Animal or plant?

What is it?

Finding a strange or unfamiliar living thing immediately prompts the question, ‘What is it?’ Is it an animal or a plant? Are there other kinds of organisms? This is a brief introduction to the major kinds of living things.

The kinds of living things

Living things are often thought of as either animals or plants, but many organisms are neither animal nor plant. For example, mushrooms are not plants, and neither are seaweeds. Bacteria are not animals.

Attempts by scientists to discover the most fundamental differences between types of living things remains an active area of research, and the results are likely to change our understanding of how life evolved. Some scientists classify living things into only two major divisions: bacteria, and everything else! However, since the ‘everything else’ category contains most of the organisms we are familiar with, it is usually divided further. The following classification into five major categories (usually referred to as Kingdoms) is widely used:

Bacteria (Kingdom Bacteria)

Bacteria have the simplest cells of all living things. These single-celled microorganisms include the bacteria that cause disease (though many do not), and similar organisms called cyanobacteria or blue-green algae. Their fossils are so widespread in ancient rocks that we know cyanobacteria once dominated the Earth. Bacteria can be found virtually anywhere on Earth.

Protozoans (Kingdom Protoctista)

Protists are mostly unicellular, but have cells with internal structures that are more complex than bacteria. Some protozoans, like the marine radiolarians and foraminifera, may seem like little single-celled animals. Seaweeds and some other kinds of algae are multicellular protists that can grow using the energy of sunlight and appear plant-like. However, protozoans are not animals or plants and are more simple–for example, they have no embryo stage in their development. Organisms similar to today’s protozoans may have been the ancestors of all animals and plants.

Illustration of protists

Protists
Artist / Source: Sharyn Madder

Animals (Kingdom Animalia)

We all know many animals, such as dogs, insects, and ourselves. But other animals, such as sea sponges and sea anemones, are sometimes mistaken for plants. Animals must feed on other living things because they cannot obtain energy directly from sunlight. Animals (unlike protozoans) all have an embryo stage in their life cycle. The cell walls in animals are mostly soft, unlike those of fungi and plants, and animals depend on skeletons or shells for strengthening and protecting their bodies.

Photo of a Giant Sand Cockroach

Giant Sand Cockroach, Polyzosteria magna
Photographer: Alan Henderson / Source: Museum Victoria

Fungi (Kingdom Fungi)

Fungi are familiar as mushrooms, of which there are a huge variety. Other fungi are yeasts (such as those used to make bread and beer), and moulds (like those that grow on old fruit). Lichens are also classified as fungi although they are a partnership between a fungus and an alga. Unlike plants, fungi cannot use the energy of sunlight directly. Instead, they get their energy by growing on living or dead plants and animals. The cell walls in a fungus contain chitin, which gives them rigidity.

Photo of Purple Tree Toadstool

Purple Tree Toadstool, Mycena clarkeana
Photographer / Source: Bruce Fuhrer

Plants (Kingdom Plantae)

Unlike fungi, plant cell walls get their strength from cellulose. Plant cells contain little green packages called chloroplasts. Chloroplasts use the energy of sunlight to produce the substances needed to make plant tissues, in a process called photosynthesis. Photosynthesis consumes carbon dioxide and produces the oxygen we breathe.

Further Reading

Barnes, R. S. K. (ed.). 1998. The Diversity of Living Organisms. Blackwell Science, Oxford.

Margulis, L. and Schwartz, K. V. 1998. Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth. Third Edition. W. H. Freeman, New York.

Comments (12)

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Diana Foletta 12 July, 2012 10:44
Would it be possible for there to be a small Asian otter in our billabong on the Goulburn River flats? We saw what look like one yesterday, swimming fast across the surface, duck diving, about the size of a possum approx 40cm with a short tail which was triangular ie thicker at base near animal ending thinner, but not long with white tip as in water rat - we are very curious as to what it could be, do you have any thoughts, would be much appreciated. Diana Foletta (Alexandra)
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Discovery Centre 13 July, 2012 12:08

Hi Diana

Although it isn't possible to be 100% certain in the absence of images, we think it would be highly unlikely that the animal you describe is an otter; we can't find any reference to these animals being introduced and establishing themselves anywhere in Australia. It is remotely possible that the animal you saw was an escapee from captivity, but it is far more likely that what you are seeing could instead be a Platypus. If you manage to get a photograph of the animal, please feel free to contact us through the Ask the Experts form and we will do our best to identify the animal.

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jeane rose 30 September, 2012 19:06
i've learned more,.thanks......better luck next time!.,.,....
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bob 23 April, 2013 09:44
I really <3 this website thnx for da help ;)
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charlotte 8 September, 2013 18:42
nice i learn more about this. thank you!
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laura 27 April, 2014 20:26
Wonderfully succinct explanations that are accessible for all - thanks!
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Tiffany 3 July, 2014 12:59
I like learning!
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arnel maravilla 5 September, 2014 07:02
So what are mushroom,algae,bacteria,and funji,,,,,are this are animal or plants?????
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Biyaya 26 October, 2014 21:58
Well thanks alot, I've improved alot.
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Elite 24 February, 2016 14:46
I like turtles
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sophiesartorius 12 June, 2016 12:37
what are three characteristics that make a mushroom different to a plant? thxs
jojos 27 October, 2016 04:38
that was intresting
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Internet Resources

Classification of Living Things
An article on the classification of all living things based on the books of Professor Lynn Margulis, particularly (with K. V. Schwartz) Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth.
[Microscopy UK and Micscape]

Life on Earth
Describes the ancestor–descendant relationships connecting all organisms that have ever lived.
[University of California Museum of Palaeontology]