Biology 9700 · AS & A Level · Structure of nucleic acids and replication of DNA

Structure of nucleic acids and replication of DNA — practice question

A student studied root growth in broad bean, Vicia faba. Sections were cut from the root tip of this plant and examined using a light microscope. Fig. 1.1 shows a photomicrograph of one of the sections. The cell labelled D is in interphase.
(a)[5]

Complete the table below by: • naming the stages of mitosis in the correct sequence following interphase • identifying one example from the cells labelled A to H that is in each stage of mitosis that you have named.

(b)[2]

In animal cells, centrioles assemble microtubules to form the spindle at the start of mitosis. Describe what the spindle does during mitosis.

(c)[2]

State two roles of mitosis in plants and animals besides growth.

(d(i))[2]

V. faba is a legume. Roots of legumes often show swellings at intervals called nodules. Cells in the nodules contain nitrogen-fixing bacteria. Explain the role of nitrogen fixation in the nitrogen cycle.

(d(ii))[3]

In some parts of the world, farmers grow legume crops and cereal crops together in the same field. This is called intercropping. Explain how intercropping leads to an increase in cereal yield when the legumes die.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: Correct sequence of the cell-cycle stages together with the correct cell matched to each stage: prophase - A/H; metaphase - G; anaphase - C/E/F; telophase - B

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