Question

What is meant by "alternation of generations"? What two generations are involved? How does each reproduce?

Short answer

Alternation of generations is a reproductive cycle in certain plants and algae involving two multicellular forms: the diploid sporophyte generation and the haploid gametophyte generation. The sporophyte generation produces haploid spores through meiosis, which develop into gametophytes. The gametophyte generation creates male and female gametes through mitosis, which fuse during fertilization, forming a diploid zygote that grows into a new sporophyte. These generations alternate, creating a continuous cycle of reproduction and growth.

Step-by-step solution

Definition of Alternation of Generations

Alternation of generations is a reproductive cycle found in certain plants and algae, wherein two distinct multicellular forms (or generations) alternate, with each form giving rise to the other through reproduction. This cycle involves a diploid, spore-producing generation (known as sporophyte) and a haploid, gamete-producing generation (known as gametophyte).

Sporophyte Generation

The sporophyte generation is the diploid (2n) stage of the alternation of generations, wherein cells contain two sets of chromosomes. Sporophytes produce spores through the process of meiosis - a type of cell division that reduces the chromosome number from diploid to haploid (n). These haploid spores, released by the sporophyte, will then develop into the gametophyte generation.

Gametophyte Generation

The gametophyte generation is the haploid (n) stage of the alternation of generations, with cells containing only one set of chromosomes. In this stage, the gametophyte generates reproductive cells called gametes (male and female) through mitosis - a type of cell division where a single cell divides into two identical daughter cells with the same number of chromosomes as the original cell. The male and female gametes fuse during fertilization to form a diploid zygote, which then grows into the sporophyte generation.

Summary and Comparison

In summary, alternation of generations refers to the cyclical sequence in certain plants and algae involving two multicellular generations with distinct reproductive methods. - The sporophyte generation is diploid and produces haploid spores through meiosis - The gametophyte generation is haploid, creating male and female gametes through mitosis, which then unite during fertilization to form a diploid zygote. The sporophyte and gametophyte generations alternate, with each one giving rise to the other, creating a continuous cycle of reproduction and growth.