The image displays what the water in the Caltech Turtle Pond contains, and there are many bacteria in the sample. This photo is taken at CaltechBi1 Recitation at Broad 300 at 7:40 pm, 04/10/2019. In order to obtain the picture, I placed a small drop of the water collected from Caltech Turtle Pond to the microscope slide and put a coverslip on top of it. Then I used the self-made foldscope to observe the sample and took the picture with my cellphone.

Here are some interesting questions about the picture: Approximately, what is the volume of the water in this drop? How large is a bacterium in the photo? How many bacteria there are in the drop? In order to solve the questions, we shall read the scale from the Foldscope and compare the scale with the observation to get the estimations. With the help of these questions, we can estimate how many bacteria there are in the Caltech Turtle Pond.

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