Question 1
Paper 4 short-answer style1 markState why a plant needs magnesium ions. (1 mark)
Model answer
To make chlorophyll.
Why this scores
One mark for 'to make chlorophyll'.
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Detailed notes on Plant Nutrition for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
Plants don't live on photosynthesis alone — they also need NITRATES (for proteins) and MAGNESIUM (for chlorophyll). Cambridge wants the deficiency symptom for each.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Photosynthesis only makes glucose. Plants need extra elements (N, Mg, P, K) to build proteins, chlorophyll, DNA and run their enzymes.
Plants are autotrophic — they make their own food. But food (glucose) is only carbon, hydrogen and oxygen. Plants also need nitrogen, magnesium, phosphorus, potassium, sulfur, and traces of other elements to build everything else they use.
Where do they get them?
Cambridge focus. The syllabus highlights TWO key minerals: nitrates and magnesium ions. Memorise the role + the deficiency symptom for each.
| Mineral ion | Needed to make | Deficiency symptom |
|---|---|---|
| Nitrate (NO₃⁻) | Amino acids → proteins (also DNA, chlorophyll, ATP) | Stunted growth; older leaves yellow |
| Magnesium (Mg²⁺) | Chlorophyll | Chlorosis — yellowing between the veins; older leaves first |
Plants combine glucose + nitrates to make amino acids → proteins. No nitrate, no growth.
Why plants need nitrogen.
Why NITRATE, not N₂?
Deficiency symptoms.
Worked qualitative. Why do farmers add NITROGEN-CONTAINING FERTILISERS to fields?
Cambridge tip. Always say "amino acids and proteins". Saying just "for protein" misses a mark — the chain of reasoning is glucose + nitrate → amino acid → protein.
Magnesium sits at the centre of every chlorophyll molecule. No magnesium, no chlorophyll, no photosynthesis.
Why plants need magnesium.
Deficiency symptoms.
How plants take up magnesium.
Worked qualitative. A houseplant has yellow leaves between green veins. Likely cause?
Cambridge tip. "Yellow leaves" is partial — say "yellow leaves due to lack of chlorophyll".
Minerals enter root hair cells by ACTIVE TRANSPORT — needs ATP from respiration.
The challenge. Soil concentration of mineral ions is usually LOWER than concentration inside root cells. Diffusion would push ions OUT, not in.
The solution: active transport.
Why root hair cells are good at this.
Worked qualitative. Why does waterlogged soil kill plants?
Cambridge tip. When asked HOW minerals enter, say "active transport" — and pair it with "requires energy from respiration". Avoid saying "diffusion": that only works when soil > root, which is rare.
Verbatim phrases and definitions Cambridge mark schemes credit.
Mineral requirements appear regularly on Paper 2 (3-4 marks: name the mineral and its role) and Paper 4 (5-6 marks: explain deficiency symptoms or active transport mechanism). Examiner reports flag students saying 'plants take in nitrogen from the air' (wrong — they need nitrate from soil) and confusing osmosis with active transport.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (6.3); 0610/22 Oct/Nov 2024 — Q5 (mineral requirements); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on mineral requirements, written exactly the way a tutor would explain them at the board.
Question
Why are nitrate ions essential for plant growth, and what are the symptoms of nitrate deficiency?
Step-by-step solution
Step 1
Plants need nitrogen (from nitrate ions) to make amino acids, which join to form proteins.
Step 2
Plants take up nitrate ions (NO₃⁻) from the soil through their root hairs (they cannot use nitrogen gas from the air).
Step 3
Proteins are needed for growth and for making enzymes.
Step 4
Deficiency: poor, stunted growth (less protein for new cells) and often yellowing of the older leaves.
Answer
Nitrate ions provide nitrogen to make amino acids and proteins (for growth and enzymes). Deficiency causes stunted growth and yellow older leaves.
Examiner tip
Cambridge wants 'amino acids and proteins' — 'for growth' alone is too vague.
Question
Why is magnesium essential for plants, and what is the symptom of magnesium deficiency?
Step-by-step solution
Step 1
Magnesium ions are needed to make chlorophyll.
Step 2
Without magnesium, the plant cannot make enough chlorophyll.
Step 3
Less chlorophyll → less light absorbed → less photosynthesis → less glucose for growth.
Step 4
Deficiency: yellow leaves (chlorosis), and poor growth.
Answer
Magnesium is needed to make chlorophyll. Deficiency causes yellow leaves (chlorosis) and reduced photosynthesis, so growth is poor.
Question
A gardener has two unhealthy plants. Plant A is small and stunted with poor overall growth. Plant B is a normal size but has noticeably yellow leaves. Suggest which mineral each plant is short of, and explain your reasoning.
Step-by-step solution
Step 1
Plant A is stunted, which points to a lack of protein for making new cells.
Step 2
Protein needs nitrogen, so Plant A is most likely short of nitrate ions.
Step 3
Plant B has yellow leaves, which suggests too little chlorophyll.
Step 4
Chlorophyll needs magnesium, so Plant B is most likely short of magnesium ions.
Answer
Plant A lacks nitrate ions (stunted growth from too little protein); Plant B lacks magnesium ions (yellow leaves from too little chlorophyll).
Examiner tip
Both deficiencies cause poor growth, but the EMPHASIS differs: nitrate → mainly stunted; magnesium → mainly yellow leaves.
Question
Explain how plants absorb mineral ions from the soil even when the soil concentration is lower than that inside the root.
Step-by-step solution
Step 1
Mineral ions are usually MORE concentrated inside the root cells than in the soil water.
Step 2
So the ions must move AGAINST the concentration gradient — diffusion alone cannot do this.
Step 3
They are taken in by active transport, using energy from respiration and protein carriers in the cell membrane.
Step 4
Root hair cells are adapted for this with many mitochondria (to release energy) and a large surface area for absorption.
Answer
By active transport: energy from respiration drives the ions in against the concentration gradient through membrane carrier proteins. Root hair cells have many mitochondria and a large surface area.
Question
Describe how you would use water (mineral) culture to find out whether nitrate ions are needed for healthy plant growth.
Step-by-step solution
Step 1
Grow similar seedlings in test tubes of mineral solution: one tube with a complete solution (all minerals) and one with a solution that contains all minerals except nitrate.
Step 2
The complete solution acts as the control, for comparison.
Step 3
Keep all other conditions the same — light, temperature, type and size of seedling — so only the presence of nitrate differs (a fair test).
Step 4
After a few weeks, compare the growth. The seedling without nitrate should be stunted (and may have yellow older leaves), while the control grows normally — showing nitrate is needed for healthy growth.
Answer
Grow seedlings in a complete solution (control) and in a solution lacking only nitrate, keeping all else equal. The nitrate-free plant grows poorly (stunted), showing nitrate is needed.
Examiner tip
The control (complete solution) and changing only ONE mineral are the marking points. Cover the solution to exclude light/algae and aerate it for root respiration if asked.
Question
Seedlings were grown for three weeks in different solutions. Complete solution → tall, green, healthy. Solution lacking nitrate → short, thin, pale. Solution lacking magnesium → normal height but yellow leaves. Explain these results.
Step-by-step solution
Step 1
The complete solution has every mineral, so the plant grows normally — this is the control for comparison.
Step 2
Without nitrate, the plant cannot make enough amino acids and proteins, so it cannot make new cells properly — hence it is short and thin (stunted).
Step 3
Without magnesium, the plant cannot make enough chlorophyll, so the leaves are yellow (chlorosis); it still has enough protein to reach a normal height.
Step 4
Comparing each with the control shows that nitrate is needed mainly for growth (protein) and magnesium mainly for green colour (chlorophyll).
Answer
The control grows normally. The nitrate-free plant is stunted because it lacks protein for new cells; the magnesium-free plant is yellow because it lacks chlorophyll. Each result matches the mineral's known role.
Examiner tip
Always refer back to the control. Link each symptom to the mineral's function (nitrate → protein/growth; magnesium → chlorophyll/colour).
High-scoring sample answers for mineral requirements on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State why a plant needs magnesium ions. (1 mark)
Model answer
To make chlorophyll.
Why this scores
One mark for 'to make chlorophyll'.
State why a plant needs nitrate ions, and give one symptom of nitrate deficiency. (2 marks)
Model answer
Nitrate ions are needed to make amino acids (and proteins). A symptom of nitrate deficiency is stunted/poor growth (or yellowing of the older leaves).
Why this scores
One mark for the use (amino acids/proteins) and one for a correct deficiency symptom (stunted growth).
Describe the symptom of magnesium deficiency in a plant and explain why it occurs. (3 marks)
Model answer
A plant short of magnesium develops yellow leaves (chlorosis). This happens because magnesium is needed to make chlorophyll, so without it the plant cannot make enough chlorophyll. With less chlorophyll the leaves are yellow rather than green, and less light is absorbed, so photosynthesis and growth are reduced.
Why this scores
Three marks: yellow leaves/chlorosis; magnesium needed for chlorophyll; less chlorophyll → less photosynthesis/poor growth.
Explain how a root hair cell takes up nitrate ions from the soil. (4 marks)
Model answer
Nitrate ions are usually at a lower concentration in the soil water than inside the root hair cell, so they must be moved against their concentration gradient, which diffusion cannot do. They are taken in by active transport, in which protein carrier molecules in the cell membrane move the ions into the cell. This requires energy released by respiration, which is why root hair cells contain many mitochondria.
Why this scores
Four marks: ions lower in soil than in cell / against the gradient; active transport; protein carriers; energy from respiration (mitochondria).
Describe how you would investigate whether magnesium ions are needed for healthy plant growth, using water culture. (5 marks)
Model answer
Take similar seedlings of the same type and size. Grow one in a test tube of complete mineral solution (containing all the minerals) as a control, and grow an identical seedling in a solution that is the same except that it contains no magnesium. Keep all other conditions — light, temperature, and the volume and type of solution — the same so that only the magnesium differs. Leave them for several weeks, then compare the plants. If the plant grown without magnesium develops yellow leaves while the control stays green and healthy, this shows magnesium is needed for healthy growth (to make chlorophyll). Repeating with several plants makes the result more reliable.
Why this scores
Five marks: complete solution as a control; solution lacking only magnesium; controlled variables for a fair test; compare growth; valid conclusion (yellow leaves without magnesium). Repeats add reliability.
In an experiment, identical seedlings were grown for four weeks in three solutions. In the complete solution the plant was tall and green. In a solution lacking nitrate the plant was short and thin. In a solution lacking magnesium the plant was normal height but had yellow leaves. Explain these results, referring to the role of each mineral. (6 marks)
Model answer
The plant in the complete solution had every mineral it needed, so it grew tall and green — this is the control that the others are compared with. The plant in the nitrate-free solution was short and thin because nitrate ions are needed to make amino acids and proteins; without enough protein, the plant could not make new cells properly, so its growth was stunted. The plant in the magnesium-free solution grew to a normal height but had yellow leaves, because magnesium is needed to make chlorophyll; without it, too little chlorophyll was made, so the leaves were yellow (chlorosis), although there was still enough protein for the plant to grow tall. Together the results show that nitrate is needed mainly for growth (protein) and magnesium mainly for the green colour (chlorophyll), matching the known roles of the two minerals.
Why this scores
Up to 6 marks: identifies the control; nitrate-free → stunted because nitrate makes amino acids/proteins; magnesium-free → yellow because magnesium makes chlorophyll; clear comparison with the control; correct overall conclusion linking each symptom to the mineral's role.
Definitions to memorise and the exact keywords mark schemes credit for mineral requirements answers — sharpened from recent examiner reports for the 2026 0610 sitting.
A nitrogen-containing ion taken up by plant roots from the soil. Used to make amino acids and proteins.
A mineral ion taken up by plant roots. Used to make chlorophyll.
Yellowing of leaves caused by a lack of chlorophyll. A typical symptom of magnesium deficiency.
Movement of mineral ions into root hair cells against the concentration gradient, using energy from respiration.
The traps other students keep falling into on mineral requirements questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
Water enters by osmosis, so students assume everything does.
How to avoid it
Osmosis is for WATER only. Mineral IONS enter by ACTIVE TRANSPORT (when soil concentration is lower than the root, which is usual) or by diffusion (when soil is higher).
Why it happens
Air is about 78% nitrogen — students assume plants use it like CO₂.
How to avoid it
Plants CANNOT use nitrogen gas directly. They take in NITRATE IONS from the soil water through their roots.
Why it happens
Both make the plant look unhealthy.
How to avoid it
Emphasis differs: nitrate deficiency → mainly stunted growth (less protein); magnesium deficiency → mainly yellow leaves (less chlorophyll).
The things students keep getting wrong in this sub-topic, answered.