Biological life cycle

Discovery and Evolution of Life Cycles

• Botanists and zoologists studied reproduction and development.
• Wilhelm Hofmeister demonstrated alternation of generations in plants in 1851.
• Nils Svedelius and Karl Gottlieb Grell introduced terms for life cycle descriptions.
• Complex life cycles contributed to disproving spontaneous generation ideas.
• Primitive life cycles likely had haploid individuals with asexual reproduction.
• Asexual reproduction is common in many eukaryotes.
• Germ line cells and their descendants are potentially immortal.
• Bacteria, archaea, and some eukaryotes exhibit similar life cycles.

Types of Life Cycles

• Haplontic life cycle characterized by haploid individuals with zygotic meiosis.
• Diplontic life cycle involves gametic meiosis and diploid individuals.
• Haplodiplontic life cycle includes sporic meiosis and haploid/diploid phases.
• Vegetative meiosis observed in red and green algae in diplontic and haplodiplontic cycles.
• Parasitic life cycles involve stages of infection, reproduction, and transmission.

Parasites and Hosts in Life Cycles

• Parasites rely on hosts for survival.
• Some parasites need multiple hosts to complete their life cycles.
• Parasites have evolved strategies to adapt to different hosts.
• Obligate parasites must infect specific hosts to complete their life cycle.
• Definitive and intermediate hosts play roles in parasite reproduction and development.

Life Cycles and Immortality

• Individual organisms age and die, while germ line cells are potentially immortal.
• Continuity of the germline in sexual organisms depends on DNA damage repair.
• Sexual processes in eukaryotes facilitate effective repair of DNA damages.
• Immortality of cell lineages relies on maintaining cell division potential.
• Ancestry of present-day cells traces back over 3 billion years.

Additional Concepts in Life Cycles

• Alternation of generations in plants and algae.
• Apomixis, haplodiploidy, parthenogenesis, and metamorphosis as related concepts.
• Various scientific studies and references on the architecture and biology of life cycles.
• Immortality of the germ line and genetic mechanisms involved.
• Evolutionary aspects of life cycles with haploid and diploid phases.

Biological life cycle Data Sources