Answer:

The correct answer is option 'C', which states that the serum in the growth medium for mammalian cells must be filter sterilized to remove mycoplasma and microorganisms. Let's understand why this is the correct answer.

Introduction to Serum in the Growth Medium:
Serum is a crucial component of the growth medium for mammalian cells. It provides essential nutrients, growth factors, hormones, and attachment factors that are necessary for the cells' growth and survival. However, serum can also potentially contain various contaminants, including mycoplasma and microorganisms, which can be harmful to the cell culture.

Importance of Sterilization:
Sterilization is a critical step in cell culture to ensure the purity and safety of the culture. Contamination with mycoplasma or microorganisms can have detrimental effects on the cells, leading to compromised experimental results or even loss of the entire culture. Therefore, it is essential to remove these contaminants before introducing the serum into the growth medium.

Filter Sterilization:
Filter sterilization is a widely used method to remove contaminants from serum. This process involves passing the serum through a sterilizing filter with a defined pore size that can retain microorganisms and mycoplasma, while allowing the serum components to pass through.

Removal of Mycoplasma:
Mycoplasma is a type of bacteria that can easily contaminate cell cultures. They are small in size and can go unnoticed under a microscope. Mycoplasma contamination can result in changes in cell behavior, metabolism, and gene expression, affecting experimental outcomes. Therefore, filter sterilization is crucial to remove mycoplasma from the serum before using it in the growth medium.

Removal of Microorganisms:
Microorganisms, including bacteria and fungi, can also contaminate serum and pose a risk to cell cultures. These contaminants can multiply rapidly and cause cell death, altered growth rates, or the production of unwanted metabolites. Filter sterilization effectively removes these microorganisms, ensuring the purity of the serum used in the growth medium.

Conclusion:
In summary, the correct answer 'C' states that serum in the growth medium for mammalian cells must be filter sterilized to remove mycoplasma and microorganisms. This step is crucial to maintain the purity and safety of the cell culture, preventing contamination-related issues and ensuring reliable experimental results.