The graph shows how the mass of DNA per cell changes before, during and after a nuclear division in a diploid cell.
Which row describes the type of nuclear division and the chromosome number of the daughter cells shown in the graph?
▶️ Answer/Explanation
Ans: C
The graph shows DNA mass doubling (S-phase) before division and returning to the original mass after division, characteristic of mitosis. In mitosis, diploid cells produce diploid daughter cells (2n → 2n). Meiosis (A/B) would halve chromosome number (2n → n), while option D incorrectly suggests haploid daughter cells from mitosis. Thus, C (mitosis, 2n) is correct.
The mitotic index of a tissue is the percentage of cells in the tissue that are dividing by mitosis. The table shows information about two tissue samples, X and Y.
Which statement is correct?
A) Tissue X is growing fastest with a mitotic index of 31.3%.
B) Tissue X is growing fastest with a mitotic index of 45.4%.
C) Tissue Y is growing fastest with a mitotic index of 13.6%.
D) Tissue Y is growing fastest with a mitotic index of 15.8%.
▶️ Answer/Explanation
Ans: A
The mitotic index is calculated as:
\[ \text{Mitotic Index} = \left(\frac{\text{Number of cells in mitosis}}{\text{Total number of cells}}\right) \times 100\% \]
For Tissue X: \[ \frac{42}{134} \times 100\% = 31.3\% \] For Tissue Y: \[ \frac{21}{154} \times 100\% = 13.6\% \]
Tissue X has a higher mitotic index (31.3% vs 13.6%), indicating faster growth. Option B incorrectly states 45.4%, while options C and D refer to Tissue Y’s lower index. Thus, the correct answer is A.