Question

CRITICAL THINKING

1) When pouring Nutrient agar into Petri plates, the procedure instructs you to keep the covers slightly ajar. Explain why the plates don’t get contaminated from organisms suspended in the air?

2) How could you determine the turbidity in your nutrient broth tube was from a mixture of different microbes or from the growth of only one kind of microbe?

Answer 1

2.Identification of kind of microbe - first take a sterile pippete take the turbid solution into the paper and mix it with distilled water then stay in it with safranin or methylene blue or Crystal Violet ( about1% stain ) and observe it under microscope you could identify different shapes and sizes and distinguish between microbes based on the stain they have taken .

1. Petri dish slightly ajar - the petri dish is kept slightly ajar to provide moisture and light to the colony or the culture. And since the petri dish is kept in incubator during the process the chances of contamination are very low. The dishes usually sterilized so this also lowers the risk of contamination.