3.1.7 Water Flashcards
(Water) State the 8 roles water plays in biology.
Solvent, transport, surface tension, specific heat capacity, latent heat of vaporisation, ice, metabolite and transparent.
(Water) Describe the role of water as a solvent.
Water is polar (slightly charged) so it will dissolve any:
- Charged molecules e.g. salt ions
- Any other ‘polar’ molecules e.g. glucose, amino acids.
Water can act as a medium for biochemical reactions in cells / organelles.
(Water) Describe the role of water as a transport mechanism.
Dissolved biological molecules can be transported around organisms e.g. blood stream in mammals, xylem / phloem in plants.
The transpiration stream in plants works as all the water molecules are hydrogen bonded to each other along the entire column.
(Water) Describe the role of water regarding surface tension.
Water is cohesive and hydrogen bonds to other water molecules. This creates a surface tension on ponds and a habitat for some organisms e.g. pond skaters.
(Water) Describe the role of water regarding specific heat capacity.
Liquid water will have many hydrogen bonds within it. Therefore a lot of energy is required to raise water by 1°C and it cools slowly.
Large bodies of water are thermally stable and buffer changes in temperature. This stabilises aquatic habitats.
(Water) Describe the role of water regarding latent heat of vaporisation.
Due to extensive hydrogen bonds, a small volume of water requires a lot of energy to break all of these and evaporate.
Therefore a small volume of water can have a big cooling effect in mammals.
(Water) Describe the role of water regarding ice.
Water freezes at 0°C where all molecules have 4 hydrogen bonds.. This solid / ice structure is less dense than liquid water so it floats. This can:
- Thermally insulate liquid water below
- Provide a habitat on the surface.
(Water) Describe the role of water as a metabolite.
Water is a chemical USED AND PRODUCED IN CHEMICAL REACTIONS. It is used in photosynthesis to help make sugars. It is used to break biochemical bonds (HYDROLYSIS) and is released when some bonds are made (CONDENSATION).
(Water) Describe the role of water regarding transparency.
This enables aquatic plants to photosynthesis.
(Water) What important metabolic reactions is water in?
Condensation and hydrolysis reactions.
(Water) Some substances dissolve in water, what does this tell us?
That water is a solvent.
(Water) Where do most metabolic reactions take place in?
Solution (cytoplasm of eukaryotic and prokaryotic cells) - water is essential.
(Water) Why does water help with temperature control?
It has a high latent heat of vaporisation and high specific heat capacity.
(Water) How does cohesion help water molecules?
Helps water transport in plants as well as transport in other organisms.
(Water) What makes up a molecule of water?
One atom of oxygen (O) joined to two atoms of hydrogen (H₂) by shared electrons (covalent).
(Water) Why does one side of each hydrogen atom have a slight positive charge? (δ+)
The shared negative electrons are pulled towards the oxygen atom, leaving one side of each H atom with a slight positive charge.
(Water) What charge do the unshared negative electrons on the oxygen atom have?
A slight negative charge (δ-).
(Water) Why is water a polar molecule?
It has a slight negative charge on one side and a slight positive charge on the other.
(Water) What is a hydrogen bond?
A weak bond between a slightly positively charge hydrogen atom in one molecules and a slightly negatively charged atom in another molecule.
(Water) Why do hydrogen bonds form between water molecules?
Water molecules have a slightly negatively charged oxygen atom which attracts the slightly positively charged hydrogen atoms.
(Water) What is a metabolic reaction?
Reaction that occurs in a living organism to keep the organism alive.
(Water) What is a metabolite?
A substance involved in a metabolic reaction.
(Water) What is latent heat?
The heat energy that is needed to change a substance from one state to another, e.g. from a liquid to a gas.
