All living organisms -- from small to big -- share characteristics that separate them from the divisions in nature that do not exhibit life, like rocks or soil. Living creatures have cells, DNA, the ability to convert food into energy, grow, reproduce, respire and move. These characteristics become the criteria for scientists to separate the living elements in nature from the non-living ones.
Cells and DNA
All living creatures consist of cells. Organized into groups such as organelles, molecules and other multi-cellular classifications, cells can also reproduce themselves, showcase movement and display a response to certain stimuli for a scientist to consider the organism as living. Each cell carries deoxyribonucleic acid or DNA, the material made up of chromosomes that passes down genetic information which includes inherited traits of its lineages.
For something to live, it must consume food and convert that food into energy for the body. All living entities employ interior chemical reactions to convert eaten food into energy through a form of digestion, and then transmit the energy extracted to the cells of the body. Plants and trees convert energy from the sun into food and absorb nutrients in the soil through their roots.
Sciencing Video Vault
Internal Environment Changes
Organisms that are alive make changes to their internal environment. Called homeostasis, this represents the actions a body takes to protect itself. For instance, when the body gets cold, it shivers to generate heat. All living organisms share this feature.
Living Organisms Grow
To grow, a living organism must have cells that divide in an orderly way to create new cells. As cells grow, expand and divide, the creature becomes larger over time. Scientists use growth and development as a measure of life.
The Art of Reproduction
Living organisms grow and reproduce to make more living organisms like themselves. This can occur through asexual reproduction or by producing other living organisms through sexual reproduction. The new organism’s DNA is like that of the cell it came from.
Ability to Adapt
Plants, animals, people, and even microorganism that live can adapt to the world around them. Adaptability involves the traits that help a living organism survive in its environment. One such trait includes the way different animal’s coats change through the seasons to make it hard for prey or predator to be seen.
Ability to Interact
A living organism will interact with another living organism -- whether it is the same type of organism, a threat or a neutral organism, there is some form of interaction between the two. For example, flowers interact with bees by releasing pollen for it to be picked up and dispersed among female plants during reproduction. Plants like the Venus flytrap interact with nature by enclosing itself over flies, lizards and other edible insects that land within its grasp.
The Process of Respiration
Respiration is more than just breathing. It represents the ability of a living organism to convert energy to feed the cells, using oxygen to break down sugars and produce carbon dioxide as a by-product expelled during exhalation. All living organisms have some form of respiration, though the process may differ between them.
Living Creatures Move
To classify an organism as living, it must exhibit some form of movement. Though humans and animals obviously move, other items such as plants also move though it is hard to see without a time-lapse camera. Plants move their buds or leaves toward sunlight or away from shaded areas to promote growth.