Question

[A] What is meant by pollination ? Explain the structure of a germinating pollen grain with the help of a labelled diagram.

[B] With the help of suitable diagrams, describe :

• Binary fission in plants
• Budding in Yeast cell

Answer 1

Answer

• The method of transferring pollen grains to the stigma from the anthers is known as pollination.
• It can be of two types:

1. Cross pollination
2. Self-pollination

• Shown below is the structure of a pollen grain -

• The pollen tube is produced as soon as the pollen falls on the stigma of carpel and grows down through the style towards ovary.
• By the process of mitosis, the egg nucleus divides into two male gametes.
• After entering the ovary, the tip of pollen tube releases the two male gametes into the embryo sac

[B]
Binary fission is common in lower organisms such as bacteria.

• It is one of the types of asexual reproduction in plants.
• First, the nucleus of the bacteria separates into two.
• Then, the bacterial cell is divided across the middle and a wall is formed.
• Finally, two identical cells are formed known as daughter cells.

Yeast commonly reproduce by the asexual method of budding.

• Budding in yeast cell takes place to form a genetically identical organism.
• At first, an outgrowth is produced by the parent cell, known as bud.
• The bud grows eventually with time.
• The parent cell nucleus divides into daughter nucleus, which then separates into the daughter cell.