Biology 9700 · AS & A Level · Structure of nucleic acids and replication of DNA
Structure of nucleic acids and replication of DNA — practice question
Fig. 3.1 shows a scanning electron micrograph of two human chromosomes at a stage in the mitotic cell cycle.
(a)[2]
Calculate the actual length, to the nearest $0.1\,\mu\text{m}$, of the chromosome in Fig. 3.1 shown by line $X$-$Y$. Write the formula used for your calculation.
(b)[1]
Outline one feature of Fig. 3.1 that shows the microscope used to produce the image was a scanning electron microscope rather than a transmission electron microscope.
(c)[1]
With reference to Fig. 3.1, explain how it can be inferred that DNA replication has already occurred.
Worked solution & mark scheme
This 4-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The actual length is derived from $\text{image length} / \text{magnification}$” …