Question

How does cleistogamy ensure autogamy?
State one advantage and one disadvantage of cleistogamy to the plant.

Answer 1

When pollen grains are transferred from the anthers to the stigma of the same flower, it is called self-pollination or autogamy. cleistogamy is a type of automatic self-pollination of certain plants which can reproduce through the use of unopened self-pollinating flowers.

Complete answer:
First of all before answering the question let’s understand what is pollination
Transfer of pollen grains from open anthers of flowers to the pistil is called pollination.
Autogamy or self pollination-When pollen grains are transferred from the anthers to the stigma of the same flower, it is called self-pollination. that is. Commelina benghalensis from Commelinaceae, Argemone mexicana from Papaveraceae, and others.
Geitnogamy-The process of transferring pollen grains from one flower anther (same-sex or bisexual flower) to the pistil of another flower (same-sex or bisexual) that appears on the same plant is called geitonogamy.]
Xeno-gamy-it involves the transfer of pollen grains from the flower of one plant to the pistil of another plant. It is the only type of pollination that genetically stigmatizes different types of pollen during pollination, such as papaya, corn and others.
Self-pollination only occurs in bisexual flowers and is never unisexual. There are various devices that ensure self-pollination
Now we start with first part of the question
1.Cleistogamy: Some plants produce small, closed bisexual flowers alongside normal flowers. These tiny flowers remain in or underground and never open, so self-pollination is obvious. Such flowers are called Cleistogamous flowers.
These types of flowers are invariably autogamous (self pollinated) as there is no chance of cross-pollination. Cleistogamous flowers produce assured seed sets even in the absence of pollinators, example- Oxalis .
Now we can easily answer the second part of the question.
2.Advantages
The purity of the breed is maintained through self-pollination.
Pollen waste is negligible. The likelihood of pollination failure is much lower.
Disadvantage
Production of new species and varieties is hampered. Due to self-pollination that lasts for several generations, the offspring become weak.

Note: Obligate Cleistogamy :The flowers are usually cleistogamous and never open, example-Small underground flowers of Commelina benghalensis from Commelinaceae
Facultative Cleistogamy: Flowers stay open for a short time and then close permanently, example-Drosera burmannii from Droseraceae , Oxalis corniculata from Oxalidaceae, and others.
Homogamy In this method, the anthers and the pistil ripen together, for example mirabilis. It also ensures cross pollination.