Gaseous Exchange and Respiration in Plants

20 Grade 10 Biology questions on Gaseous Exchange and Respiration in Plants, with worked marking schemes. 20 questions are available on this topic in full.

1. Question 1

   1 mark

   In a cell of a stored potato tuber, most of the energy in glucose is released in the

   A. mitochondrion

   B. chloroplast

   C. cytoplasm outside the organelles

   D. sap vacuole

   (1 mark)

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2. Question 2

   3 marks

   State three factors that affect the rate of respiration in plant tissues.

   (3 marks)

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3. Question 3

   3 marks

   Describe three ways in which the leaf of a bean plant is adapted for efficient gaseous exchange.

   (3 marks)

   Marking scheme

   Any three of the following, each with its function (1 mark each): - Numerous stomata in the epidermis; provide many pores through which gases diffuse in and out. - Large, interconnected air spaces in the spongy mesophyll; allow gases to reach every living cell and act as a reservoir of gases. - Broad, flat and thin lamina; gives a large surface area and a short diffusion distance between the air and the cells. - Moist surfaces of the mesophyll cells; gases dissolve before diffusing through the cell membrane. Accept: thin, transparent epidermis; stomata concentrated on the lower, shaded surface.

4. Question 4

   6 marks

   Describe an experiment you would carry out in the school laboratory to show that germinating bean seeds give out carbon dioxide.

   (6 marks)

   Marking scheme

   1 mark each for any six of: - Soak bean seeds overnight and allow them to germinate; place the germinating seeds in a boiling tube or flask fitted with a delivery tube. - Set up a second, identical tube containing seeds that have been boiled and soaked in disinfectant, to act as a control. - Draw air slowly through both set-ups using a suction pump or filter pump. - Pass the incoming air first through soda lime (or concentrated potassium hydroxide) so that it enters each tube free of carbon dioxide. - Pass the air leaving each tube through lime water (or hydrogencarbonate indicator) in a receiving tube. - Leave both set-ups at the same temperature for about 30 to 60 minutes. - Result: the lime water connected to the germinating seeds turns milky, while that connected to the dead seeds remains clear. - Conclusion: the living germinating seeds release carbon dioxide during respiration. Maximum 6 marks; a description without a control scores no more than 4.

5. Question 5

   1 mark

   Maize grain kept for three months in a warm, moist crib in Kitale loses much more dry mass than the same grain kept in a cool, dry store. The best explanation is that in the warm, moist crib the grain

   A. absorbs carbon dioxide from the warm air and swells

   B. respires faster, so more of its stored food is broken down

   C. photosynthesises and uses up its own starch

   D. loses starch because warm air dissolves it out of the seed

   (1 mark)

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6. Question 6

   2 marks

   Distinguish between gaseous exchange and respiration in a plant.

   (2 marks)

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7. Question 7

   3 marks

   Describe how gaseous exchange takes place in the roots of a young bean seedling growing in well-drained soil.

   (3 marks)

   Marking scheme

   1 mark each for any three of: - Oxygen from the air spaces between the soil particles dissolves in the film of water surrounding the particles and the root hairs. - The dissolved oxygen diffuses across the thin, moist, permeable wall and cell membrane of the root hair, down a concentration gradient, because the respiring cells keep the oxygen concentration inside low. - From the root hair the oxygen passes from cell to cell and through the intercellular air spaces of the cortex to the inner living cells. - Carbon dioxide produced by the respiring root cells diffuses in the opposite direction, out into the soil water and the soil air spaces.

8. Question 8

   1 mark

   In an experiment on heat production, one vacuum flask contained soaked germinating bean seeds. An identical flask contained seeds that had been boiled, cooled and then soaked in a disinfectant. The disinfectant was used in order to

   A. supply the boiled seeds with oxygen

   B. kill microorganisms whose respiration would also raise the temperature in the flask

   C. absorb the carbon dioxide given out by the boiled seeds

   D. prevent the boiled seeds from germinating

   (1 mark)

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9. Question 9

   3 marks

   Name three structures through which gaseous exchange takes place in a flowering plant and state where each of them is found.

   (3 marks)

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10. Question 10

    3 marks

    A dairy farmer in Uasin Gishu chops green maize fodder, packs it into a pit, compacts it with a tractor and covers it tightly with polythene. Explain how this treatment preserves the fodder as silage.

    (3 marks)

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11. Question 11

    1 mark

    Unlike a goat, a maize plant has no special system for transporting respiratory gases around its body. This is mainly because

    A. the cells of a plant respire only at night, when their demand for oxygen is very low

    B. the xylem sap carries dissolved oxygen from the roots to every living cell of the plant

    C. diffusion through the continuous air spaces of the plant is fast enough to supply its slowly respiring cells

    D. the plant makes all the oxygen it needs from the carbon dioxide it absorbs through its stomata

    (1 mark)

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12. Question 12

    3 marks

    State three ways in which anaerobic respiration in a plant cell differs from aerobic respiration.

    (3 marks)

    Marking scheme

    Any three differences, each stated as a contrast (1 mark each): - Anaerobic respiration takes place without oxygen; aerobic respiration requires oxygen. - Anaerobic respiration yields ethanol and carbon dioxide; aerobic respiration yields carbon dioxide and water. - Anaerobic respiration releases much less energy per molecule of glucose; aerobic respiration releases much more. - Anaerobic respiration is an incomplete breakdown of glucose; aerobic respiration oxidises the glucose completely. - Anaerobic respiration occurs in the cytoplasm; the energy-yielding stages of aerobic respiration occur in the mitochondria. A one-sided statement (e.g. "no oxygen is used") scores the mark only if the aerobic contrast is clear.

13. Question 13

    1 mark

    Shortly after sunrise, the rate of photosynthesis in a sukuma wiki plant becomes exactly equal to its rate of respiration. At that moment,

    A. the leaf gives out oxygen only

    B. both processes stop until the light intensity rises further

    C. the plant stops respiring and only photosynthesises

    D. there is no net exchange of carbon dioxide between the leaf and the surrounding air

    (1 mark)

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14. Question 14

    2 marks

    State two uses to which a growing plant puts the energy released during respiration.

    (2 marks)

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15. Question 15

    1 mark

    On a bright morning, carbon dioxide from the air reaches the photosynthesising cells inside a bean leaf mainly by

    A. dissolving in the water that is drawn up the xylem from the roots

    B. diffusing through the stomata into the air spaces of the mesophyll and dissolving in the moist cell walls

    C. passing through the waxy cuticle of the upper epidermis straight into the palisade cells

    D. being carried into the leaf in the phloem sap together with dissolved sugars

    (1 mark)

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16. Question 16

    1 mark

    The stem of a mature mango tree in Makueni is covered by thick woody bark that has replaced the epidermis. Gaseous exchange in this stem takes place mainly through the

    A. stomata found in the bark

    B. lenticels

    C. cuticle covering the bark

    D. xylem vessels, which carry dissolved oxygen up the stem

    (1 mark)

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17. Question 17

    4 marks

    A farmer at Ahero finds that after his field has stood under water for two weeks, the maize crop wilts and the lower leaves turn yellow. Explain these observations.

    (4 marks)

    Marking scheme

    Any four (1 mark each): - Water fills the soil air spaces and drives out the air, so the soil around the roots has little or no oxygen. - Root cells can no longer respire aerobically; they respire anaerobically. - Anaerobic respiration releases very little energy per unit of glucose, so there is too little energy for the active uptake of mineral salts. - Ethanol accumulates in the root cells and is toxic; root cells and root hairs die. - With damaged roots the plant absorbs less water than it loses by transpiration, so its cells lose turgor and the plant wilts. - Shortage of absorbed mineral salts such as nitrogen and magnesium prevents the making of chlorophyll, so the leaves turn yellow.

18. Question 18

    1 mark

    A water hyacinth leaf floating on the surface of Lake Victoria has almost all of its stomata on the upper surface. The most likely reason is that

    A. the upper surface receives more light, and stomata are needed to let light into the leaf

    B. the lower surface is in contact with water, through which gases diffuse very slowly

    C. the lower surface is covered by a thick waxy cuticle that keeps the leaf afloat

    D. the plant must lose as much water as possible through the upper surface

    (1 mark)

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19. Question 19

    1 mark

    One gram of glucose respired aerobically in a plant cell releases much more energy than one gram respired anaerobically. This is because

    A. in anaerobic respiration much of the energy remains locked up in the ethanol that is formed

    B. anaerobic respiration is not controlled by enzymes and so wastes the glucose

    C. oxygen itself supplies extra energy to the cell when it combines with the glucose

    D. most of the energy released in anaerobic respiration escapes from the cell as light

    (1 mark)

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20. Question 20

    1 mark

    At about 2 p.m. on a hot, dry day in Machakos, the stomata of a maize plant close. Which change in the guard cells brings this about?

    A. The guard cells lose their chloroplasts and can no longer manufacture sugar

    B. The thick inner wall of each guard cell stretches more than the thin outer wall

    C. The guard cells take in water, become turgid and the pore between them closes

    D. Potassium ions move out of the guard cells, water follows by osmosis and the guard cells become flaccid

    (1 mark)

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