Question

How does double fertilization occur in flowering plants? a. The two sperm in a pollen tube fertilize the two egg cells present in each female gametophyte. b. One of the two sperm in a pollen tube fertilizes the single egg in a female gametophyte, and the other fuses with the two nuclei present in the central cell. c. Two sperm, one contributed by each of two different pollen tubes, fertilize the two egg cells in a single female gametophyte. d. Two sperm contributed by separate pollen tubes enter a single female gametophyte; one of the sperm fertilizes the egg cell, and the other fertilizes the central cell. e. None of the above is correct.

Short answer

The correct answer is Option b. One of the two sperm in a pollen tube fertilizes the single egg in a female gametophyte, and the other fuses with the two nuclei present in the central cell.

Step-by-step solution

Understanding terminologies

To attempt this question, one needs to be familiar with following biological terms:1. Sperm: Male reproductive cell or gamete 2. Pollen tube: a tubular structure produced by the male gametophyte of seed plants when it germinates and it is involved in delivery of the sperm to the ovule.3. Female Gametophyte: The female reproductive organ also called embryo sac that is involved in sexual reproduction of plants.4. Egg cell: The female reproductive cell or gamete.5. Central cell: Special cell only present in flowering plants. It contains two haploid polar nuclei. During fertilization process, it is visited by the sperm.

Understand the process of double fertilization

In higher plants, there is a unique mechanism of double fertilization. It occurs when two sperms from each pollen tube fertilize separately with two cells in the female gametophyte. The fertilization involves two distinct processes:1. One of the sperm fertilizes the egg cell and forms a zygote or the future plant embryo.2. The other sperm fuses with two polar nuclei in the central cell to form a triploid cell which develops into the endosperm, a tissue which provides nourishment to the developing embryo.

Match the understanding of process with the options

Now match the understanding of the process of double fertilization with the provided options in the question. The option that correctly describes the process of double fertilization is 'Option b. One of the two sperm in a pollen tube fertilizes the single egg in a female gametophyte, and the other fuses with the two nuclei present in the central cell.'

Key concepts

Pollen Tube

The pollen tube plays an integral role in the sexual reproduction of flowering plants. After a pollen grain lands on the stigma of a flower, it germinates and forms the pollen tube, a microscopic tunnel that serves as a conduit for sperm cells. Guided by chemical signals from the ovary, the tube grows down the style and penetrates the ovule, where the female gametophyte, or embryo sac, resides. The pollen tube's journey ensures the sperm cells are safely delivered to the precise location for fertilization to occur.

Likening the pollen tube to a natural pipette emphasizes its purpose in targeting the delivery of sperm cells to the egg and central cell within the female gametophyte. It's a critical step that sets the stage for the complex process of double fertilization.

Female Gametophyte

The female gametophyte in plants, commonly known as the embryo sac, is the plant's equivalent of a female egg in animals. Embedded within the ovule of a flowering plant, it plays a starring role in plant reproduction. It houses the egg cell and is ready to combine its genetic material with that of the sperm cell delivered by the pollen tube. This union is the spark that ignites the creation of a new plant.

Understanding the female gametophyte's components, which include the egg cell, synergids, and the central cell, provides clarity on how each part contributes to successful fertilization. By recognizing its structure as the site where double fertilization occurs, its significance in plant reproduction becomes apparent.

Sexual Reproduction in Plants

Sexual reproduction in plants is a fascinating and multifaceted process, involving the combination of genetic material from two different plants to produce a new organism. Flowering plants have perfected this dance of chromosomes through a process that encourages genetic diversity, necessary for the adaptation and survival of plant species.

Double fertilization, a distinctive feature of flowering plants, is the highlight of this sophisticated reproductive strategy. By exploring the steps leading to double fertilization in plants, we gain insight into the remarkably orchestrated interactions between male and female gametes that underpin the success and diversity of angiosperms.

Embryo Sac

At the heart of the flower's ovule lies the embryo sac, which is the female gametophyte of flowering plants. It contains multiple cells, including the egg cell and the central cell which holds two polar nuclei. The embryo sac is the destination for pollen tubes and the site where the magic of double fertilization takes place. It’s a microscopic chamber of life that sets the stage for the next generation of plants.

Understanding the structure of the embryo sac is key to understanding plant fertilization. It’s not just a space filler within the ovule; it's the nurturing ground that will either give rise to new life or, without successful fertilization, lay dormant.

Plant Fertilization Mechanisms

In the world of botanical romance, plant fertilization mechanisms ensure the continuation of plant species through the meeting of sperm and egg cells. Double fertilization is a prime example of the sophisticated evolution of these mechanisms. One sperm fertilizes the egg, forming the zygote, while the second sperm merges with the polar nuclei in the central cell, giving rise to a food storage tissue called the endosperm.

This dual fertilization process is unique to flowering plants and highlights the intricate nature of plant reproductive systems. The reliability and efficiency of these fertilization mechanisms underlie the ecological success of flowering plants, shown in their dominance across diverse ecosystems.

Sperm and Egg Cells in Plants

Sperm and egg cells represent the meeting point of new life in plants. Just like in animals, these haploid cells carry genetic information from the parent plants and combine to form the diploid zygote. However, plant sperm cells have a unique journey, traveling within the pollen tube to reach the egg cell in the ovule.

Their fusion—egg cell with one sperm cell, and central cell with another sperm cell—reflects the elegance of the plant’s reproductive strategy. Decoding the roles of these specialized cells not only aids in understanding plant biology but also provides the key to unlocking the secrets of successful plant breeding and agriculture.