Cambridge IGCSE Biology 0610: Plant nutrition – Study Guide

This study guide teaches topic 6, Plant nutrition, from the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028. It covers section 6.1 (Photosynthesis) and section 6.2 (Leaf structure). Most of the topic is Core, so it can appear on every paper. The two Supplement outcomes (the balanced equation and limiting factors) are marked Extended only: they are tested on Papers 2 and 4, not on Papers 1 and 3.

Useful links: the Cambridge IGCSE Biology hub, the printable 0610 checklist, the condensed plant nutrition revision notes and the plant nutrition practice questions. To see where you stand across the whole course, try the Core diagnostic or the Extended diagnostic.

What this topic covers

Syllabus ref.	What you must be able to do	Tier
6.1.1	Describe photosynthesis as making carbohydrates from raw materials using light energy	Core
6.1.2	State the word equation	Core
6.1.3–6.1.4	State where chlorophyll is found and what it does	Core
6.1.5	Outline how the carbohydrates made are used and stored	Core
6.1.6	Explain why plants need nitrate ions and magnesium ions	Core
6.1.7	Investigate the need for chlorophyll, light and carbon dioxide, with controls	Core
6.1.8	Investigate and describe the effects of light intensity, carbon dioxide concentration and temperature on rate	Core
6.1.9	Investigate gas exchange of an aquatic plant in light and dark with hydrogencarbonate indicator	Core
6.1.10	State the balanced chemical equation	Extended only
6.1.11	Identify and explain limiting factors	Extended only
6.2.1–6.2.3	Leaf shape, the named leaf tissues, and how each adapts the leaf for photosynthesis	Core

Photosynthesis and hydrogencarbonate indicator are named experimental contexts for Papers 5 and 6, so expect method and data questions.

6.1 Photosynthesis

What photosynthesis is

Photosynthesis is the process by which plants synthesise carbohydrates from raw materials using energy from light. The raw materials are carbon dioxide (taken in from the air through the stomata) and water (taken up by the roots and carried to the leaves in the xylem).

Word equation (Core):

carbon dioxide + water  →  glucose + oxygen
      (in the presence of light and chlorophyll)

Balanced chemical equation (Extended only):

6CO₂ + 6H₂O  →  C₆H₁₂O₆ + 6O₂

Check the balancing by counting atoms: 6 carbon, 12 hydrogen and 18 oxygen on each side.

Chlorophyll

• Chlorophyll is a green pigment found in chloroplasts.
• Chlorophyll transfers energy from light into energy in chemicals, which is used to make carbohydrates.

What happens to the glucose

The syllabus limits you to five uses:

Product	Use
Starch	Energy store
Cellulose	Builds cell walls
Glucose	Used in respiration to provide energy
Sucrose	Transported around the plant in the phloem
Nectar	Sugary liquid that attracts insects for pollination

The sucrose link leads on to translocation in Transport in plants.

Mineral ions

Plants also need mineral ions, absorbed from the soil by the root hairs.

• Nitrate ions are needed to make amino acids, which make proteins. Without nitrate, growth is poor.
• Magnesium ions are needed to make chlorophyll. Without magnesium, leaves turn yellow and absorb less light.

Write “nitrate ions”, not “nitrogen”.

Investigating the need for chlorophyll, light and carbon dioxide

All three investigations use the starch test on a leaf. Starch is present only if the leaf has been photosynthesising.

Step 1 – destarch the plant. Keep it in the dark for about two days so it uses up its stored starch. Any starch found later was then made during the experiment.

Step 2 – set up the treatment (see the table below) and leave the plant in bright light for several hours.

Step 3 – test a leaf for starch:

1. Boil the leaf in water for about a minute. This kills the cells and makes them easier for iodine to get into.
2. Put the leaf in a tube of ethanol and stand the tube in hot water. The ethanol removes the chlorophyll so the colour change can be seen. Turn off any flame first: ethanol is flammable.
3. Dip the leaf in hot water to soften it (ethanol makes it brittle).
4. Spread the leaf on a white tile and add iodine solution. Blue-black means starch is present; orange-brown means no starch.

Factor tested	Treatment	Control
Chlorophyll	Use a variegated leaf (green and white areas)	The green areas of the same leaf
Light	Cover part of a leaf with foil or black card on both sides	The uncovered part of the same leaf
Carbon dioxide	Enclose a leaf or plant with a chemical that absorbs carbon dioxide, such as soda lime	An identical set-up with no absorber

Worked example. A destarched variegated leaf has a strip of foil across its middle. After six hours in light it is tested with iodine. Predict the results for (a) a green uncovered area, (b) a white uncovered area and (c) a green area under the foil.

• (a) Blue-black. It had chlorophyll and light, so it made glucose and stored it as starch.
• (b) Orange-brown. There was no chlorophyll, so no light energy was transferred.
• (c) Orange-brown. There was chlorophyll but no light.

Comparing (a) with (b) tests chlorophyll; comparing (a) with (c) tests light.

Investigating the rate of photosynthesis

Pondweed gives off oxygen bubbles as it photosynthesises. Count bubbles per minute, or collect the gas and measure its volume.

Factor you vary	How you vary it	What you keep constant
Light intensity	Change the distance of the lamp from the plant	Temperature, carbon dioxide concentration, same plant
Carbon dioxide concentration	Add different concentrations of sodium hydrogencarbonate to the water	Light intensity, temperature
Temperature	Stand the tube in a water bath at different temperatures	Light intensity, carbon dioxide concentration

A lamp close to the plant also warms the water, so control temperature with a water bath when light is the variable.

Describing the results (Core):

• As light intensity increases, the rate increases, then levels off.
• As carbon dioxide concentration increases, the rate increases, then levels off.
• As temperature increases, the rate increases up to an optimum, then falls sharply. Photosynthesis is controlled by enzymes, which are denatured at high temperatures.

Worked example (data processing). A student counts bubbles from pondweed for one minute, three times, at each lamp distance.

Distance / cm	Count 1	Count 2	Count 3	Mean / bubbles per min
10	42	45	39	42.0
20	30	28	32	30.0
30	17	21	19	19.0
40	11	9	10	10.0

Working for 10 cm: (42 + 45 + 39) ÷ 3 = 126 ÷ 3 = 42.0. Conclusion: the closer the lamp, the higher the light intensity and the faster the rate. If one repeat were far out of line (say 31 instead of 19 at 30 cm), treat it as anomalous and average the other two: (17 + 21) ÷ 2 = 19.0.

Bubbles differ in size, so collecting the gas is more accurate. If 2.4 cm³ of gas is collected in 5 minutes, the rate is 2.4 ÷ 5 = 0.48 cm³ per minute.

Gas exchange in light and dark: hydrogencarbonate indicator

Hydrogencarbonate indicator changes colour with the carbon dioxide concentration of the water:

Carbon dioxide concentration	Colour
Higher than normal air	Yellow
Same as normal air	Orange-red
Lower than normal air	Purple

Plants respire all the time, in light and dark. In bright light, photosynthesis is faster than respiration, so the plant removes carbon dioxide overall and the indicator turns purple. In the dark there is no photosynthesis, only respiration, so carbon dioxide builds up and the indicator turns yellow. In dim light the two rates can balance, so the colour does not change. A tube with no plant is the control. The practice set has a full three-tube question on this.

Limiting factors (Extended only)

A limiting factor is the factor in shortest supply, which stops the rate of photosynthesis rising any higher. Increasing that factor increases the rate; increasing any other factor does not.

To read a graph of rate against light intensity:

• On the rising part, light intensity is the limiting factor (more light gives a faster rate).
• On the flat part, light intensity is no longer limiting. Something else is: carbon dioxide concentration or temperature.

Worked example. A graph shows rate against light intensity for four conditions: 0.04% and 0.4% carbon dioxide, each at 15 °C and 25 °C. The line for 0.4% CO₂ at 25 °C levels off highest. The line for 0.4% CO₂ at 15 °C levels off lower. Identify the limiting factor on the flat part of the 0.4% CO₂, 15 °C line.

• Not light: the line is flat, so more light makes no difference.
• At the same 0.4% CO₂, the 25 °C line is higher.
• So temperature is limiting.

Name the factor and quote the evidence. Growers add heating, lighting or carbon dioxide to glasshouses only where that factor is limiting; adding a non-limiting factor costs money without raising yield.

6.2 Leaf structure

Leaf shape

Most leaves have a large surface area and are thin.

• Large surface area: more light is absorbed, and there is more surface for carbon dioxide to enter.
• Thin: carbon dioxide has only a short distance to diffuse to the mesophyll cells, and light reaches all the cells.

Tissues of a dicotyledonous leaf

Identify each structure in a diagram or image of a leaf section, and explain how it helps photosynthesis. From the top down:

Structure	How it adapts the leaf for photosynthesis
Cuticle	Waxy, transparent layer that reduces water loss but lets light through
Upper epidermis	Thin and transparent, with no chloroplasts, so light passes to the mesophyll
Palisade mesophyll	Column-shaped cells near the upper surface, packed with chloroplasts, so they absorb most of the light
Chloroplasts	Contain chlorophyll, which absorbs light; the site of photosynthesis
Spongy mesophyll	Loosely arranged cells with some chloroplasts, surrounded by air spaces
Air spaces	Let carbon dioxide diffuse to the mesophyll cells and oxygen diffuse away; give a large internal surface for gas exchange
Vascular bundle	Contains xylem and phloem
Xylem	Brings water (a raw material) and mineral ions to the leaf
Phloem	Carries sucrose made in the leaf away to other parts of the plant
Lower epidermis	Contains most of the stomata
Stomata and guard cells	Stomata let carbon dioxide in and oxygen out; guard cells open and close each stoma

In a section, the vascular bundle usually sits in the midrib or a vein. Xylem is on the upper side of the bundle and phloem on the lower side.

Worked example. Explain how the palisade mesophyll is adapted for photosynthesis. [3]

• The cells are near the upper surface, so they receive the most light. [1]
• They contain many chloroplasts, containing chlorophyll to absorb light. [1]
• They are tall and closely packed, so many cells fit under the surface to absorb light. [1]

Each point links a feature to photosynthesis.

Common errors

• Saying plants photosynthesise instead of respiring in the light. They do both; they respire all the time.
• Saying chlorophyll “makes energy” or “absorbs sunlight to make glucose” with no idea of energy transfer.
• Forgetting to destarch, or giving no control, in the starch-test investigations.
• Heating ethanol directly over a flame.
• Getting the hydrogencarbonate colours the wrong way round: more carbon dioxide is yellow, less is purple.
• (Extended) Naming light as limiting on the flat part of a light-intensity graph.
• Mixing up the palisade (most chloroplasts, near the top) and spongy (air spaces) mesophyll.

Where next

• Recall drill and a quick self-test: plant nutrition revision notes
• Exam-style questions with marked answers: plant nutrition practice
• How water reaches the leaf and sucrose leaves it: Transport in plants study guide
• Diffusion and osmosis background: Movement into and out of cells

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.