## NCERT Exemplar Class 10 Science Solutions

##### Class X-Biology

Q.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.
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.

Q.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.
Q.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.

Q.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.
Q.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.
Q.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.
Q.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.
Q.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.
(c) To provide resistance against various diseases.
Q.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)
Q.45. Leaves of a healthy potted plant were coated with vaseline. Will this plant remain healthy for long? Give reasons for your 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.
(c) Since transpiration pull drive the upward movement of water and minerals in xylem, water transport will be hampered.
Q.46. How does aerobic respiration differ from anaerobic respiration?
Answer. The aerobic respiration differ from anaerobic respiration is as

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

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

Q.48. Differentiate between an artery and a vein.
Answer. The differentiate between an artery and a vein are as below

Q.49. What are the adaptations of leaf 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.
Q.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.
Q.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.
Q.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.
Q.53. What causes movement of food inside the alimentary canal?
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.

Q.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 finger like 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.
(c) Wall of small intestine is richly supplied with blood vessels which take the absorbed food to different body part.
Q.55. Match the words of column (A) with column (B).

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

Q.56. Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms?
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.
Q.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.
Q.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.
Q.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 $CO_{2}$ to produce carbohydrates using energy of ATP and NADPH.
Q.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) 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.
Q.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.
Q.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).
Q.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.
(c) Tongue serves in mixing of food with saliva.
Q.64. What are the functions of gastric glands present in the wall of the stomach?
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.
Q.65. Match the words of column (A) with column (B).

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

Q.66. Name the correct substrates for the following enzymes
(a) Trypsin
(b)Amylase
(c) Pepsin
(d) Lipase
(a) Trypsin: Proteins (peptides)
(b)Amylase: Starch
(c) Pepsin: Proteins
(d) Lipase: Emulsified fats
Q.67. Why do veins have thin walls as compared to arteries?
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.
Q.68. What will happen if platelets were absent in the blood?