The Five Kingdoms of Living Things
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Learning Objective
In this lesson we will learn about the classification of living things into five kingdoms.
Learning Outcomes
By the end of this lesson you will be able to:
- Describe different systems for classifying living things.
- List the kingdoms of the five kingdom classification system and discuss the defining characteristics of each kingdom, with examples.
- List the levels of classification within a kingdom.
- Describe what is meant by the terms ‘species’, ‘hybrid’ and ‘subspecies’.
(Image: betka82, Adobe Stock)
Lesson Summary
- The classification of living things has changed a lot over time and continues to evolve as new scientific information and ideas develop.
- Currently, there are several major classification systems, which group living things into five, six, seven or eight kingdoms, or three domains.
- One of the most widely accepted classification systems is the five kingdom classification system, which places all living things into the following five kingdoms:
- Animalia
- Plantae
- Fungi
- Protista
- Monera
- The distinctions between the different kingdoms are primarily based on cell structures, but also the number of cells making up the organism and how the organism obtains nutrients.
- Animals, plants, fungi and protists are composed of eukaryotic cells, which contain a nucleus and other membrane-bound organelles.
- Bacteria are composed of prokaryotic cells, which lack a nucleus and other membrane-bound organelles.
- Kingdoms are subdivided into the following levels of classification:
- Phyla
- Classes
- Orders
- Families
- Genera
- Species
- Moving down the levels of classification, there are less species in each group and they are more closely related.
- Kingdom Animalia consists of all animals, which are composed of cells that lack a cell wall.
- All animals are multicellular, heterotrophic organisms.
- Kingdom Plantae consists of all plants, which are composed of cells that contain chloroplasts and a cell wall made of cellulose.
- All plants are multicellular, autotrophic organisms that are able to synthesise their own food through photosynthesis.
- Kingdom Fungi consists of all fungi, which are composed of cells that contain a cell wall made of a chitin.
- Most fungi are multicellular organisms and all are heterotrophic.
- Kingdom Protista consists of all protists, which are mostly composed of cells that lack a cell wall and which may contain chloroplasts, cilia or flagella.
- Most protists are unicellular organisms. Protists with chloroplasts are autotrophic, while those without chloroplasts are heterotrophic.
- Kingdom Monera consists of all bacteria, which are composed of cells that contain a cell wall made of a peptidoglycan.
- All bacteria are unicellular organisms. Most bacteria are heterotrophic, while some are autotrophic.
- The term ‘species‘ refers to a group of organisms that can produce fertile offspring.
- A scientific species name includes two parts – the genus name, which has a capital first letter, and the specific epithet, which is all in lowercase.
- Sometimes different species can mate to produce hybrids, but these offspring are infertile.
- Separate populations of the same species that have acquired different characteristics can be classified as subspecies.
Kingdom Cell Type Cell Wall Organism Feeding Animalia Eukaryotic Absent Multicellular Heterotrophic Plantae Eukaryotic Present (cellulose) Multicellular Autotrophic Fungi Eukaryotic Present (chitin) Mostly multicellular Heterotrophic Protista Eukaryotic Usually absent Mostly unicellular Autotrophic or heterotrophic Monera Prokaryotic Present (peptidoglycan) Unicellular Autotrophic or heterotrophic
(Header image: corbacserdar, Adobe Stock)