Chapter 4 - The chemicals of life

WATER

• Almost 80% of our body is made up of water. 
• Metabolic reactions can only take place if the chemicals which are reacting are dissolved in water.
• Water is an important solvent. 
• Plasma, the liquid part of blood, contains a lot of water, so that substances like glucose can dissolve in it. These dissolved substances are transported around teh body.
• Water is also needed to dissolve enzymes and nutrients in the alimentary canal, so that digestion can take place.
• We also need water to help us get rid of waste products. 

CARBOHYDRATES

• Carbohydrates include starches and sugars.
• Their molecules contain three kinds of atoms - carbon (C), hydrogen (H) and oxygen (O). 
• A carbohydrate molecule has about twice as many hydrogen atoms as carbon or oxygen atoms. 
• Monosaccharides, disaccharides and polysaccharides are all types of carbohydrates. 

• Carbohydrates release energy. One gram of carbohydrate releases 17kJ of energy; this energy is released by respiration. 
• The carbohydrate that is normally used in respiration is glucose. 

• Plants use glucose in respiration, to provide them with energy. However, they do not transport glucose around their bodies. Instead, they transport sucrose. The cells change the sucrose to glucose when they need to use it. 

• …