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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Biology > The Role of Water to Living Organism - Essay Plan

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Contents 1 Role of water as a solvent 2 Role of water in metabolic reactions 3 Role of water in support 4 Role of water in temperature regulation 5 Comments

Role of water as a solvent

Water is a solvent for numerous biochemical moleculesm giving solutions and enabling:

1. Transport of nutrients, e.g. glucose and amino acids in blood, and sucrose in phloem
2. Removal of excretory products, e.g. ammonia, urea
3. Secretion of substances, e.g. hormones, digestive juices.

Role of water in metabolic reactions

The majority of essential metabolic reactiosn take place in solution in water. Water is a raw material or a product of many metabolic reactions.

1. Hydrolysis involves the addition of water (hydro) in the breakdown (lysis) of large biological molecules into their monomers/subunits, e.g. proteins into amino acids. (Water is release during condensation reactions).
2. Water produced as a metabolic product of respiration is essential for organisms, especially those living in dry habitats.
3. Water is needed for photosynthesis.

Role of water in support

Water is not easily compressed and has an important role in support in plants and animals

1. The uptake of water by plant cells creates a pressure against the rigid cell wall.
2. This tugor pressure helps non-woody plants to remain upright.
3. Water provides buoyancy for aquatic organisms, e.g whales.
4. Water has a high specific tension and water molecules have cohesive forces holding them together, due to hydrogen bonding between water molecules.
5. These properties allow aquatic insects to walk on the surface of water, and water to be pulled through xylem in plants.

Role of water in temperature regulation

Water has a high specific heat capacity which means it adsorbs a lot of heat energy for its temperature rise, and loses a lot to cool. This help to:

1. Reduce temperature fluctations in organisms - especially large ones.
2. Minimise increases in temperature in cells as a result of biochemical reactions.
3. Reduce fluctations in temperature in aquatic habitats.

A lot of heat is needed to turn water into vapour (it has a high latent heat of vaporisation)

1. This helps some animals to maintain a constant body temperature as a high amount of heat energy is removed from the body to evaporate sweat or during planting.
2. In plants evaporation of water from leaves has a cooling effect.

At 4*C water is at its maximum density and becomes less dense as it freezes.

1. Water is denser as a liquid than as a solid
2. Thus cold water forms ice on the upper surface, insulating the aquatic organisms below.
3. Water must lose a relatively large amount of heat energy to freeze, making the formation of ice crystals in cells less likely.

Comments

These notes are aimed at people studying for A2 Biology, but are suitable for other exams and levels too.

Originally written by froggymills on TSR Forums.