What are the Kingdoms of Life?

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll be exploring the wide world of living things. Today, you'll learn the largest category for classifying living organisms, the five kingdoms of life. We'll look at what type of organisms are classified in each kingdom and the criteria scientists use to sort them.

What Is a Biological Kingdom?

Think about moving into a new house. All of your things need to be boxed up and organized so you can find them again later. How would you start organizing? It makes more sense to keep like things together, like packing all the kitchen things in one box. Within these large boxes you might keep the pots in one box and the silverware in another.

Biologists use a similar system called taxonomy to organize or classify living things. They sort living things into the largest category, called a kingdom. From there, they sort organisms that are more like each other into smaller categories. Today we'll be looking at the five kingdom system: Animalia, Plantae, Fungi, Monera, and Protista.

Animalia

Animalia is the kingdom you are probably most familiar with. Think of some animals you know. Humans are animals too, as are insects like cockroaches. Let's look at what characteristics make something an animal.

Spiders are animals
spider

All animals are multicellular. They consist of more than one cell working together as a single organism. Animals are heterotrophic, meaning they have to eat to get their food. Most animals are motile, moving around in their environment, however a few are sessile.

Their cells are eukaryotic, meaning they have a specific structure called a nucleus that holds their DNA. Their cells have a soft outer covering called the plasma membrane, as all cells do, but no cell wall. A cell wall is a thick rigid structure that plants, fungi and bacteria have.

You might be surprised at what is considered an animal. Sea coral for example, is a multicellular organism. Coral filters water through pores, collecting tiny pieces of algae and plankton from the ocean to feed on. Sea anemones are also animals. Soft, floating tentacles might resemble plants, but these animals actually have stinging cells that capture small prey like zooplankton.

Sea anemones are animals
anemone

Plantae

Plants, like animals are also multicellular. The difference is that plants are autotrophic, meaning they make their own food. Plants use a process called photosynthesis, which uses light energy to make food. Plants use a pigment called chlorophyll to do this, which makes the plants green. Plants can live on land, like the trees and grass we are familiar with, or underwater, like ferns and seagrass.

Like animals, plants are made of eukaryotic cells. However, they have cell walls made of cellulose in addition to the plasma membrane like animal cells. Plants are not motile. Plants may drift around in their environment, such as water lilies, but do not move on their own.

Water lilies are a type of aquatic plant
water lily

Fungi

You might be surprised to learn that fungi are heterotrophs. Clearly, fungi don't have a mouth, so how do they 'eat'? Macroscopic fungi have special parts called hyphae that extend like a root system into the ground. The hyphae latch onto other organisms, either dead material, like a fallen tree, or living things like grass, trees, or sometimes animals. The hyphae extract nutrients from the organism, providing the fungi with energy. This type of heterotrophic feeding is called saprophytic feeding.

This extensive underground system is also why simply kicking over a mushroom cap won't rid your lawn of the problem. The visible caps are only the reproductive organs. The hyphae will just grow a new cap in place of the old.

Fungi can be single or multicellular, unlike plants which are only multicellular. Bakers yeast is an example of a single-celled fungi. Single-celled fungi can move around their environment, but larger fungi, like mushrooms cannot.

Mushrooms are in kingdom Fungi
mushrooms

Monera

Monerans are bacteria and archae. These organisms are single-celled and prokaryotic, or lack a nucleus. They are microscopic and live in literally every environment on the planet. Some monerans can cause disease, like Staphylococcus aureus, which causes staph infections. Other bacteria, like some strains of Escherichia coli are actually helpful and live in our guts, helping us break down nutrients.

A micrograph of Escherichia coli
Escherichia coli

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