Knowledge Organiser
Part of Plant Transport Systems · GCSE GCSE Biology revision
This topic summary covers Knowledge Organiser within Plant Transport Systems for GCSE Biology. Xylem and phloem structure, water and sugar transport, root hair adaptations, translocation, and practical investigations It is section 17 of 17 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 17 of 17
Practice
19 questions
Recall
24 flashcards
Knowledge Organiser
Key Terms
- Xylem — dead, hollow, lignified, water + minerals, one-way up
- Phloem — living, sieve plates, sugars + amino acids, two-way
- Translocation — sugar movement in phloem
- Transpiration — water loss through stomata
- Lignin — polymer strengthening xylem walls
- Companion cell — provides ATP to sieve tubes
- Root hair cell — large surface area for osmosis
- Cohesion — water molecules sticking together
- Tension — negative pressure in xylem from transpiration
Must-Know Facts
- Xylem cells die at maturity — lumen is hollow
- Xylem carries water AND mineral ions (not food)
- Phloem cells are living — maintain turgor and active loading
- Phloem carries sugars (as sucrose) and amino acids
- No pump needed for xylem — transpiration pull drives flow
- Active transport needed for phloem loading/unloading (ATP)
- Root hairs increase surface area by up to 1000x
- Lignin prevents xylem collapsing under tension
- Cohesion: hydrogen bonds between water molecules
Xylem vs Phloem — Quick Compare
- Dead vs Living
- Lignin walls vs Sieve plates
- Water + minerals vs Sugars + amino acids
- One-way up vs Two-way
- No energy needed vs ATP required
- Passive (osmosis/cohesion) vs Active loading
Required Practical Points
- Potometer measures water uptake (not transpiration directly)
- Cut shoot underwater — prevents air locks in xylem
- Rate = distance bubble moves / time
- Dye experiment proves water travels in xylem
- Phloroglucinol stain — xylem walls stain red
Common Mistakes
- Saying xylem carries food/sugar: Xylem carries water and mineral ions only — sugars are transported in phloem by translocation.
- Saying xylem cells are living: Xylem cells die at maturity — their hollow dead lumen is what allows water to flow. Phloem cells are living.
- Claiming a potometer measures transpiration directly: A potometer measures water uptake by the shoot, which is an estimate of transpiration — not a direct measurement of water lost from leaves.
- Forgetting active transport is needed for phloem loading: Sugars are actively loaded into phloem sieve tubes using ATP from companion cells — phloem transport is not passive.
- Saying phloem only transports upwards: Phloem carries sugars in both directions — from leaves to roots AND to growing shoot tips — unlike xylem which is one-way upward.
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Practice Questions for Plant Transport Systems
Which substance does xylem tissue transport?
Explain how root hair cells are adapted for their function.
Quick Recall Flashcards
19 questions on Plant Transport Systems — practise free
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