The image is an electron micrograph of the lining of the small intestine.

(i) Label the microvilli using the letter M and a nucleus using the letter N.

(ii) State the function of the goblet cell.

(iii) Deduce, with a reason, whether or not the goblet cell is likely to divide.

Explain how the cell cycle is controlled.

(i)

Award [1] for one microvillus labelled M and one nucleus labelled N.

Both are essential for the mark.

Do not award the mark if any structure is labelled incorrectly.

(ii)

secretion/exocytosis / produce mucous

Candidates are not required to have studied goblet cells, so are just expected to deduce from the vesicles that the function is secretion; allow enzyme secretion but reject answers suggesting secretion of something that is clearly incorrect such as secretion of bile.

(iii)

not likely to divide as specialized/differentiated
OR
not likely to divide (as nucleus) is in interphase/not in mitosis

Do not award a mark for stating that the goblet cell lacks a nucleus.

a. cell cycle is a sequence of stages / cell cycle is G₁, S, G₂ and mitosis

b. (control of the cell cycle) by cyclins/cyclin

c. levels of cyclins rise (and fall)/fluctuate during the cell cycle/surge at different times/have to reach a certain concentration

d. conditions inside as well as outside the cell affect regulation

e. four cyclins/different cyclins to enter different stages of/events in the cell cycle / cyclins regulate the sequence/timing of the cell cycle / cyclins trigger the next stages

The idea of different cyclins acting at different phases must be clear.

f. cyclin-dependent kinases / cyclins bind to kinases and activate them

g. kinases phosphorylate other proteins

h. phosphorylated proteins perform specific functions in the cell cycle