Biology – Water | e-Consult

Water's properties are fundamental to its transport in plants. Cohesion, arising from hydrogen bonding, allows water molecules to stick together, forming continuous columns of water within the xylem. This is essential for the continuous upward flow of water from the roots to the leaves. Adhesion, also due to hydrogen bonding, allows water molecules to stick to the xylem walls. This helps to counteract the force of gravity and maintain the water column.

High specific heat capacity helps to buffer the plant against temperature fluctuations, preventing damage from overheating or freezing. Latent heat of vaporisation is important for transpiration. The evaporation of water from the leaves creates a tension (transpiration pull) in the xylem, which draws water up from the roots. This process is driven by the continuous evaporation of water from the leaf surface, requiring energy (latent heat of vaporisation) which is drawn from the xylem.

Examples:

• Xylem transport: Cohesion and adhesion work together to create a continuous water column in the xylem, allowing water to be transported upwards against gravity.
• Transpiration: The evaporation of water from leaf mesophyll cells creates a tension that pulls water up the xylem. The latent heat of vaporisation is required for this evaporation.
• Root water uptake: Adhesion helps water to climb up the xylem from the roots, ensuring a continuous supply of water to the leaves.