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Figure 1 shows all the chromosomes present in one human cell during mitosis - AQA - A-Level Biology - Question 1 - 2018 - Paper 1
Question 1
Figure 1 shows all the chromosomes present in one human cell during mitosis. A scientist stained and photographed the chromosomes. In Figure 2, the scientist has ar... show full transcript
Worked Solution & Example Answer:Figure 1 shows all the chromosomes present in one human cell during mitosis - AQA - A-Level Biology - Question 1 - 2018 - Paper 1
Step 1
Give two pieces of evidence from Figure 1 that this cell was undergoing mitosis. Explain your answers.
Answer
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The chromosomes are visibly condensed and distinct, which indicates that they are in the process of separating during mitosis. This visibility suggests active division rather than resting phase.
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Each chromosome is composed of two sister chromatids, demonstrating that DNA has replicated prior to the division. This replication is a hallmark of the mitotic phase.
Step 2
Step 3
Suggest how this procedure moved the chromosomes apart.
Answer
The solution with a higher water potential would cause water to move into the cells via osmosis, leading to an increase in cell volume. As the cell expands, it helps push the chromosomes apart, reducing overlap and allowing for clearer observation under a microscope.
Step 4
Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas.
Answer
The chromosome could have varying densities of DNA or different regions of chromatin, such as heterochromatin versus euchromatin. Heterochromatin is more tightly packed and may bind more stain, giving a striped appearance.
Step 5
Step 6
Give two ways in which the arrangement of prokaryotic DNA is different from the arrangement of the human DNA in Figure 1.
Answer
- Prokaryotic DNA is circular, whereas human DNA is linear in structure.
- Prokaryotic DNA is not associated with proteins or histones, while human DNA is organized around histones, forming a complex structure known as chromatin.