Importance of water in organisms

Water – 3.1.7

• Major component in cells 

• Metabolite – condensation and hydrolysis reactions 

• Solvent for biochemical reactions 

• High specific heat capacity – buffer temperature changes 

• High latent heat of vaporisation – provide cooling effect 

• Strong cohesion – cohesion tension theory and surface tension theory 

• Polar molecule 

• Cohesion tension – provide habitat for some aquatic organisms – link to increase in biodiversity – avoid predators  

• Buffering = maintain enzyme activity even if environment is in extreme conditions 

Mass transport in plants – 3.3.4.2 

• Transpiration 

• Water through xylem through cohesion tension theory – cohesion between water molecules and adhesion to the walls + link to structure of water – polar & forms hydrogen bonds between molecules 

• Water as solvent so can carry dissolved ions like nitrates  

• Combined with organic substances made in photosynthesis to make proteins such as enzyme rubisco which is essential for photosynthesis 

Digestion and absorption – 3.3.3 

• Hydrolysis – breaking bonds using water to split apart molecules 

• e.g. starch gets hydrolysed into maltose and then maltose gets hydrolysed into glucose 

• Digestion of carbs – emphasis on water 

• Glucose can be absorbed by cotransport into epithelial cells and the blood stream and then it can be used in respiration in glycolysis to produce ATP for metabolism or it can be stored as glycogen 

• w/o water, hydrolysis in digestion would not be possible and starch wouldn't be broken down – wouldn't be able to get valuable molecules 

Mass transport in animals – 3.3.4.1 

• Focus on tissue fluid 

• High hydrostatic pressure = forces water and small molecules to be forced out blood stream to form tissue fluid 

• Able to bathe tissues with useful molecules e.g. glucose and oxygen and water 

• Water reabsorbed into capillaries – any waste produced by tissues e.g. co2 are transported with water back into the blood and can be transported around the body and removed 

Photosynthesis – 3.5.1 

• Light dependent reaction – photolysis 

• Water split using light energy – protons, electrons and oxygen 

• Electrons replaced the electrons lost in chlorophyll from electron transfer chain and that the protons are used to reduce the NADP 

• Means we can produce ATP and NADPH – important in light independent reaction 

• ATP can be hydrolysed to release energy to provide energy for regeneration of RUBP but also for the energy needed for the reduction of GP into triose phosphate  

• Glucose is made which is an essential respiratory substrate for the plant to produce ATP for all of its metabolic processes