Water - physical and chemical properties Flashcards
Define the term cohesion in relation to water molecules
The strong attraction between water molecules that is present due to hydrogen bonding.
Why is cohesion important for living organisms?
Transport of water under tension in the xylem vessels of plants.
The use of water surfaces as habitats due to surface tension.
Define adhesion in the context of water
When water molecules form hydrogen bonds with other polar or charged molecules
Examples of adhesion
Capillary action in xylem, soil, plant cell walls
Define hydrophobic
“water-hating” - repels or fails to mix with water
Define hydrophilic
“water-loving” - readily dissolves or mixes with water
Are polar molecules generally hydrophilic or hydrophobic?
Hydrophilic - polar molecules with positive or negative charges can form hydrogen bonds with water (and dissolve).
Why are non-polar molecules hydrophobic?
Have no positive or negative charge - cannot form hydrogen bonds with water.
Why is water regarded as the universal solvent?
Most biological molecules are hydrophillic and can be dissolved
Why do different solutes have different solubilites?
Different solutes have different hydrophobic and hydrophilic properties
Examples of hydrophilic and hydrophobic substances
Hydrophilic: salts, glucose
Hydrophobic: fats, phospholipids
How does solubility affect transportation?
Highly soluble molecules can be easily transported in solution
Give an example of a low solubility molecule and its adaptation for transportation
Oxygen - bind with haemoglobin to allow more oxygen to be carried
Why do most enzymes require water?
To hold their shape and improve their stability, enabling them to catalyse reactions in aqueous solutions.
Why is hydrogen bonding necessary for substrate bonding?
Hydrogen bonds will often facilitate the binding of the enzyme active site and its substrate molecule - the enzyme substrate complex
Define specific heat capacity
The energy required to raise the temperature of 1kg of a substance by 1°C
Does water have a high or low specific heat capacity and why?
Higher SHC - a relatively large amount of energy is required to raise its temperature.
Due to the presence of many hydrogen bonds.
What are the advantages of water’s high specific heat capacity?
Provides temperature-stable aquatic habitats, maintains a constant temperature for enzyme activity
Define thermal conductivity
The ability of a substance to conduct heat
How does the thermal conductivity of water compare to that of the air?
The thermal conductivity of water is higher than that of air, which makes air a very good insulator for organisms living in colder climates.
Define buoyancy
The ability of an object to float in water
Define viscosity
The resistance of a fluid to flow
How does viscosity differ between air and water? How does this affect organisms?
Viscosity of water is higher than air - aquatic organisms (e.g. seals, loons) need body shapes adapted to move efficiently through viscous water
Give examples of adaptations of animals that live in water and air.
The ability to regulate buoyancy - solid bones in loons
Streamlined body and webbed feet / flippers to move through viscous water - seal, loons
Insulation that functions in water & in air - feathers (loons), blubber (seals)
