3.2.2 All cells arise from other cells

Question 1

Q: What is the cell cycle in eukaryotic cells that retain the ability to divide?

Answer 1

A: The cell cycle is the process that eukaryotic cells go through when they divide, consisting of stages like interphase, mitosis, and cytokinesis.

Question 2

Q: When does DNA replication occur during the cell cycle?

Answer 2

A: DNA replication occurs during the interphase of the cell cycle.

Question 3

Q: What is mitosis, and what does it produce?

Answer 3

A: Mitosis is the part of the cell cycle where a eukaryotic cell divides to produce two daughter cells, each with identical copies of DNA as the parent cell.

Question 4

Q: What are the stages of mitosis?

Answer 4

A: The stages of mitosis are interphase, prophase, metaphase, anaphase, telophase, and cytokinesis.

Question 5

Q: What happens to chromosomes during interphase?

Answer 5

A: During interphase, chromosomes are replicated and exist as loosely packed chromatin in preparation for mitosis.

Question 6

Q: Describe the behaviour of chromosomes during prophase.

Answer 6

A: During prophase, chromosomes condense and become visible, and the nuclear envelope begins to break down. Spindle fibres also start to form.

Question 7

Q: What occurs during metaphase in mitosis?

Answer 7

A: During metaphase, chromosomes line up along the metaphase plate (equator) of the cell, with spindle fibres attached to their centromeres.

Question 8

Q: What is the role of spindle fibres during anaphase?

Answer 8

A: During anaphase, spindle fibres pull sister chromatids apart to opposite poles of the cell.

Question 9

Q: What happens during telophase of mitosis?

Answer 9

A: During telophase, the separated chromatids reach the poles of the cell, nuclear envelopes reform around each set of chromosomes, and the chromosomes begin to decondense.

Question 10

Q: What is cytokinesis, and what does it produce?

Answer 10

A: Cytokinesis is the division of the cytoplasm, which usually follows mitosis, producing two new daughter cells.

Question 11

Q: What can result from uncontrolled cell division?

Answer 11

A: Uncontrolled cell division can lead to the formation of tumours and cancers.

Question 12

Q: How do many cancer treatments work in relation to cell division?

Answer 12

A: Many cancer treatments work by controlling the rate of cell division.

Question 13

Q: What is binary fission in prokaryotic cells?

Answer 13

A: Binary fission is a process in prokaryotic cells where the circular DNA and plasmids replicate, and the cytoplasm divides to produce two daughter cells, each with a single copy of the circular DNA and a variable number of plasmid copies.

Question 14

Q: Do viruses undergo cell division?

Answer 14

A: No, viruses do not undergo cell division. Instead, they inject their nucleic acid into a host cell, which then replicates the virus particles.

Question 15

Q: What is involved in the preparation of stained squashes of cells from plant root tips?

Answer 15

A: It involves preparing stained samples of plant root tips to observe cells under an optical microscope and identify stages of mitosis.

Question 16

Q: How do you calculate the actual size of cells in a root tip using microscopy?
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Answer 16

A: The actual size of cells is calculated using the formula:
Actual size = Size of Image / Magnification

Question 17

Q: What is the mitotic index?

Answer 17

A: The mitotic index is a measure of the proportion of cells in a tissue sample that are undergoing mitosis.

Question 18

Q: What are the main phases of the cell cycle in eukaryotic cells?

Answer 18

A: The main phases of the cell cycle are Interphase (which includes G1, S, and G2 phases), Mitosis (which includes Prophase, Metaphase, Anaphase, and Telophase), and Cytokinesis.

Question 19

Q: What happens during the G1 phase of interphase?

Answer 19

A: During the G1 phase, the cell grows in size, synthesizes proteins, and produces organelles. This phase is also where the cell prepares for DNA replication.

Question 20

Q: What occurs during the S phase of interphase?

Answer 20

A: In the S phase (Synthesis phase), the cell replicates its DNA, so each chromosome consists of two sister chromatids. This ensures that the daughter cells will have identical genetic material.

Question 21

Q: What is the G2 phase of interphase?

Answer 21

A: The G2 phase involves further growth and preparation for mitosis. The cell checks for any DNA damage and ensures all the necessary proteins for mitosis are available.

Question 22

Q: What major events occur during prophase of mitosis?

Answer 22

A: During prophase, chromosomes condense and become visible under a microscope as distinct structures. The nuclear envelope begins to break down, and the mitotic spindle, composed of microtubules, starts to form. Centrosomes (which have duplicated during interphase) begin moving to opposite poles of the cell.

Question 23

Q: Describe the key processes during metaphase.

Answer 23

A: In metaphase, chromosomes align at the cell’s equator, also known as the metaphase plate. Each chromosome’s centromere attaches to spindle fibres emanating from opposite poles of the cell. This alignment ensures that each daughter cell will receive one copy of each chromosome during the next stage.

Question 24

Q: What happens during anaphase?

Answer 24

A: During anaphase, the centromeres split, and the spindle fibres shorten, pulling the sister chromatids apart toward opposite poles of the cell. This ensures that each new daughter cell will receive an identical set of chromosomes.

Question 25

Q: Explain the events that occur during telophase.

Answer 25

A: In telophase, the separated chromatids, now individual chromosomes, reach the poles of the cell. The nuclear envelope reforms around each set of chromosomes, forming two distinct nuclei. The chromosomes begin to decondense, returning to their less visible, thread-like chromatin state.

Question 26

Q: What is cytokinesis, and how does it differ from mitosis?

Answer 26

A: Cytokinesis is the process of dividing the cell’s cytoplasm to form two separate daughter cells. It usually occurs after mitosis. In animal cells, a contractile ring of actin filaments pinches the cell membrane to form two cells. In plant cells, a cell plate forms along the centerline of the cell and eventually develops into a separating wall.

Question 27

Q: How do the stages of mitosis ensure genetic consistency between daughter cells?

Answer 27

A: The stages of mitosis (prophase, metaphase, anaphase, and telophase) are designed to ensure that each daughter cell receives an identical set of chromosomes, preserving the genetic information from the parent cell.