Water essay plan

Question 1

3.1.7 Water properties and structure

Answer 1

-Water is a metabolite that is involved in many essential reactions, such as photosynthesis, and condensation and hydrolysis reactions
-Due to its dipolar nature, water is a solvent. The slightly positive hydrogen can attract negative ions, whilst the slightly negative oxygen can attract positive ions
-Due to a lot of energy being required to break H bonds, water has a high specific heat capacity, and a large latent heat of vaporisation
-Water ‘sticks’ together by H bonds, making it a cohesive molecule, so it can form columns and has high surface tension
-Important because water can act as a habitat, as cohesion provides a high surface tension that allows animals to survive on the surface and avoid predators in the water. The high specific heat capacity allows water to act as a buffer and maintain a constant temperature, which is better for organisms to survive in. Providing habitats increases biodiversity

Question 2

3.3.4.2 Mass transport in plants-cohesion tension theory

Answer 2

-Water is lost from the leaf by transpiration from the mesophyll
-This lowers the water potential of the leaf
-Water is pulled up the xylem, which creates tension
-Water molecules cohere due to hydrogen bonding, allowing them to form columns
-Adhesion of water to the xylem walls, which is made of a waterproof lignin
-This is important because water is a solvent, so can carry dissolved ions, such as nitrates, that would have been absorbed from the soil. This provides the leaf with the raw materials required for photosynthesis, which provides energy to the cells

Question 3

3.5.1 Photosynthesis-LDR

Answer 3

-Photolysis of water occurs, where light energy is used to split water molecules in the thylakoid lumen
-Oxygen is a waste product that diffuses out of the leaf
-Protons are used to reduce NADP to NADPH
-Electrons replace those in the chlorophyll lost during photoionisation, where electrons move to and through the ETC, releasing energy as they do so
-This is important because the products formed are used in the light independent reaction, the ATP produced is hydrolysed, releasing energy for RUBP regeneration, and the reduction of GP to triose phosphate. These lead to glucose production, which is an essential respiratory substrate

Question 4

3.3.3 Digestion of starch

Answer 4

-Amylase is produced by the salivary glands and the pancreas, and hydrolyses the polysaccharide starch to form the disaccharide maltose
-This is done in a hydrolysis reaction, which involves the addition of a water molecule to break a bond, in this case glycosidic bonds
-Membrane-bound disaccharides in the ileum then hydrolyse the maltose to two glucose molecules, again using the addition of a water molecule in a hydrolysis reaction
-This is important because glucose is small enough to be absorbed by co-transport into epithelial cells and the blood stream, where glucose can be used during respiration, where it is broken down during glycolysis to form two pyruvate molecules that can enter the link reaction and krebs cycle to form ATP