Science (086) — AI-generated practice question

(i) Direction of transport:
Xylem transports water and minerals unidirectionally — from roots to leaves (upward). Phloem transports food (sucrose, amino acids) bidirectionally — from leaves to other parts as needed.

(ii) Driving force:
Xylem: transpiration pull (suction created by water evaporation from leaves) and root pressure. Phloem: osmotic pressure gradient created by active loading of sugars.

(iii) Role of energy:
Xylem transport is a physical/passive process — no ATP is directly required. Phloem transport is an active process — ATP energy is needed to load sugars into phloem.

(iv) Substances transported:
Xylem — water and dissolved minerals. Phloem — sucrose (food/sugars) and amino acids.

Application: A herbicide blocking ATP synthesis in phloem companion cells would stop active loading of sugars into phloem, halting food translocation. Water transport through xylem is passive and requires no ATP, so it would be unaffected.

Source: Life Processes, Section 5 (Transport in Plants)

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• Examiners expect all four heads addressed — missing any costs marks.
• The key distinction is active vs. passive: xylem = passive (no ATP); phloem = active (needs ATP from companion cells).
• The application (herbicide) directly tests this distinction — always link back to ATP dependency of phloem.
• Use terms like transpiration pull, root pressure, bidirectional, and companion cells to score full marks.