A-LevelBiologyCell structure9700/23 · Oct/Nov 2018 · Q111 Marks

Aphids are small insects which feed directly on phloem sap. The salivary glands of aphids have secretory cells that make and release a variety of proteins that assist in feeding. Fig. 1.1 is a transmission electron micrograph of a small area of a salivary gland cell of an aphid. [Figure 1.1]

(a)Describe the role of Golgi bodies in secretory cells, such as the salivary gland cells of aphids.[3]
(b)(i)Explain why secretory cells have large numbers of mitochondria.[2]
(b)(ii)Mitochondria are partly controlled by the nucleus, but can also function independently. Suggest the features of mitochondria that allow them to function independently of the nucleus.[2]
(c)(i)Aphids are important vectors of plant viral diseases. Describe the structure of a typical virus.[3]
(c)(ii)Suggest how viruses are able to pass from one plant cell to the next without crossing membranes.[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 (Oct/Nov 2018). The mark or mark type is shown in brackets.

[(a) any three from]
[1] modification / process / described, of, proteins / polypeptides ;
[2] further detail of modification; examples of modification folding of polypeptides / protein folding assembly of polypeptides to form quaternary structure addition of (named) prosthetic group addition of sugars / addition of carbohydrate / glycosylation cutting of polypeptides removal of, methionine / first amino acid making proteins functional
[3] packaging into vesicles / formation of Golgi vesicles / formation of secretory vesicles ; A 'budding off' / 'breaking off' / transport proteins in Golgi vesicles
[4] formation of (primary) lysosomes ;
[5] AVP; e.g. modification of lipids synthesis of, phospholipids / glycolipids synthesis of cell wall polysaccharides
[(b)(i)] (mitochondria) provide / make / produce, ATP ; A needs a lot of, ATP / energy R 'produce / make, energy'
[(b)(i)] (ATP/energy required for) protein synthesis / movement of (secretory / Golgi) vesicles / exocytosis ;
[(b)(ii) any two from]
[1] mitochondria have (circular) DNA ;
[2] mitochondria, have / make, (70S) ribosomes (for, protein synthesis / translation) ; R if 80S ribosomes
[3] mitochondria can divide; R by mitosis
[4] AVP;
[5] AVP; e.g. (mitochondrial / mt) DNA codes for (some mitochondrial) proteins mRNA transcribed from mtDNA mitochondria produce their own tRNA can replicate DNA I mitochondria have a double membrane
[(c)(i) any three from]
protein coat/capsid; A protein layer R 'cell wall of protein'
nucleic acid (core); R if 'in a nucleus'
DNA or RNA ;
acellular/non-cellular / 'not a cell' ;
size - accept within range 15 nm to 1000 nm ;
AVP; e.g. (protein coat made of) capsomeres surrounded by, membrane / envelope / (phospho)lipid bilayer I antigens / enzymes
[(c)(ii) any one from]
(viruses) pass through plasmodesmata ;
A 'cytoplasmic strands, through cell walls / between cells'
via symplast pathway;