Water (biological roles and structure) Flashcards
(15 cards)
Water
-Water is the medium in which all metabolic reactions take place in cells and in which all substances are transported around the body
Water as a solvent
-Water is an excellent solvent (lots of other substances can dissolve in water)
Water as a solvent in eukaryotic and prokaryotic cells
-Both eukaryotic and prokaryotic cells contain large amounts of dissolved substances
-For example the chemical reactants used in metabolic reactions such as respiration, as well as the enzymes needed to carry out the reaction
Water as a habitat
-Bodies of water such as ponds and rivers contain dissolved oxygen
-This is used by organisms living in the water to carry out respiration, which makes water an excellent habitat for these organisms
Waters use in transporting substances + blood plasma as a transporter
-Since water is an excellent solvent, it can be used to transport substances around the body
-For example, blood plasma (the liquid part of the blood) contains a large number of substances: carbon dioxide, mineral ions, glucose, amino acids, etc
-Water is also used to transport substances in the xylem vessels in plants
Cohesion + use of cohesion in transport (plants)
-Water tends to stick together (cohesion)
-This is due to the hydrogen bonds between water molecules
-Allows long columns of water to travel up xylem tubes
Surface tension
-Cohesion also causes surface tension where the water meets the air
-Surface tension is useful as it allows the surface of the water to act as a habitat e.g for insects such as pond skaters
Adhesion
-Adhesions means that water molecules are able to hydrogen bond to other molecules
-I.e water molecules adhere to the side of a vessel
Water’s role in metabolic reactions
-Water is a reactant in many different reactions
-For example hydrolysis reactions and photosynthesis
-Water is also produced in many different reactions
-for example condensation reactions and aerobic respiration
Bonding in water
-Water is comprised of one oxygen atom chemically bonded to two atoms of hydrogen
-These bonds are covalent bonds
Why is water considered a polar molecule and what does this cause
-the oxygen atom in water is slightly negatively charged while the hudrogen atoms in water are slightly positively charged, making water a polar molecule
-These opposite charges mean that water molecules are attracted to each other
-These forces of attraction are called hydrogen bonds
Hydrogen bonds in water + arrangement of molecules in water
-Hydrogen bonds are quite weak bonds
-However, even in a small volume of water there are a large amount of hydrogen bonds, meaning that the hydrogen bonds have a large effect on the properties of water
-Water in liquid form move randomly and are not arranged neatly; hydrogen bonds are still present
Specific heat capacity of water
-Water has a very high specific heat capacity- meaning that it takes a lot of energy to change the temperature of water
-This is because the energy goes towards weakening or breaking the hydrogen bonds between water molecules, rather than increasing the kinetic energy of the water molecules
-Because of this, water acts as a buffer against rapid temperature changes
-This makes it a suitable habitat as aquatic organisms would not be able to function if the temperature of water changed rapidly i.e on hot or cold days
Ice
-Ice is less dense than water so floats
-Ice can act as a habitat for a number of organisms
-Ice also acts as an insulator for the water below, meaning that it does not freeze
-This means that organisms can continue to live in the water under the ice
latent heat of vaporisation
-Water has a high latent heat of vaporisation which means it takes a lot of energy to evaporate water
-This is useful for organisms as they can cool themselves down without losing a lot of water
-This is evident in sweating, where heat energy is used to evaporate water from the surface of the skin, this transfer of heat energy helps the organism to cool down
