A-LevelBiologyCell structure9700/21 · Oct/Nov 2017 · Q513 Marks

Fig. 5.1 is a transmission electron micrograph of part of a cell.

(a)(i)Name the organelle labelled X.[1]
(a)(ii)Put a tick (✔) in the box beside the type, or types, of cell that contain this organelle. animal cell [ ] plant cell [ ] bacterial cell [ ][1]
(b)Use the scale bar to calculate the magnification of Fig. 5.1. Write down the formula and use it to make your calculation. Show your working. formula ................................................................ magnification × ................................[3]
(c)The organelle in Fig. 5.1 is made from structures surrounded by a single membrane. Name two organelles that are surrounded by double membranes.[2]
(d)(i)The structure of the cell surface membrane is described as a fluid mosaic. Explain what is meant by the term fluid mosaic.[2]
(d)(ii)Outline the roles of the cell surface membrane.[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 (Oct/Nov 2017). The mark or mark type is shown in brackets.

[1] (a)(i) Golgi (body / apparatus / complex);
[1] (a)(ii) animal cell ✔ plant cell ✔ bacterial cell ;
[3] (b) magnification = scale bar length / actual length ; A M = I / A_M = 1 / O or magnification triangle 14 500 ;; for 29 mm scale bar length A 14 000 (for 28 mm) or 15 000 (for 30 mm) allow one mark only for incorrect answer but correct calculation using scale bar e.g. 29 000 √2 correct answer but units given correct measurement and correct calculation but incorrect conversion
[2] (c) mark first two only nucleus ; mitochondria ; chloroplasts ;
[2] (d)(i) fluid idea of phospholipid (and protein) molecules, move about / diffuse (within their monolayer) ; mosaic protein (molecules), interspersed / scattered / AW ; A different / AW, proteins ;
[4] (d)(ii) any four from 1 barrier between cytoplasm and, external environment / AW; e.g. tissue fluid A protects, organelles from damage / from pathogens, I keeps cell contents in / membrane surrounds the organelles 2 cell signalling or has receptors for, cell signalling substance / hormone / neurotransmitter / AW 3 cell recognition / acts as cell surface antigen; 4 cell-to-cell adhesion ; 5 site for, enzymes / catalysing reactions ; 6 anchoring the cytoskeleton / AW ; 7 selection of substances that enter or leave a cell; AW 8 formation of hydrogen bonds with water for stability; 9 AVP; e.g. ref. to, changing shape of cell / flexibility of cells e.g. phagocytosis

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