Biological molecules: Water And Its Functions Flashcards
Why is the water molecule described as dipolar?
Because although the molecule doesn’t have an overall charge, the oxygen atom has a slight negative charge and the hydrogen atoms have a slight positive charge due to the unfair sharing of electrons between the atoms
What causes the hydrogen bond between water molecules?
The attractive force between the positive pole of one water molecule and the negative pole of the other water molecule (cohesion)
What is cohesion?
The tendency of molecules to stick together
What prevents water being a gas under the temperatures common on earth?
The hydrogen bonds between the molecules
Why is the boiling point of water higher than expected?
Cohesion
Why does water have a high specific heat capacity?
Because of the hydrogen bonds and cohesion between the water molecules causing a need for a lot of energy to separate the water molecules
What are the advantages of water’s high specific heat capacity?
- it acts as a buffer against sudden temperature variations making aquatic environments temperature stable
- it acts as a buffer within organisms as they are mostly made of water and buffers them against sudden temperature changes especially in terrestrial environments
Why is sweat in mammals very effective?
As water has a high latent heat of vaporisation, it means a lot of energy is required to evaporate one gram of water as a result of the hydrogen bonds between molecules. This means that when the molecules evaporate they transfer a lot of energy by heating and so effectively cools down the mammal without excessive use of water molecules so limiting dehydration
Give examples where the cohesion of water is useful to organisms
- cohesion allows molecules to form surface tension as they stick to each other rather than the air and so can support small organisms like pond skaters
- cohesive and adhesive forces allow water to be pulled up tubes like a plant’s xylem vessels
What is adhesion of a water molecule?
The water molecule being attracted to any other material other than itself
Give three examples where water is useful in the metabolism of organisms
- water is used to break down many complex molecules by hydrolysis for example proteins to amino acids and water is also produced in condensation reactions
- aqueous mediums are where chemical reactions take place
- water is a major raw material in photosynthesis
Give 4 examples of substances water readily dissolves making it a useful solvent
- gasses like oxygen and carbon dioxide
- wastes like ammonia and urea
- inorganic ions and small hydrophilic molecules like amino acids, monosaccharides and ATP
- enzymes whose reactions take place in solution
Give three overall important features of water
- its evaporation cools organisms and allows them to control their temperature
- its not easily compressed and so provides support, e.g. the hydrostatic skeleton of animals such as the earthworm and turgor pressure in herbaceous plants
- its transparent and so aquatic plants can photosynthesise and also rays of light can penetrate the vitreous in the eye and so reach the retina
Give examples of inorganic ions in organisms and how they are beneficial
- Hydrogen: important in determining the pH of solutions and so therefor the function of enzymes
- sodium: important in the transport of amino acids and glucose across plasma membranes
- calcium: *extra cellular component of the bone matrix
* forms exoskeletons
* stimulates synaptic transition between neurones
* used in muscle contractions - nitrogen:*used in chlorophyll
* part of the amino group of amino acids - iron: found in the haemoglobin and aids the transport of oxygen
- phosphorus: *phospholipids make up the plasma membrane
* part of the sugar phosphate backbone in DNA structure
* the bonds between phosphate ions store energy in ATP - sulphur: *a source of energy for chemosynthic bacteria in hydrothermal vents
* found in the R group of the amino acid cysteine and can form disulphides bridges in protein folding
