Question

What is heterospory? Briefly comment on its significance. Give two examples.

Answer 1

Hint: Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these is the microspore is male and the larger megaspore is female.

Complete answer:
Heterospory is considered to be a prerequisite to seed formation, in addition to heterospory the seed plants show the following characteristics that have led to the formation of seed.
- The sporangia show greater specialization than those of ferns.
- They are differentiated into micro and mega sporangia.
- The microsporangium possesses microspores whereas mega sporangia contains megaspores in them.
- Each microsporangium contains a large number of microspores whereas megasporangium possesses usually only four megaspores.
- The microspore germinates to form the male gametophyte and the megaspore germinates to form the female gametophyte.
- The male gametophyte releases the male gametes and these reach the female gametophyte to fuse with the egg.
- The development of the zygote takes place inside the female gametophyte.
- This retention and germination of the megaspore within the megasporangium ensures proper development of the zygote.
- The zygote develops into the future sporophyte.
- The evolution of the seed habit is related to the retention of the megaspore.
- Heterospory is thus considered an important step in evolution as it is a precursor to the seed habit.
- Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.
- The seed habit is the most complex and evolutionary successful method of sexual reproduction.
- It is found in vascular plants.

Note: Homospory: It is the production by a cryptogamic plant of spores that are all of uniform type and size and from which develop gametophytes which usually contain both male and female cells. For example: It includes most of the ferns and lycophytes.