Biology editorial review is supported by the
named review panel.
Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Key concept
Plants need mineral ions from the soil for healthy growth. Nitrate ions provide nitrogen for making amino acids and proteins (deficiency → stunted growth, yellow older leaves). Magnesium ions are needed for making chlorophyll (deficiency → yellow leaves / chlorosis).
Although photosynthesis produces glucose, plants need additional raw materials from the soil to grow properly. Mineral ion deficiency is a short but important part of the syllabus. Examiners test your ability to link specific mineral ions to their roles and to identify deficiency symptoms.
Key Mineral Ions and Their Roles
Mineral ion
Role in the plant
Deficiency symptoms
Nitrate (NO₃⁻)
Provides nitrogen for making amino acids → proteins. Essential for growth.
Component of chlorophyll molecules. Essential for photosynthesis.
Yellow leaves (chlorosis): especially older leaves. Reduced photosynthesis rate.
Potassium (K⁺)
Needed for enzyme action and stomatal function.
Yellow leaves with dead edges (necrosis); poor flower/fruit production.
Phosphate (PO₄³⁻)
Needed for DNA, RNA and ATP. Essential for energy transfer and cell division.
Poor root growth; purple/dark green older leaves; stunted growth.
How Plants Absorb Mineral Ions
Mineral ions are dissolved in soil water at very low concentrations. Plants absorb them through root hair cells by active transport.
Why active transport? The concentration of mineral ions inside the root hair cell is usually higher than in the soil solution. This means ions must be moved against the concentration gradient, which requires energy from respiration.
This is why root cells have many mitochondria: they need to produce a lot of ATP for active transport of mineral ions.
Investigating Mineral Deficiency
A classic experiment grows plants in different mineral solutions:
Set up several identical seedlings in separate containers of mineral solution.
Each solution lacks one specific mineral ion (e.g. One lacks nitrate, one lacks magnesium).
One container has a complete mineral solution as a control.
All other conditions (light, temperature, volume) are kept the same.
After several weeks, compare the growth and appearance of each plant.
The plant lacking nitrate will show stunted growth. The plant lacking magnesium will show yellow leaves. The control plant will grow normally.
Try a focused question (3 marks)
A plant grown in a solution lacking magnesium ions develops yellow leaves. Explain why. (3 marks)
Show the answer and marking guidance
Magnesium ions are needed to make chlorophyll.
Without magnesium, the plant cannot produce sufficient chlorophyll.
Without chlorophyll, the leaves cannot absorb light energy for photosynthesis, so they appear yellow instead of green.
Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.
Common mix-ups to avoid
Check these points against your own answer before moving on.
Confusing the roles of nitrate and magnesium: nitrate is for proteins; magnesium is for chlorophyll.
Saying minerals are absorbed by osmosis or diffusion: mineral ions are absorbed by active transport.
Forgetting to state that active transport requires energy from respiration.