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What differentiates us from a robot? How do you know if something is alive? Of course, you may think, "If it breathes." But what about plants that don't breathe as obviously as humans? Well, there are some basic characteristics all organisms must have to be considered life.
1. They are composed of cells.
Hey, remember cells, the things you learned about in middle school? All living organisms are made of cells, the basic unit of life.
2. They use energy.
Living things take in energy sources and use them to function. Plants need sunlight, humans need food; whatever we eat, we use the nutrients for our own growth!
3. They respond and adapt to their environment.
Living organisms make changes according to changing stimuli of their surroundings. It could be as simple as you moving when a car honks at you, to the survival of the fittest, or natural selection.
4. They grow.
No, I'm not talking about just the size of an organism (considering I'm still the same height I was in middle school..). Living organisms become more complex over time, using cell growth or division.
5. They reproduce.
All living things have the ability to reproduce, whether it be asexual, or sexual. Asexual organisms, like bacteria, can multiply by themselves. Sexual organisms, such as humans, need both sex cells to produce an offspring.
6. They have levels of organization.
Cells are organized at various levels.
-tissue: group of cells with a common function
-organ: group of tissues with a common function
-organ system: group of organs with a common function
-organism: the complete living creature