OCR GCSE Biology Practice Exam 2025 – Comprehensive All-in-One Guide to Exam Success

Transpiration is primarily driven by evaporation, which occurs when water evaporates from the surfaces of leaves. This process creates a negative pressure within the plant's xylem (the tissue responsible for water transport), allowing water to be pulled up from the roots through the stem and into the leaves. As water vapor exits the plant through small openings called stomata, it is replaced by water taken up from the soil, facilitating continuous water movement.

Photosynthesis is a process through which plants convert light energy into chemical energy, and while it involves water, it is not the primary driver of transpiration. Osmosis is the movement of water across a semi-permeable membrane, essential for plant health but not specific to the mechanism of water loss through transpiration. Active transport refers to the energy-requiring movement of molecules against their concentration gradient, primarily relevant for nutrient uptake but not directly related to the process of transpiration. Thus, evaporation is the key process that facilitates transpiration in plants.