The importance of water Flashcards
What kind of a molecule is water?
A polar molecule that allows for hydrogen bonding
How does water work as a solvent and why is this important?
It is able to dissociate ( break down) certain molecules making them easier to transport which is essential for the functioning of organisms. With larger molecules, it separates them creating a colloidal suspension, this is important as it can create an osmotic effect for example helping draw water into blood vessels.
How does waters thermal properties help living organisms maintain a constant temperature?
Water has a high specific heat capacity so lots of energy needed to raise or lower temperature. this allows living organisms to maintain certain temperatures, so its a temperature buffer.
Why does ice float and why is this important?
When water is frozen , its molecules spread out over a larger area, making it less dense and able to float on water. Because water freezes top down organisms are able to exist below ice.
How is water important in transport?
- Uptake of minerals by plants from soil across root hairs occurs in solution.
- Transpiration stream and water-based movement of sugars and amino acids, hormones etc. in phloem occurs in solution.
- All transport fluids used in animals (e.g. cytoplasm, blood, plasma and tissue fluid) are water-based.
- Many essential metabolites dissolve completely e.g. glucose, amino acids,vitamins and minerals.
- Larger molecules e.g. proteins are transported as colloids.
- Transpiration stream is held together by cohesion (water molecules hydrogen bond to other water molecules) and adhesion (water molecules bind to side of xylem vessel).
- Such forces also give rise to capillarity in tubes of very small diameter.
- Low viscosity of water enables it to flow easily through tubes e.g. xylem vessels.
How is water used in chemical reactions?
- All enzyme reactions of photosynthesis, respiration, excretion etc. occur in solution.
- Water also acts as a reactant for example, in:
1. Light dependent stage of photosynthesis when photolysis splits water to release electrons which move to photosystem II (PSII) and then through electron carriers in non-cylic photophosphorylation pathway (NCP).
2. Hydrolytic reactions (e.g. digestive enzymes).
How is water important for temperature control?
High specific heat capacity allows water to act as a buffer; essential in endothermic organisms that need to maintain a constant body temperature in order to optimise enzyme activity and thereby regulate metabolism. High incidence of hydrogen bonding also makes at it difficult for water molecules to evaporate. When they do so, much energy is released and this is involved in cooling mechanisms. Water remains a liquid over a huge temperature range - essential for metabolism and useful for aquatic organisms which avoid freezing.
How is water important for support?
In plant cells water confers turgidity. This is essential for example, in:
1.Maintaining maximum leaf surface area, hence light absorption, hence photosynthesis.
2.Maintaining aerial parts of the plant to maximise seed dispersal or pollination.
Loss of water in very hot conditions may lead to leaves wilting. This decreases their surface area, hence light absorption, temperature and water loss.
For aquatic organisms, water provides support through buoyancy.
How is water formed as a molecule?
Two hydrogens bond covalently to oxygen, it is a polar molecule due to a dipole.
How should hydrogen bonding be drawn?
Along a straight line that makes HOHO
