Biology: Alternation of Generations

Alternation of Generations

Alternation of Haploid and Diploid Generations

• In this type of life cycle, there is a regular alternation between haploid and diploid generations.
• Haploid generation: consists of cells with a single set of chromosomes (n).
• Diploid generation: consists of cells with a double set of chromosomes (2n).
• The haploid generation produces gametes (sex cells) by mitosis, while the diploid generation produces spores by meiosis.

Life Cycles of Plants

Sporophyte-Dominant Life Cycle (e.g., flowering plants)

• Diploid sporophyte generation is dominant and produces spores by meiosis.
• Haploid gametophyte generation is reduced and produces gametes by mitosis.
• Fertilization of gametes forms a zygote, which develops into a sporophyte.

Gametophyte-Dominant Life Cycle (e.g., mosses, liverworts)

• Haploid gametophyte generation is dominant and produces gametes by mitosis.
• Diploid sporophyte generation is reduced and produces spores by meiosis.
• Fertilization of gametes forms a zygote, which develops into a sporophyte.

Isothetic Life Cycle (e.g., some algae, fungi)

• Haploid and diploid generations are equally represented and similar in structure.
• Both generations produce gametes by mitosis and spores by meiosis.
• Fertilization of gametes forms a zygote, which develops into a sporophyte.

Key Features of Alternation of Generations

• Alternation between haploid and diploid generations ensures genetic variation and adaptation.
• Provides a mechanism for genetic recombination and increases diversity.
• Allows for the production of spores, which are adapted for dispersal and survival in harsh environments.

Alternation of Generations

Characteristics

• Regular alternation between haploid and diploid generations
• Haploid generation: single set of chromosomes (n)
• Diploid generation: double set of chromosomes (2n)

Life Cycles of Plants

Sporophyte-Dominant Life Cycle

Characteristics

• Diploid sporophyte generation dominant
• Produces spores by meiosis
• Haploid gametophyte generation reduced
• Produces gametes by mitosis
• Fertilization forms a zygote, developing into a sporophyte

Examples

• Flowering plants

Gametophyte-Dominant Life Cycle

Characteristics

• Haploid gametophyte generation dominant
• Produces gametes by mitosis
• Diploid sporophyte generation reduced
• Produces spores by meiosis
• Fertilization forms a zygote, developing into a sporophyte

Examples

• Mosses
• Liverworts

Isothetic Life Cycle

Characteristics

• Haploid and diploid generations equally represented
• Both generations produce gametes by mitosis
• Both generations produce spores by meiosis
• Fertilization forms a zygote, developing into a sporophyte

Examples

• Some algae
• Fungi

Key Features of Alternation of Generations

• Ensures genetic variation and adaptation
• Provides mechanism for genetic recombination
• Increases diversity
• Allows for production of spores, adapted for dispersal and survival in harsh environments

Kingdoms of Life

Animalia

• Multicellular, eukaryotic organisms that are heterotrophic, meaning they cannot make their own food.
• Characteristics of animals include movement, sensitivity, and ingestive nutrition.
• Examples of animals include humans, insects, fish, and other animals.

Monera

• Single-celled, prokaryotic organisms that lack a nucleus.
• Characteristics of monera include peptidoglycan or pseudopeptidoglycan cell walls, autotrophic or heterotrophic nutrition, and binary fission reproduction.
• Examples of monera include bacteria and archaea.

Protista

• Eukaryotic organisms that do not fit into other kingdoms.
• Characteristics of protista include unicellular or multicellular structure, autotrophic or heterotrophic nutrition, and varied nutrition methods (photosynthesis, absorption, ingestion).
• Examples of protista include protozoa, algae, and slime molds.

Fungi

• Multicellular, eukaryotic organisms that are heterotrophic, meaning they cannot make their own food.
• Characteristics of fungi include absorptive nutrition, where they break down organic matter, and reproduction through spores.
• Examples of fungi include mushrooms, molds, and yeasts.

Plantae

• Multicellular, eukaryotic organisms that are autotrophic, meaning they make their own food through photosynthesis.
• Characteristics of plants include photosynthetic nutrition and cell walls made of cellulose.
• Examples of plants include plants, trees, and flowers.

Learn about the alternation of haploid and diploid generations in the life cycle of plants, including gamete production by mitosis and spore production by meiosis.