Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants produced within specialized structures called megasporangia. The megaspore, or large spore, germinates into a female gametophyte, which produces egg cells. These are fertilized by sperm produced by the male gametophyte.

Majority of flowering plants use a range of animals as pollinating agents. Bees, butterflies, flies, beetles, wasps, ants, moths, birds (sunbirds and humming birds) and bats are the common pollinating agents. Entomophily is the type of pollination in which the pollination is done by insects. Majority of insect-pollinated flowers are large, colourful, fragrant and rich in nectar. When the flowers are small, a number of flowers are clustered into an inflorescence to make them conspicuous. Animals are attracted to flowers by colour and/or fragrance. The flowers pollinated by flies and beetles secrete foul odours to attract these animals. To sustain animal visits, the flowers have to provide rewards to the animals. Nectar and pollen grains are the usual floral rewards. For harvesting the reward(s) from the flower the animal visitor comes in contact with the anthers and the stigma. The body of the animal gets a coating of pollen grains, which are generally sticky in animal pollinated flowers. When the animal carrying pollen on its body comes in contact with the stigma, it brings about pollination. In some species floral rewards are in providing safe places to lay eggs; an example is that of the tallest flower of Amorphophallus . A similar relationship exists between a species of moth and the plant Yucca where both species – moth and the plant – cannot complete their life cycles without each other. The moth deposits its eggs in the locule of the ovary and the flower, in turn, gets pollinated by the moth. The larvae of the moth come out of the eggs as the seeds start developing.

Differentiate between microsporogenesis and megasporogenesis.

Features Microsporogenesis Megasporogenesis Definition Microsporogenesis involves the formation of microspores from microspore mother cells by meiotic division. Megasporogenesis is the process of formation of megaspores from the megaspore mother cell. Occurrence It occurs inside the pollen sac of the anther. It occurs in the ovule of the ovary. Number of spores produced In microsporogenesis, four microspores are produced from each microsporocyte cell. Megasporogenesis results in the formation of a single functional megaspore from each megasporocyte cell. The other three megaspores usually degenerate and do not contribute to female gametophyte formation. Function and Development: Microspores produced during microsporogenesis develop into pollen grains, which contain the male gametophyte. These pollen grains are eventually released and transported to the female reproductive organ for fertilization. The surviving megaspore formed during megasporogenesis undergoes subsequent development to form the female gametophyte (embryo sac). The female gametophyte contains the egg cell and other cells necessary for fertilization and embryo formation.