A-LevelBiologyCell structure9700/21 · May/June 2021 · Q111 Marks

Fig. 1.1 is a transmission electron micrograph of cells from duckweed, Spirodela oligorrhiza. [Figure 1.1]

(a)Calculate the actual width of the cell labelled X. Write down the formula you will use to make your calculation. Show your working and give your answer in micrometres to one decimal place. formula μm[3]
(b)(i)Table 1.1 lists some biological molecules found in plant cells. Complete Table 1.1 by choosing one letter from Fig. 1.1 that indicates a cell structure where each biological molecule is found. Table 1.1 biological molecule | letter from Fig. 1.1 ---|--- DNA | cellulose | phospholipid | histone proteins |[4]
(b)(ii)State the name of a cell structure, visible in Fig. 1.1, where ATP is synthesised.[1]
(b)(iii)Name a cell structure that produces mRNA.[1]
(c)Describe the evidence from Fig. 1.1 that shows that the image is a transmission electron micrograph.[2]

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 2021). The mark or mark type is shown in brackets.

[3] actual width = image width ÷ magnification ;
A A = I ÷ M M = I ÷ A I = A × M or magnification triangle
working = width divided by 4275;
e.g. 16 000 ÷ 4275 17 000 ÷ 4275 18 000 ÷ 4275 19 000 + 4275 ;
3.7 (μm) 4.0 (μm) 4.2 (μm) 4.4 (μm);
R answer if given to more than 1 dp or whole number
[4] DNA – A / B / C ;
cellulose - E ;
phospholipid – A / C ;
histone proteins – A / B ;
[1] chloroplast / mitochondrion ;
[1] nucleus; A chloroplast / mitochondrion
R nucleolus
[2] any two from
1 (section at) high resolution;
A suggestion of a correct value of resolution for a TEM
2 any named structure visible in Fig. 1.1 that can, only be seen in a TEM/ not be seen in a photomicrograph;
e.g. internal structure of chloroplasts / thylakoid(s) / grana
e.g. internal structure of mitochondria / cristae
3 high magnification / higher magnification (magnification > 1000 / higher than with light microscope);
in context of higher than light microscope
4 (very) thin;
5 2D/no surface contours / no surface features / AW; A not 3D

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