{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Experiment2-Bacteria

Experiment2-Bacteria - Experiment 2(Lab Periods 2 and 3...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Experiment 2 (Lab Periods 2 and 3) Determining the Number of Bacteria in a Colony Bacteria are found throughout the biosphere, inhabiting places that eukaryotes find uninhabitable, sharing all the places where eukaryotes live, and living in and on the bodies of eukaryotes. Most of the time, however, their presence is not obvious, and detection of live bacteria requires the employment of special techniques that must achieve two ends at once: (l) Allowing bacteria in a given sample to multiply until a number sufficient for them to be observable is attained, while (2) Avoiding allowing bacteria from any other material to grow and multiply. A commonly-used technique for the first purpose is the viable count, in which a sample of bacteria is mixed with a liquid (and diluted further in liquid if necessary) then spread out on the surface of a growth- supporting medium, usually agar in a petri plate. The bacteria are then allowed to grow and reproduce until each bacterium has produced so many offspring that the accumulated mass is macroscopically visible. Such a mass of bacteria is a colony, and the cell or cluster of cells that initiated development of the colony is a colony-forming unit (cfu). (The container of growth medium plus growing bacteria is a culture, whether it is liquid or solidified with agar.) The number of colonies on the plate’s surface tells you how many bacterial cells were in the solution you added. The methods for achieving the second purpose are collectively known as aseptic technique, or asepsis (literally, without infection). The first basic rule for asepsis is that all materials that come into contact your sample must be sterile. With reasonable care, this is possible except for air, which contains bacteria and fungi. Therefore, the second basic rule of asepsis is that all containers must be kept closed except when the experimenter must work within the containers, e.g., to inoculate (introduce the bacteria into) the medium or to remove some of the culture for one purpose or another. In this experiment, you will perform a viable count aseptically in order to determine how many live bacteria (cfu) are in a colony that you scrape off of an agar plate. Petri plates containing colonies different microorganisms (one organism per plate) will be distributed to the class. The colonies formed by different species of bacteria look different--in shape, size (diameter), color, whether they are shiny or matte in appearance, and the smoothness of the edge of the colony. At some time during the laboratory period, examine the colonies of all the organisms and record a description (including maximum diameter, in mm) of a typical colony of each organism; your description should be adequate to help you recognize the colonies of each organism.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern