Question

practice 2
answer the following questions about the cell cycle. darken the circle that corresponds to your answer choice.
a student observes onion cells using a compound microscope. the diagram below shows her observations. use this
diagram to answer questions 1 and 2.
graphic based on:
williamson, daniel 1.3.1 the cell cycle and mitosis
connexions. 16 feb. 2012
<http://cnx.org/content/m43135/1.1/>

1. which of the following statements best explains why most of the cells are observed in interphase?

a cytokinesis hasnt happened yet.
b the cells are stuck in interphase.
c interphase is the shortest phase of the cell cycle.
d interphase is the longest phase of the cell cycle.
2 in the image above, how many cells are in anaphase?
a 1 b 3 c 6 d 23

Explanation:

• Question 1:
• Option A: Cytokinesis is part of the mitotic phase (after anaphase, telophase). Interphase being long is the reason for more cells in interphase, not lack of cytokinesis.
• Option B: Cells are not “stuck” in interphase. Interphase is a normal, active part of the cell cycle where the cell grows, replicates DNA etc.
• Option C: Interphase is the longest, not the shortest phase of the cell cycle.
• Option D: Interphase is the longest phase of the cell cycle (comprising G1 - growth, S - DNA synthesis, G2 - preparation for mitosis). So, more cells are in interphase as it takes up most of the cell cycle time.
• Question 2:
• In anaphase, sister chromatids are pulled apart to opposite poles of the cell. By carefully observing the onion - cell diagram (assuming standard anaphase morphology where chromosomes are in a “V” or “J” shape as they are being separated), we can count the number of cells in anaphase.

Answer:

1. D. Interphase is the longest phase of the cell cycle.
2. B. 3