A-LevelBiologyCell structure9700/21 · May/June 2018 · Q19 Marks

Fig. 1.1 is a transmission electron micrograph of a cell from the root of thale cress, Arabidopsis thaliana. [Figure 1.1]

(a)(i)The structures labelled A and B on Fig. 1.1 are sections of two mitochondria. Suggest why A and B are different shapes.[1]
(a)(ii)The structure labelled D on Fig. 1.1 is a mitochondrion about to divide. Explain the importance of the division of mitochondria for the cell shown in Fig. 1.1 and for cells in the root tips of thale cress.[2]
(b)Within a cell, substances move between the nucleus and the cytoplasm. The area labelled C in Fig. 1.1 shows an area where this communication occurs. Make a large, labelled drawing of area C to show where this communication occurs.[2]
(c)Outline the functions of the nucleus in non-dividing cells, such as the cell in Fig. 1.1.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[1] one from: idea that the sections are orientated differently / cut in different planes / cut at different angles / AW ; A is a cross section / AW, and B is a longitudinal section / AW mitochondria show a variety of, sizes / shapes ; mitochondria, are flexible / change shape; A and B are of, different ages / stages of development ;
[2] two from: replace, old/worn out / damaged, mitochondria ; require more mitochondria as cells, enlarge / grow; more mitochondria are needed, for new cells / when cell divides ; A so numbers remain the same in the new cells / after cell division A idea that mitochondria are shared out (between daughter cells) (mitochondria) provide (most), energy / ATP ; I cell needs (much) energy without stating mitochondria provide energy R energy production I uses of energy
[2] two from: nuclear envelope shown as two membranes with closed ends and a gap; label to nuclear pore;
[4] four from: 1 contains / AW, chromosomes / chromatin / DNA / genes / genetic material / inherited material / genetic information ; 2 (coded) information for synthesis of, polypeptides / proteins; A controls protein synthesis 3 ref. to sequence(s) of bases (in DNA); 4 transcription (of genes) / production of mRNA ; 5 contains nucleolus ; 6 manufacture of ribosomal sub-units; A makes ribosomes 7 idea that DNA is protected from degradation / enzymes / AW ; 8 AVP; e.g. responds to signals that control, gene expression / AW post-transcription modification / modifies mRNA / any example repairs DNA I controls cell's activities I sends mRNA to cytoplasm / mRNA travels through nuclear pores