Which group of cells would be least likely to contain cells in the S phase of the cell cycle?

• A. Neurons in the adult human brain
• B. Gastrointestinal tract lining cells
• C. Hematopoietic stem cells in the bone marrow
• D. Epithelial cells in the skin

Answer: (A)

Verified step by step guidance

1. Understand the S phase of the cell cycle: The S phase is the part of the cell cycle where DNA replication occurs, preparing the cell for division. Cells actively dividing or preparing to divide will be in the S phase.
2. Consider the characteristics of neurons in the adult human brain: Neurons are highly specialized cells that typically do not divide after differentiation. Most adult neurons are in a permanent state of rest known as G0 phase, making them unlikely to be in the S phase.
3. Examine gastrointestinal tract lining cells: These cells are constantly being replaced due to wear and tear from digestion, meaning they frequently enter the cell cycle, including the S phase, to replicate and replace old cells.
4. Evaluate hematopoietic stem cells in the bone marrow: These stem cells are responsible for producing new blood cells, which requires regular cell division. Therefore, they are often in the S phase as they prepare for division.
5. Assess epithelial cells in the skin: Similar to gastrointestinal tract lining cells, skin epithelial cells are regularly replaced due to external damage and wear, necessitating frequent cell division and presence in the S phase.