Introduction

I’ve looked at a lot of ways that people teach kids about living and nonliving things. The problem is that there isn’t really a standard definition of life. In fact there is an ongoing debate about which category to put viruses in. For the very youngest kids it may be confusing if you introduce sessile organisms like sponges, but I think it’s good to stress reproduction and metabolism instead of things like movement and growth (Crystals grow when minerals come out of solution, but they are not alive).

What do living things do?

Here we have two schools of thought on how to define what life is.

Simplest Definition

Passes DNA or RNA (organism’s instruction book) from one generation to the next

More Complicated Definition

Boarder between it and outside environment

Can regulate internal environment through metabolism(breathing, feeding, waste excretion)

Movement*

Growth

Reproduction

Evolves over generations to respond to changes in the environment

*Not all organisms universally recognized as living can move on their own.

The first thing I did for this lesson was to show a series of pictures and ask the kids if the things were alive. The first ones I asked were very obvious, but I included things like a refrigerator because it controls it’s internal environment and a robot because it moves. This was to illustrate that some nonliving things do items on the list. The next set of pictures was harder. They were pictures of invertebrate sea creatures including sponges, and also mold and bacteria. This was to dig a little deeper into the notion of what is alive.

Cells

At this point I needed to review the concept of cells for two reasons. All agreed upon living organisms are made up of cells. Also, viruses are discussed in this lesson and the kids must learn what a cell is to understand how viruses reproduce. This will also give them something to think about when they try to decide if viruses are living things. You can find a more detailed explanation in my post on cells, but briefly I used an image of a castle to describe cells, with the walls being the cell’s outer membrane and a library (nucleus) with books(DNA) for example.

Viruses

I asked the kids give their thoughts on whether viruses are living things. First, I had to explain how viruses copy themselves. Viruses inject their RNA or DNA into a cell. The DNA (DNA is reverse transcribed from RNA) inserts itself into the cell’s DNA and then this drives the cell to make and assemble the proteins that make up the virus. Once there are many copies of the virus in the cell, the cell breaks apart (cell lysis) and releases the new viruses. A virus can not reproduce on it’s own, it must use the machinery of a cell to produce copies. Viruses do have a nucleic acid blueprint, and they do evolve over time to respond to host’s immune systems. Some scientists think viruses are not alive because they do not engage in metabolism. Others think that viruses are alive because they reproduce and evolve over time with a DNA blueprint.