Phylogeny of the generative organs of plants
Generative organs serve reproduction. Algae multiply by division and zoospores, and in unfavourable conditions gametes fuse to form a zygote with a tough wall. Land plants evolved sporangia and multicellular organs in which gametes mature (archegonia, antheridia). Spore plants show alternation of generations: the gametophyte (n) makes gametes, after fertilisation a sporophyte (2n) develops and spores mature. In mosses the gametophyte dominates, in clubmosses, horsetails and ferns the sporophyte dominates; they need water for fertilisation. Seed plants evolved the seed, which consists of an embryo, food reserve and coat, so it endures unfavourable conditions; the pollen tube freed fertilisation from dependence on water, and the gametophyte became tiny. In gymnosperms the ovule lies exposed and the endosperm is haploid (n). In angiosperms the seed ripens inside the fruit; the flower, double fertilisation (one sperm fuses with the egg cell, the other with the central cell, giving triploid endosperm, 3n), and pollination and seed dispersal by insects, wind and animals secured their dominance.
Observe a section of a fruit (apple or pear): seed coat, embryo, parts of the fruit. Draw it and mark which parts came from the ovule and which from the ovary. Safety: an adult does the cutting; a child with allergies must not taste it.