Which growth medium is often used to cultivate bacteria in liquid form?

Broth is a liquid growth medium specifically designed for cultivating bacteria. It typically consists of various nutrients, such as sugars, proteins, vitamins, and minerals, in a water-soluble form, which allows for optimal bacterial growth and proliferation. In liquid broth cultures, bacteria can grow more freely without the constraints of a solid surface, facilitating quicker and often more robust multiplication compared to other forms of culture.

In contrast, agar is a solidifying agent derived from seaweed, primarily used for creating solid media in petri dishes, and while it supports bacterial growth, it is not a liquid form. Gelatin also serves as a gelling agent and is only effective in solidifying media, making it less suitable for liquid cultures. Silica is not typically a growth medium for bacteria but is more often used in laboratory settings for purposes like chromatography and purification processes. Hence, broth is the medium that specifically allows for liquid cultivation of bacteria, making it the correct answer.