Problem 6 - Campbell Biology

Question

Identify each of the following structures as haploid or diploid. \begin{equation} \begin{array}{ll}{\text { (A) sporophyte }} & {\text { (C) gametophyte }} \\\ {\text { (B) spore }} & {\text { (D) zygote }}\end{array} \end{equation}

Step-by-Step Solution

Answer

Sporophyte and zygote are diploid. Spore and gametophyte are haploid.

Step 1 - Understand Haploid and Diploid

Haploid cells contain one set of chromosomes (n), while diploid cells have two sets of chromosomes (2n). Haploid cells include gametes (sperm and egg) and spores, and diploid cells include structures formed after fertilization, such as zygotes.

Step 2 - Identify the Sporophyte

The sporophyte is a diploid (2n) stage in the life cycle of plants. It develops from the zygote and undergoes meiosis to produce haploid spores.

Step 3 - Identify the Spore

Spores are haploid (n) structures produced by the sporophyte through meiosis. They give rise to the gametophyte stage.

Step 4 - Identify the Gametophyte

The gametophyte is a haploid (n) stage in the plant life cycle. It develops from a spore and produces gametes (sperm and egg) by mitosis.

Step 5 - Identify the Zygote

The zygote is a diploid (2n) cell formed by the fusion of two haploid gametes (sperm and egg). It will develop into the sporophyte.

Key Concepts

Plant Life Cycle

Plants go through a complex life cycle that alternates between two generations: the sporophyte and the gametophyte. This cycle, known as the alternation of generations, is crucial for plant reproduction. During this cycle, plants switch between a haploid phase (gametophyte) and a diploid phase (sporophyte). Both phases have distinct roles and structures, and they reproduce in different ways. Understanding these stages can help us comprehend the broader picture of plant reproduction and development.

Haploid Cells

Haploid cells carry one set of chromosomes. These cells are represented by the notation (n). In the plant life cycle, haploid cells include:

• Gametes (sperm and egg)
• Spores

Haploid cells are essential for sexual reproduction. Gametes combine during fertilization to form a diploid zygote, while spores grow into haploid gametophytes, completing an important part of the life cycle.

Diploid Cells

Diploid cells contain two sets of chromosomes, represented by (2n). These cells form through the fusion of two haploid gametes. Key diploid structures in the plant life cycle include:

• Zygotes
• Sporophytes

Diploid cells undergo meiosis to produce genetically diverse haploid spores, ensuring variation and adaptability in plant populations.

Sporophyte

The sporophyte is the diploid (2n) stage in the plant life cycle. It develops from the zygote formed after fertilization. Sporophytes have the following roles:

• Undergo meiosis to produce haploid spores
• Serve as the dominant stage in many plants, including ferns and seed plants

Sporophytes are crucial for creating the haploid spores that give rise to the next generation of gametophytes.

Gametophyte

The gametophyte is the haploid (n) stage in plants. It evolves from haploid spores produced by the sporophyte. Gametophytes perform the following functions:

• Produce haploid gametes (sperm and egg) through mitosis
• Participate in sexual reproduction by fusing gametes to form a diploid zygote

Gametophytes play a critical role in maintaining genetic diversity and enabling the next sporophyte generation.

Spore

Spores are haploid (n) cells produced by the sporophyte through meiosis. They serve as a means of asexual reproduction and development. Spores have the following characteristics:

• Give rise to haploid gametophytes
• Enable plant dispersal and colonization of new environments

Spores are vital for the propagation of plants, ensuring their survival and adaptation.

Zygote

The zygote is the first stage of the diploid (2n) generation. It forms when two haploid gametes (sperm and egg) fuse during fertilization. The zygote's main functions are:

• Developing into a new sporophyte
• Undergoing mitosis to create a multicellular organism

As the bridge between haploid and diploid phases, zygotes are essential for completing the plant life cycle.