Food
All organisms need Food. 
Food is needed for: 
(a)	For energy (for heat and to drive metabolism) 
(b)	To provide the materials needed for growth, maintenance and repair of cells 
(c)	To control chemical reactions in cells
Chemical Elements in Food
The six main elements present in food are 
•	Carbon (C)
•	Hydrogen (H)
•	Oxygen (O)
•	Nitrogen (N)
•	Phosphorus (P)
•	Sulphur (S) 
The five mineral elements found dissolved in salts are
•	Sodium (Na) 
•	Magnesium (Mg)
•	Chlorine (Cl)
•	Potassium (K)
•	Calcium (Ca) 
There are three trace elements present in food
•	Iron (Fe) 
•	Copper (Cu)
•	Zinc (Zn) 
Trace Elements: Elements required in tiny amounts by the body 
Biomolecules
The fourteen elements combine in different ratios to form different biomolecules. For example, during photosynthesis, plants use carbon dioxide and water to combine atoms of carbon (C) and hydrogen (H) and oxygen (O) to form the biomolecule glucose. 
The four major biomolecules found in food are carbohydrates, lipids, proteins and vitamins. 
Carbohydrates
Carbohydrates contain the elements Carbon (C), Hydrogen (H) and Oxygen (O). These elements are always present in the fixed ratio Cx(H2O)y. 
For example, the formula for Glucose is C6H12O6. There is always twice as much hydrogen present compared to the amount of oxygen present. 
There are 3 main types of carbohydrates 
1.	Monosaccharides – the smallest unit of a Carbohydrate. They consist of one sugar unit. 
Examples include Glucose and Fructose. 
Monosaccharides are all sweet to taste and are soluble in water. 
Glucose is the main molecule that organisms get their energy from. 
2.	Disaccharides – consists of two sugar units (two monosaccharides) joined together. 
Examples include Maltose (glucose + glucose), and Sucrose (glucose + fructose). 
Disaccharides are sweet to taste and are soluble in water
3.	Polysaccharides – consist of many monosaccharides joined together. 
Polysaccharides are insoluble or only slightly soluble in water. 
Examples include Starch, Cellulose & Glycogen. 
Starch – made from many glucose molecules joined together. Starch is made by plants during photosynthesis and is stored by plants. Starch is found in bread, flour, potatoes and pasta. 

Cellulose – made of many glucose molecules joined together. Cellulose is very strong and is found in the cell wall. 
Glycogen – Made from many glucose molecules joined together. It is stored in animals in the liver and the muscle and can be converted into glucose when needed as a source of energy. 
Functions of Carbohydrates 
1.	Structural role – Cellulose in the cell wall of plants provide support and prevent the cell from bursting 
2.	Metabolic role – glucose is used to produce energy during respiration. Glycogen is an energy store in animals. Starch is an energy source in plants. 

Lipids
Lipids contain the elements Carbon (C), Hydrogen (H) and Oxygen (O) but unlike carbohydrates they have no particular ratio and do not contain much oxygen. 
•	Lipids that are solid at room temperature are called fats e.g. butter 
•	Lipids that are liquid at room temperature are called oils e.g. vegetable oil 
•	The basic unit of a lipid is called a triglyceride, which is made up of three fatty acids joined to one glycerol molecule. 

•	There are different fatty acids and the type of lipid depends on which fatty acids it contains. For example, a phospholipid, found in the cell membrane, has the same structure as a triglyceride expect that one of the fatty acids is replaced by a phosphate group. 

•	Excess lipids in the body are converted into adipose tissue. 
Functions of Lipids 
1.	Structural role – to form a protective later around delicate organs e.g. heart 
2.	Metabolic role – lipids are a long-term energy store in the body 

Protein
Proteins always contain the elements Carbon (C), Hydrogen (H), Oxygen (O) and Nitrogen (N). Sometimes they contain Phosphorus (P) and Sulphur (S).
Protein is the only biomolecule to contain Nitrogen, the element needed for growth. 
These elements combine to form the basic units of a protein called amino acids. 
There are 20 common amino acids. 
Amino acids are bonded together via peptide links. 

•	A chain of less than 20 amino acids = A Peptide 
•	A chain of more than 20 amino acids = A Polypeptide 
•	A chain of at least 200 amino acids = A protein 
Proteins are made in the cells, in an organelle called the ribosome. 
Types of Proteins
1.	Fibrous Proteins – these proteins form long straight chains. Examples include Keratin, a protein found in hair, skin & nails, and Collagen, a protein which holds tissues together such as blood vessels. 
2.	Globular Proteins – these proteins are folded into spherical shaped chains. Examples include enzymes, which control metabolic reactions, and hormones such as Insulin, which regulates blood sugar levels. 
Functions of Protein
1.	Structural role – protein called Keratin forms our hair, skin and nails 
2.	Metabolic role – All enzymes are made from protein. Enzymes alter the rate of chemical reactions. 
Storage of Proteins in the Body
•	Unlike carbohydrates and lipids, excess proteins cannot be stored in the body. 
•	The liver breaks down excess proteins in the body through a process called Deamination. This process converts excess proteins into urea where it will eventually become urine where it is excreted. 
Vitamins
Vitamins are needed in small amounts by organisms. They only have a metabolic role and no structural role. There are two main types of Vitamins 
1.	Fat soluble Vitamins – A, D. E and K 
2.	 Water-Soluble Vitamins – B and C 

Vitamin D
•	Soluble in fat 
•	Found in liver, fish oils and milk 
•	Is made when ultra-violet light rays in the sun act on our skin 
•	Function is to absorb calcium from our small intestine 
•	Deficiency of Vitamin D results in rickets in children and osteoporosis in the elderly (brittle bone disease) 

Vitamin C
•	Soluble in water 
•	Found in green vegetables and citrus fruits such as oranges and lemons 
•	Function is to form connective tissue in our gums, ligaments and blood vessels 
•	Deficiency of Vitamin C causes a disease called Scurvy which includes bleeding gums and loose teeth

Minerals
Minerals are required in minute amounts by living organisms. 
Minerals needed by Plants: 
1.	Calcium – absorbed from the soil and is used to form the middle lamella that cements plant cells together 
2.	Magnesium – absorbed from the soil – is needed to form chlorophyll, the green pigment that absorbs sunlight during photosynthesis 
Minerals needed by Animals:
1.	Calcium – found in cheese and milk – helps form bones and teeth 
2.	Iron – found in liver and green vegetables – forms part of haemoglobin (a globular protein) found in red blood cells that is used to carry oxygen. 

Water
Water makes up between 75% and 95% of body fluids 
•	It is an excellent solvent. - that many molecules can dissolve in it - important for cell reactions to take place 
•	Water helps to transport materials in and out of cells 
•	Water heats up and cools down very slowly – this helps to keep the body temperature constant (homeostasis). 
Food Tests
Substance 	Chemical 	Heat	Original colour 	Colour if Positive result 	Control 	
Starch	Iodine 	No 	Orange 	Blue/black 	Water instead of starch 	
Reducing Sugar (Glucose)	Benedicts Solution 	Yes 	Blue 	Brick Red 	Water instead of glucose 	
Protein	Biuret Solution 	No 	Blue 	Violet 	Water instead of protein 	
Lipid (Fat)	Brown Paper 	No 	Not translucent 	Translucent 	Water instead of fat 	

Note: Glucose is an example of a Reducing Sugar, Sucrose is not.