Final answer:
A culture medium with ingredients that are not chemically definable is known as a complex medium. Complex media contain extracts of organic materials and their exact composition is variable, making the nutrients provided by them also variable.
Step-by-step explanation:
A culture medium which contains materials that are not chemically definable is known as a complex medium. A complex medium, also referred to as an undefined medium, is a type of culture medium that contains extracts and digests of yeasts, meat, or plants. Unlike chemically defined media, where the exact chemical composition is known, the ingredients within a complex medium can vary between batches, so the exact amounts of individual components are undetermined and potentially variable.
Culture media are essential for the growth of cells or bacteria in a laboratory setting. In complex media, such as Tryptic Soy Broth (TSB), Nutrient Broth, and Brain Heart Infusion, the exact composition is unknown because they are made from natural products like yeasts, meat, or plants, whose exact quantities of nutrients cannot be precisely quantified. These types of media are used to grow bacteria that do not require specific nutritional needs or when the exact nutritional profile needed for growth is not known.
Complex media are contrasted with chemically defined media, which contain only substances with a known chemical composition, like small molecules and genetically engineered proteins or peptides. This allows for precise control over the growth conditions, which is necessary when the exact nutritional requirements of the microorganism are understood.