You have probably noticed that it is not that easy to say why plants and animals are different. This is especially true when you investigate some of the weird and wonderful living things that exist on the Earth.
For example, is a green praying mantis a plant or an animal? What about a Venus fly trap that eats insects.
These living things are not easily recognisable as plants or animals. A praying mantis is an animal. A Venus flytrap is a plant.
What do you think makes plants different from animals?
Take a look at two of these ideas and see how useful they are for classifying plants and animals.
Animals move more than plants
When animals respond to changes in their environment, it is often obvious immediately. Animals usually move away from things like heat whereas plants don't move much at all. Plant movement is usually only fairly slow growth.
Animals may move from place to place whereas plants may not. Is this really true?
Sea anemones, sponges, oysters and barnacles are examples of animals that are unable to move their entire bodies. They are fixed to a particular place.
But you can say that most animals are able to move from place to place. In the ocean, there are tiny plants called phytoplankton. This word comes from the Greek language. Phyto- means plant. Plankton means drifting. So, phytoplankton are drifting plants, able to move from place to place.
Phytoplankton
However, you can say that most plants are not able to move from place to place.
Plants are green but animals are not
Plants are green. Well, what about wheat in the summertime, fruit trees in the autumn? Most plants are green but some are not. What makes plants green? There is colouring matter called chlorophyll present in plants. Chloro - means green in Greek and -phyll means leaf. Therefore, chlorophyll means green leaf. Chlorophyll is present in any parts of plants that are green, such as leaves and stems and flowers.
Are there animals that are green? You may have thought of animals like tree frogs, caterpillars, grasshoppers, tree snakes, praying mantis, sea horse or grass parrots.
There are quite a number of green animals, but most animals are not green. Animals do not generally contain chlorophyll - even the green ones do not contain chlorophyll. Chlorophyll is generally only present in plants. Some marine animals such as giant clams and corals do contain some cells with chlorophyll in their bodies. But this is a special case and its more like these animals have plants living within their bodies.
By now you probably have realised that identifying the differences between plants and animals is not as easy as you might have thought. In fact, the scientific community has used many different methods of sorting, or classifying, living things over the years.
For example, writings from ancient China suggest that this culture used movement and growth to classify plants and animals.
The classification system that is used by biologists today has developed from the ideas of other cultures. Additionally, the modern classification system has been greatly influenced by two technological developments. These are:
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the development of the printing press in 1440, because this enabled descriptions of living things to be communicated more easily between scientists
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the development of the microscope, because this enabled biologists to study living things more closely.
So now, look at how modern biologists decide if a living thing is a plant or an animal. |
