Question Constellation Sign up for free AQA · GCSE · Biology · Higher
Sugar Movement Between Phloem Cells
| Part shown | Visible features |
|---|---|
| Cell X | A small plant cell beside the phloem cell. It contains many oval organelles with folded inner membranes. A large clear internal compartment is labelled Y. |
| Phloem cell | An adjacent elongated plant cell with very little visible cell contents, no visible nucleus and an end wall containing many small openings. |
The phloem tissue transports sugars to other parts of the plant. The concentration of dissolved sugars in the phloem cell in Figure 3 is higher than in cell X.
Explain how sub-cellular structures help to move dissolved sugars from cell X into the phloem cell.
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Marking points
- 1 Identifies the mitochondria visible in cell X.
- 2 Links mitochondria to aerobic respiration and release of energy.
- 3 Explains that the released energy drives active transport of sugar against the concentration gradient.
Full-mark answer
Cell X contains many mitochondria. Aerobic respiration in the mitochondria releases energy. That energy is used for active transport, moving dissolved sugar from the lower concentration in cell X to the higher concentration in the phloem cell, against the concentration gradient.
Why this answer loses marks
Mitochondria produce energy so sugar diffuses into the phloem.
Energy is released by respiration, and movement against the concentration gradient is active transport, not diffusion.