Characteristics of Living Things Objective: 1. Identify the characteristics of living things. 1. Living things are highly organized, from the smallest part to the largest. On the chemical level: atoms make up elements. Each element has a specific number of electrons that orbit the nucleus. In the center of the element, the nucleus has protons and neutrons. The number of protons in an element is always equal to the number the electrons. The number of neutrons may vary to make isotopes of that element. Elements come together to give up, accept or equally share electrons to make molecules. The smallest part of an organism is a cell. Some single-celled organisms are free-living and contain structures, called organelles that allow them to be self-sufficient. More complex organisms are multicellular. In the case of a human, cells are organized into tissues. These have a common function like a muscle. Tissues are organized into organs like the heart. Organs are organized into organ systems, like the cardiovascular system. Organ systems functioning together make up a living organism. A population is an organization of more than one individual. This is generally all of one species in a particular area. We could talk about the population of squirrels in our area or dogs or cats. Enlarging our view, next comes a community. An example of a community is the town or place we live. A more accurate biological description would include all the living things in that area. A community is composed of many species, including plants and animals An ecosystem not only considers the living things in an area, but also the physical environment and the interrelated flow of energy. You may live in a desert ecosystem, a forest ecosystem, or another kind of ecosystem. Most complex of all is the biosphere. In our case, this includes the all the areas of our planet where living things are found. 2.