Grade 10 biology – Gaseous Exchange and Respiration Quiz
1. Which structure is the main site of gaseous exchange in the leaves of most terrestrial plants?
Stomata are pores on the leaf surface surrounded by guard cells; they open and close to allow gases (CO2 in, O2 and water vapour out) to diffuse into and out of the leaf.
2. What is the primary gas taken in by leaves for photosynthesis during the day?
Photosynthesis uses carbon dioxide from the air as the carbon source to make sugars; leaves take in CO2 through open stomata during daylight.
3. Which cells control the opening and closing of stomata?
Guard cells flank each stoma; changes in their turgor (water pressure) cause stomata to open or close, regulating gas exchange and water loss.
4. During the night, plants typically close most stomata. What is the main reason for this?
At night photosynthesis stops (no light), so closing stomata reduces unnecessary water loss while CO2 uptake is not needed.
5. In woody stems, which structures allow gaseous exchange?
Lenticels are porous regions in bark that permit the diffusion of gases between internal tissues and the atmosphere in woody stems.
6. Which process in plants uses oxygen and releases carbon dioxide continuously, both day and night?
Cellular respiration breaks down sugars to release energy and consumes oxygen while producing carbon dioxide; it occurs continuously to meet energy needs.
7. Where does aerobic respiration primarily occur in plant cells?
Mitochondria are the organelles where aerobic respiration takes place, producing ATP through oxidation of glucose in the presence of oxygen.
8. Which of the following best describes diffusion in the context of gaseous exchange?
Diffusion is the passive movement of molecules (like O2 and CO2) from regions of higher concentration to regions of lower concentration until equilibrium is reached.
9. Why do submerged aquatic plants often have thin leaves with large air spaces (aerenchyma)?
Aerenchyma provides air spaces that allow gases to move internally between shoots and roots and help the plant remain buoyant in water.
10. Which factor will generally decrease the rate of stomatal opening?
During drought, guard cells lose turgor and stomata close to reduce water loss, decreasing stomatal opening despite other cues.
11. Which gas is produced during anaerobic respiration (fermentation) in plant cells when oxygen is limited?
Under anaerobic conditions some plant cells convert pyruvate to ethanol and CO2 (fermentation), releasing less energy than aerobic respiration.
12. How does increased temperature generally affect the rate of gaseous diffusion in plant tissues?
Higher temperatures increase kinetic energy of gas molecules, speeding up diffusion, though very high temperatures may damage tissues and affect stomatal behavior.
13. Which adaptation helps desert plants reduce water loss while still allowing some gas exchange?
Desert plants have a thick waxy cuticle and stomata set in pits (sunken) to reduce water loss by creating a localized humid microenvironment that slows transpiration.
14. Which pathway allows some plants (e.g., maize) to fix carbon efficiently in hot, dry conditions and affects gaseous exchange patterns?
C4 photosynthesis (found in maize and sugarcane) concentrates CO2 in bundle-sheath cells, reducing photorespiration and allowing efficient gas use in hot, dry climates.
15. What role do lenticels play in roots of plants grown above ground, such as sweet potato vines?
Lenticels are porous structures in the bark or periderm that permit gaseous exchange between internal tissues and the air in organs like aerial roots and stems.
16. Why do root cells often rely on diffusion for oxygen supply rather than direct contact with air?
Oxygen reaches root cells by diffusion through soil pores; waterlogged soils limit oxygen diffusion, which can cause root hypoxia.
17. Which process is directly responsible for producing ATP used for active transport in plant root cells?
ATP used for active transport (e.g., nutrient uptake) is generated mainly by aerobic respiration in mitochondria in root cells.
18. What happens to oxygen produced in the chloroplast during photosynthesis?
Oxygen produced as a by-product of photosynthesis diffuses out through stomata or can be consumed by the plant's own respiration.
19. Which of the following increases the rate of gas exchange in a leaf?
Having more stomata per unit area provides more openings for gases to diffuse in and out, increasing the rate of gas exchange.
20. What is photorespiration and when does it commonly occur in plants?
Photorespiration happens when the enzyme RuBisCO fixes O2, leading to loss of fixed carbon and energy, and it is more common under hot, dry conditions with stomatal closure.
21. Which adaptation would you expect in aquatic plants to facilitate gas exchange in anoxic sediments?
Aerenchyma and internal air channels transport oxygen from aerial parts to roots, helping plants survive in oxygen-poor sediments.
22. How does high atmospheric carbon dioxide concentration affect stomatal density over time in many plants?
Plants grown under elevated CO2 often develop fewer stomata as a long-term adaptation because they can obtain sufficient CO2 with fewer openings, reducing water loss.
23. Which statement best explains why waterlogged (flooded) soils harm many crop roots?
Water fills soil pores and drastically reduces oxygen diffusion, so root cells cannot get enough oxygen for aerobic respiration and may die.
24. Which gas is produced as a direct result of glycolysis under anaerobic conditions in plant cells?
During anaerobic fermentation some pathways (e.g., conversion of pyruvate to ethanol) release carbon dioxide as a by-product of glycolysis in plants.
25. Why do some plants open stomata at night (CAM plants) instead of during the day?
CAM plants open stomata at night to fix CO2 when temperatures are cooler and humidity higher, thereby reducing water loss while storing CO2 for daytime photosynthesis.
26. Which statement best describes the relationship between transpiration and gaseous exchange?
Stomata are the main openings for both water vapour loss (transpiration) and gas exchange (CO2 and O2), so the two processes are closely linked.
27. Which observation would indicate that a leaf is respiring more than it is photosynthesising at a given time?
If a leaf releases more CO2 than it absorbs, respiration is exceeding photosynthesis at that time, which often occurs in the dark or under stress.
28. Which plant structure is the main site of gaseous exchange in most terrestrial leaves?
The spongy mesophyll has loosely packed cells and many air spaces that allow gases (CO2, O2, water vapour) to diffuse between the stomata and photosynthesising cells, making it the main site of gaseous exchange in leaves.
29. What is the primary function of stomata on a leaf?
Stomata are pores on the leaf surface that permit gases (CO2 in, O2 and water vapour out) to move between the leaf and the atmosphere, and guard cells control their opening and closing to regulate transpiration and gas exchange.
30. What causes guard cells to open the stomatal pore during the day?
In daylight, guard cells actively accumulate K+ ions, lowering their water potential. Water enters by osmosis, guard cells become turgid and bow apart to open the stomatal pore, allowing gas exchange.
31. Which gas is produced during aerobic respiration in plant cells?
During aerobic respiration glucose is oxidised in the mitochondria to produce energy, with carbon dioxide and water as waste products; oxygen is consumed, not produced.
32. Which statement correctly contrasts photosynthesis and respiration in plants?
Photosynthesis fixes carbon dioxide and releases oxygen as a by-product, whereas aerobic respiration consumes oxygen to oxidise sugars and releases carbon dioxide; both can occur in daytime but photosynthesis is light-dependent.
33. Which tissue in aquatic plants helps transport gases to submerged parts?
Aerenchyma is specialised tissue with large air spaces that facilitate internal diffusion of gases (O2 and CO2) from aerial parts to submerged tissues in aquatic plants.
34. Lenticels on woody stems primarily function to:
Lenticels are spongy openings in bark that permit gases to diffuse into and out of internal stem tissues, enabling respiration in woody plants where stomata are absent on stems.
35. Which of the following best describes diffusion in plant gaseous exchange?
Diffusion is the passive movement of molecules from regions of higher concentration to lower concentration down a concentration gradient and does not require metabolic energy.
36. Why do most dicot leaves have more stomata on the lower surface than the upper surface?
Having more stomata on the lower (shaded) surface reduces exposure to direct sunlight and wind, lowering transpiration while still permitting gas exchange for photosynthesis.
37. Which process occurs continuously in plant cells, both day and night?
Respiration occurs continuously to provide ATP for cellular processes, day and night. Photosynthesis requires light and therefore only occurs during the daytime.
38. During anaerobic respiration (fermentation) in plant cells (e.g., waterlogged roots), which products are commonly formed?
Under anaerobic conditions some plant cells ferment sugars to ethanol and CO2 (alcoholic fermentation) to regenerate NAD+ so glycolysis can continue producing small amounts of ATP.
39. Which factor would increase the rate of gaseous diffusion through a stomatal pore?
Wind reduces the boundary layer resistance by removing stagnant air, steepening concentration gradients at the leaf surface and increasing the rate of diffusion of gases through stomata.
40. Which organelle is primarily responsible for producing ATP during aerobic respiration in plant cells?
Mitochondria are sites of aerobic respiration where the electron transport chain and oxidative phosphorylation generate most ATP in plant cells; chloroplasts are for photosynthesis.
41. In an experiment to show that germinating seeds respire, which observation would indicate respiration is occurring?
Germinating seeds consume oxygen during respiration. Measuring a drop in oxygen concentration (or uptake of oxygen) in a closed system indicates active respiration; temperature may rise slightly, not decrease.
42. Which statement about the leaf cuticle is true in relation to gaseous exchange?
The waxy cuticle reduces water loss by evaporation but also creates a barrier to gas diffusion; most gas exchange therefore occurs via stomata rather than through the cuticle.
43. Which measurement in a respirometer would show that a plant sample is respiring faster?
An increased rate of aerobic respiration consumes oxygen more quickly and releases more carbon dioxide; a respirometer detects these changes in gas exchange as an indicator of respiration rate.
44. Why do submerged leaves of aquatic plants often lack a thick cuticle?
Submerged leaves are surrounded by water so they are not exposed to desiccation; a thin or absent cuticle allows dissolved gases to diffuse more easily between water and internal tissues.
45. Which factor does NOT directly affect the rate of respiration in plant tissues?
While light influences photosynthesis, respiration (particularly dark respiration) occurs independently of light. Temperature, oxygen availability, and substrate supply directly affect respiration rates.
46. How does a decrease in atmospheric CO2 around a leaf affect stomatal behaviour in many plants?
A lower internal CO2 concentration signals the leaf to open stomata so more CO2 can diffuse in for photosynthesis; the response helps maintain CO2 supply to mesophyll cells.
47. Which part of a leaf provides the greatest surface area for gas exchange inside the leaf?
The air spaces between spongy mesophyll cells create a large internal surface area where gases can diffuse to and from photosynthesising cells and stomata.
48. When a plant is waterlogged and oxygen is scarce around roots, what anatomical adaptation helps some plants survive?
Aerenchyma forms air-filled channels that allow oxygen from shoots to diffuse down to roots, helping roots respire when soil oxygen is low during waterlogging.
49. Which of the following best explains why respiration yields less energy than photosynthesis stores?
Photosynthesis stores solar energy in glucose bonds; respiration breaks these bonds to release energy as ATP for cellular processes. Photosynthesis stores more total energy in sugars than the portion respiration releases as usable ATP.
50. Which experimental treatment would reduce gas exchange through a leaf most effectively?
Applying vaseline seals stomatal pores and the surrounding epidermis, preventing diffusion of gases and thus strongly reducing gas exchange; humidity or temperature changes affect rates but do not block exchange completely.
51. Which gas concentration difference drives oxygen into root cells from the soil?
Gases diffuse from regions of higher concentration to lower. Root cells consume O2 during respiration so their internal O2 concentration is lower than in the surrounding soil air spaces, causing diffusion into the roots.
52. Why do CAM plants open stomata at night?
CAM plants open stomata at night to fix CO2 into organic acids, minimising water loss in hot, dry conditions; CO2 is then released internally during the day for photosynthesis while stomata remain closed.
53. Which chemical equation represents aerobic respiration of glucose in plant cells (simplified)?
Aerobic respiration oxidises glucose with oxygen to produce carbon dioxide and water while releasing energy as ATP; the second option is photosynthesis, and the third is anaerobic fermentation.
54. What role do stomatal guard cells play in conserving water during drought?
Under drought stress guard cells lose turgor (become flaccid) and close the stomatal pore, which reduces water loss through transpiration and helps the plant conserve water.
55. Which observation would indicate that a plant tissue is carrying out anaerobic respiration rather than aerobic respiration?
Anaerobic respiration (fermentation) occurs when oxygen is limited; it produces small amounts of ATP and leads to accumulation of products like ethanol (in plants/yeasts) or lactic acid, while oxygen consumption is low.