Biology 9700 · AS & A Level · Homeostasis in plants

Homeostasis in plants — practice question

Guard cells sit in the epidermis of most plant leaves. When environmental conditions alter, the guard cells change in ways that regulate whether stomata are open or closed.
(a)[4]

Describe the structural features of guard cells.

(b)

Stomata show daily opening-and-closing rhythms. Fig. 6.1 presents the percentage of stomata open at various times of day, across three days, in the thale cress plant, Arabidopsis thaliana.

(b(i))[2]

Using Fig. 6.1, describe how stomatal opening and closing follow a rhythm.

(b(ii))[2]

Suggest other environmental influences, apart from the time of day, that can lead to stomatal closure.

(i)[2]

Using Fig. 6.1, describe the pattern of stomatal opening and closing.

(ii)[2]

Name other environmental factors, apart from the time of day, that can lead to stomatal closure.

(c)[4]

Table 6.1 presents some of the events that happen during closure of a stoma. They are not arranged in the correct sequence. Complete Table 6.2 so that it shows the proper order of the events listed in Table 6.1. Three of the events have already been done for you.

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This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: Uneven thickness of the cell wall

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