AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(A) Both A and R are true and R is the correct explanation of A.
Phloem translocates food (sucrose) both upward and downward depending on the plant's needs. This bidirectional transport is driven by ATP energy (active loading) and osmotic pressure differences, which together explain why movement can occur in either direction.
The key concept here is the pressure flow hypothesis: sugar is actively loaded into phloem using ATP, raising osmotic pressure at the source, and unloaded at the sink, driving flow. Because the "source" and "sink" can be anywhere in the plant (e.g., leaves → roots or leaves → growing shoot tips), movement is bidirectional — and R correctly explains why A is true. Examiners expect you to link ATP-driven active transport and osmotic pressure to bidirectional flow.