How Do You Decide What Is Alive in Biology


M. Binder

The term organism is used to describe something that is deemed to be alive. Organisms have specific qualities that scientists and students look for when classifying things as either alive or non-living. The four characteristics that are used to define something as alive are the ability to react to stimuli, the ability to reproduce, the ability to grow and develop and the presence of homeostasis.

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Reactions to Stimuli One of the most obvious signs that something is alive in biology is that it reacts to stimuli. Stimuli can be anything from a light source to a physical probe. For example, if you poke your friend in the arm with your finger they will respond by giving you a dirty look or moving away from you. Smaller life forms also respond to stimuli be movement or other physical responses. Sometimes these responses are visible, however, this is not always the case. Responses can also be chemical or very subtle. An inorganic, or a non-living object, is not going to react to stimuli in the same ways that an organic thing would. For example, if you shine a light on a rock the rock will not move to get out of the way. It is important for students to understand the difference between a reaction to a stimuli and an inorganic reaction to force or heat. For example, a candle that is exposed to heat will change its form as the wax melts. This is not a reaction to stimuli but rather a physical manipulation by the force or energy source. Reproduction Reproduction is another characteristic of something that is alive. Reproduction is the replication of an organism. Organic reproduction can be sexual or asexual. In-organic processes that break apart a larger object into many smaller objects is not reproduction. Nothing new has been created. The original object has just been eroded or broken. Growth and Development Things that are alive will grow and develop throughout their life cycle. In humans growth and development starts with the fertilization of an egg. The fertilized egg grows and develops into a baby, that once born develops into a toddler, a child, a teen and then an adult. Things that are inorganic do not grow or develop. Their forms may be altered, but this alteration of form is caused by external forces and not internal forces. This is what makes inorganic objects different than organic objects. Homeostasis The final characteristic of a living thing in biology is the presence of homeostasis. Homeostasis is the condition of being a stable system. The living things has internal control systems that keeps the overall organism stable and in one form. This is very different from inorganic objects that are evolved constantly in response to outside forces like erosion, heat and pressure. Conclusion There are four things that science students need to look for to determine if something is alive. These things are the ability to react to stimuli, the ability to reproduce, the ability to grow and develop and the presence of homeostasis. While there are inorganic processes that are similar to these organic characteristics the big difference is that inorganic objects are influenced by external forces and processes while living things are rules by internal processes and forces.

As an education specialist I have tried for years to produce materials that help kids to explore and enjoy science.

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How Do You Decide What Is Alive in Biology

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