1.1 Viruses are different from other micro organisms as they do not breed outside of the host cell, they do not eat food to grow, where as bacteria grows by gaining energy from things such as sugars and fats. Parasites are usually larger than bacteria, can be made by one cell or many cells. Fungi are multi cellular and reproduce with spores rather than feeding from something. 1.2 Common illnesses caused by bacteria are ear infections, tonsillitis and food poisoning. Viruses is usually such things as the common cold or a stomach bug. Fungi is things such as athletes foot and ring worm and parasites is usually things such as worms and malaria. 1.3 Colonisation is when a bacteria or virus is present in someones body but is not causing them any harm, where as an infection invades someones immune system and makes them ill.