outline the characteristic features of the kingdoms Protoctista, Fungi, Plantae and Animalia

Classification – Kingdoms

The five‑kingdom system groups organisms based on fundamental cellular organisation, nutrition, and life‑cycle characteristics. The following notes outline the key features of four of these kingdoms: Protoctista, Fungi, Plantae and Animalia.

Protoctista

Protoctista (also called Protista) is a diverse group of eukaryotic organisms that do not fit neatly into the other kingdoms.

• Mostly unicellular, but some are simple multicellular (e.g., algae).
• Cells contain a true nucleus and membrane‑bound organelles.
• Nutrition varies: autotrophic (photosynthetic algae), heterotrophic (amoebae), or mixotrophic.
• Habitat: primarily aquatic (freshwater and marine) and moist terrestrial environments.
• Reproduction can be asexual (binary fission, budding) or sexual (formation of gametes).

Fungi

Fungi are primarily decomposers and obtain nutrients by absorption.

• Eukaryotic cells with a true nucleus; cell walls contain chitin.
• Predominantly multicellular (moulds, mushrooms) but also unicellular (yeasts).
• Heterotrophic – external digestion of organic matter.
• Habitats: soil, decaying matter, symbiotic relationships (mycorrhizae, lichens).
• Reproduction: both asexual (spores, budding) and sexual (spore formation after meiosis).

Plantae

Plants are primarily photosynthetic, producing their own organic compounds.

• Multicellular eukaryotes with cell walls made of cellulose.
• Chloroplasts contain chlorophyll a and b for photosynthesis.
• Autotrophic – convert CO₂ and water into sugars using sunlight.
• Habitats: terrestrial (most) and aquatic (aquatic plants).
• Reproduction: alternation of generations (haploid gametophyte and diploid sporophyte); both sexual (flowers, cones) and asexual (runners, tubers).

Animalia

Animals are multicellular, heterotrophic organisms that ingest food.

• Eukaryotic cells lacking cell walls; tissues are organized into specialized systems.
• Nutrition by ingestion and internal digestion.
• Mostly motile at some life stage.
• Habitats: virtually all environments – terrestrial, freshwater, marine.
• Reproduction: primarily sexual (gametes) with diverse developmental patterns; some asexual reproduction (budding, fragmentation).

Comparative Summary