cell cycle homework questions

1. during which stage of the cell cycle does replication of the dna occur?

2. why is it necessary that the cell copies its dna?

3. why are chromosomes visible during mitosis but not at other times?

4. under a microscope, some cells can appear to be between metaphase and anaphase. explain this observation.

5. which stage or phase of the cell cycle corresponds to each of the descriptions below?
a) a new cell wall begins to form
b) the membrane of the nucleus dissolves.
c) daughter chromosomes begin to separate
d) the cell begins to pinch together along its centre.
e) thick chromosome threads are visible in two distinct regions of the cell.
f) the cell grows and copies its dna.

6. create a table to summarize what happens during the three stages of the cell cycle. use this page.

7. identify a name used to describe interphase as the
esting phase\. based on what we know, what was wrong with this term?

Question

cell cycle homework questions

1. during which stage of the cell cycle does replication of the dna occur?

2. why is it necessary that the cell copies its dna?

3. why are chromosomes visible during mitosis but not at other times?

4. under a microscope, some cells can appear to be between metaphase and anaphase. explain this observation.

5. which stage or phase of the cell cycle corresponds to each of the descriptions below?
   a) a new cell wall begins to form
   b) the membrane of the nucleus dissolves.
   c) daughter chromosomes begin to separate
   d) the cell begins to pinch together along its centre.
   e) thick chromosome threads are visible in two distinct regions of the cell.
   f) the cell grows and copies its dna.

6. create a table to summarize what happens during the three stages of the cell cycle. use this page.

7. identify a name used to describe interphase as the
esting phase\. based on what we know, what was wrong with this term?

Accepted Answer

### Question 1 # Brief Explanations: DNA replication occurs during the S (synthesis) phase of interphase in the cell cycle. Interphase has G₁ (growth), S (DNA synthesis), and G₂ (pre - mitotic growth) phases. In the S phase, the cell's DNA is replicated to ensure that each daughter cell gets a complete set of genetic material. # Answer: During the S (synthesis) phase of interphase. ### Question 2 # Brief Explanations: Cell division (mitosis or meiosis) results in the formation of new cells. For the daughter cells to be genetically identical (in mitosis) or to have the correct genetic complement (in meiosis), the parent cell must copy its DNA. This ensures that each new cell receives a full set of genetic instructions necessary for its function, growth, and development. # Answer: To ensure that each daughter cell produced during cell division receives a complete set of genetic information (DNA) so that the daughter cells can function properly, grow, and carry out all necessary cellular processes. ### Question 3 # Brief Explanations: In non - mitotic phases (interphase), the DNA is in the form of chromatin, which is a loose, uncoiled structure composed of DNA and proteins. During mitosis, the chromatin condenses into tightly coiled chromosomes. This condensation process makes the chromosomes visible under a microscope as distinct, rod - like structures. The condensation is necessary for the proper segregation of genetic material during cell division. # Answer: In interphase, DNA is in the form of loose chromatin. During mitosis, chromatin condenses into tightly coiled chromosomes, making them visible. ### Question 4 # Brief Explanations: The transition between metaphase and anaphase is a continuous process, not an instantaneous switch. Cells are observed at different moments in time under the microscope. Some cells may be in the process of moving from the metaphase (where chromosomes are aligned at the equator) to anaphase (where sister chromatids start to separate). So, their appearance shows characteristics of both phases as they are in the middle of this transition. # Answer: The transition from metaphase to anaphase is a continuous process. Cells observed are at different time points in this transition, so they show features of both phases (e.g., chromosomes starting to separate from the metaphase plate). ### Question 5 #### a) # Brief Explanations: In plant cells, during cytokinesis (the final stage of cell division), a new cell wall begins to form. This occurs after mitosis is completed, during the cytokinesis phase. In plant cells, a cell plate forms which develops into the new cell wall. # Answer: Cytokinesis (in plant cells, the formation of the cell plate which becomes the cell wall occurs during cytokinesis). #### b) # Brief Explanations: During prophase of mitosis, the nuclear membrane (nuclear envelope) dissolves. This allows the spindle fibers to have access to the chromosomes and is part of the preparation for chromosome movement and separation. # Answer: Prophase (of mitosis). #### c) # Brief Explanations: During anaphase of mitosis, the sister chromatids (now called daughter chromosomes) are pulled apart by the spindle fibers and begin to move towards opposite poles of the cell. # Answer: Anaphase (of mitosis). #### d) # Brief Explanations: In animal cells, during cytokinesis, the cell membrane begins to pinch together along the cell's equator (the cleavage furrow forms). This process eventually divides the cell into two daughter cells. # Answer: Cytokinesis (in animal cells, the formation of the cleavage furrow occurs during cytokinesis). #### e) # Brief Explanations: During telophase of mitosis, the chromosomes (which have been separated) reach the opposite poles of the cell. At this stage, the thick chromosome threads are visible in two distinct regions (the poles) of the cell as the nuclear membranes start to reform around them. # Answer: Telophase (of mitosis). #### f) # Brief Explanations: During interphase (specifically the G₁ and S phases, with the S phase being where DNA is copied), the cell grows and replicates its DNA. The G₁ phase is for growth and preparation for DNA synthesis, the S phase is for DNA replication, and the G₂ phase is for further growth and preparation for mitosis. # Answer: Interphase (specifically the S phase for DNA replication, with growth occurring throughout interphase). ### Question 6 # Brief Explanations: The three main stages of the cell cycle are interphase, mitosis, and cytokinesis. Interphase has G₁ (cell growth, normal functions, preparation for S phase), S (DNA replication), and G₂ (cell growth, preparation for mitosis) sub - phases. Mitosis has prophase (chromosome condensation, nuclear envelope breakdown), metaphase (chromosomes align at equator), anaphase (chromosome separation), and telophase (nuclear envelope reform, chromosome de - condensation). Cytokinesis is the division of the cytoplasm, forming two daughter cells. | Stage of Cell Cycle | Key Events | | ---- | ---- | | Interphase | - G₁: Cell grows, performs normal functions, prepares for DNA synthesis.
- S: DNA replication occurs.
- G₂: Cell grows, prepares for mitosis. | | Mitosis | - Prophase: Chromosomes condense, nuclear envelope dissolves, spindle forms.
- Metaphase: Chromosomes align at cell equator.
- Anaphase: Sister chromatids separate and move to opposite poles.
- Telophase: Nuclear envelopes reform, chromosomes de - condense. | | Cytokinesis | - Animal cells: Cleavage furrow forms, cell pinches into two.
- Plant cells: Cell plate forms, develops into new cell wall, dividing the cell. | # Answer: | Stage of Cell Cycle | Key Events | | ---- | ---- | | Interphase | - G₁: Cell growth, normal functions, prep for S.
- S: DNA replication.
- G₂: Growth, prep for mitosis. | | Mitosis | - Prophase: Chromosome condense, nuclear envelope breaks.
- Metaphase: Chromosomes align at equator.
- Anaphase: Sister chromatids separate.
- Telophase: Nuclear envelopes reform, chromosomes de - condense. | | Cytokinesis | - Animal: Cleavage furrow, cell pinches.
- Plant: Cell plate forms, new cell wall. | ### Question 7 # Brief Explanations: Interphase is not a "resting phase" because the cell is actively carrying out many functions. During G₁, the cell grows, synthesizes proteins, and performs its normal metabolic functions. In the S phase, it replicates its DNA. In the G₂ phase, it continues to grow and prepares for mitosis by synthesizing necessary proteins (like those for the spindle apparatus). So, the cell is metabolically active and preparing for cell division during interphase, not resting. # Answer: Interphase is misnamed as a "resting phase" because the cell is actively growing (G₁, G₂), replicating DNA (S), and performing metabolic functions, preparing for cell division.

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