Cell specialization practice questions.

State what is meant by a stem cell.

• A cell that has fully differentiated and can no longer divide
• A cell that can divide repeatedly and differentiate
• A cell that lacks a nucleus and therefore cannot express genes
• A cell found only in the embryo that dies once tissues have formed

Answer: A cell that can divide repeatedly and differentiate

A stem cell retains the capacity for continuous cell division (self-renewal) and can differentiate into one or more specialized cell types.

Distinguish between the potency of an embryonic stem cell in the early morula and a haematopoietic (bone marrow) stem cell.

• The morula cell is multipotent; the bone marrow cell is totipotent
• The morula cell is pluripotent and the bone marrow cell is totipotent
• The morula cell is totipotent; the bone marrow cell is multipotent
• Both are unipotent because they can only form one cell type

Answer: The morula cell is totipotent; the bone marrow cell is multipotent

Early cleavage cells (morula) are totipotent and can form any cell type plus placental tissue, whereas adult haematopoietic stem cells are multipotent, forming only a limited range of blood cell types.

Explain what makes two cells with identical genomes differentiate into different specialized types.

• They have different DNA sequences produced by mutation
• They express different subsets of their genes
• They contain different numbers of chromosomes
• One has lost its nucleus and the other has not

Answer: They express different subsets of their genes

Differentiation depends on differential gene expression: the same genome is regulated so that different genes are switched on in different cell types.

Which statement about the surface area to volume ratio of a cell as it increases in size is correct?

• The ratio increases, so large cells exchange materials more easily than small ones
• The ratio decreases, so above a certain size exchange cannot meet the cell's needs
• The ratio stays constant, so cell size has no effect on exchange
• The ratio decreases, but this speeds up diffusion into the cell

Answer: The ratio decreases, so above a certain size exchange cannot meet the cell's needs

As a cell grows, volume increases faster than surface area, lowering the SA:V ratio and eventually limiting the rate of exchange relative to metabolic demand.

In the emergence of multicellularity, cell specialization allows a division of labour. Which statement best describes the trade-off involved?

• Specialized cells are more efficient at one task but rely on others for lost functions
• Specialized cells can perform every function independently, so they need no other cells
• Specialization always increases the SA:V ratio of each cell
• Specialized cells divide faster than unspecialized cells in all cases

Answer: Specialized cells are more efficient at one task but rely on others for lost functions

Division of labour improves efficiency for a specific role but creates interdependence, as specialized cells rely on others for the functions they have given up.

Therapeutic uses of stem cells rely on which key property of stem cells?

• Their ability to secrete antibodies
• Self-renewal and differentiation
• Their lack of a plasma membrane
• Their ability to photosynthesize

Answer: Self-renewal and differentiation

Stem cell therapies exploit self-renewal and the capacity to differentiate into the specific cell types needed to replace damaged tissue.