We have this science experiment on how to grow a bacteria, our teacher told us to use gelatin, beef stock, and sugar as an alternative for agar. I am confused on why we need gelatin, beef stock, and sugar in growing a bacteria. What ingredient is in those 3 materials that can aid in growing bacteria?


2 Answers 2


There are several requirements for bacteria to grow.

  • A carbon source - Sugar
  • A nitrogen / amino acids source - Beef stock
  • Gelatin is there to hold everything in place, it doesn't provide any nutrients.
  • $\begingroup$ The list is incomplete. $\endgroup$
    – user37894
    Sep 2, 2018 at 21:33

Everything that lives needs food to grow. That food may be as simple as nutrients needed to build parts to more complex tasks like storing and/or converting energy.

Different bacteria require different things. A nutrient source like beef stock contains lots of amino acids and proteins which can feed a large spectrum of bacteria.

Sugar is a densely packed energy store that many bacteria can use for powering biologic processes.

Gelatin is a mixture of peptides and proteins which adds even more nutrients to the system. More importantly, its thick gelatinous structure acts as a binding agent/ substrate which keeps everything from sloshing around in the dish (which can be very inconvenient when moving it around).

In short the simple petri dish is about providing a wide variety of nutrients so that it can support the growth of a wide variety of microbes.

  • $\begingroup$ "Converting" rather than "producing" energy. $\endgroup$
    – user37894
    Sep 2, 2018 at 21:35
  • 1
    $\begingroup$ You know you could just edit it for a point that small $\endgroup$
    – anon
    Sep 2, 2018 at 21:39
  • $\begingroup$ i only edit my own answers. $\endgroup$
    – user37894
    Sep 3, 2018 at 5:53

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