Yeasts are unicellular organisms from the kingdom Fungi. Saccharomyces cerevisiae is one species of yeast that can carry out either asexual reproduction by mitosis or sexual reproduction by meiosis. Budding in S. cerevisiae is a process where a small daughter cell forms as a bud on the parent cell. The bud contains a copy of the parent cell nucleus and it eventually separates from the parent cell to form a new cell. S. cerevisiae can exist in two forms: haploid cells or diploid cells. • Haploid cells can be one of two different mating types: a and α. • Haploid cells can only mate with other haploid cells of the opposite mating type. Fig. 2.1 shows the life cycle of S. cerevisiae with its asexual and sexual reproductive stages. Key: mating type a (a) mating type α [Figure 2.1]

1. (a)With reference to Fig. 2.1, state the numbers of the stages 1–5 that: involve mitosis involve meiosis produces new genetic variation shows only haploid cells shows only diploid cells[5]
2. (b)When there is a lack of nutrients, cells made in stage 3 will carry out stage 4 to make spores, which germinate only when conditions improve. Suggest and explain how the type of reproduction that makes spores during stage 4 is advantageous for S. cerevisiae in a changing environment.[4]
3. (c)Haploid and diploid cells of S. cerevisiae can carry out asexual reproduction. 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.[3]
4. (d)State two features, other than reproduction using spores, of the kingdom Fungi.[2]

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