All matter, both living and non-living, is composed of miniature chemical building blocks called atoms. Your body contains billions of hydrogen, oxygen, nitrogen, phosphorus and carbon atoms. The notebook you are looking at is also composed of billions of various atoms. However, there is a very important distinction between yourself and your notebook - you are alive.
What is life? What does it mean do be alive? How is something made “living”? Scientists have identified seven basic characteristics of life. For something to be described as living, that something must display all seven of these characteristics. Although many different people have many different opinions about what "living" means, the following characteristics were designated "characteristics of living things" with the consensus of the scientific community.
All living things...
1) ...Are Composed of Cells
Cells are the basic components of all living things. Some organisms are single celled, like bacteria, or multi-celled, like humans.
/ This is a single-celled organism called an amoeba.
2) ...Require Energy
Living organisms require energy, usually in the form of ATP. They use this energy to carry out energy-requiring activities such as metabolism and locomotion.
/ This is a molecular model of ATP, the metabolic "energy currency" of all cells.
3) ...Reproduce
All living organisms reproduce, either by sexual or asexual means.
/ This is an image of a plant cell undergoing mitosis (metaphase stage), part of cell division.
4) ...Display Heredity
Living organisms inherit traits from the parent organisms that created them. This is called heredity.
/ These are two daughter cells containing identical genetic material.
5) ...Respond to the Environment
All living things respond to stimuli in their environment.
/ This is an image of a stomata in a plant leaf opening in response to light stimulus.
6) ...Maintain Homeostasis
All living things maintain a state of internal balance. This is called homeostasis.
Humans maintain a body temperature of 98.6°F
7) ...Adapt and 8) Evolve
Living organisms adapt to their environment and evolve over time.
/ This is a petri dish containing bacteria that cause tuberculosis. Antibiotics were once effective in combating this bacteria, but unfortunately these organisms have adapted a resistance to these antibiotics.
Using these characteristics, one can categorize things as living or non-living. Imagine if you were a biologist who had never been to Earth before. You have been sent on a mission to determine whether these things called “trees” are alive. How do trees satisfy the seven characteristics of living things?
Are viruses qualified as living? (Think of what you read in The Hot Zone this summer.)
Characteristics of Life Key Terms to understand
Term / DefinitionCell
ATP
Metabolism
Locomotion
Sexual Reproduction
Asexual Reproduction
Heredity
Stimulus
Environment
Homeostasis
Adaptation
Evolution
Draw/cut and paste one pictorial representation for each of the characteristics of living organisms. You may NOT use any of the examples we have discussed in class.
Made up of cells / Require EnergyReproduce / Display Heredity
Draw/cut and paste one pictorial representation for each of the characteristics of living organisms. You may NOT use any of the examples we have discussed in class.
Respond to Environment / Maintain HomeostasisAdapt to Environment / Evolve over time