Cambridge IGCSE Biology 0610: Transport in plants – Study Guide

This study guide teaches topic 8, Transport in plants, from the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028. It covers sections 8.1 (Xylem and phloem), 8.2 (Water uptake), 8.3 (Transpiration) and 8.4 (Translocation). Core content can be tested on every paper. Supplement content is marked Extended only and is tested on Papers 2 and 4. Section 8.4 has no Core outcomes, so translocation is Extended only as a whole.

Useful links: the Cambridge IGCSE Biology hub, the printable 0610 checklist, the condensed transport in plants revision notes and the transport in plants practice questions. For a whole-course check, try the Core diagnostic or the Extended diagnostic.

What this topic covers

Syllabus ref.	What you must be able to do	Tier
8.1.1	State the functions of xylem and phloem	Core
8.1.2	Identify xylem and phloem in sections of roots, stems and leaves	Core
8.1.3	Relate the structure of xylem vessels to their function	Extended only
8.2.1–8.2.2	Identify root hair cells, state their functions and the effect of their large surface area	Core
8.2.3	Outline the pathway of water: root hair cells → root cortex cells → xylem → mesophyll cells	Core
8.2.4	Investigate the pathway of water using a stain	Core
8.3.1–8.3.2	Describe transpiration and where the water leaves	Core
8.3.3	Investigate and describe the effects of temperature and wind speed	Core
8.3.4	Relate water vapour loss to internal surface area and to stomata size and number	Extended only
8.3.5	Explain the transpiration pull	Extended only
8.3.6	Explain the effects of temperature, wind speed and humidity	Extended only
8.3.7	Explain how and why wilting occurs	Extended only
8.4.1–8.4.3	Translocation, sources and sinks	Extended only

Transpiration is named as an experimental context for the practical papers (Paper 5 and Paper 6), so expect to plan, read and process transpiration data.

8.1 Xylem and phloem

Functions (Core)

Tissue	Function
Xylem	Transport of water and mineral ions, and support
Phloem	Transport of sucrose and amino acids

Water only goes up in the xylem, from roots to leaves. Phloem can carry substances up or down, to wherever they are needed.

Where xylem and phloem are (Core)

You must identify them in sections of the root, stem and leaf of a non-woody dicotyledonous plant.

Organ	Arrangement
Root	Xylem in the centre, often shaped like a star or cross; phloem in small groups between the arms of the xylem
Stem	Vascular bundles in a ring near the outside; in each bundle, phloem faces outwards and xylem faces inwards
Leaf	In the midrib and veins; xylem on the upper side, phloem on the lower side

Worked example. A cross-section of a young sunflower stem shows eight vascular bundles arranged in a ring. Each bundle has a region of large, thick-walled cells nearer the centre and a region of small cells nearer the edge. Identify the xylem and the phloem.

• The large, thick-walled cells nearer the centre are the xylem: in a stem, xylem is on the inner side of each bundle.
• The small cells nearer the edge are the phloem: phloem is on the outer side.

Use position first, then cell appearance. Xylem vessels are wide and have thick walls.

Structure of xylem vessels (Extended only)

The syllabus limits you to three features. For each, give the feature and how it helps.

Feature	How it helps
Thick walls with lignin	Strengthen the vessel so it does not collapse, and support the plant
No cell contents	Nothing blocks the flow of water
Cells joined end to end with no cross walls	Form a long continuous tube from root to leaf

You do not need details of how lignin is laid down.

8.2 Water uptake

Root hair cells (Core)

A root hair cell is a cell on the outside of a young root with a long, thin extension that grows out between soil particles. Its functions are to take up water and mineral ions from the soil. The long extension gives a large surface area, which increases the uptake of water and mineral ions.

Water enters root hair cells by osmosis, and (Extended) root hairs take up some mineral ions by active transport. Both processes are covered in Movement into and out of cells.

The pathway of water (Core)

Learn this sequence exactly as the syllabus gives it:

root hair cells → root cortex cells → xylem → mesophyll cells

Water crosses the root cortex to the xylem in the centre of the root, travels up the xylem in the stem, and reaches the mesophyll cells of the leaf. From there it evaporates (see 8.3).

Investigating the pathway with a stain (Core)

1. Stand a freshly cut celery stalk (or a leafy stem with white flowers) in water coloured with a dye, such as methylene blue or food colouring.
2. Leave it in a warm, bright place for a few hours so that it transpires.
3. Cut a thin transverse section of the stalk with a scalpel, cutting away from your fingers.
4. Look at it with a hand lens.

Result: coloured spots appear in a ring near the outside of the stalk. These are the xylem in the vascular bundles. The veins of the leaves also become coloured, showing that water travels all the way to the leaves in the xylem.

8.3 Transpiration

What transpiration is (Core)

Transpiration is the loss of water vapour from leaves. Water evaporates from the surfaces of the mesophyll cells into the air spaces, and then diffuses out of the leaves through the stomata as water vapour.

Two separate processes happen: evaporation inside the leaf, then diffusion out through the stomata.

Internal surface area and stomata (Extended only)

• The interconnecting air spaces between mesophyll cells give a large internal surface area. More water can evaporate from this large wet surface, so more water vapour is lost.
• More stomata, or larger stomata, give more openings for water vapour to diffuse out, so the rate of water vapour loss is higher.

How water moves up the xylem (Extended only)

1. Water evaporates from mesophyll cells and is lost through the stomata.
2. This creates a transpiration pull, which draws water up the xylem.
3. The water is pulled up as a continuous column of water molecules.
4. The column holds together because of forces of attraction between water molecules.

The pull starts at the leaves. Water is not pushed up from the roots.

Factors affecting the rate of transpiration

Core (describe): as temperature increases, the rate of transpiration increases. As wind speed increases, the rate of transpiration increases.

Extended only (explain):

Factor	Effect on rate	Explanation
Temperature up	Increases	Water molecules have more kinetic energy, so they evaporate from mesophyll surfaces and diffuse out faster
Wind speed up	Increases	Wind carries water vapour away from around the leaf, keeping a steep concentration gradient between the air spaces and the outside air
Humidity up	Decreases	There is more water vapour in the outside air, so the concentration gradient is less steep and diffusion out is slower

Investigating transpiration

Two common methods:

• Mass loss. Water a potted plant, seal the pot and soil inside a plastic bag so water can only be lost from the plant, and weigh it at intervals. The fall in mass is the water lost.
• Potometer. A leafy shoot is fitted, under water, into a tube full of water with an air bubble in a capillary tube. The distance the bubble moves in a set time shows the rate of water uptake. Joints are sealed with petroleum jelly so they are airtight. Uptake is close to, but not exactly the same as, water loss, because a little of the water is used by the plant’s cells.

Worked example (mass loss). Two similar potted plants, prepared as above, are left for 4 hours: one in still air, one in front of a fan.

	Start mass / g	End mass / g	Loss / g	Rate / g per hour
Still air	312.4	309.2	3.2	0.8
Fan	311.8	305.4	6.4	1.6

Working for the fan: 311.8 − 305.4 = 6.4 g; 6.4 ÷ 4 = 1.6 g per hour. The plant in moving air lost water twice as fast (1.6 ÷ 0.8 = 2). Conclusion: increasing wind speed increases the rate of transpiration. To make the comparison fair, both plants need the same temperature, humidity and light, and ideally a similar leaf area.

Worked example (potometer). The air bubble moves 45 mm in 3 minutes. Rate = 45 ÷ 3 = 15 mm per minute. If the capillary tube has a cross-sectional area of 0.5 mm², the volume of water taken up is 15 × 0.5 = 7.5 mm³ per minute. Reset the bubble and repeat to get a mean.

Wilting (Extended only)

Why it happens: the plant loses water by transpiration faster than it takes up water from the soil. This happens on hot, dry or windy days, or when the soil is dry.

How it happens:

1. Cells lose water by osmosis and are no longer turgid.
2. The turgor pressure pushing the cell membrane and contents outwards on the cell wall falls.
3. The cells become flaccid and no longer support the leaves and non-woody stems.
4. The leaves and stems droop: the plant wilts.

This builds on the terms turgid, turgor pressure and flaccid from section 3.2 of the syllabus.

8.4 Translocation (Extended only)

Translocation is the movement of sucrose and amino acids in phloem from sources to sinks.

• A source is a part of the plant that releases sucrose or amino acids. Example: a mature leaf that is photosynthesising.
• A sink is a part of the plant that uses or stores sucrose or amino acids. Examples: growing roots and shoot tips, developing fruits and seeds, storage organs being filled.

Source at one time, sink at another

Some parts change role, depending on what they are doing.

Worked example. Explain why a leaf can act as a sink and later as a source.

• When the leaf is young and still growing, it cannot yet make enough sugar for its own growth, so it receives and uses sucrose and amino acids from the phloem. It is a sink.
• Once it is fully grown and photosynthesising, it makes more sugar than it uses, so it releases sucrose into the phloem. It is now a source.

A storage organ works the same way. It is a sink while it is filling with starch, and a source when the starch is broken down to sucrose and sent to new growth. The practice set has a question on this for a potato tuber.

Common errors

• Swapping the jobs of xylem and phloem, or writing a blend of the two words.
• Saying phloem carries glucose. It carries sucrose and amino acids.
• Placing the xylem on the outside of the stem bundles, or on the lower side of a leaf vein.
• Saying root hairs “absorb nutrients” instead of water and mineral ions.
• Writing that water “evaporates through the stomata”. It evaporates inside the leaf and diffuses out through the stomata.
• (Extended) Saying the wind “blows water off the leaf” instead of linking wind to the concentration gradient.
• (Extended) Explaining wilting as “the plant runs out of water” with no mention of turgor.
• (Extended) Defining a sink only as a store. A sink uses or stores.

Where next

• Recall drill and a quick self-test: transport in plants revision notes
• Exam-style questions with marked answers: transport in plants practice
• Why the leaf needs water and where sucrose comes from: Plant nutrition study guide

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 8, Transport in plants: sections 8.1 to 8.4.