Living Organisms: Key Features and Differences

Living Organisms: Key Features and Differences

• Five Kingdoms of Life (excluding viruses): Animals, plants, fungi, protists, and bacteria.
• Eukaryotes (Animals, Plants, Fungi, Protists): Contain a nucleus where DNA is housed as chromosomes. Cells are more complex.
• Prokaryotes (Bacteria): DNA is free-floating in the cell; lacks a nucleus. Cells are structurally simpler.
• Viruses: Non-living particles that need to infect living cells to reproduce. Viruses are much smaller than prokaryotic cells.
• Multicellular vs. Unicellular Organisms: Multicellular organisms (animals and plants) have many cells combining to create the organism; unicellular organisms (some protists and bacteria) each cell is an entire organism..

Animal Kingdom

• Estimated 5-10 million species.
• Multicellular: Composed of numerous cells working together.
• Heterotrophic: Obtain energy by consuming other organisms.
• Mostly reproduce sexually.
• Examples: Humans, cattle, ladybirds, and lionfish.
• The estimated number of cells in an adult human is 40 trillion.

Plant Kingdom

• Estimated around 300,000 species.
• Multicellular.
• Autotrophic: Obtain energy from sunlight via photosynthesis.
• Examples: Redwood trees, orchids, tomatoes, and water lilies.

Fungi Kingdom

• Can be unicellular (e.g., yeast) or multicellular (e.g., mushrooms).
• Heterotrophic (but often also saprophytic - absorbing nutrients from dead organic matter).
• Secrete enzymes outside their body to digest food and then absorb the breakdown products.
• Mycelium: The body of multicellular fungi, consisting of hyphae.
• Hyphae: Thread-like structures forming the mycelium.
• Some fungi can be pathogens (e.g., causing athlete's foot).

Protist Kingdom

• Primarily unicellular.
• Exhibit diverse characteristics: Some are photosynthetic (e.g., chlorella, euglena), like plants, while others are predatory (e.g., amoeba), like animals.
• Some are pathogenic (e.g., Plasmodium causing malaria).

Bacteria Kingdom

• Unicellular prokaryotes.
• Found nearly everywhere (skin, intestines).
• Heterotrophic or photosynthetic.
• Estimated to have a larger diversity of species than all other kingdoms combined.
• Some are pathogens (e.g., Salmonella causing food poisoning).
• Many beneficial bacteria aid digestion.

Virus Kingdom

• Nonliving particles, not considered organisms.
• Extremely small (millions can fit on a fingernail).
• Protein coat surrounding genetic material (DNA or RNA).
• Reproduce only inside living cells.
• Always pathogenic.
• Examples: Influenza, tobacco mosaic virus, HIV, COVID-19.