Common Characteristics of Members of the Animal Kingdom

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

From a bat to a sea anemone, the animal kingdom contains a diverse group of organisms. This lesson will outline the characteristics animals share and will explain why critters that seem so different are included in the same kingdom.

What is a Kingdom?

What do a bat, a sea anemone, and a grasshopper have in common? Not much, you're probably thinking. But, believe it or not, these three critters all belong to the same kingdom! A kingdom, in case you're wondering, is a group in a classification system.

An overview of the six-kingdom system

There are different classification systems, but this lesson will focus on the six-kingdom system, which includes the following kingdoms: Animalia, Plantae, Fungi, Eubacteria, Archaebacteria, and Protista. Kingdoms can be further divided into phyla, which can be divided down even further.

Take a moment to see where kingdom fits into the taxonomic system

So, back to our bat, sea anemone and grasshopper. It's hard to believe these three organisms have anything in common. One can fly, one lives in the ocean and one is an insect hopping around in a field. What possible characteristics do these three share that lands them in the same kingdom? I'm so glad you asked!

Common Characteristics of the Animal Kingdom

The animal kingdom is an extremely diverse group of critters consisting of three-quarters of all of the organisms living on Earth. In fact, it is estimated that there are between nine and ten million species in this kingdom alone!

Some animals are giant, like the blue whale, whereas others are tiny, like the grasshopper. Some have complex nervous systems and are very intelligent, whereas others are simpler, like the sponge. I could go on and on, but let's start by examining the characteristics all animals share. See, I bet you didn't know you had that much in common with a sea anemone!

Animals are heterotrophs, which means they need to ingest their food. Plants and some protists and bacteria are autotrophs, meaning they make their own food. For example, plants undergo photosynthesis to make their own food, whereas you chomp down on a turkey sandwich to get the nutrients you need.

Next, let's look at the characteristics animal cells share. Animals are multicellular, meaning they are made up of more than one cell. Contrast this with members of some of the other kingdoms, like Protista, Eubacteria and Archaebacteria, who are single-celled. Animal cells are eukaryotic, meaning their cells are more complex than the cells of other organisms, like bacteria. For example, animal cells contain membrane-bound organelles, or tiny organs, which help the cell undergo certain processes it needs to function.

In addition, animals use the protein collagen to attach cell tissue together. Other multicellular organisms like fungi and plants do not use collagen; instead they use other types of molecules to bind tissues together.

Finally, animal cells are diploid, meaning each cell has a homologous pair of chromosomes. Wait, what does that mean? Almost all of the cells in your body (and the body of other animals, too) contain a set of chromosomes from your mom and a set from your dad. Each set of homologous chromosomes has the same genes.

Human chromosomes. Notice there are two copies, one from mom and one from dad. These are called homologous chromosomes.

And speaking of genes, most animals have Hox genes, which are a set of genes that determines how an organism is built. These genes can turn other genes off and on during specific times of embryonic development. Hox genes help to determine where body parts grow on an organism, so you can thank your Hox genes for having two arms that grow out of your torso and not out of your head. Let's take a moment to quickly go over some genetics. There are going to be a lot of vocabulary words that start with the letter 'H', but hang in there, it'll all make sense shortly.

Homeotic genes are regulatory genes and have a specific chunk of DNA known as a homeobox. If there is a mutation on a homeobox, then the organism will have developmental problems. Our example of arms growing out of the top of your head isn't too far off. For example, a mutation in a homeobox on a homeotic gene for fruit flies can cause legs to grow where antennae should be. And it's not just animals that have homeotic genes with the homeobox segments! But Hox genes are a type of homeobox that are unique to animals. Whew. I told you that was a lot of H vocab words. The take-home message is that animals have Hox genes, which help regulate development! Of course, knowing the other H vocab words is handy, too!

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