GCSE Biology Plant Tissues & Transport Revision

Overview

What you’ll learn

Name every tissue in a leaf section and match each to its function.
Explain how root hair cells, xylem and phloem are each adapted to their transport jobs.
Describe the transpiration stream and translocation in one sentence each.
Explain how guard cells open and close stomata — and why plants need the trade-off.
Predict how temperature, humidity, air movement and light each change transpiration rate.
Calculate water-uptake rates and mean stomata counts from raw data.

Specification checklist (AQA 8461 · Edexcel 1BI0 · OCR Gateway J247)

Statements are paraphrased from the shared DfE subject content and grouped by tier. Foundation content is studied by every student; Higher statements are examined on Higher-tier papers only, and statements badged Biology only are examined in separate (triple) Biology, not Combined Science. QuizQuip is not affiliated with AQA, Pearson Edexcel or OCR.

Foundation — every student

6.1Explain how the structures of plant tissues are related to their functions, including epidermal tissues, palisade mesophyll, spongy mesophyll, xylem and phloem, and meristem tissue at the growing tips of shoots and roots.
6.2Describe the leaf as a plant organ, limited to the epidermis, palisade and spongy mesophyll, xylem and phloem, and guard cells surrounding stomata.
6.3Explain how the structures of root hair cells are adapted to their functions — a large surface area, thin walls and many mitochondria for absorbing water and mineral ions.
6.4Explain how the structures of xylem and phloem are adapted to their functions: hollow lignified xylem tubes carrying water and mineral ions upwards in the transpiration stream, and elongated phloem cells with sieve plates carrying dissolved sugars up and down in translocation.
6.5Describe the processes of transpiration and translocation, including the structure and function of stomata and guard cells.
6.6Explain the effects of changing temperature, humidity, air movement and light intensity on the rate of transpiration.
6.7Measure and calculate the rate of transpiration by water uptake, using simple compound measures, and process stomata-count data to find arithmetic means and understand sampling.
6.8Translate information between graphical and numerical form, and extract and interpret information from graphs, charts and tables about transpiration rates.

Key points

1Leaf layers: waxy cuticle → upper epidermis → palisade mesophyll → spongy mesophyll → lower epidermis (stomata + guard cells), with xylem and phloem in the veins.
2Palisade mesophyll = most chloroplasts, near the top, for photosynthesis; spongy mesophyll = air spaces for gas diffusion.
3Xylem: dead, hollow, lignified tubes — water and mineral ions up only (the transpiration stream).
4Phloem: living elongated cells with sieve plates — dissolved food (sugars) both up and down (translocation).
5Root hair cells: huge surface area, thin walls, many mitochondria — water in by osmosis, ions in by active transport.
6Stomata are pores in the lower epidermis; guard cells open them (swollen with water) and close them (flaccid) to balance gas exchange against water loss.
7Transpiration is faster when it is hotter, drier, windier and brighter — slower in cool, humid, still, dark conditions.
8Rate maths: water uptake ÷ time (g/h or cm³/h) and mean stomata counts from sampled fields of view.

Notes · 1 of 3

Inside the leaf

A factory stacked floor by floor, each tissue with one job.

Leaf tissues and their functions
Tissue	Job	Structure that does it
Waxy cuticle (on epidermis)	Reduces water loss	Waxy, waterproof layer on the outside
Upper epidermis	Lets light through; protects	Transparent cells with few chloroplasts
Palisade mesophyll	Photosynthesis	Tall cells packed with chloroplasts, near the top where light is strongest
Spongy mesophyll	Gas exchange	Loose cells with air spaces so carbon dioxide and oxygen diffuse to every cell
Xylem (in veins)	Carries water and mineral ions up	Hollow lignified tubes
Phloem (in veins)	Carries dissolved sugars around	Elongated living cells with sieve plates
Lower epidermis + guard cells	Controls water loss and gas entry	Stomata — pores whose size guard cells adjust
Meristem (shoot and root tips)	Growth	Undifferentiated cells that keep dividing

The leaf is a plant organ — tissues working together — and the whole root-to-leaf arrangement is a plant organ system for transport. Notice the design logic: the water supply (xylem) runs right beside the sugar factory (palisade cells), so raw material and product barely have to travel.

Notes · 2 of 3

Root hair cells, xylem and phloem

One collector, one lifter, one distributor.

Root hair cells jut into the soil like microscopic fingers. Their large surface area speeds absorption, their thin walls shorten the path, and their many mitochondria power the active transport of mineral ions in from very dilute soil solutions (chapter 2’s story, seen from the plant’s side). Water enters by osmosis and is drawn up through the root into the xylem.

The two transport tissues compared
Feature	Xylem	Phloem
Carries	Water and dissolved mineral ions	Dissolved sugars (food)
Direction	Upwards only — roots to leaves (transpiration stream)	Both directions — source to sink (translocation)
Cells	Dead, hollow tubes with no end walls	Living elongated cells with end walls bearing sieve plates
Strengthening	Walls stiffened with lignin, resisting tension	Supported by companion cells
Job in one word	Lift	Deliver

Notes · 3 of 3

Transpiration and stomata

The price of breathing: water evaporates out of the pores.

Transpiration is the loss of water vapour from the leaves. Water evaporates from the moist surfaces of the spongy mesophyll, diffuses through the stomata — tiny pores mostly in the lower epidermis — and drifts away. Evaporation pulls a column of water up through the xylem from the roots: the transpiration stream, which happens to deliver mineral ions at the same time. Each stoma is flanked by two guard cells: when they are swollen with water (turgid) they bow apart and the pore opens; when they lose water (flaccid) the pore closes. Open stomata let carbon dioxide in for photosynthesis but let water escape — the plant’s permanent trade-off, which is why stomata close at night and in drought.

Factors affecting transpiration rate
Factor	Increase it	Why
Temperature	Higher temperature → faster transpiration	Water molecules evaporate and diffuse faster in the warm
Humidity	Lower humidity → faster transpiration	Dry air holds more vapour, so the concentration gradient out of the leaf is steeper
Air movement (wind)	More air movement → faster transpiration	Moving air sweeps vapour away, keeping the gradient steep
Light intensity	Brighter light → faster transpiration	Stomata open in the light for photosynthesis, so more pores are available

Exam tips

Worked example — transpiration rate from water uptake. A leafy shoot takes up 6.5 cm³ of water in 30 minutes. Rate = 6.5 ÷ 0.5 h = 13 cm³ per hour. If a fan is switched on and uptake rises to 9 cm³ in 30 minutes, the new rate is 18 cm³ per hour — moving air increased the rate by 5 cm³ per hour, because it swept water vapour away from the stomata and steepened the diffusion gradient.
Worked example — mean stomata count. A student counts stomata in five sampled fields of view on a leaf peel: 12, 15, 11, 14 and 13. Mean = (12 + 15 + 11 + 14 + 13) ÷ 5 = 65 ÷ 5 = 13 stomata per field. Sampling several fields and taking the mean smooths out local variation — and if each field is 0.2 mm², the density is 13 ÷ 0.2 = 65 stomata per mm².
Worked example — water loss from a balance reading. A detached leaf on a balance loses 2.7 g of water in 45 minutes. Rate = 2.7 ÷ 45 = 0.06 g per minute, which is 0.06 × 60 = 3.6 g per hour. Because almost all the water a shoot absorbs leaves as vapour, a mass-loss or uptake reading estimates the transpiration rate — move the leaf into a draught and the rate climbs for the same reason a potometer reading does.

Revise

Key terms

The words examiners expect you to use precisely.

Palisade mesophyll: Tissue of tall chloroplast-packed cells near the leaf’s upper surface; the main site of photosynthesis.
Spongy mesophyll: Loose leaf tissue with air spaces for gas exchange.
Epidermis: The protective outer layer of the leaf; its lower side carries the stomata.
Guard cells: The paired cells that open and close a stoma by swelling or losing water.
Stoma (plural stomata): A pore in the leaf’s lower epidermis through which gases and water vapour diffuse.
Xylem: Dead, hollow, lignified tubes carrying water and mineral ions upwards from the roots.

Show 6 more key terms

Phloem: Living elongated cells with sieve plates carrying dissolved sugars around the plant.
Transpiration: The loss of water vapour from leaves through the stomata.
Transpiration stream: The upward flow of water from roots to leaves pulled by evaporation.
Translocation: The transport of dissolved sugars through the phloem from source to sink.
Meristem: Undifferentiated tissue at shoot and root tips where cells keep dividing.
Potometer-style apparatus: Equipment measuring water uptake by a shoot, used to estimate transpiration rate.

Revise

Common mistakes

Where students most often lose marks in this chapter — and what to do instead.

Mistake: Saying xylem carries sugars.
Sugars travel in the phloem.
Instead: Xylem: water and mineral ions up. Phloem: dissolved sugars both directions.
Mistake: Saying phloem cells are dead and hollow.
That is xylem.
Instead: Phloem cells are living, with sieve plates between them.

Show 10 more mistakes

Mistake: Saying transpiration happens through the waxy cuticle.
Almost all water vapour leaves through the stomata.
Instead: The cuticle reduces water loss; stomata are the exit route.
Mistake: Placing most stomata on the upper epidermis.
They sit mostly on the lower surface, away from direct sun.
Instead: Stomata are concentrated in the lower epidermis to limit water loss.
Mistake: Saying guard cells close stomata by filling with water.
It is the reverse.
Instead: Turgid (swollen) guard cells open the pore; flaccid guard cells close it.
Mistake: Saying humidity increases transpiration.
Humid air is already nearly full of vapour.
Instead: Higher humidity means a shallower gradient, so transpiration slows.
Mistake: Saying light has no effect on transpiration.
Light opens the stomata.
Instead: Brighter light opens more stomata for photosynthesis, so water loss rises.
Mistake: Forgetting mineral ions travel in xylem with the water.
The transpiration stream is the delivery route for ions too.
Instead: Xylem carries water and dissolved mineral ions upwards.
Mistake: Saying root hair cells absorb ions by osmosis.
Ions are taken up against the gradient.
Instead: Water enters by osmosis; mineral ions enter by active transport using respiration energy.
Mistake: Calculating rate as time ÷ volume.
Inverted.
Instead: Rate = volume (or mass) of water uptake ÷ time.
Mistake: Quoting one field of view as the stomata count.
A single field is unrepresentative.
Instead: Sample several fields and report the arithmetic mean.
Mistake: Calling the leaf a tissue.
It contains many tissues.
Instead: The leaf is an organ; epidermis, mesophyll, xylem and phloem are its tissues.

Check yourself

Quick quiz

30 questions with instant explanations. About 5 minutes.

Question 1 of 3

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Recall plant transport tissues

Which tissue carries water upwards through a plant?

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Practise

Topical questions

18 exam-style questions with model answers and mark schemes.

A set of structured and calculation questions matched to this chapter, in three tiers, each with a model answer, mark scheme and examiner tip. Higher-tier and Biology-only questions are tagged.

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Exam practice

Practice paper

A 30-mark paper in the style of a GCSE paper, with a separate mark scheme. Give yourself 40 min.

Question paper

Chapter 6 Practice Paper

30 marks · 40 min · 5 pages

10 multiple-choice questions and structured questions with answer lines. Chapter 6: leaf tissues and the leaf as an organ, root hair cells, xylem and phloem adaptations, transpiration and translocation, stomata and guard cells, transpiration-rate factors, and rate and mean calculations.

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Mark scheme

PRO

Chapter 6 Practice Paper — mark scheme

Answers · Marking points · 3 pages

Model answers with a mark for each creditworthy point — for marking at home or in class.

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How is this chapter examined?

Paper 1

1 h 45 · 100 marks

Topics 1–4: cell biology, organisation, infection and response, bioenergetics (chapters 1–10)

Paper 2

1 h 45 · 100 marks

Topics 5–7: homeostasis and response, inheritance variation and evolution, ecology (chapters 11–18)

Tiers

Foundation (grades 1–5) · Higher (grades 4–9)

Higher assumes all Foundation content; ten required practicals are examined on the papers

Want a full paper? Try the Paper 1-style (Foundation), Paper 1-style (Higher), Paper 2-style (Foundation), Paper 2-style (Higher), Required practicals practice sets.

Questions

Frequently asked questions

How do I keep xylem and phloem straight?

X is for Xylem and for eXit upward — water and ions leave the roots and rise. Phloem is food plumbing: sugars flow wherever they are needed, both ways.

Why does the exam love the guard-cell mechanism?

Because it links osmosis to a visible consequence: turgid guard cells open the pore for photosynthesis, flaccid ones shut it to save water. Say the water movement and the pore response.

Which factors do I quote for transpiration rate?

Temperature up → faster; humidity up → slower; air movement up → faster; light up → faster (more open stomata). Four factors, four mechanisms.

How do I answer rate questions from uptake data?

Rate = volume ÷ time, converted to the units asked (usually cm³ per hour). From a table of cumulative uptake, use the change in volume over the change in time for that window.

Why count stomata in several fields of view?

One field is a sample of one; several fields averaged give a mean that is more representative of the whole leaf — the same sampling logic as quadrats in ecology.

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