Problem 155 - Objective Biology for NEET

Question

Male gametophyte which is highly reduced and confined to only limited numbers of cells is called (a) Antherozoid (b) Spermatozoid (c) Pollen grain (d) All of these

Step-by-Step Solution

Answer

The correct answer is (c) Pollen grain.

Step 1: Understanding the Definitions

Understanding the definitions of the given terms is crucial. An Antherozoid is a motile male sex cell, typically produced by water plants. A Spermatozoid is essentially another term for the same thing i.e., a motile sperm cell produced by plants. A Pollen grain, however, is the male gametophyte in seed plants which is highly reduced and confined to only a limited number of cells.

Step 2: Matching Term to Definition

The given question is asking for the male gametophyte which is highly reduced and confined to only a limited number of cells. From the definitions understood in the previous step, it becomes clear that the term that fits this definition is 'Pollen Grain'.

Key Concepts

Pollen Grain

The pollen grain is a small, yet crucial component of plant reproduction, particularly in seed plants. It represents the male gametophyte which is remarkably reduced and generally consists of just a few cells. Within each pollen grain, there are typically two main cells: the vegetative cell and the generative cell. The vegetative cell is responsible for pollen tube formation, which is essential for transporting the genetic material to the female gametophyte.

The generative cell divides to form either two sperm cells in a process called mitosis or remains undivided, which later happens inside the pollen tube. This carefully coordinated structure allows the pollen to effectively fulfill its role in fertilization, ensuring the continuity of plant species. One fascinating aspect of pollen grains is their outer coat, called the exine, which is often incredibly resistant to environmental stressors. This attribute not only protects the genetic material during travel but also aids in the preservation of pollen fossils, giving scientists clues about ancient ecosystems.

• The pollen grain carries the male gametophyte in seed plants.
• Main cells within a pollen grain: vegetative and generative.
• The exine helps protect and preserve pollen grains.

Antherozoid

Antherozoids are a type of mobile male gamete, more commonly found in non-seed plants like aquatic algae, ferns, and bryophytes. They are flagellated, meaning they have one or more whip-like appendages that enable movement, facilitating their journey to reach the female gametophyte for fertilization. In environments where water is present, antherozoids are well-adapted to swim towards female reproductive structures.

There are several key characteristics to keep in mind about antherozoids:

• Produced in specific structures called antheridia, hence the name "antherozoid".
• Flagella aid their swimming towards the egg cells.
• Crucial for fertilization in water-dependent plant species.

Understanding antherozoids' role in plant reproductive cycles helps us comprehend how plants without seeds reproduce. While less complex than pollen grains, antherozoids exemplify early plant reproductive strategies which rely heavily on water as a medium for fertilization.

Spermatozoid

Spermatozoids, much like antherozoids, are mobile male reproductive cells prevalent in several plant and lower plant groups, including algae and some plants without seeds. The terms 'spermatozoid' and 'antherozoid' can often be used interchangeably, but the usage can vary depending on the plant type or scientific convention.

Their mobility is also attributed to the presence of flagella, allowing these cells to swim through water to reach the female gamete. This motility is crucial in ensuring the continuation of species where water plays a pivotal role in reproductive success. The evolutionary significance of spermatozoids is notable, as they represent one of the earliest mechanisms developed by plants for achieving sexual reproduction outside of those with seeds.

• Spermatozoids are similar in function to antherozoids.
• They rely on flagella for movement.
• Common in non-seed plants, particularly those requiring water for reproduction.

In studying spermatozoids, one gains insight into plant reproductive strategies before the advent of seed-based propagation. They highlight the diversity of approaches plants have evolved to adapt and thrive across varying environmental conditions.