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NCERT Exemplar · Class 10 Science Life Processes

82 questions · 82 still being checked

Long Answer Questions 73–82 (part 9 of 9)

  1. Exercise 73

    Explain the process of nutrition in Amoeba.

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    NCERT’s answer
    Hints— Finger like projections Food vacuoles Diffusion of simpler substances.
    Amoeba is holozoic; it lacks a fixed mouth.\[\text{Pseudopodia encircle food} \Rightarrow \text{Food vacuole forms (phagocytosis)} \] \[\text{Enzymes secreted into vacuole} \Rightarrow \text{Food broken into diffusible molecules} \] \[\text{Digested food diffuses into cytoplasm (absorption)} \Rightarrow \text{Undigested matter expelled at the surface (egestion)} \] Answer: Nutrition in Amoeba is holozoic, via phagocytosis, intracellular digestion, absorption and egestion.

  2. Exercise 74

    Describe the alimentary canal of man.

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    NCERT’s answer
    Hints— Mouth cavity Oesophagus Stomach Intestine
    One continuous tube, mouth to anus; salivary glands, liver and pancreas pour secretions into it.\[\text{Mouth} \to \text{Pharynx} \to \text{Oesophagus} \to \text{Stomach} \to \text{Small intestine} \to \text{Large intestine} \to \text{Anus} \] \[\text{Mouth: teeth chew, tongue mixes;}\quad \text{Starch} \xrightarrow{\text{salivary amylase}} \text{Sugar} \] \[\text{Oesophagus: peristalsis pushes the food down} \] \[\text{Stomach: gastric glands secrete mucus,}\ \mathrm{HCl};\quad \text{Protein} \xrightarrow{\text{pepsin}} \text{Peptides} \] \[\text{Small intestine: bile + pancreatic juice} \Rightarrow \text{digestion completes;}\ \text{villi} \Rightarrow \text{absorption} \] \[\text{Large intestine: water absorbed} \Rightarrow \text{Anus: sphincter, egestion} \] Answer: A tube from mouth to anus; each part digests, moves, absorbs or egests as shown, aided by the salivary glands, liver and pancreas.

  3. Exercise 75

    Explain the process of breathing in man.

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    Hints— 1. Passage of air 2. Gaseous exchange 3. Role of diaphragm 4. Function of rib muscles and alveoli
    Air passage, then the two phases of breathing.\[\text{Nostrils} \to \text{Nasal cavity} \to \text{Pharynx} \to \text{Larynx} \to \text{Trachea} \to \text{Bronchi} \to \text{Bronchioles} \to \text{Alveoli} \] Inspiration: \[\text{Diaphragm contracts (flattens), rib muscles lift ribs up/out} \Rightarrow V_{thorax}\uparrow \Rightarrow P_{lung} < P_{atm} \Rightarrow \text{air enters} \] Expiration: \[\text{Diaphragm relaxes (domes up), ribs move down/in} \Rightarrow V_{thorax}\downarrow \Rightarrow P_{lung} > P_{atm} \Rightarrow \text{air leaves} \] Gas exchange across the thin, moist alveolar wall: \[\mathrm{O_2}:\ \text{alveolus} \to \text{blood in capillaries};\qquad \mathrm{CO_2}:\ \text{blood} \to \text{alveolus} \] Answer: Air reaches the alveoli through the respiratory passage; diaphragm and rib movements change thoracic volume and pressure to draw air in and push it out, while \(\displaystyle \mathrm{O_2}\) and \(\displaystyle \mathrm{CO_2}\) diffuse across the alveoli.

  4. Exercise 76

    Explain the importance of soil for plant growth.

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    NCERT’s answer
    Hints— 1. Anchoring the plant 2. Source of water and minerals 3. Availability of oxygen for respiration of root cells 4. Symbiotic association with microbes
    1. Anchorage: roots grip the soil and hold the plant upright.2. Water: held in the pores between soil particles; roots absorb it.3. Minerals: dissolved in that water -- macronutrients (\(\displaystyle \mathrm{N, P, K, Ca, Mg, S}\)) and micronutrients (\(\displaystyle \mathrm{Fe, Zn, B}\), etc.) -- taken up with it.4. Air: pore spaces supply \(\displaystyle \mathrm{O_2}\) for root respiration.5. Microbes: Rhizobium in the root nodules of legumes fixes atmospheric \(\displaystyle \mathrm{N_2}\); mycorrhizal fungi help roots take up minerals; decomposers break dead matter down into humus and release minerals.Answer: Soil anchors the plant and supplies water, minerals and air, and its microbes, symbiotic and decomposer, keep nutrients available.

  5. Exercise 77

    Draw the diagram of alimentary canal of man and label the following parts. Mouth, Oesophagus, Stomach, Intestine

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    NCERT_Solution_Class10_Science_Exemplar_Ch6_Q77_ncert
    \[\text{Mouth} \to \text{Oesophagus} \to \text{Stomach} \to \text{Intestine (small} \to \text{large)} \to \text{Anus} \] Answer: Mouth \(\displaystyle \to\) Oesophagus \(\displaystyle \to\) Stomach \(\displaystyle \to\) Intestine, as labelled.

  6. Exercise 78

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

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    Hints— Mouth cavity Stomach Intestine
    Enzymes act stage-wise along the alimentary canal, each on one substrate.\[\text{Starch} \xrightarrow[\text{mouth}]{\text{salivary amylase}} \text{Maltose} \] \[\text{Proteins} \xrightarrow[\text{stomach, HCl activates it}]{\text{pepsin}} \text{Peptones} \] \[\text{Fats} \xrightarrow[\text{liver}]{\text{bile}} \text{Emulsified fat} \xrightarrow[\text{pancreas}]{\text{lipase}} \text{Fatty acids + Glycerol} \] \[\text{Peptones} \xrightarrow[\text{pancreas}]{\text{trypsin}} \text{Peptides} \xrightarrow[\text{intestine}]{\text{peptidases}} \text{Amino acids} \] \[\text{Residual starch} \xrightarrow[\text{pancreas}]{\text{amylase}} \text{Maltose} \xrightarrow[\text{intestine}]{\text{maltase}} \text{Glucose} \] Bile only emulsifies fat, enlarging the surface for lipase -- it digests nothing itself. Answer: Carbohydrates end as glucose, proteins as amino acids, fats as fatty acids and glycerol, absorbed by the small intestine's villi.

  7. Exercise 79

    Explain the mechanism of photosynthesis.

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    NCERT’s answer
    Hints— Absorption of light energy by chlorophyll Conversion of light energy into chemical energy Reduction of \(\displaystyle \mathrm{CO}_2\) into carbohydrates.
    Three events in the chloroplast: light absorption, conversion of light energy into chemical energy with water splitting, and reduction of \(\displaystyle \mathrm{CO_2}\).Light absorbed by chlorophyll is stored as chemical energy in the thylakoid, and water is split: \[h\nu \Rightarrow \text{ATP} + \text{NADPH} \] \[2\mathrm{H_2O} \xrightarrow[\text{chlorophyll}]{h\nu} 4\mathrm{H^+} + 4e^- + \mathrm{O_2}\uparrow \] The \(\displaystyle \mathrm{H^+}\) and electrons reduce \(\displaystyle \mathrm{CO_2}\) in the stroma: \[\mathrm{CO_2} + 4\mathrm{H^+} + 4e^- \to \tfrac{1}{6}\mathrm{C_6H_{12}O_6} + \mathrm{H_2O} \] Net: \[6\mathrm{CO_2} + 12\mathrm{H_2O} \xrightarrow[\text{chlorophyll}]{h\nu} \mathrm{C_6H_{12}O_6} + 6\mathrm{H_2O} + 6\mathrm{O_2} \] The released \(\displaystyle \mathrm{O_2}\) comes from water, not \(\displaystyle \mathrm{CO_2}\) -- shown with \(\displaystyle ^{18}\mathrm{O}\)-labelled water. Answer: Chlorophyll traps light, stores it as chemical energy (ATP, NADPH) while splitting water to release \(\displaystyle \mathrm{O_2}\), and the hydrogen then reduces \(\displaystyle \mathrm{CO_2}\) to glucose.

  8. Exercise 80

    Explain the three pathways of breakdown in living organisms.

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    NCERT’s answer
    Hints— Pyruvate to ethanol, \(\displaystyle \mathrm{CO}_2\) and energy Pyruvate to lactic acid and energy Pyruvate to \(\displaystyle \mathrm{CO}_2, \mathrm{H}_2 \mathrm{O}\) and energy
    Glycolysis is common to every organism; only pyruvate's next step branches. \[\text{Glucose (6C)} \xrightarrow[\text{cytoplasm, no O}_2\text{ needed}]{\text{glycolysis}} 2\,\text{Pyruvate (3C)} \] \[\text{Pyruvate} \xrightarrow[\text{yeast, cytoplasm}]{\text{absence of O}_2} \text{Ethanol} + \mathrm{CO_2} + \text{Energy} \] \[\text{Pyruvate} \xrightarrow[\text{muscle cell, cytoplasm}]{\text{absence of O}_2} \text{Lactic acid} + \text{Energy} \] \[\text{Pyruvate} + \mathrm{O_2} \xrightarrow[\text{mitochondria}]{\text{presence of O}_2} \mathrm{CO_2} + \mathrm{H_2O} + \text{much more energy} \] Lactic acid, not ethanol, is what cramps muscles during vigorous exercise -- the two anaerobic routes are not interchangeable. Answer: Glycolysis to pyruvate, then ethanol + \(\displaystyle \mathrm{CO_2}\) + energy (yeast) or lactic acid + energy (muscle) without \(\displaystyle \mathrm{O_2}\), or \(\displaystyle \mathrm{CO_2}\) + \(\displaystyle \mathrm{H_2O}\) + much more energy (mitochondria) with \(\displaystyle \mathrm{O_2}\).

  9. Exercise 81

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

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    Hints— Atrium Ventricles Oxygenated blood De-oxygenated blood
    Two loops, driven by the four chambers.\[\text{Body (deoxygenated)} \to \text{Venae cavae} \to \text{Right atrium} \to \text{Right ventricle} \to \text{Pulmonary artery} \to \text{Lungs} \] \[\text{Lungs (oxygenated)} \to \text{Pulmonary veins} \to \text{Left atrium} \to \text{Left ventricle} \to \text{Aorta} \to \text{Body} \] The tricuspid and bicuspid valves shut as the ventricles contract, forcing blood only forward into the arteries, never back into the atria. Answer: Deoxygenated blood: body to right atrium to right ventricle to lungs; oxygenated blood: lungs to left atrium to left ventricle to body -- double circulation.

  10. Exercise 82

    Describe the process of urine formation in kidneys.

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    NCERT’s answer
    Hints— Nephrons Filtration Selective reabsorption
    Urine forms in three steps along the nephron.Filtration -- glomerular blood pressure forces water, glucose, amino acids, salts and urea into Bowman's capsule; cells and proteins are too large to pass. Reabsorption -- along the tubule, glucose, amino acids, most water and needed salts return to the surrounding capillaries. Secretion -- \(\displaystyle \mathrm{H^+}\), \(\displaystyle \mathrm{K^+}\) and ammonia pass from blood into the tubule. \[\text{Filtrate} \approx 180\ \mathrm{L\,day^{-1}} \xrightarrow[\text{tubule}]{\sim 99\%\text{ reabsorbed}} \text{Urine} \approx 1\text{--}1.5\ \mathrm{L\,day^{-1}} \] Glucose or protein appearing in urine marks a filtration or reabsorption fault, not normal function. Answer: Glomerular filtration, then selective reabsorption and secretion along the tubule, concentrate about $\displaystyle 180$ L of filtrate a day down to about $\displaystyle 1$-$\displaystyle 1.5$ L of urine.