Sexual reproduction in algae is of three types :
(i) Isogamy: The fusion of morphologically and physiologically similar gametes. As a result the zygospore is formed.
(ii) Anisogamy: Fusion of two dissimilar gametes (morphologically or physiologically dissimilar).
(iii) Oogamy: There is a formation of male sex organ (antheridium) and female sex organ (oogonium).
The male gamete and female gamete fuses to form zygospore. Zoospores are thin-walled motile asexual spores.
Zygote is the result of sexual fusion of male and female gametes in higher plants.