(f) the significance of meiosis in life cycles

The idea

Meiosis matters in life cycles because it halves the chromosome number and reshuffles alleles, so gametes carry one set of chromosomes and fusion at fertilisation restores the diploid number. In animals, meiosis produces gametes directly and keeps the chromosome number constant across generations. In plants and many algae, meiosis produces spores that grow into a haploid gametophyte, and gametes form later by mitosis, so the haploid stage is multicellular. In fungi, meiosis follows fusion in the zygote. Genetic variation arises from crossing over in prophase I and independent assortment in metaphase I, giving offspring a new allele combination.

What earns the marks

• Meiosis halves the chromosome number, producing haploid cells from a diploid parent cell.
• Fusion of two haploid gametes at fertilisation restores the diploid number, keeping chromosome number constant between generations.
• In animals meiosis produces gametes directly; in plants and many algae meiosis produces spores that develop into a haploid gametophyte.
• Crossing over in prophase I and independent assortment in metaphase I generate genetic variation among the products.
• In fungi, meiosis occurs in the zygote after fusion, so the diploid phase is brief.

Common mistakes and how to put them right

• Saying meiosis doubles the chromosome number.

  Put it right: Is that it halves it, from diploid to haploid.

• Claiming meiosis always produces gametes directly.

  Put it right: Is that in plants and many algae it produces spores that grow into a gametophyte.

• Ignoring variation: correction is that crossing over and independent assortment are part of meiosis's significance, not an optional extra.

Exam tips

• Link each significance point to a named organism group (animal, plant, fungus) so the answer is specific.
• State the diploid-to-haploid change and the fertilisation reversal explicitly, using the terms haploid and diploid.
• When asked about variation, name crossing over and independent assortment and the stage at which each occurs.