1. What is the role of mycorrhizae ?
Answer
Increase the surface area of the plant for uptake of water and ions including phosphates and nitrates.
2. Use of artiïcial fertilisers can cause eutrophication (or damage to lakes and rivers). Explain how.
Answer
Artificial fertilisers can cause eutrophication. Increased nitrates lead to rapid algal growth, forming an algal bloom. This blocks sunlight, causing aquatic plants to die. Saprobionts then decompose the dead material, using up oxygen through respiration. As oxygen levels fall, aquatic animals die.
3. A student investigated the effects of fungal mycorrhizae on plant growth. She sterilized soil samples by baking them for one hour and used seeds from both mycorrhizal-dependent species (marigold and corn) and a non-mycorrhizal species (broccoli). For each species, she set up two treatments: one with mycorrhizae added and one without. Each treatment involved three trays of sterilized soil with the same number of seeds. The trays were kept under identical conditions and watered equally. After seven weeks, she harvested the plants and measured total biomass. Describe how the student could measure the total plant biomass.
Answer
Remove plant from soil. Heat to 100°C in order to remove water. Measure mass of whole plant: root, stem and leaves.
4. The student sterilised the soil before the investigation. Explain why.
Answer
The student sterilised the soil to kill all other organisms present. This ensured that any differences between treatments were due only to the presence or absence of mycorrhizal fungi.
5. The data obtained by the student is shown in the table below. Evaluate the effect of mycorrhizae on the plants after 7 weeks.
Answer
Broccoli had a lower mass when fungi was present. Corn and marigold both had a much higher mass in the presence of fungi. No overlap in standard deviations. Difference in mean was real (or significant) in all three plant species.
6. Explain the difference in mass for marigold.
Answer
With fungi present, marigold plants were able to obtain more nitrates. They were then able to use these nitrates for amino acid production. This then allowed the plant to synthesise more proteins for growth.
7. There is a difference in mass of broccoli for the two treatments. Suggest why.
Answer
The presence of mycorrhizae caused the mean mass of the plants to be much lower. The fungi may have competed with the broccoli for nutrients. They may also have infected the plants, causing disease.