Cell cycle and division：練習問題

Which of the following best describes the main biological significance of meiosis in organisms that reproduce sexually?

If a cell has a diploid number of \(2n = 8\), what is the total number of DNA molecules present in the cell during metaphase I of meiosis?

An organism has a diploid number of \(2n=12\). If non-disjunction of one homologous pair occurs during the first meiotic division, which of the following describes the chromosome count of the resulting gametes?

Which of the following processes occurs in eukaryotic cells to ensure that each daughter cell receives an identical set of chromosomes for growth and repair?

A specific chemical is applied to a plant root tip that prevents the formation of the cell plate during cytokinesis. Which of the following would be the most likely result of this treatment?

State the primary function of cytoplasmic division in the cell cycle.

In a multicellular organism, explain the significance of nuclear division occurring before cytoplasmic division during the cell cycle.

A somatic cell of a diploid organism with \(2n = 6\) chromosomes is observed. A specific mutation occurs that allows DNA replication and nuclear division to proceed normally, but completely inhibits cytoplasmic division (cytokinesis) during mitosis. Describe the nuclear condition and the total chromosome number of the resulting single cell once it reaches the next \(G_1\) phase.

The cell cycle is a controlled sequence of events that prepares a cell for division. It consists of interphase and the mitotic phase.

(a) Identify the specific sub-phase of interphase during which DNA replication occurs.
(b) Explain why it is essential for the cell to double its DNA content before undergoing mitosis.
(c) State the biological consequence for the daughter cells if the cell bypasses the DNA replication phase and proceeds directly to mitosis from the \(G_1\) phase.

Cytokinesis is the process of cytoplasmic division that follows nuclear division. This process differs significantly between animal and plant cells due to their structural differences.

(a) Describe the process of cytokinesis in an animal cell, making reference to the behaviour of the cell membrane.
(b) Explain why the mechanism described in (a) cannot occur in plant cells.
(c) Describe the role of vesicles in the formation of the new cell boundary during cytokinesis in plant cells.