Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Alternation of Generations: Plants have two distinct multicellular phases in their life cycle—the haploid gametophyte () and the diploid sporophyte (). These phases alternate with each other during the sexual life cycle.
Haplontic Life Cycle: The dominant, photosynthetic phase is the free-living gametophyte (). The diploid stage is represented only by the single-celled zygote (), which undergoes meiosis to produce haploid spores. Found in many algae like Volvox, Spirogyra, and some species of Chlamydomonas.
Diplontic Life Cycle: The diploid sporophyte () is the dominant, independent, photosynthetic phase. The gametophytic phase is represented by a single to few-celled haploid () gametophyte. Seen in all seed-bearing plants (Gymnosperms and Angiosperms) and the alga Fucus.
Haplo-diplontic Life Cycle: Both haploid and diploid phases are multicellular and often free-living. However, they differ in their dominant phases. In Bryophytes, the dominant phase is the gametophyte (); in Pteridophytes, the dominant phase is the sporophyte ().
Exceptions: While most algae are haplontic, some like Ectocarpus, Polysiphonia, and Kelps are haplo-diplontic, and Fucus is diplontic.
📐Formulae
seeds the gametophytic generation.
involves no reduction division.
restores the diploid phase.
💡Examples
Problem 1:
In a moss plant (Funaria), if the chromosome number in the leaf cell is , what would be the chromosome number in the spores and the zygote?
Solution:
Spores: , Zygote: .
Explanation:
In Bryophytes (mosses), the main plant body (including leaves) is a gametophyte (). Thus, . Spores are produced via meiosis but are also part of the haploid generation, so spores = . The zygote is the first cell of the sporophytic generation and is formed by fusion (), thus zygote = .
Problem 2:
Identify the life cycle pattern where the sporophyte is represented only by a single-celled zygote.
Solution:
Haplontic Life Cycle.
Explanation:
In the haplontic life cycle, there is no multicellular sporophyte. The zygote () undergoes immediate meiosis (zygotic meiosis) to form haploid () spores, which then grow into the dominant gametophyte.