Explain why a plant with a deficiency of magnesium ions would eventually die.

Cambridge International IGCSE Biology (0610) — 6.1 Photosynthesis · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Magnesium ions are required to synthesise chlorophyll.
Without Mg2+ chlorophyll cannot be produced, so the light‑dependent reactions of photosynthesis cannot occur and the rate of photosynthesis falls.
Consequently glucose and other carbohydrates are not produced.
Without these carbohydrates the plant cannot carry out cellular respiration to release energy, nor can it synthesise new tissue, so it eventually dies.

Examiner tips

Use the chain of cause and effect: Mg2+ → chlorophyll → photosynthesis → glucose → growth/energy → survival
Show the link between photosynthesis and respiration

Common mistakes

Failing to mention that glucose is needed for respiration
Confusing chlorophyll with other pigments
Not linking the lack of photosynthesis to the plant’s death

Mark scheme (4 marks)

Magnesium ions are needed to make chlorophyll
Without magnesium ions, chlorophyll cannot be made, so photosynthesis cannot occur / rate of photosynthesis decreases
Without photosynthesis, glucose / carbohydrates cannot be produced
Without glucose the plant cannot respire to release energy / cannot grow or repair cells, leading to death

Key terms in this question

magnesium ions