Problem 5 - Biology: Science for Life with Physiology

Question

As a result of fertilization in flowering plants, ________ A. pollen is picked up at the stigma by an animal for transfer to an anther; B. a single sperm is released by a pollen grain; \(\mathrm{C}\). a seed begins to absorb water and break free of its coat; D. a triploid tissue called endosperm is formed; E. a carpel is produced that later becomes a seed

Step-by-Step Solution

Answer

Option D: a triploid tissue called endosperm is formed.

Step 1: Understand Fertilization

Fertilization in flowering plants involves the fusion of sperm from pollen grains with the egg in the ovule, which occurs inside the flower's ovary. This is a process known as double fertilization.

Step 2: Recognize the Result of Double Fertilization

During double fertilization, one sperm cell fuses with the egg to form a zygote, and another sperm cell fuses with two other nuclei in the ovule to form a triploid cell, which becomes the endosperm.

Step 3: Analyze Options Based on Steps

Evaluate each option given: - A: Insects or animals transfer pollen to the stigma, not the other way around. - B: Incorrect, as it does not result from fertilization itself. - C: This describes germination, not fertilization. - D: Formation of a triploid endosperm is a direct result of the process. - E: Carpels are part of the flower structure, not directly formed as a result of fertilization.

Step 4: Select the Correct Option

The correct outcome of fertilization, known as double fertilization, is option D, where a triploid tissue called endosperm is formed.

Key Concepts

Double Fertilization

In flowering plants, the process of double fertilization is a defining and fascinating phenomenon. It involves two distinct fertilization events within the same cycle. When a pollen grain lands on the stigma of a flower, it grows a tube that extends down into the ovary. This tube carries two sperm cells. In double fertilization, one sperm cell fuses with the egg cell, forming a diploid zygote, while the other sperm combines with two polar nuclei in the ovule, resulting in a triploid cell that develops into the endosperm. This unique process ensures that seed formation only occurs if there is a successful fertilization, making plants energy-efficient. Double fertilization is essential for providing nutrients to the developing seeds.

Endosperm Formation

The endosperm is a vital tissue that forms during the double fertilization process. It arises when one of the two sperm cells from the pollen fuses with two polar nuclei in the ovule to form a triploid cell. This triploid cell undergoes rapid division to become the endosperm, which serves as a food source for the developing plant embryo.
The endosperm can be either consumed completely by the growing embryo, as seen in beans and peanuts, or remain as a nutrient-rich tissue inside the seed, like in grains such as wheat and corn.

• Provides essential nutrients like carbohydrates, proteins, and fats.
• Supports embryo development until the seedling can perform photosynthesis.
• Can influence the seed's final structure and nutritional value.

Zygote Formation

The formation of the zygote is one of the key outcomes of double fertilization. This occurs when one of the sperm cells from the pollen tube fuses with the egg cell in the ovule. The resulting zygote is diploid, meaning it contains two sets of chromosomes - one from each parent.
The development of the zygote into an embryo involves a series of cell divisions and differentiation processes. These steps transform the zygote into a mature plant embryo, ready to grow into a new plant once the seed germinates. The zygote itself marks the beginning of a new life cycle, carrying genetic material that combines traits from both parent plants.

• Lays the groundwork for the new plant's genetic makeup.
• Is the critical first step in the lifecycle of a flowering plant.
• Triggers embryo development through subsequent cell divisions.

Ovule Fertilization

Ovule fertilization in flowering plants is an intricate process that leads to the formation of seeds. The ovule is located inside the flower's ovary and contains the egg cell and two polar nuclei. When the pollen tube reaches the ovule, it releases two sperm cells.

• One sperm cell unites with the egg cell to form a zygote.
• The other sperm cell combines with the two polar nuclei to form the triploid endosperm.

The successful fertilization of the ovule is crucial for seed development, and ultimately, for the propagation of the plant species. This process not only ensures genetic diversity but also lays the foundation for the next generation of plants.