7. What is heterospory? Briefly comment on its significance. Give two examples.
Heterospory- It refers to the existence of two types of meiospores i.e. microspores and megaspores in a single plant. These microspores and megaspores are formed respectively within microsporangia and megasporangia which in turn are borne on two distinct sporophylls called microsporophylls and megasporophylls respectively. The microspores and megaspores upon germination give rise to male and female gametophyte respectively. The megaspore is retained in megasporangia and it ensures proper development of the zygote. which is formed after the fusion of microgametes with the megagametes. The zygote is retained on the plant and it is considered to be a precursor of seed habit.
Significance of heterospory- Heterospory is considered to be an important step in evolution as it is a precursor of seed habit which is seen in higher plants. Heterospory was first observed in pteridophyte Selaginella and Salvinia.