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

Pollen tin exist defined every bit a bristly or fine powder that consists of microgametophytes and mass produces sperm cells or male gametes. The co-operative of biology that focuses on the study of pollen and its backdrop is called Palynology. Pollen grains are transferred by wind, water, 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 Too: Class 12 Reproduction

Pollen Grains: Definition and Construction

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

Construction of pollen grains

Pollen grains take microscopic frameworks differing in their structure and size. The size of pollen grains ranges from species to species. The accurate size of a pollen grain ranges from two to three hundred micrometers. The pollen grain might be ovule, triangular, circumvolve, disc, or bean-shaped having a smooth to spiky texture. The original color of pollen grains is white; however, this may vary depending on the found species. Many may also exist orange, cream, or yellowish in colour.

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 called exine, it is made up of sporopollenin and is highly resistant. It belongs to the various organic class called terpenes.
3. The inside of the prison 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. Later on maturing, the pollen grains have two cells named the vegetative and generative cells.

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

Read More About Sexual Reproduction in Flowering Plants

Formation of Pollen Grains

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

• Augmentation of the microscope.
• Development of a large vacuole.
• Microspore nucleus replaced to an eccentric position against microspore wall.
• The nucleus undergoes first pollen mitosis.
• A small generative cell and a large vegetative cell are formed.
• The generative jail cell removes itself from the pollen grain wall.
• The generative cell is enveloped by the vegetative cell.
• A structure is formed having two cells between each other called a 'cell within a cell'.
• The generative cell further goes through mitosis.
• 2 sperm cells are formed within the cytoplasm of the vegetative cell.

Formation of Pollen Grain

Important Notes on Asexual reproduction

Pollination

Transfer of pollen grains from anther to the stigma is termed as pollination. The same occurs with the help of pollinating agents like wind, air, water, birds, insects, etc.

Types of pollination

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

Example- Polygala, Viola

2. Xenogamy: The transportation of pollen grains from anther to the stigma of a different flower. It facilitates cross-pollination functionally besides every bit genetically.
3. Geitonogamy- Transportation of pollen grains from the anther to the stigma of a different flower belonging to the same plant. It facilitates cross-pollination functionally but self-pollination genetically.

Process of Pollination

1. Pollinating agents: Agents which help in transferring the pollen grains from the anther to the stigma of the aforementioned/dissimilar constitute are termed every bit pollinating agents. Pollinating agents tin be divided into two types-

• Biotic- Biotic agents are living organisms that take the part of pollinating agents such as insects and birds.
• Abiotic agents- Abiotic agents are non-living resources that act every bit agents such as wind, air, h2o, or wherein pollination occurs as a matter of run a risk.

Procedure of Pollination

The process of pollination takes place through diverse mediums such as:

1. Pollination by wind- Wind is known to carry pollen grain from anther to stigma. The same is very ordinarily observed in grasses. Some characteristics of the plant that is pollinated by wind are the following-

• Much exposed stamens;
• Light pollen grains;
• Large plumage-similar stigma;
• Non-sticky texture pollen grain

2. Pollination by insects- The most seen biotic pollinating agents are bees. Apart from insects several animals like bats, lizards, and rats also aid in the procedure of pollination. Some of the components that attract insects are the bright, attractive color of the flowers, nectar every bit well as fragrance they emit. In some rare cases, the plant and the insect brandish a reciprocal relationship.

          For example- The Moth-Yucca human 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 person flowers navigate to the water surface with the help of a stalk wherein the male gametes were previously released. East.yard. Vallisneria
• Male gametes are released inside water wherein flowers are present. E.yard. Seagrass
• H2o acts every bit a channel for gamete transportation in lower plants. E.g. bryophytes

Pollination in Plants

Fertilization

• The pollen tube dispatches the pollen grains to the ovary mail service pollination.
• Followed by which, i of the several male person gametes unifies with the ovule/female 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 2nd gamete unifies with the polar nuclei, the endosperm nucleus is formed.
• Information technology supplies nutrients to the embryo.
• The ovules grow into seeds subsequently fertilization while the ovary grows into a fruit.

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Pollen Grains: Things to Recollect

• 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 3 parts: intine, exine, and the within of the cell filled with cytoplasm.
• Pollination refers to the transfer of pollen grains from anther to the stigma of the flower.
• There are 3 types of pollination: Autogamy, Xenogamy, and Geitonogamy.
• The original color of pollen grains is white, however, it may seem yellow in various species.
• Sexual Reproduction in Flowering plants is an important topic of the CBSE Course 12 Board Test. Objective or long respond types of questions are framed from this department for 2 to v marks. The entire unit of reproduction has a weightage of 14 marks in the board examination.

Sample Questions

Ques. Fill in the blanks to complete the process- 1 mark

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

Ans. Generative Cell

Ques. What is fertilization? 1 mark

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

Ques. Define self-incompatibility. How exercise cocky-incompatible plants pollinate? 2 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 by cross-pollination.

Ques. The pollen grains in the flowering plants produce male gametes. What are the functions of the male gametes? 2 marks

Ans. Ane male gamete unifies with the nucleus of the egg cell while another male person gamete navigates towards the two polar nuclei in the cardinal cell and fusion occurs to requite ascent to a tripod endosperm nucleus.

Ques. Pen down the several agents of pollination. 2 marks

Ans. At that place are biotic pollination agents such as insects, birds, and abiotic pollinating agents such equally wind, water, air, etc.

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

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

1. Wind pollinated flowers: No special odor, not brightly colored, stigma is feathery and can take hold of pollen from the wind, pollen is low-cal and smooth and can be blown past the wind.
2. Insect pollinated flowers: Big, bright flowers with large petals, possess a special fragrance and accept nectar, pollen is sticky and tends to stick to the insect'south torso.
3. Water pollinated flowers: Possess minor flowers which are not visible, large and feathery stigmas of female person flowers release lots of pollen, pollen tends to float on the surface of the h2o till caught past 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 proper noun of intine, it is composed of cellulose and pectin. This layer degenerates briskly during fossilization.
2. The harder outer layer is called exine, information technology is fabricated up of sporopollenin and is highly resistant. It belongs to the diverse organic course called terpenes.
3. The inside of the jail cell, filled with living cytoplasm, degrades rapidly during fossilization.

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