Structure of Pollen Grain: Definition, Structure, Formation, Types, Functions, Description, Characteristics

Structure of Pollen Grain: Definition, Structure, Formation, Types, Functions, Description, Characteristics

Irshad AnwarUpdated on 02 Jul 2025, 07:11 PM IST

Pollen grains are small, powdery structures bearing male reproductive cells in seed plants. Pollen is made in anthers of flowering plants or cones in gymnosperms. They move from one place to another through pollination via different agents like wind and water. Pollen is protected by a strong outer covering called sporopollenin. It is part of class 12 Sexual Reproduction in Flowering Plants.

This Story also Contains

  1. What Are Pollen Grains?
  2. Structure Of Pollen Grain
  3. Cellular Components Of Pollen Grain
  4. Difference Between Angiosperm and Gymnosperm Pollen
  5. Recommended video on "Structure of Pollen Grain"
Structure of Pollen Grain: Definition, Structure, Formation, Types, Functions, Description, Characteristics
Structure of Pollen Grain: Definition, Structure, Formation, Types, Functions, Description, Characteristics

In biology, the study of pollen is called palynology, which is useful in archaeology, genetic diversity, forensic science (crime scene geographical linkage). Pollen grains affect human health and cause pollen allergies. The pollen grains are produced and released by dithecous anthers having four pollen sacs. This article includes Pollen Grain Structure, its cellular contents and the Difference Between Angiospem and Gymnosperm Pollen.

What Are Pollen Grains?

A pollen grain is the microstructure that bears the male gametes, otherwise known as the sperm cells of plants, which are capable of forming seeds. A bilobed anther has two parts, and each part makes and stores pollen grains. The hard outer coat of pollen protects the genetic material being transported from the male anther to the female stigma. Microsporogenesis is the process by which pollen grains are formed from microspore mother cells through stages of meiosis inside the pollen sac. The pollen transfer process is called pollination in plants to the female ovule, providing it for fertilisation and forming the seeds and fruits.

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Structure Of Pollen Grain

The structure of a pollen grain is made up of two main layers—exine and intine. These layers protect the pollen and help in pollination and fertilisation. Understanding the exine and intine layers is important for learning how pollen survives and grows during reproduction. The detailed structure of the pollen grain is described below-

Exine (Outer Layer)

  • Composition and Function

Exine is the outer, harder layer of the pollen grain and consists of sporopollenin—one of the most resilient organic compounds known. The exine acts to protect the pollen during its travels from the anther to the stigma from damage by UV radiation, drying out, and microbial assault.

  • Role in Protection

The exine plays a vital role in the maintenance of the integrity of a pollen grain vis-à-vis adverse environmental conditions. Its solidity, hence, secures the safe transportation of the genetic material.

  • Patterns and Apertures

The exine surface may be very elaborate. It may develop specific patterns, like reticulate or net-like, spinate or spiny, or psilate (smooth), to facilitate identification. The apertures are the thinner regions of exine and typically involve structures called colpi, which are long furrows, and pores that are the entry point for the pollen tube when germination takes place.

Intine (Inner Layer)

  • Composition and Function

The intine is the inner layer of any pollen grain. Since the intine is made up of a mixture of mostly cellulose and pectin, the intine is pretty loose compared to the exine; thus, it can grow, expand, and stretch throughout the formation process of a pollen tube.

  • Flexibility and Growth Role

The intine, responsible for supporting the physiological activity of a pollen grain, participates in hydration and consequent germination of the latter upon its fall on the stigma. The elasticity in the intine is quite important in the germination process, as the pollen tube has to penetrate through these exine apertures to fertilise the ovule.

Differences Between Exine and Intine

While exine protects the spore/pollen externally and imparts typical characteristics for identification purposes, intine participates in internal physiological functions during fertilisation in plants.

Cellular Components Of Pollen Grain

The pollen grain has two main cells: the generative cell and the vegetative cell. These cellular components help in pollen tube formation and play a key role in fertilisation in flowering plants. The cellular components of the pollen grain are listed below-

Generative Cell

The generative cell is the main cell in the pollen grain. It undergoes mitotic division to produce two sperm cells for fertilisation.

  • Structure and Function

The generative cell is small with the male genetic material. It travels within the pollen tube to reach the ovule.

During the pollen tube growth, the generative cell undergoes division that leads to the formation of two sperm cells. This step is significant in angiosperms while performing double fertilisation.

Vegetative Cell

It is the larger cell of the pollen grain that contains the generative cell.

  • Structure and Function

The vegetative cell provides the controlling factor for pollen tube growth and the direction towards the ovule via the style.

  • Role in Pollen Tube Formation

The vegetative cell's nucleus guides the extension of the pollen tube and also helps in delivering the sperm cells into the ovule.

Commonly Asked Questions

Q: What is the function of the vegetative cell in a pollen grain?
A:
The vegetative cell in a pollen grain has several important functions:
Q: What are the main layers of a pollen grain, and what are their functions?
A:
The main layers of a pollen grain are:
Q: How do pollen grains form, and what is the process called?
A:
Pollen grains form through a process called microsporogenesis. This occurs in the anthers of flowers, where diploid microspore mother cells undergo meiosis to produce haploid microspores. These microspores then develop into mature pollen grains through mitosis and differentiation.
Q: What is pollen viability, and why is it important?
A:
Pollen viability refers to the ability of pollen grains to germinate and fertilize ovules. It is crucial for successful plant reproduction. Factors affecting pollen viability include temperature, humidity, and storage time. Understanding pollen viability is important for plant breeders, conservationists, and farmers to ensure successful pollination and seed production.
Q: How do scientists study the structure of pollen grains?
A:
Scientists use various microscopy techniques to study pollen grain structure, including:

Difference Between Angiosperm and Gymnosperm Pollen

Pollen grains are produced in both angiosperms—the flowering plants and gymnosperms—the cone-bearing plants. Although their main function is to carry the male gametophyte for fertilisation but they differ in origin, structure, and pollination method. Some of the differences between angiosperm and gymnosperm pollen are given below:

Feature

Angiosperm Pollen

Gymnosperm Pollen

Site of Production

Produced in anthers (part of the stamens)

Produced in microsporangia of male cones

Structure

Usually smaller, with smooth or varied surface

Larger, often winged for wind pollination

Pollination Method

Insects (entomophily), animals, wind, and water

Mainly wind (anemophilous)

Pollen Tube Formation

Forms after reaching the stigma

Forms even before pollination (in some cases)

Fertilisation Type

Double fertilisation (unique to angiosperms)

Single fertilisation

Germination Site

On the stigma of a flower

Near the ovule inside the female cone

Adaptations

Sticky or spiny for animal pollination

Lightweight and winged for air travel

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Frequently Asked Questions (FAQs)

Q: What is the role of pollen in the carbon cycle?
A:
Pollen plays several roles in the carbon cycle:
Q: How do pollen grains contribute to ecosystem services?
A:
Pollen grains contribute to ecosystem services in multiple ways:
Q: What is the role of callose in pollen grain development?
A:
Callose, a complex carbohydrate, plays several important roles in pollen grain development:
Q: How do pollen grains interact with the plant immune system?
A:
Pollen grains interact with the plant immune system in complex ways:
Q: What is the role of sporopollenin in pollen grain structure and function?
A:
Sporopollenin is a complex polymer that forms the main component of the pollen exine. Its roles include:
Q: How do pollen grains adapt to extreme environments?
A:
Pollen grains from plants in extreme environments show various adaptations:
Q: How do pollen grains contribute to the study of plant evolution?
A:
Pollen grains contribute to the study of plant evolution in several ways:
Q: What is pollen heteromorphism, and how does it affect plant reproduction?
A:
Pollen heteromorphism is the production of different types of pollen grains within the same plant species. It can affect plant reproduction by:
Q: How do scientists use pollen analysis in forensic investigations?
A:
Forensic palynology uses pollen analysis in criminal investigations:
Q: How do pollen grains adapt to aquatic environments?
A:
Pollen grains of aquatic plants have adapted to water-based dispersal in several ways:
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