I have published a compilation of study notes on every topic of the CIE IGCSE Biology course. Using these study notes, I got an A* in Biology (well actually a 9 out of 9) and I found that without them, this would have been impossible. Each document is worth 5$ which is a very reasonable price, as m...
BIOLOGICAL MOLECULES / THE CHEMICALS OF LIFE: TOPIC 4
4. 1. W HA T A R E YO U M A D E O F ?
OUR BODIES made up of → water, carbohydrates, fats and proteins
WATER
Most organisms → almost 80% of the body → made up of WATER
WHY IS WATER IMPORTANT?
1. This is because METABOLIC REACTIONS can only take place if the reactants (chemicals) are dissolved in water
2. WATER IS AN IMPORTANT SOLVENT
3. If the cells dry out, the reactions stop and the organism dies.
OTHER REASONS
1. Dissolved substances can be easily transported around organisms –dissolved food molecules in the blood
2. Digested food molecules are in the alimentary canal but need to be moved to cells all over the body
3. Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to remove from the
body in URINE
4. 2. CA R B O HY D R A T ES
Include → starches and sugars
SUGARS
Simplest kinds of carbohydrates → simple sugars or MONOSACCARIDES (e.g. glucose – C6H12O6)
2 simple sugars join together → DISACCARIDE is formed (e.g. sucrose and maltose)
POLYSACCARIDES
Many simple sugars join together → POLYSACCARIDE is made (e.g. cellulose, starch and glycogen)
Many are insoluble
FUNCTIONS OF CARBOHYDRATES
1. They are needed for energy (during the process of RESPIRATION) (carbohydrate that is normally used = glucose (in animals) = sucrose (in plants))
2. They are stored as starch in plants and glycogen in animals
4. 3. F A TS
• Also known as → LIPIDS
• A fat molecule → made of 4 smaller molecules joined together (one of these is GLYCEROL, which has 3
long molecules attached to it called FATTY ACIDS)
• They are insoluble in water
• Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)
• Most fats (lipids) in the body are made up of TRIGLYCERIDES
FUNCTIONS OF FATS
1. They can be used in a cell to release energy
2. They are useful for storing energy
3. ADIPOSE TISSUE → stores of large drops of fats and oils underneath the skin, that can be used to release energy when needed (helps keep heat in the
body)
4. 4. P R O T EI N S
• As well as carbon, oxygen and hydrogen, they contain NITROGEN and small amounts of SULFUR
• They are long chains of AMINO ACIDS, there are about 20 different amino acids
• The amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins
• Some proteins are SOLUBLE IN WATER (e.g. haemoglobin) others are INSOLUBLE (e.g. keratin)
• For most protein molecules, their shape directly affects their function (e.g. with enzymes and antibodies)
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