Cambridge IGCSE Biology 0610: Plant nutrition – Revision Notes

These notes condense topic 6, Plant nutrition, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028: section 6.1 (Photosynthesis) and section 6.2 (Leaf structure). Everything is Core unless it is marked Extended only (the balanced equation, 6.1.10, and limiting factors, 6.1.11), which is examined on Papers 2 and 4, not Papers 1 and 3. For full explanations and worked examples, use the plant nutrition study guide.

Also useful: the Cambridge IGCSE Biology hub, the 0610 printable checklist, the plant nutrition practice questions, and the Core and Extended diagnostics.

6.1 Photosynthesis: the essentials

Definition (6.1.1): photosynthesis is the process by which plants synthesise carbohydrates from raw materials using energy from light.

Item	What to write
Word equation (Core)	carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll
Balanced equation (Extended only)	6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Chlorophyll	Green pigment found in chloroplasts
Role of chlorophyll	Transfers energy from light into energy in chemicals, for making carbohydrates
Source of carbon dioxide	Air, entering the leaf through the stomata
Source of water	Soil, via root hairs and the xylem

Uses of the carbohydrates made (6.1.5)

Five uses only. A memory line: “Store, Structure, Respire, Transport, Pollinate.”

Use	Carbohydrate
Energy store	Starch
Building cell walls	Cellulose
Respiration to provide energy	Glucose
Transport in the phloem	Sucrose
Attracting insects for pollination	Nectar

Mineral ions (6.1.6)

Ion	Needed to make	If it is lacking
Nitrate	Amino acids (then proteins)	Poor growth
Magnesium	Chlorophyll	Yellow leaves, less photosynthesis

Investigations (6.1.7–6.1.9)

Method in steps: starch test on a leaf

1. Destarch the plant: dark for about two days.
2. Apply the treatment, then leave in light for several hours.
3. Boil the leaf in water (kills cells, lets iodine in).
4. Warm in ethanol in a hot water bath, flame off (removes chlorophyll).
5. Rinse in warm water (softens the leaf).
6. Add iodine solution on a white tile: blue-black = starch; orange-brown = no starch.

Testing the need for	Treatment	Control
Chlorophyll	Variegated leaf: white areas	Green areas of the same leaf
Light	Foil or black card over part of the leaf	Uncovered part of the same leaf
Carbon dioxide	Carbon dioxide absorber (e.g. soda lime) sealed with the leaf	Same set-up without absorber

Worked reminder: a destarched variegated leaf, half covered with foil, is tested after a day in light. Only the green, uncovered area turns blue-black. White areas (no chlorophyll) and covered areas (no light) stay orange-brown. The comparisons show that both chlorophyll and light are needed.

Method in steps: rate of photosynthesis with pondweed

1. Put pondweed in water with some sodium hydrogencarbonate (a carbon dioxide source).
2. Change one factor: lamp distance (light intensity), sodium hydrogencarbonate concentration (carbon dioxide) or water bath temperature.
3. Keep the other two constant. A lamp close to the tube also heats the water, so control the temperature.
4. Let the plant adjust for a few minutes at each setting.
5. Count bubbles per minute, or collect the gas and measure its volume (more accurate: bubbles vary in size).
6. Repeat and calculate a mean, leaving out anomalous results.

Worked reminder: 36 bubbles counted in 3 minutes → 36 ÷ 3 = 12 bubbles per minute.

Describing rate graphs (Core)

Factor increased	Effect on rate
Light intensity	Rises, then levels off
Carbon dioxide concentration	Rises, then levels off
Temperature	Rises to an optimum, then falls (enzymes denatured)

Hydrogencarbonate indicator (6.1.9)

Colour	Carbon dioxide level	When you see it with a water plant
Purple	Lower than air	Bright light: photosynthesis faster than respiration
Orange-red	Same as air	Start colour; dim light where the two rates balance; or the no-plant control
Yellow	Higher than air	Dark: respiration only

Key fact: plants respire all the time. Only the balance between photosynthesis and respiration changes.

Limiting factors (Extended only, 6.1.11)

Definition: the limiting factor is the factor in shortest supply, which stops the rate increasing. Raising it raises the rate; raising anything else does not.

Method in steps: naming the limiting factor from a graph

1. Find the part of the line you are asked about.
2. Rising part: the factor on the x-axis is limiting.
3. Flat part: the x-axis factor is not limiting. Look for another line on the graph that is higher.
4. The factor that differs between the two lines (carbon dioxide concentration or temperature) is the one limiting the lower line.
5. Quote the evidence: “at the same light intensity, the line at higher … is higher”.

Worked reminder: two lines on a light-intensity graph are both at 25 °C, one at 0.04% and one at 0.4% carbon dioxide. Both level off, but the 0.4% line levels off higher. On the flat part of the 0.04% line, the limiting factor is carbon dioxide concentration.

Growers raise temperature, light or carbon dioxide in glasshouses only where that factor is limiting.

6.2 Leaf structure

Shape: large surface area (absorbs more light, more surface for gas exchange) and thin (short diffusion distance for carbon dioxide; light reaches all cells).

Structure	Key adaptation
Cuticle	Waxy, transparent: cuts water loss, lets light through
Upper epidermis	Transparent, no chloroplasts: light passes through
Palisade mesophyll	Near top, many chloroplasts, tall closely packed cells: absorbs most light
Spongy mesophyll	Loosely packed cells with air spaces between
Air spaces	Carbon dioxide diffuses in to cells, oxygen out; large internal surface
Chloroplasts	Contain chlorophyll to absorb light
Xylem (in vascular bundle)	Brings water and mineral ions
Phloem (in vascular bundle)	Takes sucrose away
Lower epidermis	Most stomata here
Stomata and guard cells	Stomata let carbon dioxide in and oxygen out; guard cells open and close them

In a vascular bundle in the leaf, xylem is on the upper side, phloem on the lower side.

Must-know distinctions

• Photosynthesis vs respiration: photosynthesis happens only in light and only in cells with chloroplasts; respiration happens all the time in every living cell.
• Nitrate vs nitrogen: plants take up nitrate ions, not nitrogen gas.
• Palisade vs spongy mesophyll: palisade has the most chloroplasts; spongy has the air spaces.
• Starch vs sucrose: starch is stored; sucrose is transported.
• Treatment vs control: the control is identical except for the one factor being tested.
• Word vs balanced equation: the word equation is Core; the balanced formula equation is Extended only.

Quick self-test

1. Give the word equation for photosynthesis.
2. Where in a cell is chlorophyll found?
3. Name the carbohydrate a plant makes to build cell walls.
4. Why does a magnesium-deficient plant have yellow leaves?
5. Why is a plant kept in the dark for two days before a starch test?
6. Why is ethanol used in the starch test, and why must it be heated in a water bath?
7. A pondweed gives 54 bubbles in 3 minutes. Calculate the rate in bubbles per minute.
8. The rate rises from 12 to 18 bubbles per minute when the lamp is moved closer. Calculate the percentage increase.
9. What colour does hydrogencarbonate indicator turn around a water plant kept in the dark? Explain.
10. (Extended) Write the balanced chemical equation for photosynthesis.
11. (Extended) On the flat part of a rate against light intensity graph, name two factors that could be limiting.
12. Give two ways the spongy mesophyll layer helps photosynthesis.

Answers

1. carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll).
2. In the chloroplasts.
3. Cellulose.
4. Magnesium is needed to make chlorophyll; less chlorophyll means leaves look yellow and absorb less light.
5. To remove stored starch, so any starch found was made during the experiment.
6. Ethanol removes the chlorophyll so the iodine colour can be seen; it is flammable, so no naked flame.
7. 54 ÷ 3 = 18 bubbles per minute.
8. (18 − 12) ÷ 12 × 100 = 50%.
9. Yellow: there is no photosynthesis in the dark, but the plant still respires, so carbon dioxide concentration rises.
10. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
11. Carbon dioxide concentration and temperature.
12. Its cells contain chloroplasts; the air spaces between cells let carbon dioxide diffuse to the cells (and give a large surface for gas exchange).

Where marks are usually lost

• Writing “nitrogen” instead of nitrate ions, or linking magnesium to proteins.
• Stating that plants photosynthesise in the day and respire at night. They respire all the time.
• Describing an investigation with no control, or forgetting to destarch the plant.
• Saying boiling in ethanol “kills the leaf”. Boiling in water kills the cells; ethanol removes chlorophyll.
• Reversing the hydrogencarbonate colours: yellow means more carbon dioxide.
• (Extended) Writing “carbon dioxide” when the mark needs “carbon dioxide concentration”.
• (Extended) Naming light as limiting where the line is flat.
• Listing leaf features without saying how each one helps photosynthesis.
• Forgetting that a lamp close to the plant warms the water, so temperature was not controlled.

Official syllabus

Cambridge International, Cambridge IGCSE Biology (0610) syllabus for examination in 2026, 2027 and 2028 (Version 3, published August 2026), Cambridge University Press & Assessment. Topic 6, Plant nutrition: sections 6.1 and 6.2.