'the importance of water in living organisms'

mass transport in plans - AO1

• water moves through the xylem due to the cohesion tension theory, which is cohesion between the water molecules and adhesion to walls, holding water up against gravity

• water moves into the roots by osmosis and increases the volume of liquid inside the root, increasing the pressure in the root.

• this forces it upwards

• water is a polar molecule that forms hydrogen bonds between the oxygen and hydrogen of 2 different water molecules, making them stick together and travel up the xylem as a continuous water column

• as water is pulled up xylem, creates tension

mass transport in plants - AO2

important because..

• water is a solvent so it can carry dissolved ions (nitrates) that are absorbed through the root hair cells

• ions travel up xylem to cells so cells get nitrate

• ions combine with organic substances made in photosynthesis to make proteins like enzyme rubisco which is essensial for photosynthesis

photosynthesis - AO1

• water is required in the light dependent reaction in photolysis

• this is when water is split using light energy to produce 4e-, 4h+ and O2 molecule

• electrons made replace electrons lost in chlorophyll from electron transfer chain

• proteins are used to reduce NADP to NADPH

photosynthesis - AO2

• without water, light dependent reaction can’t take place and ATP and NADPH are not produced

• these are important in the light independent reactions of photosynthesis

• ATP can be hydrolysed to release energy to provide regeneration of RUBP and for energy needed to reduce GP into triose phosphate

• useful because some of the carbon produced can be used to generate organic compounds like glucose

• glucose is essential respiratory substrate for plant to produce ATP for all metabolic processes

digestion and absorbtion - AO1

• in digestion and absorption, hydrolysis takes place which is breaking bonds using water to split apart molecules

  • EG, in digestion of carbohydrates (starch) hydrolysis of polysacchardies takes place by breaking glycosidic bonds into maltose, then then further hydroylsis of the disaccharide into glucose molecules

digestion and absorption - AO2

important because...

• the hydrolysed glucose is small enough to be absorbed by cotransport into the epithelial cells and blood stream so it can be used in respiration in glycolysis to procude ATP for metabolism OR stored as glycogen

• without water, hydrolysis in digestion would not be possible as starch couldn’t be broken down and hydrolysed

mass transport in animals - AO1

• tissue fluid is made up of water and other substances such as glucose and amino acids

• the high hydrostatic pressure causes the water and small molecules to be forced out of the blood stream to form tissue fluid

• volume of water going from a large diameter to a narrower diameter creates the high hydrostatic pressure to force out smaller molecules

mass transport in animals - AO2

important because…

• tissues and cells are bathed with useful molecules that are forced out, like glucose and oxygen

• water from tissue fluid gets reabsorbed back into the capillaries due to the water potential gradient

• this means that any waste produced like co2 in urea are transported with water back into the blood to be removed