Biology 9700 · AS & A Level · Passage of information from parents to offspring
Passage of information from parents to offspring — practice question
Yeasts are single-celled organisms belonging to the kingdom Fungi. One yeast species, Saccharomyces cerevisiae, is able to reproduce asexually by mitosis or sexually by meiosis. In S. cerevisiae, budding occurs when a small daughter cell develops as a bud on the parent cell. The bud contains a copy of the parent cell nucleus and later detaches from the parent cell to become a new cell. S. cerevisiae may be present as either haploid cells or diploid cells. Haploid cells occur in two mating types: a and $\alpha$. A haploid cell can mate only with another haploid cell of the opposite mating type. Fig. 2.1 illustrates the life cycle of S. cerevisiae, showing both its asexual and sexual reproductive stages.
(a)[5]
Using Fig. 2.1, identify the stage numbers $1\text{-}5$ that:
involve mitosis
involve meiosis
produces new genetic variation
shows only haploid cells
shows only diploid cells
(b)[4]
When nutrients are scarce, cells produced in stage $3$ will undergo stage $4$ to make spores, and these spores germinate only when conditions improve.
Suggest and explain how the form of reproduction that produces spores during stage $4$ is advantageous for S. cerevisiae in a changing environment.
(c)[3]
Haploid and diploid cells of S. cerevisiae can both reproduce asexually.
Suggest why a new harmful recessive mutation may not have a damaging effect on:
• an asexually reproducing population of haploid cells of S. cerevisiae
• an asexually reproducing population of diploid cells of S. cerevisiae.
(d)[2]
State two features of the kingdom Fungi, other than reproduction using spores.
Worked solution & mark scheme
This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: “mitosis shown in diagrams 1 and 3” …