(a) Fig. 4.1 is a scanning electron micrograph of a section of a plant cell wall. In living plant tissue cytoplasmic strands form part of structure W. [Figure 4.1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

1. [1] plasmodesmata ;
2. [2] any two from: ref. to connecting two cells; in context of connecting cytoplasm (facilitate) movement of substances between cells; A named substances ref. to symplast pathway; cell to cell communication / passage of cell signalling molecules ; AVP; e.g. removes the need to cross the partially permeable cell surface membrane (when moving between cells) increases the rate of movement of substances between cells
3. [2] protein coat/capsid; DNA or RNA / nucleic acid; A genetic material ref. to some viruses have envelope;
4. [5] allow sucrose for assimilates throughout any five from: viruses / assimilates, enter via plasmodesmata ; movement / diffusion, of assimilates into (phloem) sieve tubes, lowers water potential / AW ; (so) water enters, by osmosis / down water potential gradient / AW; hydrostatic pressure increases (at source); A turgor pressure for hydrostatic pressure unloading at, sink / named sink, lowers hydrostatic pressure (at sink); detail; e.g. assimilates move out and water follows osmotically pressure gradient created / higher pressure in source (than sink) / lower pressure in sink (than source); (so) mass flow; term to be used in context from source to sink; allow mp if terms source and sink used in correct context within complete response AVP; (viruses and assimilates travel) through sieve pores