Biology SL
Habitats and Abiotic Tolerance
- 1.
Marram grass lives on exposed sand dunes. Explain how a rolled leaf, hairs inside the rolled surface and sunken stomata can reduce water loss in this habitat.
[4 marks] · no calculator - 2.
A mangrove grows in waterlogged sediment with little oxygen. Some roots project above the sediment and have gas-permeable regions exposed at low tide. Explain how these features benefit living root cells and why submerged roots may still be oxygen-limited.
[4 marks] · no calculator - 3.
Hypothetical equal-age seedlings are grown for 14 days at soil salinities of 0, 5, 10 and 20 g dm^-3. Mean dry-mass gains are 0.8, 1.2, 0.6 and 0.0 g respectively. Other conditions are matched. Identify the best tested salinity, describe the supported tolerance pattern and explain why these results cannot establish the species' exact natural distribution.
[4 marks] · no calculator - 4.
Consider a hypothetical reef-building coral with photosynthetic symbionts. For this exercise, sustained growth requires temperature 23-29 degrees C, salinity 32-37 g kg^-1 and at least 15% of surface light. Site A has 26 degrees C, 35 g kg^-1 and 25% light; B has 27 degrees C, 34 g kg^-1 and 5% light; C has 31 degrees C, 35 g kg^-1 and 30% light. Identify which site passes all supplied requirements, explain the constraint at each other site, and explain why passing these three conditions does not guarantee a reef will form. These ranges are invented for this organism, not universal coral limits.
[4 marks] · no calculator - 5.
In a hypothetical dune transect, ten equal quadrats at each of soil pH 5, 6 and 7 contain a target grass in 2, 8 and 5 quadrats respectively. Sampling effort is equal and identification is assumed correct. Calculate percentage occupancy at each pH and identify the highest observed association. Explain why absence from a quadrat is not proof of physiological intolerance, and propose a design change that would help distinguish a pH effect from position along the dune. No fieldwork has been performed here.
[4 marks]