All living things share these characteristics that are absent from non-living things. Let’s take a closer look at these characteristics…
1. Cells and cellular organization
- A cell is the basic structural unit for all organisms.
- All living things are composed of one or more cells.
- Some organisms (bacteria, archaea, protozoa, some algae and fungi) are uni-cellular – they have a single cell.
- All other living organisms (humans, animals, trees, insects) are multi-cellular.
- These are organized into complex structures to carry out specific functions. A series of cells together form cell tissues. Tissues make up organs, and organs work together to form an organ system. An organism is, therefore, a complex series of various organ systems.
2. Metabolism – obtain and use energy
Living things need energy to do work – move, grow, reproduce, and survive. For this energy, living things need to consume nutrients. The process of consuming nutrients, obtaining & storing energy from the nutrients, and using this energy to do work are all biochemical reactions. Metabolism is the sum total of all the biochemical reactions that take place within each cell of a living organism.
3. Homeostasis – maintain a stable internal environment
Living organisms regulate their internal environment to maintain its stability, even when external conditions are not stable. This is known as homeostasis. A good example is human body temperature which needs to stay within a narrow range of 98.6°F. When it’s very cold outside, the body adapts quickly by shivering – this movement raises body temperature. When it’s very hot outside, the body compensates by sweating, which cools down body temperature.
4. Grow and develop
All living things grow and develop.
To carry out this growth, an organism uses up some of the energy it obtained during metabolism.
5. Reproduce – create new organisms like themselves.
- This can be either asexual reproduction, involving a single parent organism (bacterium, for example) splitting into two to create a new organism
- or sexual reproduction, where two parent organisms produce sperm and egg cells, and these cells fuse to form a new individual.
6. Respond to stimulus
Living organisms respond to stimuli or changes in their environment, including sunlight, water, temperature. For example, plants turn towards sunlight, sunflowers track the movement of the sun through the sky, humans pull away their hands when they touch hot pans, chameleons change body color, and some trees shed leaves in response to changes in temperature and sunlight.
7. Adapt to their environment
An adaptation is a mutation, or genetic change, that helps a living organism survive in its environment. If the mutation is helpful to the organism’s survival, it is passed down to the next generation. Over time, the mutation becomes a part of the species and is then an adaptation. Another term for this is evolution, which means a change in the genetic makeup of a species over time.
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