Problem 6 - Campbell Biology

Question

Identify each of the following structures as haploid or diploid. a. sporophyte b. spore c. gametophyte d. zygote

Step-by-Step Solution

Answer

a. Diploid, b. Haploid, c. Haploid, d. Diploid

Step 1 - Understand Haploid and Diploid

Haploid cells contain one set of chromosomes (n), while diploid cells contain two sets of chromosomes (2n). In plants, these terms help describe different stages in their life cycle.

Step 2 - Identify the Sporophyte

The sporophyte stage is typically diploid (2n) because it grows from a zygote formed by the fusion of two haploid gametes.

Step 3 - Identify the Spore

Spores are generally haploid (n). They are produced by the sporophyte via meiosis and give rise to the gametophyte.

Step 4 - Identify the Gametophyte

The gametophyte is haploid (n). It arises from a spore and produces gametes through mitosis.

Step 5 - Identify the Zygote

The zygote is diploid (2n) because it is formed by the fusion of two haploid gametes.

Key Concepts

Sporophyte

A sporophyte represents the diploid (2n) stage in a plant's life cycle. This stage begins when two haploid gametes (sperm and egg) fuse to form a zygote. The zygote then grows into a sporophyte through mitotic cell divisions. Sporophytes are important because they produce spores via meiosis. These spores will later give rise to gametophytes, continuing the cycle. In most plants, the sporophyte is the dominant and more visible phase. For example, the leafy green plant you see in ferns and flowering plants is usually the sporophyte.

Gametophyte

The gametophyte stage in the plant life cycle is haploid (n). Gametophytes develop from haploid spores produced by the sporophyte. Through mitosis, gametophytes generate haploid gametes (sperm and egg). In many plants, such as mosses, the gametophyte is the prominent phase and supports itself independently. In contrast, in flowering plants, the gametophyte is tiny and contained within the flowers. The male gametophyte is the pollen grain, and the female gametophyte is found within the ovules.

Spore

Spores are haploid (n) reproductive cells that are crucial in plant reproduction. They are produced by the diploid sporophyte through meiosis. Because spores are haploid, each one carries only one set of chromosomes. Upon landing in suitable conditions, a spore can grow into a new gametophyte. This stage is essential for spreading the species and for genetic diversity, since meiosis introduces variation. Unlike seeds, spores don't contain an embryo or food supply, making them incredibly lightweight and easy to disperse.

Zygote

A zygote is the diploid (2n) cell formed by the fusion of two haploid gametes (sperm and egg). This crucial cell is the first step in developing a new sporophyte. After fertilization, the zygote undergoes multiple rounds of mitosis to grow into a mature sporophyte. The formation of the zygote marks the transition from the haploid gametophyte stage to the diploid sporophyte stage. This foundational event ensures genetic continuity and variation through sexual reproduction, as it combines genetic material from two parents.