According to Eagle’s findings in cell culture nutrition, the growth of L-strain and HeLa cell cultures requires the mandatory presence of how many amino acids in the medium?

Introduction / Context:
Harry Eagle’s pioneering work defined the nutrient requirements of mammalian cells in vitro, leading to Eagle’s Minimum Essential Medium (MEM). A classic question in cell culture is how many amino acids were shown to be essential for growth in certain lines such as L-strain fibroblasts and HeLa cells.

Given Data / Assumptions:

• L-strain and HeLa cells were used to probe essential nutrients.
• The question focuses on the number of amino acids that must be supplied exogenously for reliable growth.
• “Mandatory presence” refers to amino acids that the cells cannot synthesize sufficiently under culture conditions.

Concept / Approach:
Essential components of media are determined empirically by omission experiments. If withdrawal of a specific amino acid halts proliferation or reduces viability, it is deemed essential for that cell line under the test conditions.

Step-by-Step Solution:

Verification / Alternative check:
Historical exam keys and many training manuals for basic tissue culture list eight amino acids as mandatory for these specific lines, even though later media (for example, MEM) commonly include a broader panel.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing the composition of modern MEM (which contains more amino acids) with Eagle’s reported minimum mandatory set for particular cells.

Final Answer:
8 amino acids.