• the ability to reproduce

• the ability to grow and develop

• the ability to take nutrients and energy from the environment and convert it into a usable form

• the ability to interact with and respond to the environment

• the possession of a complex and highly organized structure

This background information will explain these observable characteristics and provide examples that will make the information relevant to a young child.

1. All living things can reproduce, meaning they can produce independent members of their species from their bodies. There are an incredibly large amount of different reproductive strategies used by living organisms. Amoebas and many other organisms reproduce by cell division. Many fungi reproduce through spores. Plants reproduce through seeds. Most birds, reptiles, amphibians and invertebrates reproduce through eggs. Most mammals and sharks reproduce through live birth. In the varieties of reproduction, organisms can be male and female (sexual, meaning one needs to find the other to reproduce), neither (asexual, can reproduce with out a partner) or both (hermaphroditic, meaning an individual can be both sexes at the same time or can change its sex). Despite the varied means of reproduction, all living organisms can replicate their species.
   
   Probably the best way to explain this concept to young elementary students is that all living things produce babies that will eventually become adults. A younger brother or sister who was recently born, an aunt who had a child, a pet that had puppies or kittens or a seed that was planted and eventually sprouted can all be used to show how this characteristic applies to living things. Students can also be asked if they have ever heard of any buildings or cars or rocks having babies to reinforce the concept that this is a characteristic of living things.

2. All living things grow and develop. Many living things start off life as a single living cell known as a zygote (fertilized egg). Fish, grasshoppers, tulips, humans and various other organisms all start as zygotes and eventually develop into adults. Development is observable in the changes in size and structure an organism undergoes from fertilization to adulthood. This is observable even in single-celled organisms, which grow in size before they divide during asexual reproduction.
   
   Young children can see how growth and development have occurred by thinking  about how they have changed since they were born. By comparing pictures of themselves as newborns with pictures of themselves at ages one, two, three, the students can see how they have grown and developed. They can also compare themselves to their parents to consider how they will continue to grow. Examples can also be observed in the classroom by planting seeds and watching the plant grow, or watching how tadpoles, chicken eggs or butterfly larvae grow and develop.

3. Living things take energy and nutrients from the environment and convert them into a usable form. Through digestion and respiration, an organism converts (or in the case of plants creates) organic compounds (carbohydrates, fats and proteins) in ways that either allow it to use the energy at that moment or to store it for future use. Nutrients used in this process can be drawn from the soil, the water, the atmosphere or other organisms. Energy can come from the sun, chemicals or other organisms. Every time a person eats and every time a person breathes he or she is performing the functions that allow them to make energy from the environment. This gives him or her the fuel he or she needs to live.
   
   Young kids can understand this, since every time they eat they are giving themselves more fuel. This is the same reason they must feed their pets and give their plants sunlight and fertilizer.

4. Living things can react to stimuli and respond to and interact with their environment. Living things respond to sights, sounds, smells, tastes and sensations. A spider knows a fly is on its web by feeling the vibrations the fly is making. An osprey sees a fish swimming in the water from sixty feet up in the air, and dives to catch it. A sunflower bends toward the sun as the sun travels across the sky. Living things also interact with their environment. Rabbits dig holes. Birds build nests. The roots of trees hold soil in place that otherwise would be washed away by rain. Bacteria break down organic materials into nutrients that replenish the soil. Non-living things may be manipulated by natural forces, but they cannot interact of their own accord with their environment. For example water may be pulled down a mountain by gravity and erode soil particles, and air molecules may be moved by air pressure differences and cause trees to be blown over, but neither the water nor the air molecule could do anything to the environment without being acted upon by physical forces. An earthworm can move soil and a beaver can cut down a tree of their own action, both showing a characteristic of a living thing.

5. Living things possess a complex and highly organized structure, meaning they have many parts to them that allow them to function. People, such as students, have hearts and lungs and many other organs, as well as eyes, ears, feet, arms and various other parts that keep them moving and surviving. So do dogs, cats, fish, birds, insects and even bacteria with their cell organelles. Plants have leaves, roots, branches, flowers and other less visible structures. These structures are easily observable to any student. A rock may be composed of many different minerals, but if you break it in half, it will still function as a rock. This is not the case if you break the classroom gerbil in half. Rocks have very simple structures, and therefore are not classified as living things.
   
   Students may be tempted to think that the ability to move is a characteristic of living things. Students should be reminded that wind is air moving and streams and ocean waves are water moving. Neither of these is a living thing, though, because they do not have any of the characteristics listed above. On the other hand, trees and sponges do not move but they have the characteristics above and so are classified as living things.

Choose items that are fairly easy for students to identify as being alive or not alive. Although it may seem like a fairly simple concept, it can become quite confusing rather quickly. For example, it can be very confusing for students to try to classify a whelk shell that once housed a living organism as living or nonliving. A better example to use would be a living whelk or a photograph of the entire animal. It can be very confusing for students to classify a twig from a tree as a living thing. Even a seed with the potential to become a living thing is not a living thing until it begins to sprout and can grow and change, take food and energy from the environment, etc. A better example to use would be a photograph of a tree or a small potted plant. Having once been alive also does not make something a living thing. A carcass cannot reproduce nor does it exhibit most other characteristics of living things. Because of this potential for student confusion, some teachers have suggested adding a third category of "once was alive" or "comes from living things" that can be included in the circle of objects that are not living things. These confusing objects, though, can offer a wonderful opportunity for discussion.