Question

What happens when double fertilization occurs? a. Two zygotes are formed, but only one survives. b. Two sperm fertilize the egg, forming a triploid zygote. c. One sperm fertilizes the egg, while another sperm fuses with the polar nuclei. d. One sperm fertilizes the egg, while two other sperm fuse with a polar nucleus.

Short answer

c. One sperm fertilizes the egg, while another sperm fuses with the polar nuclei.

Step-by-step solution

Understand double fertilization in plants

Double fertilization is a process that occurs in the sexual reproduction of plants. It involves the fusion of two sperm cells from a pollen grain with the egg cell and the central cell of the ovule. This event leads to the formation of a zygote and the endosperm, a nutritive tissue that will support the embryo.

Analyze each option

a. Two zygotes are formed, but only one survives: This option does not accurately describe double fertilization, as it does not mention the formation of the endosperm. b. Two sperm fertilize the egg, forming a triploid zygote: This option is incorrect because in double fertilization, one sperm fertilizes the egg, and the other sperm fuses with the polar nuclei. c. One sperm fertilizes the egg, while another sperm fuses with the polar nuclei: This option accurately describes the process of double fertilization. One sperm cell fertilizes the egg to form a diploid zygote, while the other sperm cell fuses with the polar nuclei, leading to the formation of the triploid endosperm. d. One sperm fertilizes the egg, while two other sperm fuse with a polar nucleus: This option is incorrect, as it mentions an extra sperm cell that does not participate in double fertilization.

Choose the correct answer

Based on our analysis, we can determine that the correct answer is: c. One sperm fertilizes the egg, while another sperm fuses with the polar nuclei. This option represents the process of double fertilization accurately, as it involves the formation of a diploid zygote and a triploid endosperm.

Key concepts

Zygote Formation

In the process of double fertilization, which is unique to flowering plants, the formation of the zygote is a critical step. When the pollen grain lands on the stigma of a flower, it grows a pollen tube down the style towards the ovary. Inside this tube, two sperm cells travel.
The first key event is the fusion between one sperm cell and the egg cell found in the ovule. This fusion results in the formation of a zygote, which is diploid. This means that it has two sets of chromosomes, one from the sperm and one from the egg.

• The zygote will eventually develop into an embryo.
• This embryo will grow into a new plant, continuing the life cycle.

Thus, zygote formation is the starting point of the new plant's life, making it crucial for plant reproduction.

Endosperm Development

Following the formation of the zygote, the second sperm cell plays a vital role in forming the endosperm. After traveling down the pollen tube alongside the first sperm cell, this second sperm cell fuses with the polar nuclei within the ovule.
The fusion of this sperm cell with the two polar nuclei creates a triploid cell. This triploid nature, having three sets of chromosomes, is specifically important for its subsequent function.

• The triploid cell develops into the endosperm, which acts as a food reservoir.
• The endosperm provides essential nutrients to the developing embryo (the zygote).

The endosperm is a nutritive tissue crucial for the early stages of seed development, helping the embryo grow strong until the plant can perform photosynthesis on its own.

Sexual Reproduction in Plants

Sexual reproduction in plants is a fascinating process that revolves around the generation of seeds. It ensures genetic diversity, key to the adaptability and survival of plant species.
Reproduction starts with pollination, the transfer of pollen from one flower to another. Once the pollen reaches a compatible pistil, it begins the journey to the ovule.

• Double fertilization is a unique aspect that involves two fertilization events with one pollen grain.
• The zygote and endosperm formation both emerge from this process.

Ultimately, this intricate system results in the formation of seeds, each containing a baby plant, the embryo, and food supply, the endosperm. Hence, sexual reproduction in plants highlights both complexity and efficiency, ensuring the continuation of plant species in varied environments.