## NCERT Exemplar Class 10 Science Solutions

### Chapter 06-Life Processes-MCQs

Multiple Choice Questions (MCQs)
Q.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
c) They convert carbon dioxide and water into carbohydrates in the absence of sunlight
d) They constitute the first trophic level in food chains
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.
Q.2. In which of the following groups of organisms, food material is broken down outside the body and absorbed?
a) Mushroom, green plants, Amoeba
c) Paramecium, Amoeba, Cuscuta
d) Cuscuta, lice, tapeworm
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.
Q.3. Select the correct statement
a) Heterotrophs do not synthesize their own food
b) Heterotrophs utilize solar energy for photosynthesis
c) Heterotrophs synthesize their own food
d) Heterotrophs are capable of converting carbon dioxide and water carbohydrates
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.

Q.4. 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
Explanation: Human alimentary canal consists of organs of digestion which are namely, in sequence, mouth, oesophagus, stomach, small intestine, large intestine and anus.
Q.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
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.
Q.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
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.
Q.7. Which part of alimentary canal receives bile from the liver?
a) Stomach
b) Small intestine
c) Large intestine
d) Oesophagus
Explanation: Bile is secreted by liver and is stored in gall bladder from where it enters the small intestine via common duct.
Q.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
Explanation: Presence of starch in a solution turns added iodine drops in blue black colour. Hence, the blue-black colour of rice water confirms presence of starch.
Q.9. In which part of the alimentary canal food is finally digested?
a) Stomach
b) Mouth cavity
c) Large intestine
d) Small intestine
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.
Q.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 digests emulsified fats droplets
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.
Q.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
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.
Q.12. The correct sequence of anaerobic reactions in yeast is
a) $\ce{Glucose ->[{Cytoplasm}] Pyruvate ->[{Mitochondria}] Ethanol + Carbon dioxide}$
b) $\ce{Glucose ->[{Cytoplasm}] Pyruvate ->[{Cytoplasm }] Lactic Acid}$
c) $\ce{Glucose ->[{Cytoplasm}] Pyruvate ->[{Mitochondria }] Lactic Acid}$
d) $\ce{Glucose ->[{Cytoplasm}] Pyruvate ->[{Cytoplasm }] Ethanol + Carbon dioxide}$
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.
Q.13. Which of the following is most appropriate for aerobic respiration?
a) $\ce{Glucose ->[{ Mitochondria }] Pyruvate ->[{Cytoplasm}] CO2 + H2O + Energy}$
b) $\ce{Glucose ->[{ Cytoplasm }] Pyruvate ->[{Mitochondria }] CO2 + H2O + Energy}$
c) $\ce{Glucose ->[{ Cytoplasm }] Pyruvate + Energy ->[{Mitochondria }] CO2 + H2O}$
d) $\ce{Glucose ->[{ Cytoplasm }] Pyruvate + Energy ->[{Mitochondria }] CO2 + H2O + Energy}$

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.
Q.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)
(c) (i) and (iii)
(d) (ii) and (iv)
Explanation: During inhalation, diaphragm contracts and lowers while the rib cage moves upward and outward.
Q.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
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.
Q.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
Explanation: An alveolar sac is made up of simple squamous epithelium and is surrounded by blood capillaries. Thin walls and increased surface area favour 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.
Q.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)
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.
Q.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 these
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.
Q.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
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.
Q.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
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.
Q.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.
Explanation: Arteries are the valve less 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.
Q.22. The filtration units of kidneys are called
(a) Ureter
(b) Urethra
(c) Neurons
(d) Nephrons
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.
Q.23. Oxygen liberated during photosynthesis comes from
(a) Water
(b) Chlorophyll
(c) Carbon dioxide
(d) Glucose
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.
Q.24. The blood leaving the tissues becomes richer in
a) Carbon dioxide
b) Water
c) Heamoglobin
d) Oxygen
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.
Q.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
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.
Q.26. The internal (cellular) energy reserve in autotrophs is
a) Glycogen
b) Protein
c) Starch
d) Fatty acid
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.
Q.27. Which of the following equations is the summary of photosynthesis?
(a) $\ce{6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O}$
(b) $\ce{6CO2 + H2O + Sunlight → C6H12O6 + O2 + 6H2O }$
(c) $\ce{6CO2 + 12H2O + Chlorophyll + Sunlight → C6H12O6 + 6O2 + 6H2O }$
(d) $\ce{6CO2 + 12H2O + Chlorophyll + Sunlight → C6H12O6 + 6CO2 + 6H2O}$
Explanation: The reaction for the process of photosynthesis can be expressed as:
$\ce{6CO2 + 12H2O + Chlorophyll + Sunlight → C6H12O6 + 6O2 + 6H2O }$
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).
Q.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
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.
Q.29. The opening and closing of the stomatal pore depends upon
(a) oxygen
(b) temperature
(c) water in guard cells
(d) concentration of $CO_{2}$ in stomata
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.
Q.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)
Explanation: Plants absorb nitrogen from the soil in the form of nitrate $(NO_{3}^{-})$ and ammonium $(NH_{4}^{+})$. All other nitrogen sources (atmospheric nitrogen, proteins, urea etc.) must be broken down into either of these two forms to be absorbed by plants.
Q.31. Which is the first enzyme to mix with food in the digestive tract?
(a) Pepsin
(b) Cellulase
(c) Amylase
(d) Trypsin
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.
Q.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)
(c) (i) and (iv)
(d) (ii) and (iii)
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.
Q.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
(c) Non-conversion of glucose to pyruvate
(d) Conversion of pyruvate to lactic acid
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.
Q.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