Cambridge IGCSE Biology 0610: Transport in plants – Revision Notes

These notes condense topic 8, Transport in plants, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028: sections 8.1 (Xylem and phloem), 8.2 (Water uptake), 8.3 (Transpiration) and 8.4 (Translocation). Anything marked Extended only is Supplement content, examined on Papers 2 and 4, not Papers 1 and 3; all of 8.4 is Extended only. For full explanations and worked examples, use the transport in plants study guide.

Also useful: the Cambridge IGCSE Biology hub, the 0610 printable checklist, the transport in plants practice questions, and the Core and Extended diagnostics.

Key definitions

Term	Definition to learn
Xylem	Transports water and mineral ions, and gives support
Phloem	Transports sucrose and amino acids
Transpiration	Loss of water vapour from leaves
Transpiration pull (Extended only)	The pull, caused by water loss from leaves, that draws a column of water up the xylem
Translocation (Extended only)	Movement of sucrose and amino acids in phloem from sources to sinks
Source (Extended only)	Part of a plant that releases sucrose or amino acids
Sink (Extended only)	Part of a plant that uses or stores sucrose or amino acids

8.1 Xylem and phloem

Positions in a non-woody dicotyledonous plant (Core)

Organ	Xylem	Phloem
Root	Centre, star or cross shape	Between the arms of the xylem
Stem	Inner side of each bundle; bundles in a ring near the edge	Outer side of each bundle
Leaf (vein or midrib)	Upper side of the bundle	Lower side of the bundle

Memory hook: in the stem, phloem faces outwards, xylem faces inwards; in the root, xylem is in the middle.

Worked reminder: a section shows one central star-shaped tissue with small groups of cells between its arms. It has no ring of bundles, so it is a root: the star is xylem and the small groups are phloem. A ring of separate bundles would mean a stem.

Xylem vessel structure (Extended only)

Feature	Link to function
Thick walls with lignin	Strength and support; vessel does not collapse
No cell contents	Unobstructed flow of water
Cells end to end, no cross walls	Long continuous tube

8.2 Water uptake

• Root hair cells take up water and mineral ions.
• Their large surface area increases the uptake of water and mineral ions.
• Water enters by osmosis. (Extended only: mineral ions can be taken up by active transport.)

Method in steps: pathway of water (Core)

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

Then water evaporates from the mesophyll cells into the air spaces.

Method in steps: staining investigation (Core)

1. Stand a cut celery stalk in water with a dye such as methylene blue.
2. Leave it for a few hours in warm, bright conditions.
3. Cut a thin transverse section (scalpel, cut away from you).
4. Observe with a hand lens: dye in a ring of spots = xylem in the vascular bundles. Leaf veins also stained.

8.3 Transpiration

Where the water leaves (Core)

1. Water evaporates from the surfaces of mesophyll cells into the air spaces.
2. Water vapour diffuses out of the leaf through the stomata.

Structure and water loss (Extended only)

• Interconnecting air spaces give a large internal surface area → more evaporation → more water vapour lost.
• More or larger stomata → more diffusion out → more water vapour lost.

Method in steps: transpiration pull (Extended only)

1. Water vapour is lost from the leaves through the stomata.
2. This creates a transpiration pull.
3. The pull draws a continuous column of water up the xylem.
4. The column stays together because of forces of attraction between water molecules.

Factors (Core: describe; Extended only: explain)

Factor increased	Rate	Explanation (Extended only)
Temperature	Up	More kinetic energy: faster evaporation and diffusion
Wind speed	Up	Water vapour carried away; concentration gradient kept steep
Humidity	Down	More water vapour outside; smaller concentration gradient

Humidity is Extended only; temperature and wind speed are Core.

Measuring rate

Method	What you measure	Note
Mass loss	Fall in mass of a potted plant, pot sealed in a bag	Measures water lost
Potometer	Distance an air bubble moves in a set time	Measures water taken up, which is close to water lost; seal joints with petroleum jelly

Worked reminders:

• A plant loses 4.8 g in 6 hours → 4.8 ÷ 6 = 0.8 g per hour.
• A potometer bubble moves 30 mm in 5 minutes → 30 ÷ 5 = 6 mm per minute.

Worked reminder (fair test): to compare two wind speeds by mass loss, keep the same kind of plant with a similar number of leaves, the same temperature, humidity and light, and the same time. Seal the pot in a bag each time. Repeat and take a mean.

Wilting (Extended only)

• Why: water lost by transpiration faster than it is taken up (hot, dry, windy weather or dry soil).
• How: cells lose water by osmosis → turgor pressure falls → cells become flaccid → cells no longer support leaves and stems → plant droops.

Worked reminder: a lettuce wilts on a hot, windy afternoon although the soil is moist. Why? High temperature and wind speed raise the rate of transpiration, so water is lost from the leaves faster than the roots can take it up.

8.4 Translocation (Extended only)

Part of plant	Usually	Why
Mature photosynthesising leaf	Source	Makes and releases sucrose
Growing root or shoot tip	Sink	Uses sucrose for growth and respiration
Developing fruit or seed	Sink	Uses and stores sucrose
Storage organ being filled	Sink	Stores sucrose as starch
Storage organ at the start of new growth	Source	Starch broken down; sucrose released
Young growing leaf	Sink	Uses more sucrose than it makes

A part can be a source at one time and a sink at another because its role depends on whether it is releasing or using or storing sucrose and amino acids at that moment.

Links to other topics

• Water reaching the mesophyll cells supplies a raw material for photosynthesis, and the sucrose moved in translocation is made there: see the plant nutrition revision notes.
• Osmosis, turgor and active transport are in Movement into and out of cells.

Must-know distinctions

• Xylem vs phloem: xylem carries water and mineral ions (and supports); phloem carries sucrose and amino acids.
• Evaporation vs diffusion: water evaporates inside the leaf; water vapour diffuses out through the stomata.
• Water uptake vs water loss: a potometer measures uptake; mass loss measures loss.
• Transpiration vs translocation: transpiration is water vapour loss; translocation is movement of sucrose and amino acids in phloem.
• Source vs sink: a source releases; a sink uses or stores.
• Turgid vs flaccid: turgid cells are firm and support the plant; flaccid cells have lost water and pressure.

Quick self-test

1. State two functions of xylem.
2. Name the two substances transported in phloem.
3. Where is the xylem in a root?
4. Give the pathway of water from root hair cell to leaf.
5. How does the shape of a root hair cell help its function?
6. A celery stalk stands in dyed water. Which tissue becomes coloured?
7. Where exactly does water evaporate in a leaf?
8. A potted plant falls from 240.0 g to 234.0 g. Calculate the percentage loss in mass.
9. State the effect of increasing wind speed on the rate of transpiration.
10. (Extended) Explain why transpiration is slower on a humid day.
11. (Extended) What holds the column of water together in the xylem?
12. (Extended) A developing apple receives sucrose. Is it a source or a sink? Explain.

Answers

1. Transport of water and mineral ions; support.
2. Sucrose and amino acids.
3. In the centre (star or cross shape), with phloem between its arms.
4. Root hair cells → root cortex cells → xylem → mesophyll cells.
5. The long extension gives a large surface area for uptake of water and mineral ions.
6. The xylem.
7. From the surfaces of the mesophyll cells into the air spaces.
8. (240.0 − 234.0) ÷ 240.0 × 100 = 2.5%.
9. The rate of transpiration increases.
10. More water vapour in the air outside the leaf, so a smaller concentration gradient, so water vapour diffuses out through the stomata more slowly.
11. Forces of attraction between water molecules.
12. A sink: it uses or stores the sucrose it receives.

Where marks are usually lost

• Writing “xylem transports food” or “phloem transports water”.
• Saying phloem carries glucose instead of sucrose.
• Putting the phloem on the inside of the stem vascular bundles.
• Writing “root hairs absorb nutrients” or “minerals” instead of water and mineral ions.
• Leaving out the root cortex cells in the pathway of water.
• Saying water evaporates “from the stomata”; the evaporation is inside the leaf.
• (Extended) Describing water as pushed up from the roots, not pulled by transpiration.
• (Extended) Saying wind “dries the leaf” with no concentration gradient.
• (Extended) Explaining wilting without the words turgor pressure and flaccid.
• (Extended) Defining a sink as only a store, forgetting “uses”.

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.