Throat and larynx

Answer. (b)

Explanation: An alveolar sac is made up of simple squamous epithelium and is surrounded by blood capillaries. Thin walls and increased surface area favor the gaseous exchange which takes place between the oxygen rich alveolar air and the carbon dioxide rich blood in the capillaries at alveolar surface. Oxygen diffuses across the alveolar and capillary walls to enter the bloodstream, while carbon dioxide diffuses from the blood across these walls to enter the alveoli.

Question. 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)

(d) (i) and (iii)

Answer. (c)

Explanation: The left ventricle pumps blood into the aorta which in turn delivers it to the major body regions and organs which makes statement (iii) incorrect. The anterior vena cava collects deoxygenated blood from the head, chest, and arms and enters the right atrium while the inferior vena cava collects blood from the lower body regions. Both venae cavae pass the deoxygenated blood to the right atrium which makes statement (i) incorrect. Blood from right atrium enters right ventricle and pulmonary arteries carry deoxygenated blood from right ventricle to lungs for oxygenation; this makes statements (ii) and (iv) correct.

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

(a) Valves in heart

(b) Thick muscular walls of ventricles

(d) All of these

Answer. (a)

Explanation: Valves ensure that blood does not flow backwards when the atria or ventricles contract. Semilunar valves, the valves present between ventricles and their attached vessels, serve to prevent the backflow of blood to ventricles from their respective attached vessels. Likewise, atrioventricular (AV) valve between atrium and ventricle directs the flow of blood and prevents any backflow into atria.

Question. 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

(d) whale, dolphin, turtle

Answer. (b)

Explanation: The examples and the relation of animal group and heart are as

Fishes have two chambered heart and exhibit single circulation while three chambered heart of amphibian and reptiles and four chambered heart of birds and mammals exhibit double circulation. In given options, C includes all fishes which makes it correct answer.

Question. 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

(d) Pisces only

Answer (d)

Explanation: Fishes have two chambered heart and exhibit single circulation wherein deoxygenated blood is pumped to gills. Gills are the organs of gaseous exchange by diffusion. The oxygenated blood from gills is then pumped to different body parts and the deoxygenated blood from body parts is then carried to heart.

The three chambered heart of amphibian and reptiles and four chambered heart of birds and mammals exhibit double circulation and pump oxygenated blood to body.

Question. 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)

Explanation: Arteries are the valveless blood vessels which serve to transport the blood away from the heart to various body parts. The thick strong elastic walls of arteries withstand the high pressure of blood coming from heart.

Question. 22 The filtration units of kidneys are called

(a) Ureter

(b) Urethra

(d) Nephrons

Answer. (d)

Explanation: Nephrons are the structural and functional filtration unit of a kidney that serve in filtration, reabsorption and secretion. Ureters are small muscular tubes that extend from the kidney and carry urine into the urinary bladder. The urethra is a canal that carries urine from bladder and expels it out of body. Neurons are structural and functional unit of nervous system.

Question. 23 Oxygen liberated during photosynthesis comes from

(a) Water

(b) Chlorophyll

(d) Glucose

Answer. (a)

Explanation: Photosynthesis is the process wherein carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates).

The main photosynthetic pigment chlorophyll a and accessory pigments chl b, chl c and carotenoids etc trap the Sunlight to carry out the light reactions of photosynthesis. The light reaction of photosynthesis includes splitting of water into oxygen and hydrogen to produce ATP and reducing agents which in turn serve as energy source to drive the second phase of photosynthesis (dark reactions) during which carbohydrate synthesis takes place.

Question. 24 The blood leaving the tissues becomes richer in

(a) Carbon dioxide

(b) Water

(d) Oxygen

Answer. (a)

Explanation: The left ventricle pumps blood into the aorta which in turn branches and delivers oxygenated blood to the major body regions and organs. The oxygen is consumed in cellular respiration and the carbon dioxide produced during respiration enters into blood.

The anterior vena cava collects deoxygenated blood from the head, chest, and arms and enters the right atrium while the inferior vena cava collects blood from the lower body regions. Both venae cavae pass the deoxygenated blood to the right atrium. Thus, blood from tissues is rich in carbon dioxide.

Deoxygenated blood from right atrium enters right ventricle and pulmonary arteries carry deoxygenated blood from right ventricle to lungs for oxygenation.

Question. 25 Which of the following is an incorrect statement?

(a) Organisms grow with time

(b) Organisms must repair and maintain their structure

(d) Energy is essential for life processes

Answer. (c)

Explanation: A cell is structural and functional unit of a living organisms. Each cell is made up of molecules. Several chemical reactions related to life processes take place in cell and the molecules exhibit movement during these reactions. This makes option C incorrect statement and correct answer.

The growth is key character of living organisms. Various chemical changes, biological reaction cause wear and tear or organelles and alter the organized structure of living organisms. The living organisms have to repair and maintain their structures using the energy produced by cellular respiration of food.

Question. 26 The internal (cellular) energy reserve in autotrophs is

(a) Glycogen

(b) Protein

(d) Fatty acid

Answer. (c)

Explanation: Autotrophs are the organisms that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates). The main photosynthetic pigment chlorophyll a and accessory pigments chl b, chl c and carotenoids etc trap the Sunlight to carry out the light reactions of photosynthesis. The light reaction of photosynthesis produces ATP and reducing agents which in turn serve as energy source to drive the second phase of photosynthesis (dark reactions) during which carbohydrate synthesis takes place.

The carbohydrates which are not immediately consumed by plants are stored as starch (homopolysaccharide of D-glucose).

Glycogen serves as main stored form of carbohydrates in animals.

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

(a) 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O

(b) 6CO₂ + H₂O + Sunlight → C₆H₁₂O₆ + O₂ + 6H₂O

(d) 6CO₂ + 12H₂O + Chlorophyll + Sunlight → C₆H₁₂O₆ + 6CO₂ + 6H₂O

Answer. (c)

Explanation: The reaction for the process of photosynthesis can be expressed as:

6CO₂ + 12H₂O + Chlorophyll + Sunlight → C₆H₁₂O₆ + 6O₂ + 6H₂O

Photosynthesis is the process wherein light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates).

Question. 28 Choose the event that does not occur in photosynthesis.

(a) Absorption of light energy by chlorophyll

(b) Reduction of carbon dioxide to carbohydrates

(d) Conversion of light energy to chemical energy

Answer. (c)

Explanation: Photosynthesis is the process wherein light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates).

The main photosynthetic pigment chlorophyll a and accessory pigments chl b, chl c and carotenoids etc trap the Sunlight to carry out the light reactions of photosynthesis. The light reaction of photosynthesis produces ATP and reducing agents which in turn serve as energy source to drive the second phase of photosynthesis (dark reactions) during which carbohydrate synthesis takes place.

Oxidation of complex carbon compounds take place during cellular respiration which makes option C correct answer.

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

(a) oxygen

(b) temperature

(d) concentration of CO₂ in stomata

Answer. (c)

Explanation: Stomata are the tiny pores present at the leaf surface. Each stomatal pore is surrounded by two guard cells that assist in stomatal opening driven by turgidity of guard cells. When water flows in guard cells from epidermal cells, guard cells become turgid and stomata are opened. Removal of water from guard cells makes them flaccid and stomata are closed.

The only epidermal cells with unevenly thickened walls and chloroplasts are the guard cells; they are kidney shaped in dicots and dumbell shaped in monocots.

Question. 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)

(d) (i) and (iv)

Answer.None of these

Explanation: Plants absorb nitrogen from the soil in the form of nitrate (NO₃⁻) and ammonium (NH₄⁺). All other nitrogen sources (atmospheric nitrogen, proteins, urea etc.) must be broken down into either of these two forms to be absorbed by plants.

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

(a) Pepsin

(b) Cellulase

(d) Trypsin

Answer. (c)

Explanation: Chemical digestion of food starts in the mouth. Digestion of starch by salivary amylase takes place in mouth. Oesophagus serves to push the food into stomach only. NO digestion takes place here. Gastric juice of stomach digests the protein part of food. Pancreatic amylase, trypsin and lipase as well as intestinal peptidases and maltase carry out chemical digestion of food in small intestine. The simpler substances formed by chemical digestion are then absorbed small intestinal villi. Large intestine is the organ of water and salts reabsorption from undigested food and elimination of remaining undigested material out of body. This makes option C correct answer.

Question. 32 Which of the following statements (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)

(d) (ii) and (iii)

Answer. (c)

Explanation: Yeast is a unicellular organism which carries out ethanol fermentation. The first phase is break down of one molecule of glucose into two molecules of pyruvate which occurs in cytoplasm. Due to limited oxygen availability, pyruvate remains in cytoplasm where pyruvate decarboxylase and alcohol dehydrogenase enzymes carry out the second phase of anaerobic respiration and produce ethanol and carbon dioxide.

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

(a) Conversion of pyruvate to ethanol

(b) Conversion of pyruvate to glucose

(d) Conversion of pyruvate to lactic acid

Answer. (d)

Explanation: Respiration is the sole source of energy in muscles. During intense physical activity, limited oxygen supply do not support the aerobic respiration and muscles carry out lactic acid fermentation of pyruvate to meet the energy demand.

Question. 34 Choose the correct path of urine in our body

(a) Kidney → Ureter → Urethra → Urinary bladder

(b) Kidney → Urinary bladder → Urethra → Ureter

(d) Urinary → Bladder → Kidney → Ureter → Urethra

Answer. (c)

Explanation: The correct path of urine is kidney -4 Ureters -4 Urinary bladder Urethra.

Kidneys are the paired organ where urine formation takes place. Small muscular tube, called as ureter, extend from kidneys and carry blood to urinary bladder. The urethra is a small tube that extends from the urinary bladder to an external opening. Hence, option C is the correct sequence.

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

(a) Cytoplasm

(b) Chloroplast

(d) Golgi body

Answer. (a)

Explanation: Pyruvic acid to lactic acid formation is an anaerobic process which occurs in cytoplasm only.

Short Answer Type Questions

Question. 36 Name the following

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

(b) Organisms that can prepare their own food.

(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) Photosynthesis Photosynthesis is the process wherein carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates) i.e. conversion of light energy into chemical energy.

(b) Autotrophs Autotrophs are the organisms that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates).

(c) Chloroplasts it is a double membrane bound organelle that contain machinery for photosynthesis.

(d) Guard cells Each stomatal pore is surrounded by two guard cells that assist in stomatal opening driven by turgidity of guard cells.

(e) Heterotrophs The organisms that cannot make their own food from inorganic substances and depend on other organisms for their food.

(f) Pepsin A protein digesting enzyme.

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

Answer. True. Respiration is the process of oxidation of food substances that release carbon dioxide; it takes place throughout the day. Photosynthesis is the process of fixing the atmospheric carbon dioxide into organic compounds (carbohydrates) with release of oxygen gas as by product. Photosynthesis takes place during day in presence of Sunlight only. Hence, plants release oxygen during day only while carbon dioxide is released during night.

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

Answer.

Each stomatal pore is surrounded by two guard cells that assist in stomatal opening driven by turgidity of guard cells. The guard cells are the only epidermal cells with unevenly thickened walls and chloroplasts. When water flows in guard cells from epidermal cells, guard cells become turgid and stomata are opened. Loss of water from guard cells makes them flaccid and stomata are closed.

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

Answer.

Respiration and photosynthesis are the two vital processes for plant life. The plant kept in light would be able to produce oxygen, required for respiration, by the process of photosynthesis and would live longer. The one kept in dark would die as soon as the container becomes filled with carbon dioxide gas produced by respiration.

Question. 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.

Respiration is the process of oxidation of food substances that release carbon dioxide; it takes place throughout the day. Photosynthesis is the process of fixing the atmospheric carbon dioxide into organic compounds (carbohydrates) with release of oxygen gas as by product. Photosynthesis takes place during day in presence of Sunlight only.

The CO₂ released during respiration is absorbed by plants for photosynthesis in day causing net released of oxygen only. If a plant is releasing carbon dioxide and taking in oxygen during the day, it means that either rate of photosynthesis is too slow to counter balance the released of CO2 by respiration or photosynthesis is not taking place at all.

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

Answer.

Gills are the organ of gaseous exchange in fishes as they have two chambered heart and heart pump the deoxygenated blood to gills. Rich in blood capillaries, these gills serve as surface for exchange of CO2 and oxygen between deoxygenated blood and surrounding. As they are taken out of water, gills are no longer able to absorb oxygen causing its death.

Question. 42 Differentiate between an autotroph and a heterotroph.

Answer.

Autotrophs are the organisms that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates). Heterotrophs are the organisms that depend on available organic compounds and cannot carry out the photosynthesis.

Presence of photosynthetic pigment chlorophyll and carotenoids enable autotrophs to trap the Sunlight to carry out the light reactions of photosynthesis. Heterotrophs lack these pigments.

Since autotrophs are the only organisms that can fix the atmospheric carbon dioxide into organic compounds, these organisms occupies first trophic level in food chain and serve as source of food and energy for organisms of higher trophic levels. Heterotrophs occupy the higher trophic level and function as consumers.

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

Answer.
Need of nutrition for an organism is for:

(a) To serve as energy source for metabolic processes in the body.

(b) To support growth of new cells and repair and maintenance of existing cells.

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

Answer.

Green plants are autotrophs are that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates). The carbohydrates which are not immediately consumed by plants are stored as starch.

Since autotrophs are the only organisms that can fix the atmospheric carbon dioxide into organic compounds, these organisms occupies first trophic level in food chain and serve as source of food and energy for all other organisms of higher trophic levels (heterotrophs/consumers).

Hence, in absence of these plants, whole functioning of whole ecosystem will come to hault due to lack of food and energy source for consumers (herbivores, carnivores and omnivores)

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

Answer.

Coating of Vaseline will make the leaves impervious to gases and water. This will result in adverse impact on it because

(a) Plant will not be able to take in oxygen for respiration and carbon dioxide for photosynthesis.

Question. 46 How does aerobic respiration differ from anaerobic respiration?

Answer.

The aerobic respiration differ from anaerobic respiration is as

Aerobic Respiration	Anaerobic Respiration
Complete breakdown of food in presence of oxygen	Incomplete breakdown of food substances in absence of oxygen
Results in formation of Carbon dioxide and water.	Ethanol and carbon dioxide or lactic acids are the end products.
It occurs in three steps: glycolysis (cytoplasm), citric acid cycle (mitochondrial matrix) and electron transport chain (inner mitochondrial membrane).	It occurs in two steps both of which take place in cytoplasm only.
Huge amount of energy is released due to complete oxidation of glucose.	Less energy is released due to incomplete oxidation of glucose.

Question. 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.

Words of column (A) are matched with that of column (B) as below:

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

Question. 48 Differentiate between an artery and a vein.

Answer.

The differentiate between an artery and a vein are as below\

S. No.	Artery	Vein
1.	Presence of thick elastic, muscular walls with narrow lumen.	Have thin, non-elastic walls with wide lumen.
2.	Thick walls enable them to withstand higher blood pressure as blood is pumped directly from heart into arteries.	Since blood is pumped from different body parts in vein, blood pressure is much lower.
3.	Serve to carry oxygenated blood from heart to other body parts (except pulmonary artery).	Serve to carry deoxygenated blood from all body parts to heart (except pulmonary veins).
4.	Valves are absent.	Presence of valves prevents backflow of blood.

Question. 49 What are the adaptations of leaf for photosynthesis?

Answer.

Leaves shows following adaptations for photosynthesis

(a) Leaves serve to provide large surface area to facilitate maximum light absorption.

(b) The extensive network of veins helps quick transport of substances to and from the mesophyll cells.

(c) Leaves contain chloroplasts, the site for photosynthesis. Since upper surface of leaves are directly illuminated, number of chloroplast is higher in the upper surface.

(d) Presence of tiny pores called as stomata on leaf’s surface facilitate gaseous exchange and transpiration.

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

Answer.

Herbivores derive their nutrition from plants and plants product which in turn make cellulose main component of their diet. Since cellulose digestion is a long process and is done by intestinal ruminant bacteria present in gut of herbivores, complete digestion of cellulose need the food to stay for longer time in gut. Presence of longer intestine serves the purpose and allows the food to stay for longer duration to facilitate proper digestion of cellulose.

Carnivores feed on herbivores and hence cellulose is not part of their diet which in turn causes no need of longer intestine.

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

Answer.

The gastric glands of stomach produce gastric juice, which contains pepsinogen, HCl, and mucus. HCl impart highly acidic pH to stomach which in turn supports conversion of inactive pepsinogen into active pepsin.

Mucus plays an important role and protects the inner lining of stomach against erosion from hydrochloric acid produced in the stomach. In absence of mucus, HCl will cause erosion and ulcer in stomach lining.

Question. 52 What is the significance of emulsification of fats?

Answer.

Fats are large complex biomolecules present in form of large globules which in turn does not support enzymatic action on them.

Bile is secreted by liver and is stored in gall bladder. Ducts from the gallbladder and pancreas join to form common duct that enters the duodenum. The small intestine receives bile from the gallbladder via this common duct.

Bile salts carry out mechanical digestion of large fat globules into smaller ones which are then acted upon by intestinal lipase for complete digestion.

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

Answer.

Peristalsis is rhythmic contraction of muscular wall of alimentary canal which in turn pushes the food along the alimentary canal. Peristalsis begins in the esophagus and continues in all the organs of the alimentary canal.

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

Answer.

Absorption of digested food occurs mainly in small intestine because:

(a) Chemical and mechanical digestion of food reaches to completion in small intestine

(b) The fingerlike projection of mucosa into lumen of small intestine as called as villi which in turn serve to increase the surface area to facilitate maximum absorption of digested food.

Question. 55 Match the words of column (A) with column (B).

Column (A)	Column (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.

Words of column (A) are matched with that of column (B) as below:

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

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

Answer.

Aquatic organisms depend on dissolved oxygen in water while terrestrial organisms absorb oxygen air. Since concentration of dissolved oxygen is much lower as compared to that of oxygen present in air, aquatic organisms breathe faster to meet the demand of oxygen.

Aquatic organisms have same surface for absorption of oxygen and gaseous exchange while terrestrial organisms are at advantage as they have different organs for breathing and gaseous exchange.

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

Answer.

Human heart has four completely separated chambers which allow two completely separated circuits of oxygenated and deoxygenated blood; hence the name, double circulation.

The pulmonary circuit includes flow of blood through heart-lung-heart while systemic circuit includes heart-rest of the body-heart. This ensures that left side of heart receives and pumps only oxygenated blood while the right side receives and pumps only deoxygenated blood.

The blood circulation in human heart is called double circulation because the blood passes through the heart twice during one complete cardiac cycle of the body.

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

Answer.

Human heart has four completely separated chambers which allow two completely separated circuits of oxygenated and deoxygenated blood i.e. double circulation.

(a) It ensures complete separation of oxygenated and deoxygenated blood.

(b) It allows rapid pumping of oxygenated blood under high pressure which is required by active endothermic animals to maintain the constant body temperature.

Question. 59 Mention the major events during photosynthesis.

Answer.

The major events during photosynthesis are

(a) Light reaction:

Absorption of sunlight energy by main and accessory photosynthetic pigments (chl a, b,c and carotenoids)

Oxidation of water into oxygen and hydrogen driven by light energy and preservation of released energy in form of ATP and NADPH

(b) Dark reaction:

Reduction of CO₂ to produce carbohydrates using energy of ATP and NADPH.

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

(a) Cloudy days

(b) No rainfall in the area

(d) Stomata get blocked due to dust

Answer.

(a) Cloudy days will cause the rate of photosynthesis to decrease due to the low availability of Sunlight.

(b) No rainfall in the area will cause the rate of photosynthesis to decrease due to the low availability of water.

(c) Good manuring in the area will cause the rate of photosynthesis to decrease due to the improved availability of minerals necessary for plant growth and development.

(d) Stomata get blocked due to dust will cause the rate of photosynthesis to decrease due to the disturbed carbon dioxide intake through stomata.

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

Answer.

ATP (Adenosine Triphosphate) is the energy currency in the living organisms. Cellular respiration is complete oxidation of food substances into carbon dioxide and water to release the stored energy. The final stage of cellular respiration is the step wise flow of electrons through or within a membrane from a reduced compound (NADH and FADH2) to electron acceptor (oxygen) accompanied by ATP synthesis. It occurs in inner mitochondrial membrane.

Question. 62 What is common for Cuscuta, ticks and leeches?

Answer.

Cuscuta ticks and leeches, all are parasites. Parasitism is association of two organisms wherein one (parasite) is benefitted at the cost of other partner (host).

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

Answer.

(a) The teeth serve the function of mechanical digestion by chewing and grinding.

(b) Three pairs of salivary glands in mouth secrete saliva which contain bicarbonate ions and salivary amylase. Salivary amylase starts the chemical digestion of starch into maltose in mouth itself.

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

Answer.

The gastric glands of stomach produce gastric juice, which contains pepsinogen, HCl, and mucus.

HCl impart highly acidic pH to stomach which in turn supports conversion of inactive pepsinogen into active pepsin.

Mucus plays an important role and protects the inner lining of stomach against erosion from hydrochloric acid produced in the stomach.

Pepsinogen is inactive precursor of pepsin and is first converted into active form in acidic environment of stomach to start protein digestion.

Question. 65 Match the words of column (A) with column (B).

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

Answer.

Words of column (A) are matched with that of column (B) as below:

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

Question. 66 Name the correct substrates for the following enzymes

(a) Trypsin

(b)Amylase

(d) Lipase

Answer.

(a) Trypsin: Proteins (peptides)

(b)Amylase: Starch

(d) Lipase: Emulsified fats

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

Answer.

The thick elastic walls of arteries serve to withstand the high blood pressure as blood is pumped directly from heart into them. On the other hand, veins serve to carry oxygen poor blood from different body parts to heart and thus, do not need thick walls as blood pressure is very low in them.

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

Answer.

Platelets are the cellular component of blood that serves in the constriction of broken blood vessels and coagulation. In absence of platelets, the injured blood vessels would cause leakage of blood as well as the process of blood clotting would not occur at the place of wound. The overall effect would be excessive blood loss causing even death.

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

Answer.

Plants are stationary and exhibit movement in terms of growth and development only i.e.at cellular level. In addition, plants have dead scleranchymatous cells in many of their organ which in turn produce mechanical strength but are not involved in cellular process because of being dead. Animals move from one place to another and have lesser fraction of dead cells in their body. This poses high demand of energy for them as compared to plants.

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

Answer.

When soil moisture is high, movement of water and dissolved minerals from soil into root hair and finally to the root xylem cells build up root pressure which in turn pushes the water up the xylem vessels. The increased soil moisture and the high root pressure causes increased rate of water absorption which in turn forces water droplets to come out from stomata. Stomatal transpiration creates transpiration pull which in turn carry the water and minerals up in stem thereby decreasing root pressure.

Question. 71 Why is transpiration important for plants?

Answer.

(i) It creates transpiration pull required for absorption and upward movement of water and minerals from roots to leaves.

(ii) The cooling effect as provided by transpiration prevents the plant parts from heating up.

Question.72 How do leaves of plants help in excretion?

Answer.

(a) Stomatal transpiration removes the gaseous waste of respiration and photosynthesis.

(b) Most of waste products are stored in large central vacuoles. Shedding of old senescing leaves help eradication of these wastes from the plant body.

Long Answer Type Questions

Question. 73 Explain the process of nutrition in Amoeba.

Answer.

Amoeba follows the holozoic type nutrition. Holozoic refers to engulfment of whole/part of plant/animal in liquid/solid state. The heterotrophic Amoeba engulf the particulate food. The process of obtaining food by Amoeba is called phagocytosis. It is carried out as per the following steps:

(i) Ingestion: Engulfment of food particle by forming temporary projections called pseudopodia is called as ingestion. The engulfed food is taken inside the body by pinching off the food vacuole of pseudopodia.

(ii) Digestion: Breakdown of complex substances into simpler ones by digestive enzymes takes place in food vacuole only.

(iii) Absorption: The digested food present diffuses from food vacuole into the cytoplasm causing disappearance of food vacuole.

(iv) Assimilation: Food absorbed is used by Amoeba for various metabolic processes.

(v) Egestion: The waste products of Amoeba are disposed off in surrounding water by the process of simple diffusion through its cell membrane/ body surface.

Question. 74 Describe the alimentary canal of man.

Answer.

Human alimentary canal consists of organs of digestion which are namely, in sequence, mouth, oesophagus, stomach, small intestine, large intestine and anus.

Mouth cavity: It is the oral cavity inside mouth, containing teeth, tongue and three pairs of salivary glands.

Pharynx: The oral cavity opens into the pharynx. It is the part where food passage and air passage cross each other.

Oesophagus: It is a long muscular, tube that passes through thoracic cavity and diaphragm into abdominal cavity and carries the food down to the stomach by peristalsis.

Stomach: The stomach is a thick-walled, J-shaped organ present on the left side of the abdominal cavity and is continuous with the esophagus above and the duodenum of the small intestine below.

Small intestine: The pyrolic valve ofStomach leads to a tubular structure called as small intestine. It has three divisions, i.e., duodenum, jejunum and ileum.

Large intestine: The ileoceacal valve of small intestine leads to large intestine, which can be divided into two parts as anterior colon and posterior rectum.

The rectum opens at the anus, which in turn serves as site of defecation, the expulsion of feces.

Question. 75 Explain the process of breathing in man.

Answer.

Breathing in humans involves inspiration and expiration that are explained below:

(i) Inspiration: Inspiration, the active phase of ventilation, includes contraction of diaphragm and the external intercostals muscles and movement of rib cage upward and outward. Deep inspiration involves contraction and lowering down of diaphragm to facilitate expansion of lungs by increasing volume of thoracic cavity. The expansion of thoracic cavity and expansion of lungs create the air pressure difference outside the lung and alveoli to facilitate flow of air into alveoli.

(ii) Expiration: It is passive phase of breathing that involves relaxed stage of diaphragm (now dome-shaped) and intercostals muscles causing downward and inward movement of rib cage. This causes decreased volume of thoracic cavity and recoiling of lungs. The resultant increased air pressure in alveoli as compared to atmospheric pressure causes air to move outside the body.

Question. 76 Explain the importance of soil for plant growth.

Answer.

Soil is important for plant growth due to the reasons given below:

(i) Anchorage: Soil holds the plants and provides the base on which^–all the terrestrial and some aquatic plants grow.

(ii) Source of water and mineral: Soil serve as reservoir of water and minerals absorbed by plant roots to support growth and development.

(iii) The roots of a plant also take the oxygen required for respiration from the soil particles by the process of diffusion.

(iv) Symbiotic association of plants with soil microbes help plant absorb otherwise unavailable nutrients such as nitrogen.

Question. 77 Draw the diagram of alimentary canal of man and label the followingparts.

Mouth, Oesophagus, Stomach, Intestine

Answer.

The diagram of alimentary canal of man and its parts are shown below:

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

Answer.

Digestion of carbohydrates:

(i) Oral cavity: Salivary amylase present in saliva breaks down starch into maltose.

(ii) Small intestine:

(a) Pancreatic amylase presents in pancreatic juice breakdown the remaining starch into maltose.

(b) Maltase of intestinal juice breakdown maltose into glucose units.

Digestion of Proteins

(i) Mouth does not have any digesting enzyme for proteins and hence proteins digestion does not start in oral cavity.

(ii) Stomach Pepsin is a protein digesting enzyme secreted by chief cells of stomach wall in its inactive form called as pepsinogen which in turn is converted into active pepsin upon exposure to HCl. Pepsin starts protein digestion into small peptides.

(iii) Small intestine:

(a) Pancreatic juice secretes Trypsinogen, chymotripsinogen (inactive from of trypsin). Trypsin and chymotrypsin digest proteins into peptides.

(b) Peptidases of intestinal juice digest the peptides into amino acids.

Digestion of Fats

(i) Small intestine:

(a) Emulsification of large globules of fats into smaller droplets by bile salt.

(b) Pancreatic lipase digests the emulsified fat globules into glycerol and fatty acids.

(c) Glycerol and fatty acids enter the villi cells where they are rejoined and packaged as lipoprotein droplets before entering the lacteals.

Question. 79 Explain the mechanism of photosynthesis.

Answer.

Photosynthesis is the process involving production of carbohydrates by using carbon dioxide as a chief carbon source and water as electron donor. It can be represented as.

Photosynthesis can be divided into two phases: light dependent phase and light independent phase (dark phase).

(a) Light reaction: Since these reactions cannot take place in absence of light, they are called as light dependent reactions or light reactions. It includes:

Absorption of sunlight energy by main and accessory photosynthetic pigments (chl a, b, c and carotenoids)
Oxidation of water into oxygen and hydrogen driven by light energy and preservation of released energy in form of ATP and NADPH

(b) Dark reaction: Since these reactions do not require Sunlight and can occur in presence or absence of Sunlight, they are termed as dark reaction or light independent reactions.

Reduction of CO₂ to produce carbohydrates using energy of ATP and NADPH
The extra glucose is stored as starch in the leaves of the plant.

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

Answer.

Cellular respiration is the process of breakdown of food substances into simpler ones to release the stored energy. On the basis of presence or absence of oxygen, it can occur through aerobic or anaerobic pathway.

(i) Aerobic respiration: Glucose in the presence of oxygen (air), breaks down to carbon dioxide and water with release of large amount of energy. It occurs in three steps, glycolysis , citric acid cycle and ETC.

Glycolysis is breakdown of glucose into pyruvate. It is oxygen independent pathway occurs in cytoplasm. Pyruvate is decarboxylated into acetyl coA in cytoplasm only.

Citric acid cycle is the second phase of cellular respiration in which acetyl Co are enzymatically oxidized into carbon dioxide and the released energy is stored in NADH and FADH2.

Electron transport chain includes downhill flow of electrons to final electron acceptor (Oxygen, which is then reduced into water) through a chain of membrane-bound carriers to facilitate the uphill transport of protons across a proton-impermeable membrane and ATP synthesis.

Enzymes of citric acid cycle are present in mitochondrial matrix while the electron transport chain is present in inner mitochondrial membrane, hence, the last two phases of aerobic respiration takes place in mitochondria only.

(ii) Anaerobic respiration: Glycolysis is breakdown of glucose into pyruvate. It is oxygen independent pathway and is common to both aerobic and anaerobic respiration. Fate of pyruvate depends on oxygen availability. Anaerobic respiration can occur via lactic acid fermentation or alcohol fermentation.

Alcohol fermentation Due to limited oxygen availability, pyruvate remains in cytoplasm where pyruvate decarboxylase and alcohol dehydrogenase enzymes carry out the second phase of anaerobic respiration and produce ethanol and carbon dioxide with limited amount of energy being released.

Lactic acid fermentation Due to limited oxygen availability, pyruvate remains in cytoplasm where it is broken down into lactic acid with limited amount of energy being released.

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

Answer.

Human heart has four completely separated chambers which allow two completely separated circuits of oxygenated and deoxygenated blood; hence the name, double circulation.

Two pulmonary veins come from each lung and pass O2-rich blood to left atrium. The left ventricle pumps blood into the aorta which in turn branches and delivers blood to the major body regions and organs. The anterior vena cava collects deoxygenated blood from the head, chest, and arms and enters the right atrium while the inferior vena cava collects blood from the lower body regions. Both venae cavae pass the deoxygenated blood to the right atrium. Blood from right atrium enters right ventricle and pulmonary arteries carry deoxygenated blood from right ventricle to lungs for oxygenation.

Question. 82 Describe the process of urine formation in kidneys.

Answer.

Urine formation occurs in the kidneys involves the following steps:

(i) Glomerular Filtration: Glomerular filtration is passive filtration of the blood that starts with entry of blood through glomerulus, a special ball of capillaries. The overall process leads to removal of 15-25% water and solutes from the plasma entering the glomerulus. Filtration of any substance through glomerular filtration depends on molecular size, protein binding, ionization, polarity, and working conditions of kidney in general.

(ii) Tubular reabsorption: Glomerular filtrate enters the proximal convoluted tubule wherein nutrient and salt molecules are actively reabsorbed and pushed into the peritubular capillary network while water flows passively. The filtrate is now composed of urea, some salts and water.

(iii) Tubular secretion: It includes active secretion of certain substances (H+, K+, ammonia, drug etc) from the peritubular capillary network into the distal convoluted tubule.

The urine formed is collected in the urinary bladder.

NCERT Exemplar Class 10 Science Chapter 6 Life Processes

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