A plant has green stems that grow above ground and pale stems that grow underground.
Scientists investigate cells from both types of stem. Their results are shown in the table.
| Plant cell | Source of cell | Mean number of chloroplasts per cell | Response when molecule X is added |
|---|---|---|---|
| P | above-ground green stem | 32 | response |
| Q | underground pale stem | 0 | no response |
Molecule X is too large to pass through the cell membrane.
The scientists also investigate a bacterium, R, living on an underground stem. Cell R releases large amounts of an enzyme protein. An antibiotic-resistance gene can be copied and passed between cells separately from the main genetic material.
Cell R contains particularly large numbers of one sub-cellular structure.
Give the name of this structure.
Describe how differences between the cell membranes of P and Q could account for their different responses to molecule X.
Describe how the main genetic material and the antibiotic-resistance gene are likely to be arranged inside cell R.
Explain the difference between the mean numbers of chloroplasts in cells P and Q.
130 exam-style questions on OCR GCSE Biology 1.1 Cell structures, covering 1.1.1 Viewing cells with light microscopes, 1.1.2 Sub-cellular structures and functions, and 1.1.3 Electron microscopy and resolution. Each one has a worked solution and a mark scheme showing where the marks go.