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A-LevelBiologyTransport in plants9700/21 · Oct/Nov 2022 · Q513 Marks

When water molecules enter a plant through the roots, the molecules cross the cortex and enter the xylem tissue to be transported to other parts of the plant. There are two pathways that water can take when crossing the root to the xylem tissue. Complete Table 5.1 with information about the two pathways. [Table 5.1]

  1. (a)When water molecules enter a plant through the roots, the molecules cross the cortex and enter the xylem tissue to be transported to other parts of the plant. There are two pathways that water can take when crossing the root to the xylem tissue. Complete Table 5.1 with information about the two pathways. Table 5.1 name of pathway outline of pathway movement of water from cell to cell through plasmodesmata[2]
  2. (b)Fig. 5.1 is a photomicrograph of a transverse section through the stem of a flowering plant. On Fig. 5.1, draw a label line and the letter T to identify xylem tissue.[1]
  3. (c)(i)Name an organelle found in animal cells that has a similar function to the vacuole in the developing xylem vessel elements.[1]
  4. (c)(ii)The rupture of the tonoplast during development of xylem vessel elements is due to changes in permeability of the tonoplast. Suggest how the permeability of the tonoplast changes and explain how this change could result in the rupture of the tonoplast.[3]
  5. (c)(iii)During development of the xylem vessel elements the pH of the cytoplasm decreases. This change in pH activates enzymes in the cytoplasm that cause organelles to swell. Suggest how a change in pH of the cytoplasm can activate enzymes.[2]
  6. (d)(i)When an insect feeds on the xylem fluid it can act as a vector of plant diseases such as Pierce's disease. This bacterial disease affects many fruit trees causing the leaves to turn brown and drop from the plant, resulting in much less fruit being produced. Explain why Pierce's disease can be described as an infectious disease.[2]
  7. (d)(ii)Malaria is another infectious disease that also involves an insect vector. State the type of organism that causes malaria and name one organism that causes malaria in humans. type of organism name[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

  1. [2] (a) one mark for named pathways; one mark for outline of apoplastic pathway ;
  2. name of pathway | outline of pathway symplast / symplastic | movement of water from cell to cell via plasmodesmata apoplast / apoplastic | movement of water via, cell walls / intercellular spaces
  3. [1] (b) label line labelled T to any area of xylem tissue ; e.g. [Diagram shows T pointing to xylem]
  4. [1] (c)(i) lysosome ;
  5. [3] (c)(ii) any three from: increased permeability to water ;
  6. increased, aquaporins / protein channels (in the tonoplast) ;
  7. water potential in vacuole is lower than that of cytoplasm ; A more ions in vacuole lower water potential
  8. more water enters (vacuole) by osmosis;
  9. vacuole increases, in volume / pressure (until it bursts);
  10. AVP; e.g. fewer transport proteins for exit of ions
  11. [2] (c)(iii) allow two suggestions or a suggestion with further detail, for two marks active site becomes complementary to substrate ;
  12. (because) bonds altered between R groups of amino acids ; A hydrogen / ionic, bonds
  13. removal of a portion that blocks the active site; AW substrate can enter active site;
  14. idea of cofactor / AW, associates with the enzyme ; enzymes becomes functional ;
  15. sets off an enzyme cascade / ref. cell signalling;
  16. AVP;
  17. [2] (d)(i) any two from: caused by a pathogen;
  18. idea that it is transmissible / passed from infected plant to uninfected plant ;
  19. results in harm being caused / AW ;
  20. [2] (d)(ii) protoctist;
  21. Plasmodium falciparum / Plasmodium malariae / Plasmodium ovale / Plasmodium vivax ; A Plasmodium knowlesi

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About this question

Topic
Transport in plants, A-Level Biology (syllabus 9700). Structured question, 13 marks.
Source
A-Level Biology, Oct/Nov 2022 Paper 2 Variant 1, question 5.

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