Let's begin at the beginning. As recently as 2000, children were taught that everything in the universe was animal, vegetable, mineral or energy. There are only four kinds of stuff in the universe. Everything other than energy was born in stars. We also learned from Albert Einstein that matter (animals vegetables and minerals) can be converted to energy, and theoretically, the reverse is true. Animals, vegetables and minerals, according to Einstein, can be constructed from energy.
Certain living things seem to be immortal. It also seems as though the simpler the life form, the longer it can live. Think about the single celled amoeba or its cousin, the euglena (another one celled creature). They multiply through cell division -- mitosis. A cell reaches a certain point in size or age, and then splits into two cells. Those two cells reach a certain point in age or time, and split into two more cells each. This process continues indefinitely. When you see an amoeba under a microscope in a drop of pond water, that amoeba is the product of countless cell divisions over the course of millennia.
When you see a sponge on the seafloor, it is the product of budding, asexual reproduction. It is an extension of some animal which has lived for centuries, even millennia. It is as though a human could cut off an arm and growing a new person from it! Is the second person who grew from a cut off arm a new person, or an extension of the same person?
In the state of Oregon, in the United States, there is a giant mushroom. This mushroom covers nearly 800 acres of land! As it expands it kills off trees in the surrounding vicinity. Testing has shown this giant mushroom to be over 2500 years old! It may, in fact, be old.
Here is a question. What constitutes a plant or animal? What is the difference between a one celled animal and a multi-cell animal? Consider human. We die. But do we? When I die my heart, lung, eyes, skin and more can be medically transplanted to other people. Those pieces and parts are alive! How can that be, if I am no longer alive?
This brings up a very interesting question: who am I? Am I a collection of cells, or something else? Do my cell just constitute a vehicle, like an automobile, that carries around this thing called me? In that case, who is the real me? Where do I go when the vehicle, my body, which operate? Does some part of me survive to be reincarnated into a new body?
Animal, vegetable, mineral.
It used to be thought that everything on Earth fell into one of three categories. The air we breathe, the water we drink, the ground we walk on and the rocks in our flower garden fall into the category of mineral. Things that have roots, grow out of the ground and perform photosynthesis, using sunlight to convert minerals to energy make up the plant world. Animals move about in search of food, and generally exhibit characteristics that are neither plantlike nor mineral like. Well, this was the view of the world for the last century or so. Now we have figured out that it isn't true.
Consider the Venus fly trap. It has roots, it can conduct photosynthesis, but it also can trap and digest insects! The sea sponge is considered to be an animal but it is anchored to the sea floor and doesn't move. It traps its food l and digests it. It reproduces by budding.
We have now realized the amazing complexity of living things. We now realize that there are considerably more living things than animals and plants.
Currently, textbooks from the United States use a system of six kingdoms (Animalia, Plantae, Fungi, Protista, Archaea, and Eubacteria), while British and Australian textbooks describe five kingdoms (Animalia, Plantae, Fungi, Protista, and Prokaryota or Monera). Fungi, Protista, Archaea, and Eubacteria are now considered living things that are neither plans nor animals.
On top of these categories let's also consider viruses and prions, those nasty little things that cause mad cow disease and spongiform encephalopathy in humans. Are they alive? They reproduce. They grow. They changed their host cells. What are they?
https://docs.google.com/Doc?docid=0AZ1nweotz-8MZGNiNHB6YzhfNjFjenoyd2ZkYw&hl=en
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