Respiration
11 Grade 10 General Science questions on Respiration, with worked marking schemes. 11 questions are available on this topic in full.
Question 1
4 marksMany farming families in Kenya install biogas digesters that use cow dung.
(a) Describe how biogas is produced from cow dung in a digester. (3 marks)
(b) State one advantage of using biogas instead of firewood as a household fuel. (1 mark)
(4 marks)
Marking scheme
(a) Any three of the following, 1 mark each (3 marks): - Cow dung is mixed with water to form a slurry. - The slurry is fed into an airtight (oxygen-free) digester. - Bacteria break down the organic matter by anaerobic respiration (fermentation). - Methane gas is produced, together with some carbon dioxide. - The gas collects in the gas chamber or dome and is piped to the kitchen. - A warm temperature speeds up the activity of the bacteria. (b) Any one of the following (1 mark): - It burns cleanly with no smoke, so there are fewer respiratory illnesses in the home. - It reduces the cutting of trees (deforestation). - It is renewable and cheap once installed. - The leftover slurry can be used as manure. - It saves the time spent collecting firewood.
Question 2
1 markWhen bread dough mixed with yeast is left in a warm place for about an hour before baking, it rises. This is because
A. warmth makes the gluten proteins in the flour expand rapidly
B. starch in the flour swells as it absorbs oxygen from the air
C. the dough absorbs water vapour from the warm surrounding air
D. yeast releases carbon dioxide which is trapped in the dough
(1 mark)
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5 marksA group of Grade 10 learners made fermented millet porridge (uji). They mixed the flour with warm water and left it covered for two days. The porridge became sour.
(a) Explain why the porridge became sour. (2 marks)
(b) Describe how the learners could show in the laboratory that the fermented porridge is acidic. (2 marks)
(c) State one safety precaution the learners should observe while testing the porridge in the laboratory. (1 mark)
(5 marks)
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4 marksExplain how each of the following factors affects the rate of respiration in living things:
(a) temperature (2 marks)
(b) oxygen concentration (2 marks)
(4 marks)
Marking scheme
(a) Temperature, any two of the following, 1 mark each (2 marks): - Respiration is controlled by enzymes, so it is affected by temperature. - As temperature rises towards the optimum (about 37 °C in humans), the rate of respiration increases because enzyme and substrate molecules move faster and collide more often. - Above the optimum, the enzymes are denatured, so the rate falls sharply. - At low temperatures the enzymes are less active, so the rate is low. (b) Oxygen concentration, any two of the following, 1 mark each (2 marks): - As oxygen concentration increases, the rate of aerobic respiration increases. - Beyond a certain concentration the rate levels off, because another factor (such as temperature, substrate or enzymes) becomes limiting. - At low oxygen concentration, cells switch to anaerobic respiration, which releases less energy.
Question 5
4 marksA Grade 10 athlete ran a 400 m race at a county sports meeting. After the race she kept breathing deeply and rapidly for several minutes even though she was resting.
(a) Explain why she kept breathing deeply and rapidly after the race. (3 marks)
(b) Her leg muscles also felt tired and painful after the race. Explain why. (1 mark)
(4 marks)
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1 markAn organism respiring aerobically has a respiratory quotient (RQ) of about 0.9. Which respiratory substrate is it most likely using?
A. carbohydrate
B. protein
C. lipid
D. organic acid
(1 mark)
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1 markYeast cells were placed in a glucose solution with no oxygen available. Which products would the yeast cells form?
A. ethanol and water
B. ethanol and carbon dioxide
C. carbon dioxide and water
D. lactic acid and carbon dioxide
(1 mark)
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1 markWhich of the following animals would be expected to have the highest rate of respiration per kilogram of body mass?
A. a goat
B. a mouse
C. a cow
D. an elephant
(1 mark)
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4 marksThe equation below shows how a respiratory substrate is oxidised in the body: 2C₅₇H₁₁₀O₆ + 163O₂ → 114CO₂ + 110H₂O
(a) Calculate the respiratory quotient (RQ) of the substrate. Show your working. (3 marks)
(b) Name the class of food to which the substrate belongs. (1 mark)
(4 marks)
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Create a free account to see itQuestion 10
1 markWhich of the following best describes respiration in living things?
A. the exchange of oxygen and carbon dioxide across a respiratory surface
B. the movement of air into and out of the lungs during breathing
C. the building up of food substances from carbon dioxide and water
D. the breakdown of food substances in cells to release energy
(1 mark)
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5 marks(a) Name the cell organelle in which most of the reactions of aerobic respiration take place. (1 mark)
(b) State four differences between aerobic respiration and anaerobic respiration. (4 marks)
(5 marks)
Marking scheme
(a) Mitochondrion / mitochondria (1 mark) (b) Any four of the following, 1 mark each (4 marks). The learner must give both sides of a difference to earn the mark: - Aerobic respiration uses oxygen; anaerobic respiration takes place without oxygen. - Aerobic respiration releases a large amount of energy (about 38 ATP or 2,880 kJ per mole of glucose); anaerobic respiration releases a small amount of energy (2 ATP; about 210 kJ in yeast or 150 kJ in muscle). - In aerobic respiration glucose is broken down completely; in anaerobic respiration it is broken down only partly. - The products of aerobic respiration are carbon dioxide and water; the products of anaerobic respiration are ethanol and carbon dioxide (in plants and yeast) or lactic acid (in animal muscle). - Aerobic respiration finishes in the mitochondria; anaerobic respiration happens only in the cytoplasm. - The products of aerobic respiration are not toxic; the products of anaerobic respiration (ethanol, lactic acid) are toxic when they build up. - Aerobic respiration can go on for a long time; anaerobic respiration can go on only for a short time in most organisms.
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