Q4. Assertion: a cell in G2 has twice the DNA of a cell in G1 but the same number of chromosomes. Reason: S phase doubles the DNA from 2C to 4C without increasing the chromosome number. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT page 121).
Q5. Distinguish cytokinesis from karyokinesis. (NCERT Exercise 2)
Karyokinesis is nuclear division, the separation of daughter chromosomes; cytokinesis is the division of the cytoplasm that usually follows (NCERT page 121).
Q6. What happens in G2 phase?
Proteins are synthesised in preparation for mitosis while cell growth continues (NCERT page 121).
Q7. What is the average cell cycle span for a mammalian cell? (NCERT Exercise 1)
About 24 hours: NCERT’s example, human cells in culture, divide about once every 24 hours, with M phase about 1 hour of it (NCERT page 121).
Q8. Describe the events taking place during interphase. (NCERT Exercise 3)
G1: the cell is metabolically active and grows but does not replicate its DNA. S: the DNA replicates and doubles from 2C to 4C while the chromosome number stays 2n; in animal cells the centriole duplicates. G2: proteins are made for mitosis while growth continues (NCERT page 121). NCERT’s Summary adds that most organelle duplication happens in G1 (page 129).