The Five Kingdoms of Life

The Five Kingdoms of Life

• Almost all living organisms belong to one of the five kingdoms: animals, plants, fungi, protists, and bacteria.
• Viruses are not considered living organisms and therefore are not part of any kingdom.
• Animals, plants, fungi, and protists are all eukaryotes, meaning their cells have a nucleus that holds their DNA.
• Bacteria are prokaryotes, meaning their cells lack a nucleus and their DNA is not contained within a membrane.
• Viruses are much smaller than prokaryotic cells, and do not fit into the classification of eukaryotes or prokaryotes.

Animals

• There are an estimated 5 to 10 million species of animals on earth.
• All animals are multicellular, meaning they are made up of many cells.
• Animals are heterotrophs, meaning they get their energy from consuming other organisms.
• Most animals reproduce sexually.

Plants

• There are an estimated 300,000 species of plants on earth.
• Plants are multicellular.
• Plants are autotrophs, meaning they get their energy from the sun through photosynthesis.

Fungi

• Fungi can be multicellular or unicellular (single-celled).
• Unlike plants, fungi cannot photosynthesize and are heterotrophs.
• Fungi are saprotrophs, meaning they feed by secreting digestive enzymes onto food outside their body, breaking it down, and then absorbing the nutrients.
• Multicellular fungi have a body called a mycelium, which is made up of many thread-like structures called hyphae.
• Some fungi are pathogens, meaning they can cause disease in humans (e.g., athlete's foot).

Protists

• "Protists," "protista," "protoctists," and "protester" all refer to the same thing.
• Most protists are unicellular.
• Some protists have chloroplasts and can photosynthesize like plants (e.g., chlorella, euglena).
• Other protists are heterotrophs, similar to animals (e.g., amoeba).
• Some protists are pathogens and can cause disease in humans (e.g., plasmodium, which causes malaria).

Bacteria

• Bacteria are single-celled organisms found in almost every environment.
• While some bacteria can photosynthesize, they do not have chloroplasts.
• Most bacteria are heterotrophs, feeding on other organisms (living or dead).
• There are likely many more species of bacteria than all other kingdoms combined.
• While some bacteria can cause disease (e.g., salmonella), most are harmless or even beneficial (e.g., bacteria in our intestines help digest food).

Viruses

• Viruses are extremely small particles, much smaller than prokaryotes.
• Viruses are not considered living organisms as they lack the characteristics of living organisms.
• Viruses are made up of a protein coat surrounding genetic material (DNA or RNA).
• Viruses can only reproduce inside living cells, meaning they are parasites that depend on other organisms for replication.
• All viruses are considered pathogens, as they always cause harm to the host organism when they reproduce.
• Examples of viruses include: influenza virus, tobacco mosaic virus, HIV, and COVID-19.

Explore the fascinating classification of living organisms in this quiz about the five kingdoms: animals, plants, fungi, protists, and bacteria. Understand the differences between eukaryotes and prokaryotes, and learn why viruses are excluded from these kingdoms. Test your knowledge on the characteristics and diversity of life on Earth.