2.2.2 Properties of water Flashcards
(30 cards)
Name some of waters key roles
-Solvent
-Transport medium
-Medium in which chemical reactions/metabolism take place
-Coolant
Explain the importance of water as a solvent with an example
Water molecules are attracted to the charged part of solute molecules.
Respiratory and photosynthetic gases dissolve before entering cells; digestion produces soluble products; metabolism takes place in solution.
Explain the importance of water as a liquid at biological temperatures with an example
Hydrogen bonding between the water molecules means it is liquid at biologically important temperatures (0-100°C).
Transport in plants and animals require water
Explain the importance of water to do with cohesion and adhesion with an example
Water molecules stick together and are attracted to surfaces.
Surface tension on water; transport of water in xylem relies upon cohesion (and adhesion).
Explain the importance of water to do with freezing with an example.
Density changes as water freezes – less dense, so ice floats (layer of ice also insulates).
Water bodies freeze from the top down. Lakes seldom freeze completely; organisms survive in the cold, deeper water.
Explain the importance of water to do with thermal with an example.
High specific heat capacity; high latent heat of vaporization.
Water temperature quite stable ; evaporation has a cooling effect.
Explain the importance of water to do with metabolism with an example.
Metabolism takes place in aqueous solution; reactant/product in some key reactions.
Hydrolysis; condensation; H 2O used in photosynthesis.
Why is water called a universal solvent?
Water is called this as it’s highly effective at separating molecules of other substances, which can then move freely.
What is adhesion to do with water molecules?
Water molecules are attracted to other hydrophilic molecules.
What is polarity?
This characteristic describes molecules which have a different charge on opposite sides of the molecule.
What is cohesion to do with water?
Water molecules are attracted to each other due to their hydrogen bonds.
High specific heat capacity of water
A body of water can absorb a lot of energy whilst its temperature remains relatively constant.
Why is sweating a good temperature regulator?
The water in sweat evaporates from the skin and takes a lot of heat with it which has a cooling effect. This is due to its high latent heat of vaporization.
High specific heat capacity
The specific heat capacity of water (the amount of heat, measured in joules, required to raise 1kg of water 1°C) is very high: much of the heat absorbed is used to break the hydrogen bonds which hold the water molecules together.
High latent heat of vaporization of water
hydrogen bonds attract molecules of liquid water to one another and make it difficult for the molecules to escape as vapour: thus a relatively high energy input is necessary to vaporize water and water has a much higher boiling point than other molecules of the same size.
Molecular mobility of water
The weakness of individual hydrogen bonds means that individual water molecules continually jostle one another when in the liquid phase.
Density and freezing properties
As water cools from towards its freezing point the individual molecules slow down sufficiently for each one to form its maximum number of hydrogen bonds. To do this the water molecules in liquid water must move further apart to give enough space for all four hydrogen bonds to fit into it. As a result water expands as it freezes, so that ice is less dense than liquid water and therefore floats upon its surface.
Colloid formation in water
Some molecules have strong intermolecular forces which prevent their solution in water, but have charged surfaces which attract a covering of water molecules. This covering ensures that the molecules remain dispersed throughout the water, rather than forming large aggregates which could settle out. The dispersed particles and the liquid around them collectively form a colloid.
What is the biological importance of waters solvent properties?
Allow water to act as a transport medium for polar solutes. For example, movements of minerals to lakes and seas; transport via blood and lymph in multicellular animals; removal of metabolic wastes such as urea and ammonia in urine.
What’s the biological importance of water as a transportation stream?
The continuous column of water is able to move up the xylem because of cohesion between water molecules and adhesion between water and the walls of the xylem cell tissue.
What’s the biological importance of molecular mobility?
The rather weak nature of individual hydrogen bonds means that water molecules can move easily relative to one another - this allows osmosis ( vital for uptake and movement of water) to take place.
What is the biological importance of water expand on freezing?
Since ice floats it forms at the surface of ponds and lakes - it therefore insulates organisms in the water below it, and allows the ice to thaw rapidly when temperatures rise. Changes in density also maintain circulation in large bodies of water, thus helping nutrient cycling.
What is the biological importance of metabolic functions of water?
Water is used directly…
1. as a reagent (source of reducing power) in photosynthesis
2. to hydrolyse macromolecules to their subunits, in digestion for example
…and is also the medium in which all biochemical reactions take place.
What is the biological importance of volatility/stability of water?
Is balanced at Earths temperatures so that a water cycle of evaporation, transpiration and precipitation is maintained.
