Overview of Life and Kingdoms

Overview of Life

• Five kingdoms of life exist: animals, plants, fungi, protists, and bacteria.
• Viruses are not living organisms and do not belong to a kingdom.
• Animals, plants, fungi, and protists are eukaryotes.
• Bacteria are prokaryotes.
• Viruses are smaller than prokaryotic cells, which are smaller than eukaryotic cells.

Animals

• Estimated 5-10 million animal species on Earth.
• Multicellular organisms.
• Heterotrophs that obtain energy by consuming other organisms.
• Most reproduce sexually.
• Diverse in body structures, behaviors, and evolutionary histories.
• Classified based on shared characteristics, evolutionary relationships, and ecological roles.
• Includes various phyla like Porifera (sponges), Cnidaria (jellyfish, corals), Platyhelminthes (flatworms), Annelida (segmented worms), Mollusca (mollusks), Arthropoda (insects, crustaceans, arachnids), Echinodermata (sea stars, sea urchins), and Chordata (vertebrates).
• Many show bilateral symmetry (distinct left and right sides) and cephalization (sensory organs concentrated at one end).
• Exhibit various feeding strategies, locomotion methods, and reproductive methods.
• Play crucial roles in ecosystem health and stability: pollination, nutrient cycling, seed dispersal.
• Valuable sources of food, medicinal compounds, and economic resources.
• Faced with threats like habitat loss, pollution, overexploitation, and climate change.
• Conservation efforts are critical for maintaining ecosystem balance and biodiversity.

Plants

• Estimated 300,000 species.
• Multicellular organisms.
• Autotrophs—obtain energy from sunlight via photosynthesis.

Fungi

• Can be multicellular or unicellular.
• Heterotrophs—obtain energy from other organisms.
• Feed through saprotrophic nutrition (secreting enzymes to break down food, then absorbing nutrients).
• Multicellular fungi have a mycelium (body) composed of hyphae (thread-like structures).
• Some fungi are pathogens (e.g., athlete's foot).

Protists

• Mostly unicellular organisms.
• Can be photoautotrophs (have chloroplasts for photosynthesis) or heterotrophs (consume other organisms).
• Most are not harmful, but some are pathogens (e.g., Plasmodium causing malaria).

Bacteria

• Unicellular organisms found in diverse environments.
• Some can photosynthesize, but none have chloroplasts.
• Most feed off other organisms (living or dead).
• Likely more bacterial species than all other kingdoms combined.
• Some are pathogenic (e.g., Salmonella), but many are beneficial (e.g., gut bacteria aiding digestion).

Viruses

• Not considered cells or living organisms.
• Extremely small particles (millions could fit on a fingernail).
• Have a protein coat surrounding genetic material (DNA or RNA).
• Can only reproduce inside living cells (animals, plants, protists, fungi, or bacteria).
• Considered parasites (depend on others for reproduction).
• All viruses are pathogens.
• Examples: influenza virus, tobacco mosaic virus, HIV, COVID-19.