A lichen describes a mutually beneficial association of a fungus with an organism termed a photobiont. An example of a photobiont is the green alga, Trebouxia sp., which is a photosynthetic protoctist. [Figure 8.1] shows lichen attached to a tree.

1. (a)Outline the characteristic features of the kingdom Fungi.[4]
2. (b)Suggest how a fungus and a green alga benefit from the relationship shown by a lichen.[2]
3. (c)(i)A suspension of Trebouxia in water was used to investigate the effect of the intensity of light on the rate of photosynthesis. The volume of oxygen released over a set period of time was used as a measure of the rate of photosynthesis at each different light intensity. All other conditions were kept constant. Fig. 8.2 shows how light intensity affected the volume of oxygen released by Trebouxia. [Figure 8.2] State which photosystem is involved in the release of oxygen.[1]
4. (c)(ii)With reference to Fig. 8.2: • explain the curve between A and B • explain why the curve levels off after C.[4]

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