Water has a high specific heat capacity, meaning it requires a large amount of energy to raise its temperature by 1°C. This is due to the energy required to break the hydrogen bonds between water molecules. A significant amount of energy is needed to overcome these intermolecular forces and allow the water molecules to move more rapidly, thus increasing the temperature.

This high specific heat capacity is vital for living organisms. Water helps to moderate temperature fluctuations within organisms and their environments. For example, in aquatic organisms, the large volume of water helps to buffer temperature changes. In terrestrial organisms, water in blood and tissues absorbs heat, preventing rapid temperature increases during exercise or exposure to hot environments. This helps maintain a stable internal environment (homeostasis).

Water's latent heat of vaporisation is the energy required to change water from a liquid to a gas. This property is crucial for thermoregulation in organisms. Evaporation of water, such as sweating in mammals or transpiration in plants, requires energy (the latent heat of vaporisation). This energy is drawn from the organism, resulting in a cooling effect. Therefore, the evaporation of water helps to prevent overheating and maintain a stable internal temperature.

Hydrogen bonding occurs between water molecules due to the polarity of the water molecule (H₂O). Oxygen is more electronegative than hydrogen, leading to a partial negative charge (δ-) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms. This allows the partially negative oxygen atom of one water molecule to be attracted to the partially positive hydrogen atom of another water molecule. This attraction is a hydrogen bond. While individually weak, the cumulative effect of numerous hydrogen bonds between water molecules results in strong intermolecular forces.

These hydrogen bonds are crucial for water's solvent properties. Water's polarity allows it to dissolve many ionic compounds and polar molecules. The δ+ ends of water molecules are attracted to the δ- ends of anions in ionic compounds, while the δ- ends are attracted to the δ+ ends of cations. This process, known as hydration, effectively surrounds the ions and weakens the ionic bonds, allowing them to disperse in the water. Similarly, water can dissolve polar molecules through dipole-dipole interactions. This solvent action is vital for biological systems because many biochemical reactions occur in aqueous solutions, and water facilitates the transport of nutrients and waste products within organisms.

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.