1. 1. Microorganisms require about 10 elements in large quantities for the synthesis of macromolecules. State clearly all the elements. [10 marks] 2. Describe energy and carbon requirements each of the following group of microorganisms. a) Photoautotrophs b) Chemoautotrophs c) Photoheterotrophs d) Chemoheterotrophs [20 marks]

2. 3. Different species of microorganisms can grow in a wide range of environments and their growth rates are influenced by physical and biochemical factors. i. Lists four physical factors that affect microbial growth. [5 marks] ii. Define the term ‘acidophiles’ and ‘alkaliphiles’ and name one common genus from each group. [20 marks]

3. 4) Initial information obtained for bacteria found in contaminated milk is that they belonged to photoheterotrophs group. The milk was pasteurized at 72oC and then cultured on nutrient agar media. The bacteria colonies appeared after three days.
i. What are the assumptions that can be made for their carbon and energy sources?
ii. Explain the appearance of colonies and suggest the bacteria group based on the physical requirements.
[20 Marks/markah]

4. 5) Information on bacterial growth is very important in food and industrial microbiology. i. Draw and label a typical bacterial growth curve and describe the phases involved. [15 marks] ii. Fifty cells of a bacterial species with a generation time of 25 minutes are introduced into a fresh sterile medium at 9.00 AM. The culture is maintained at an optimum growth temperature throughout the experimental period. Calculate the number of bacterial cells that can be obtained in this experiment at 3.00 PM and the number of generations by 6.00 PM. [10 marks]

5. 6) An inoculum of 107 bacterial cells was introduced into a flask of culture medium and the growth was monitored. No change was observed for the first 18 minutes; then growth occurred rapidly. After a further 76 minutes, the population had increased to 4.32 × 108 cells. Calculate the doubling time (Td) of the culture?
[20 marks/markah]