Animal Angles: Life Form X

Since cucumbers and sea cucumbers both get nutrition from the soil, why are cucumbers plants and sea cucumbers animals?

Welcome to taxonomy — the science of classifying living things. Many taxonomists (not all!) sort life forms into five major categories or kingdoms. According to them, kingdom Protista contains single-cell organisms with a nucleus.

Kingdom Monera contains single-cell organisms without a nucleus. Animals are life forms that belong to kingdom Animalia, from the Latin word for “breath” or “soul.” They have more than one cell and are heterotrophs, meaning that they are nourished by other life forms. Kingdom Fungi contains multi-celled, heterotrophic life forms, such as mushrooms, which absorb nutrition from decaying organisms. Genetic studies show that mushrooms are more like animals than plants. Life forms in kingdom Plantae are multi-celled autotrophs, meaning that they make their food. Plants are producers; animals and fungi are consumers.

In general, cucumbers are plants because they create nourishment from elements in the soil. Sea cucumbers are animals because they get nourishment from plants and animals in the sediment they swallow. Dirt is just their vehicle for dinner.

People have eaten cucumbers and sea cucumbers for centuries. Cucumbers were probably first cultivated in northern India. The part we eat is actually a fruit, like grapes or melons. Some sea cucumbers go to great lengths not to be eaten. They push their intestines out and “slime” attackers, and then regenerate new intestines. (Pretty gutsy! And disgusting!)

Here's a challenge for taxonomists: Are meat-eating plants such as Venus flytraps really animals? Carnivorous plants thrive when they digest an insect or a lizard now and then. But they can survive without meat, and they have other plant-like characteristics, so they are classified as plants.

Taxonomy can be taxing!

Vocabulary

  • nucleus: Storehouse of the cell’s most important chemical information.
  • sediment: Matter that falls to the bottom of a liquid.

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Activity

  1. Do you agree or disagree with the way taxonomists have classified the Venus flytrap? Why or why not? Write down your answer.
  2. In Lesson 3, you read about the five kingdoms used to classify organisms: monerans, protists, fungi, plants, and animals. Invent an organism that has characteristics from two of the different kingdoms, such as a Venus flytrap. Write a short paragraph describing your organism. Name the two kingdoms in which it could be classified. Describe how your organism gets or makes food, moves (or doesn't move), how big or small it is, and whether it lives in a colony or alone.