This memory aid covers Memory Aids 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 12 of 17 in this topic. Use it for quick recall, then test yourself straight afterwards so the memory aid becomes usable in an answer.
Topic position
Section 12 of 17
Practice
19 questions
Recall
24 flashcards
Memory Aids
Xylem vs Phloem — The Dead/Living Rule:
"Dead Dry pipes = Xylem. Living Lunchbox = Phloem."
- Dead + Dry = Xylem (dead cells, carries water — the dry side of transport)
- Living + Lunch = Phloem (living cells, carries food — the lunchbox of the plant)
Direction of flow:
"X goes one way — X marks the top. Ph goes everywhere."
- Xylem: one-way, upward (X marks the spot at the tip — the leaf)
- Phloem: bidirectional, to wherever food is needed
Transpiration-cohesion-tension — the acronym TCT:
"The Cat Tugged (the water up)"
- T = Transpiration (creates the pull)
- C = Cohesion (water molecules stick together)
- T = Tension (negative pressure in xylem)
Xylem reinforcement:
"Lignin Locks the tube" — lignin is the strong polymer in xylem walls that prevents the tube collapsing under the negative pressure of transpiration pull.
Quick Check: A gardener removes a ring of bark all the way around a tree trunk (a process called "ring-barking"), cutting through the bark but not the wood. The leaves stay green for weeks afterwards, but the roots gradually die. Explain why.
The bark contains the phloem. Cutting the bark all the way around severs the phloem pathway between leaves and roots. Water still reaches the leaves via xylem (which is in the wood, deeper than the bark), so the leaves continue to photosynthesise and appear healthy. However, the sugars produced in the leaves can no longer be transported down through phloem to the roots. The roots are non-photosynthetic and rely entirely on sugar delivered from leaves; starved of sugar, they can no longer respire, carry out active transport, or grow — and they gradually die.
Quick Check: A student says: "Xylem vessels must be living because they need energy to pull water upwards against gravity." Identify the two errors in this statement and explain the correct biology.
Error 1: Xylem vessels are dead at maturity — their cytoplasm is removed and end walls break down, leaving hollow tubes reinforced with lignin. Living cells are not needed for function. Error 2: Water does not move upwards by an energy-requiring process. The movement is passive, driven by transpiration at the leaf surface creating tension that pulls the cohesive water column upward. Solar energy drives evaporation, but the plant expends no metabolic (ATP) energy on xylem transport.
Quick Check: A plant is placed in a sealed, dark chamber. Predict what will happen to its rate of transpiration and rate of translocation, and explain each prediction.
Transpiration rate will decrease significantly. In darkness, stomata close (guard cells lose turgor as potassium ions are pumped out). With stomata closed, the main route for water vapour to escape is blocked, so water loss falls. Translocation will also decrease over time. Without light, photosynthesis stops, so no new sugars are made in the leaves. The concentration of sugar in the phloem at source (leaves) falls, reducing the osmotic gradient that drives water entry into phloem and lowers the pressure-flow that moves sugars to sinks. Eventually translocation rate drops close to zero.