Question

In Cycas, pollination takes place
(a) 3 - Celled stage
(b) 4 - Celled stage
(c) 2 - Celled stage
(d) 1 - Celled stage

Answer 1

Hint: Microspore is the starting cell of the male gametophyte and microspore nucleus divides into two which results in the formation of two unequal cells. The smaller one is known as a prothallial cell while the large one is known as the antheridial cell.

Complete step by step answer:
Microspore is the future male gametophyte. Each microspore is uninucleated and its protoplast is surrounded by a two- layered wall. Each microspore is divided into two and daughter nuclei are separated by a wall to form two cells that are prothallial cells and a large cell. The large cell divides to form tube cells and generative. At this stage, the sporophylls separate sporangium wall raptures and release 3 - celled semi germinated male gametophytes called a pollen grain. They are then carried to the female gametophyte where further development completes.

Additional Information:
- The pollen grains are carried by wind or anemophily and caught by pollination drop secreted by ovules thus pollination is direct.
- The pollination drop is dehydrated and the pollen grains are sucked into the pollen chamber.
- The pollen grain takes a rest for some time in the pollen chamber.
- During the germination of pollen grain the exine, the outer layer is ruptured and the inner intine comes out in the form of a tube- like structure known as pollen tube.
- The pollen tube acts as a haustorium to absorb food material from the nucleus besides as sperm carrier.
- The body cell divides and forms two naked, top- shaped, motile, multiciliated male gamete antherozoids.
- The presence of multinucleated male gametes is the fern character shown by Cycas male gametophyte.
So, the correct answer is ‘3 - Celled stage.’

Note:
- Each sperm cell consists of a large nucleus surrounded by a thin layer of cytoplasm.
- The pollen tube is haustorial in nature and it digests its way to the nucleus to the archegonia.
- The egg in Cycas is the largest amongst all living plants.