A conservation group is growing young mangrove plants for a coastal restoration project. Fig. 1 shows one plant in waterlogged mud after a high tide. The mu...
Question 1 Report
A conservation group is growing young mangrove plants for a coastal restoration project. Fig. 1 shows one plant in waterlogged mud after a high tide. The mud contains much more water than air, so oxygen diffuses slowly to root cells. Some mangrove species have roots that project above the mud. A student plans to compare these plants with young mangroves whose root systems remain completely below the surface. The student will measure root growth and test the water around the roots for ethanol after seven days.
(a) Use Fig. 1 to describe how the exposed root structures could increase the oxygen supply to cells in the submerged roots. [3]
(b) What type of respiration is likely to occur in root cells if oxygen becomes unavailable? [2]
(c) Explain why prolonged anaerobic respiration can reduce the uptake of mineral ions by root hair cells. [3]
(d) Use the information in the scenario to describe a method the student could use to make a valid comparison between the two groups of plants. [5]
(e) State three variables that should be kept the same for both groups. [3]
Answer Details
(a) The exposed root structures contact the air, so oxygen can diffuse into them. Oxygen then moves through air spaces or tissues to the submerged root cells. This improves their oxygen supply in waterlogged mud. [3]
(b) If oxygen is unavailable, root cells carry out anaerobic respiration. In plant cells this produces ethanol and carbon dioxide, and releases less energy. [2]
(c) Anaerobic respiration releases less energy, so less ATP is available for active transport. Consequently, fewer mineral ions can be transported into root hair cells against a concentration gradient. [3]
(d) A valid comparison could be made as follows:
- Use similar young mangrove plants of the same species.
- Place one group with exposed roots and a second group with roots fully covered by waterlogged mud.
- Use several plants in each group.
- Keep both groups for seven days and measure root growth using the same method.
- Test water or root samples for ethanol using the same test, then compare mean results for the groups.
This isolates root exposure as the variable being investigated and uses repeats to improve reliability. [5]
(e) Any three variables to control are starting size or age, species, volume or type of mud, water depth, light intensity, temperature, duration, and mineral-ion concentration or pH of the water. [3]
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