Question
Biology Question on Gymnosperms
In Cycas, the fertilization is
zoidogamous only
siphonogamous accompanied with zoidogamy
siphonogamous only
zoidogamous accompanied with siphonogamy
zoidogamous accompanied with siphonogamy
Solution
In Cycas, pollen grains absorb water in pollen chamber and germinate to form a pollen tube. Pollen tube carries two male gametes towards archegonial chambers. The process is named as siphonogamy (siphonos - tube+gamos - fusion). A male gamete is top-shaped, broad, spirally coiled structure whose anterior half contains thousands of small cilia emerging from the spiral grooves. Pollen tube bursts and discharges its content in archegonial chamber. Male gametes swim in the fluid of archegonial chamber to reach egg. Due to presence of dlia, gametes show movements to reach egg for fertilization. This process is named as zoidogamy. So, in Cycas fertilization is siphonogamous followed by zoidogamy (fertilization by the means of motile sperms).