A-LevelBiologyCell structure9700/22 · Feb/Mar 2018 · Q19 Marks

Fig. 1.1 is an electron micrograph of part of a eukaryotic cell. [Figure 1.1]

(a)State how it is possible to deduce that Fig. 1.1 is a transmission electron micrograph and not a scanning electron micrograph.[1]
(b)Both the Golgi body and the rough endoplasmic reticulum are part of the internal network of membranes in cells. Outline structural features shown in Fig. 1.1 that identify G as the Golgi body and not the rough endoplasmic reticulum.[2]
(c)Calculate the actual diameter, X-Y, of the mitochondrion labelled in Fig. 1.1. Write down the formula that you will use to make your calculation. Give your answer to the nearest whole nanometre (nm).[2]
(d)(i)The inner and outer membranes of the mitochondrion have a fluid mosaic structure similar to other cell membranes. They are both approximately 6 to 7 nanometres (nm) thick. Outline the fluid mosaic model of membrane structure. There is space below for a diagram.[3]
(d)(ii)The inner and outer membranes of the mitochondrion differ in the detail of their membrane components. The inner membrane is also much less permeable than the outer membrane. Suggest one way in which the structure of the inner membrane may differ from that of the outer membrane to produce a less permeable inner membrane.[1]

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 (Feb/Mar 2018). The mark or mark type is shown in brackets.

[1] any one from: idea that can see internal structures; cannot see surface contours / AW ; A not 3-D appearance AVP; e.g. ref. to small(er) depth of field ;
[2] any two from: (flattened) sacs have layered appearance / no connection between membranes / AW / ora ; not, connected to / contiguous with / continuous with, (outer membrane of) nuclear envelope / ora; swellings at end of sacs (for vesicle formation) / vesicles at ends of sacs ; no ribosomes / ora;
[2] actual diameter = image length / magnification ; at 11 mm for X-Y: 234 nm ; A 213 nm (for 10 mm) A 255 nm (for 12 mm) A 223 nm (for 10.5 mm) A 245 nm (for 11.5 mm)
[3] I glycocalyx I glyco / carbohydrate chains A points from labelled diagram 1 phospholipid bilayer ; plus any two from: 2 fatty acid core / fatty acid tails orientated inwards; 3 protein; 4 further detail of proteins; e.g. integral and peripheral / AW scattered (in phospholipid bilayer) 5 cholesterol ;
[1] any one relevant suggestion: reduced gaps between membrane molecules ; higher proportion of phospholipids with saturated fatty acids / ora; fewer unsaturated fatty acids so, fewer ‘kinks' in tails / closer packing ; higher proportion of cholesterol molecules ; fewer, channel / carrier / transport, proteins; smaller diameter of channels in non-specific channel proteins ; fewer types of (specific), transport/carrier, proteins; AVP; e.g. fewer, aquaporins / channels for water

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.