Plants have two separate conducting tissues — xylem and phloem — for transport. Why can the same tissue not b…

Question

Plants have two separate conducting tissues — xylem and phloem — for transport. Why can the same tissue not be used to transport both water and the products of photosynthesis?

Accepted Answer

## Model Answer Water and minerals are transported **upward** from roots to leaves through xylem, driven by transpiration pull — a unidirectional, passive process. Food (sucrose) produced by photosynthesis must be transported **in all directions** (leaves to roots, fruits, etc.) through phloem, requiring energy (active transport). Since the direction, mechanism, and substances differ, separate tissues are necessary. *Source: Chapter 5, Section 5.4 – Transportation in Plants* --- ## Explanation - Examiners expect **two clear contrasting points**: (1) xylem transports water/minerals upward passively; (2) phloem transports food in multiple directions using energy. - Mentioning that using one tissue would cause **mixing** of water and dissolved food (disrupting concentration gradients needed for each) earns full credit. - Don't over-explain — two tight points are enough for 2 marks.

Science (086) — AI-generated practice question