Problem 177 - Objective Biology for NEET

Question

In double fertilization (a) Male gamete fuses with egg cell to form zygote. (b) Male gamete fuses with diploid endosperm nucleus to produce triploid primary endosperm nucleus. (c) Both (a) and (b) (d) Fertilization takes place in two plants simultaneously.

Step-by-Step Solution

Answer

The correct answer is (c) Both (a) and (b).

Step 1: Understanding double fertilization

Double Fertilization is a reproductive process that angiosperms (flowering plants) undergo. It involves two sperm cells; one sperm fertilizes the egg cell to form a zygote, while the other fuses with two polar bodies to form an endosperm.

Step 2: Evaluate the options

Now, let's break down each of the answer choices: (a) posits that the male gamete fuses with the egg cell to form the zygote - this is accurate. (b) proposes that the male gamete fuses with the diploid endosperm nucleus to produce a triploid primary endosperm nucleus - this is also true. The third option (c) combines both A and B, which we have identified as correct. Finally, option (d) suggests that fertilization happens in two plants simultaneously, which has nothing to do with the biological process of double fertilization itself.

Step 3: Choosing the correct answer

Since both statements in (a) and (b) are factually correct in the context of double fertilization, the correct answer is (c) Both (a) and (b).

Key Concepts

Angiosperms Reproduction

Angiosperms, commonly known as flowering plants, have a unique and complex form of reproduction that includes a process called double fertilization. This process is fundamental to the life cycle of angiosperms and plays a critical role in the development of seeds.

During reproduction, a pollen grain lands on the stigma of a flower and grows a pollen tube down the style to the ovary, where ovules reside. Each pollen grain contains two sperm cells. Upon reaching the ovule, one sperm cell fertilizes the egg cell, and the other fuses with two polar nuclei located within the ovule's central cell. This remarkable event leads to the formation of two distinct entities: the zygote and the endosperm.

Double fertilization ensures that the resources provided by the plant are not used unless fertilization occurs, thereby maximizing efficiency in resource allocation. This feature is exclusive to angiosperms and is one of the reasons for their evolutionary success and diversity.

Zygote Formation

In the intricate dance of angiosperm reproduction, zygote formation is like the first beat of a new life. Through the process of double fertilization, one of the sperm cells unites with the egg cell to form the zygote. This fusion occurs within the female reproductive structure of the plant, known as the ovule. Upon fertilization, the zygote undergoes numerous cell divisions and developmental stages to eventually become the embryo of the seed.

The formation of the zygote is critical because it represents the first diploid stage of the plant's life cycle — meaning it contains a complete set of chromosomes, half from the male parent and half from the female parent. This mixing of genetic material gives rise to genetic variation, which is a driving force in the adaptability and survival of species.

Endosperm Development

Simultaneous to the zygote's creation, another vital event unfolds: the development of the endosperm. The other sperm cell, which accompanies the one that fertilizes the egg, has its own destiny. It fuses with two polar nuclei in the central cell to form the triploid primary endosperm nucleus, as correctly described in option (b) of the exercise.

The endosperm serves as a nutritional reservoir that provides the developing embryo with essential sugars, proteins, and starches during seed development. This tissue is what makes up the bulk of many seeds and grains we consume, such as rice, wheat, and maize. Over time, the endosperm's triploid cells divide and develop into a rich, nutritious tissue, intricately designed to support the young seedling until it can photosynthesize and fetch nutrients from the soil through its own roots.

Understanding the dual objectives of double fertilization — zygote formation and endosperm development — adds a layer of appreciation for the intricate system that underlies the reproductive strategy of flowering plants.