Problem 2 - Campbell Biology

Question

Knowledge/Comprehension Double fertilization means that (A) flowers must be pollinated twice to yield fruits and seeds. (B) every egg must receive two sperm to produce an embryo. (C) one sperm is needed to fertilize the egg, and a second sperm is needed to fertilize the polar nuclei. (D) every sperm has two nuclei.

Step-by-Step Solution

Answer

C

Step 1: Understand Double Fertilization

Double fertilization is a complex process in the reproduction of flowering plants. It involves the joining of a female gametophyte (embryo sac) with two male gametes (sperm).

Step 2: Identify the Components

Determine the role of each sperm cell in double fertilization. One sperm cell fertilizes the egg cell, forming a zygote. The other sperm cell fuses with the two polar nuclei in the embryo sac to form the endosperm, a nutrient-rich tissue.

Step 3: Eliminate Incorrect Options

Review each option and eliminate those that do not align with the process of double fertilization: (A) Flowers must be pollinated twice to yield fruits and seeds - Incorrect, pollination does not need to occur twice. (B) Every egg must receive two sperm to produce an embryo - Incorrect, one sperm fertilizes the egg, while the other fuses with polar nuclei. (D) Every sperm has two nuclei - Incorrect, sperm cells do not have two nuclei.

Step 4: Select the Correct Option

Since double fertilization involves one sperm fertilizing the egg and another sperm fertilizing the polar nuclei, the correct option is (C).

Key Concepts

Plant Reproduction

Plant reproduction in flowering plants, also known as angiosperms, is a beautiful and intricate process. It involves the production of seeds and fruits through the union of male and female gametes. This process kicks off with pollination, where pollen grains from the male anther are transferred to the female stigma.
Once on the stigma, the pollen grain germinates and grows a pollen tube down the style to reach the ovule in the ovary. Within the ovule, the pollen tube releases sperm cells that eventually participate in double fertilization.
This fusion of gametes leads to the formation of seeds, ensuring the propagation of the plant species. Through effective plant reproduction, diverse species of flowering plants can reproduce and adapt to changing environments, enhancing biodiversity.

Gametophytes

Gametophytes are the reproductive cells that play a pivotal role in plant reproduction.
In flowering plants, male gametophytes are contained within pollen grains, while female gametophytes are found in the ovule inside the ovary.
The male gametophyte is responsible for producing sperm cells, whereas the female gametophyte, also known as the embryo sac, forms egg cells and polar nuclei.

• The pollen grain lands on the stigma and grows a pollen tube.
• The sperm cells travel down this tube to reach the ovule.
• The egg cell combines with one sperm to form a zygote.
• The second sperm fuses with the polar nuclei to form the endosperm.

Understanding gametophytes is crucial because they are essential for sexual reproduction in plants, leading to genetic variation and the evolution of plant species.

Endosperm Formation

Endosperm formation is a unique and critical aspect of double fertilization in flowering plants. During this process, one of the sperm cells fuses with the two polar nuclei in the female gametophyte to form the endosperm.
The endosperm serves as a nutrient-rich tissue that provides essential nourishment to the developing embryo, ensuring its successful growth into a seedling.

• It acts as a food reserve, supplying the embryo with carbohydrates, proteins, and fats.
• The formation of endosperm ensures that the seed has a built-in food supply, aiding in seedling development.
• This tissue can either be consumed during embryo development or stored in the seed for later use during germination.

The endosperm formation is vital for the survival and viability of seeds, making it a key factor in the reproductive success of flowering plants.

Zygote Formation

Zygote formation is the result of fertilization in flowering plants, where a sperm cell merges with an egg cell. This marks the beginning of a new plant's life cycle.
The zygote is a diploid cell, meaning it contains two sets of chromosomes, one from each parent.
This zygote undergoes several rounds of cell division and differentiation to develop into an embryo.

• The embryo eventually grows into a seed, which can germinate to become a new plant.
• The zygote's formation ensures that genetic material from both parent plants is combined, contributing to genetic diversity.
• This fusion process is a significant step in sexual reproduction, cementing the continuation of plant species.

Understanding zygote formation is fundamental, as it encapsulates the essence of life through the union of male and female gametes, sparking the growth of a new organism.