Life cycles

Definition

Life cycles are the series of stages an organism goes through from the beginning of its life until it reproduces and generates offspring. In sexual reproduction, life cycles include both haploid and diploid phases, involving processes like meiosis and fertilization.

5 Must Know Facts For Your Next Test

1. Life cycles can be classified into three types: haplontic, diplontic, and haplodiplontic, based on the dominant phase.
2. Meiosis plays a crucial role in reducing chromosome number by half, leading to the formation of gametes or spores.
3. Fertilization restores the diploid number of chromosomes by combining two haploid cells.
4. The alternation of generations is a characteristic feature in plants' life cycles, especially in those with haplodiplontic life cycles.
5. In animals, the diplontic life cycle dominates where the multicellular adult is diploid.

Review Questions

Related terms

Meiosis: A type of cell division that reduces chromosome number by half resulting in four genetically distinct gametes.

Fertilization:

The fusion of two haploid gametes to form a diploid zygote.

Alternation of Generations: A reproductive cycle that alternates between a multicellular diploid sporophyte and a multicellular haploid gametophyte.