A-LevelBiologyTransport in plants9700/23 · May/June 2018 · Q315 Marks

Nerium oleander is a xerophytic plant. A photomicrograph of a section through the leaf of N. oleander is shown in Fig. 3.1. [Figure 3.1]

(a)The leaf shown in Fig. 3.1 has a number of adaptations to reduce water loss by transpiration. Two of these adaptations are: • a multilayered epidermis • stomata only found in depressions, known as stomatal crypts, on the lower surface of the leaf. Explain how a multilayered epidermis and stomatal crypts will help to reduce water loss in N. oleander. multilayered epidermis stomatal crypts[3]
(b)Name the cells specialised for the transport of assimilates in N. oleander.[1]
(c)Explain the difference between a source and a sink.[2]
(d)(i)State what is meant by a gene mutation.[1]
(d)(ii)Suggest one way in which the mutation of cyFBP prevents the synthesis of cyFBPase.[1]
(e)(i)In monoclonal antibody production, a small mammal is inoculated with cyFBPase and several weeks later cells are removed from the spleen. Some of these cells are required for the production process. Describe the events occurring within the body of the small mammal that lead to the formation of the cells needed for monoclonal antibody production.[4]
(e)(ii)Anti-cyFBPase monoclonal antibody is added to extracts taken from the leaves of the plants with the cyFBP mutation. State the expected results following addition of the monoclonal antibody that would confirm the absence of cyFBPase in the leaf extracts.[1]
(f)Investigations have shown that plants with the cyFBP mutation grow to a much smaller height and have proportionately far less starch stored in their roots than normal plants. Suggest why plants with the cyFBP mutation will store less starch in their roots.[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 2018). The mark or mark type is shown in brackets.

[3] max 2 if only one section attempted
three from:
multilayered epidermis
reduces, cuticular transpiration / loss of water vapour through cuticle ;
increases distance for diffusion (of water vapour to cuticle);
ref. to protection from heat from sunlight and reduced evaporation (from spongy mesophyll cells);
stomatal crypts
creates area of moist air / AW ; I traps water
minimises effect of, external air currents / wind;
reduces / less steep, water potential gradient (between intercellular air space and external environment) ; A water vapour potential gradient A diffusion gradient if referenced to water vapour
ref. to only on lower surface / shaded, and reduced evaporation (from spongy mesophyll cells);
A lower temperature reduces rate of diffusion of water vapour (out via stomata)
[1] phloem sieve tube element(s); A phloem sieve tube (cells) A sieve elements I companion / transfer, cells
[2] allow named assimilates
source
in context of assimilates
site of synthesis ; A described e.g. photosynthesis in leaf/ storage compound breakdown in roots
sink
in context of, via phloem/from source/from leaf I nutrients / substances, unqualifed if assimilates/named assimilate, not stated when explaining source
site where assimilates are stored A described e.g. roots for storage of starch
or
area where, growth occurs / assimilates are used for growth A described e.g. growth in developing buds / growth of immature leaf
or
area that receives, assimilates / AW;
A area where sucrose unloaded
I place that needs assimilates
I place where assimilates are used, unless qualified
[1] change in the, sequence / AW, of, bases / nucleotides (in, the DNA / the gene / cyFBP) ;
[1] one valid suggestion that prevents polypeptide synthesis or prevents synthesis of functional enzyme:
e.g. no mRNA produced ; A transcription, does not / cannot, occur
mRNA produced unable to attach to ribosome ; A translation, does not / cannot, occur
no start codon on mRNA ;
shortened polypeptide chain produced ; A ref. to STOP codon
premature chain termination mutation / nonsense mutation;
polypeptide produced cannot fold to form, tertiary structure / active site ; R changes shape of active site preventing function
polypeptide produced cannot form quaternary structure of protein;
[4] accept cell for lymphocyte throughout
four from:
1 (primary) immune response ;
2 cyFBPase / enzyme, is antigen ;
3 formation of, APC / antigen-presenting cell;
A antigens presented on surface of macrophages
4 antigen, recognition / binding (in context of B-, or T-lymphocytes) ;
5 detail; e.g. clonal selection have receptors, complementary / specific, to, antigen / cyFBPase A immunoglobulin / antibody, as receptors for B-lymphocytes A surface molecules as receptors for T-lymphocytes
6 divide by mitosis / clonal expansion ;
7 (specific) B-lymphocytes form plasma cells ;
8 plasma cells, synthesise / secrete, specific antibody / antibody to cyFBPase ;
9 T-helper / Th, lymphocyte, secretes, cytokine / interleukin ;
10 stimulates, humoral / B-lymphocyte, response ;
[1] no binding of (monoclonal) antibody to, antigen / cyFBPase / enzyme / AW ;
[2] two from:
(less cyFBPase / enzyme, so) less sucrose synthesised ; A no enzyme to synthesise sucrose
less sucrose transported (source to sink); A less sucrose unloaded at sink;
ref. to less glucose for synthesis of starch / AW (on context of sucrose hydrolysis);