Q.The ..................... collects the pollen grains. The male whorl, called the ..................... produces ..................... . The pollen grains represent the ........................ The .................... contains the egg or ovum.

Sexual reproduction involves the fusion of two compatible gametes and, unlike asexual reproduction, produces genetically variable offspring, an essential source of raw material for evolution by natural selection. In flowering plants the entire process is centred on the flower, the specialised reproductive structure whose job is to produce haploid gametes and give them the best chance of fertilizing. A complete flower is organised into four whorls, arranged from outermost to innermost: the calyx (sepals, typically green, protecting the bud), the corolla (petals, often coloured to attract pollinators and sometimes accompanied by nectar or fragrance), the androecium (the male whorl of stamens), and the gynoecium (the female whorl of carpels/pistil). All of these whorls are attached to the thalamus (receptacle), the base of the flower. For study purposes, the sequence of events in sexual reproduction is grouped into three stages: pre-fertilization events (gamete formation and pollination), fertilization (the actual fusion of gametes), and post-fertilization events (development of the endosperm, embryo, seed, and fruit).