# Explain how the alternation of generations in plants, involving both a sporophyte and a gametophyte phase, contributes to reproductive success.

> IB DP Biology Standard Level (2023 syllabus) — D3.1 Reproduction · Explain · 4 marks

> Plants have a life cycle known as alternation of generations, in which a diploid sporophyte generation alternates with a haploid gametophyte generation. The relative dominance of each phase varies considerably across plant groups.

## Mark scheme (4 marks)

1. The sporophyte is diploid (2n) and produces haploid spores by meiosis.
2. The gametophyte is haploid (n) and produces gametes by mitosis, which fuse at fertilisation to restore the diploid chromosome number.
3. Meiosis during spore production introduces genetic variation through independent assortment and/or crossing over, increasing adaptability of offspring.
4. Having two distinct multicellular phases allows the plant to exploit both sexual reproduction (for genetic diversity and dispersal) and asexual spore dispersal, maximising reproductive opportunities.

## Key terms

- [alternation of generations](https://www.gradenine.co.uk/glossary/alternation-of-generations)
- [sporophyte](https://www.gradenine.co.uk/glossary/sporophyte)
- [gametophyte](https://www.gradenine.co.uk/glossary/gametophyte)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-alternation-of-generations-0fc9215a) · Published by Druglandscape Ltd.