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Lab 4 - Prokayotic Diversity A - Student0

Lab 4 - Prokayotic Diversity A - Student0 - Bsc2011 Lab 4...

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Bsc2011 Lab 4 Prokaryotic Diversity 1 As you will learn in part B, prokaryotes are simple in structure: it is not easy to visually distinguish between species. To move forward, microbiologists long ago developed many different kinds of culture media – agar infused with different nutrients – to grow prokaryotes. Each kind of medium is selective: < 1% of all the estimated prokaryotes can be grown on agar! Obviously, a culture-based effort to evaluate prokaryotic diversity will provide a small window on the world of prokaryotes, and that's why molecular methods have become so popular. But culture-based methods provide advantages: they are standardized, relatively cheap and easy, and thus provide a simple and uniform sample of diversity that microbiologists continue to find useful. You'll learn more about molecular biology in subsequent courses: for now we will use a straight-forward culture-based approach to sample prokaryotic diversity in samples with unknown numbers of species and cell densities. Along the way you will learn about aseptic technique, experimental controls, serial dilutions, and quantitative analysis. You will use results collected by your lab to write your own report – a fairly large effort and important part of your grade - so plan now to start early on your lab report. Objective: Conduct an experiment on microbial diversity, and using cultures extracted from different sources and including a group Lab Report. Your lab group will experimentally test for prokaryotic microbial diversity that comes off a vegetable or fruit when you wash it. You will also test for microbial diversity in the sterilized water used to wash the vegetable/fruit. Why is it important to test the sterilized water? Each group will culture heterotrophic microbes, share results with your lab section, and you will write a lab report based on the lab section's data. Microbial cells that grow on nutrient agar develop colonies, where each colony represents a “mother” cell: counting colonies is a way to count bacteria cells in the original sample. Diversity of any assemblage (bacteria, trees, or birds) is composed of both the species richness (number of species) and the abundance of each species. We'll get into that further below, but you should know now that you will be collecting data on the number of different microbe species you grow and the counts of each one. BSC2011 Lab 4 Prokaryotic Diversity A
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Bsc2011 Lab 4 Prokaryotic Diversity 2 An important tool in work with microbes is a negative control . The idea is that sterile water grown on sterile medium should remain sterile IF your technique was adequate, and results will be negative (no colonies). If your technique contaminated the sterile system, then your results are due to both the experiment and your non-sterile addition of microbes – you will need to take this into account when you evaluate your other results. Therefore, you will also use sterile water as your negative control. The water was autoclaved (high temperature and pressure) in the
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Lab 4 - Prokayotic Diversity A - Student0 - Bsc2011 Lab 4...

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