What does a pollen grain have to do in order to fertilize an egg?

Pollen tin be divers as a bristly or fine powder that consists of microgametophytes and mass produces sperm cells or male person gametes. The branch of biology that focuses on the study of pollen and its properties is called Palynology. Pollen grains are transferred by wind, h2o, air, birds, insects, animals to the female plants for the objective of fertilization. In this article, we will explore the type, structure, process of transfer, and sample questions for pollen grains.

Read Also: Class 12 Reproduction

Pollen Grains: Definition and Structure

Pollen grains refer to a powdery substance which is basically the male micro gametophytes of seeded plants, responsible for producing the male person gametes.

Structure of pollen grains

Pollen grains have microscopic frameworks differing in their construction and size. The size of pollen grains ranges from species to species. The authentic size of a pollen grain ranges from two to three hundred micrometers. The pollen grain might be ovule, triangular, circle, disc, or bean-shaped having a polish to spiky texture. The original color of pollen grains is white; however, this may vary depending on the plant species. Many may too be orange, cream, or yellow in color.

Structure of Pollen Grains

The pollen grain comprises mainly of 3 parts:

1. The thin inner layer goes by the proper name of intine, it is composed of cellulose and pectin. This layer degenerates briskly during fossilization.
2. The harder outer layer is chosen exine, information technology is made up of sporopollenin and is highly resistant. It belongs to the various organic grade called terpenes.
3. The within of the cell, filled with living cytoplasm, degrades rapidly during fossilization.

The exine has germ pores, which are distinct apertures that do not have sporopollenin present in them. Afterwards maturing, the pollen grains have 2 cells named the vegetative and generative cells.

Bank check out detailed notes for Sexual Reproduction in Flowering Plants.

Read More Nearly Sexual Reproduction in Flowering Plants

Formation of Pollen Grains

The formation of a pollen grain from a microspore involves the following changes-

• Augmentation of the microscope.
• Evolution of a large vacuole.
• Microspore nucleus replaced to an eccentric position confronting microspore wall.
• The nucleus undergoes first pollen mitosis.
• A pocket-size generative cell and a big vegetative jail cell are formed.
• The generative prison cell removes itself from the pollen grain wall.
• The generative cell is enveloped by the vegetative prison cell.
• A structure is formed having two cells betwixt each other called a 'prison cell within a jail cell'.
• The generative cell farther goes through mitosis.
• Two sperm cells are formed within the cytoplasm of the vegetative cell.

Germination of Pollen Grain

Of import Notes on Asexual reproduction

Pollination

Transfer of pollen grains from anther to the stigma is termed as pollination. The same occurs with the aid of pollinating agents similar current of air, air, h2o, birds, insects, etc.

Types of pollination

1. Autogamy: Transportation of pollen grains from anther to the stigma of the same blossom. Observed in plants that generate Cleistogamous and Chasmogamous flowers.

Case- Polygala, Viola

2. Xenogamy: The transportation of pollen grains from anther to the stigma of a dissimilar flower. It facilitates cross-pollination functionally too as genetically.
3. Geitonogamy- Transportation of pollen grains from the anther to the stigma of a unlike flower belonging to the aforementioned plant. It facilitates cross-pollination functionally only self-pollination genetically.

Process of Pollination

1. Pollinating agents: Agents which assistance in transferring the pollen grains from the anther to the stigma of the aforementioned/dissimilar found are termed as pollinating agents. Pollinating agents tin can exist divided into two types-

• Biotic- Biotic agents are living organisms that take the role of pollinating agents such every bit insects and birds.
• Abiotic agents- Abiotic agents are non-living resources that deed equally agents such as wind, air, water, or wherein pollination occurs as a affair of chance.

Process of Pollination

The process of pollination takes place through various mediums such equally:

1. Pollination by air current- Wind is known to carry pollen grain from anther to stigma. The same is very commonly observed in grasses. Some characteristics of the plant that is pollinated past current of air are the post-obit-

• Much exposed stamens;
• Light pollen grains;
• Large plume-like stigma;
• Not-sticky texture pollen grain

2. Pollination by insects- The almost seen biotic pollinating agents are bees. Apart from insects several animals like bats, lizards, and rats also aid in the process of pollination. Some of the components that attract insects are the bright, attractive color of the flowers, nectar too as fragrance they emit. In some rare cases, the institute and the insect display a reciprocal human relationship.

          For example- The Moth-Yucca relationship; the insect moth facilitates in pollinating the Yucca blossom.

3. Pollination by water- This is a rare method of pollination that can occur in a few ways:

• Female flowers navigate to the water surface with the assistance of a stalk wherein the male gametes were previously released. East.g. Vallisneria
• Male person gametes are released inside water wherein flowers are present. E.g. Seagrass
• Water acts as a aqueduct for gamete transportation in lower plants. E.g. bryophytes

Pollination in Plants

Fertilization

• The pollen tube dispatches the pollen grains to the ovary mail pollination.
• Followed by which, one of the several male gametes unifies with the ovule/female person gamete, and the other combines with the polar nuclei.
• The unification of a gamete with eggs produces a zygote, which gradually develops into an embryo.
• When the second gamete unifies with the polar nuclei, the endosperm nucleus is formed.
• It supplies nutrients to the embryo.
• The ovules grow into seeds after fertilization while the ovary grows into a fruit.

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Pollen Grains: Things to Remember

• Pollen grains refer to a powdery substance which is basically the male micro gametophytes of seeded plants, responsible for producing the male gametes.
• The pollen grain comprises mainly three parts: intine, exine, and the inside of the cell filled with cytoplasm.
• Pollination refers to the transfer of pollen grains from anther to the stigma of the flower.
• There are three types of pollination: Autogamy, Xenogamy, and Geitonogamy.
• The original colour of pollen grains is white, notwithstanding, it may seem yellow in various species.
• Sexual Reproduction in Flowering plants is an of import topic of the CBSE Class 12 Board Examination. Objective or long answer types of questions are framed from this department for 2 to v marks. The unabridged unit of reproduction has a weightage of fourteen marks in the board examination.

Sample Questions

Ques. Make full in the blanks to complete the process- 1 marker

Pollen mother cell→ Pollen tetrad→ Pollen Grain→ Vegetative cell→ ______

Ans. Generative Jail cell

Ques. What is fertilization? ane mark

Ans. Fertilization is the procedure of the formation of zygotes or fertilization of an egg through the fusion of male and female person gametes.

Ques. Define self-incompatibility. How do self-incompatible plants pollinate? ii marks

Ans. Self-incompatibility is a genetic process wherein the growth of the pollen tube in the pistil is impeded equally a result of which self-pollens cannot fertilize the ovules. Such plants pollinate past cantankerous-pollination.

Ques. The pollen grains in the flowering plants produce male gametes. What are the functions of the male gametes? ii marks

Ans. One male person gamete unifies with the nucleus of the egg cell while some other male gamete navigates towards the two polar nuclei in the central prison cell and fusion occurs to give rise to a tripod endosperm nucleus.

Ques. Pen downwards the several agents of pollination. two marks

Ans. In that location are biotic pollination agents such every bit insects, birds, and abiotic pollinating agents such as wind, h2o, air, etc.

Ques. What are the characteristics of wind, insect, and water pollinated flowers? 3 marks

Ans. The characteristics of air current, insect, and water pollinated flowers are:

1. Current of air pollinated flowers: No special odor, non brightly colored, stigma is feathery and can catch pollen from the air current, pollen is low-cal and smooth and can be blown by the wind.
2. Insect pollinated flowers: Big, vivid flowers with big petals, possess a special fragrance and have nectar, pollen is sticky and tends to stick to the insect's body.
3. H2o pollinated flowers: Possess small flowers which are not visible, large and feathery stigmas of female flowers release lots of pollen, pollen tends to float on the surface of the water till caught by some female flower

Ques. What are the three main parts of the structure of pollen grains? 3 marks

Ans. The pollen grain comprises mainly of 3 parts:

1. The thin inner layer goes by the name of intine, it is composed of cellulose and pectin. This layer degenerates briskly during fossilization.
2. The harder outer layer is chosen exine, it is made up of sporopollenin and is highly resistant. It belongs to the diverse organic grade chosen terpenes.
3. The within of the cell, filled with living cytoplasm, degrades rapidly during fossilization.

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