1. Biology the Study of Life

2. What is Life? No formal definition
Scientists use six characteristics to distinguish living from non-living

3. All living things are complex chemical systems
Characteristic #1
All living things are complex chemical systems
Living things are made of molecules that interact
Metabolism is the collective set of chemical processes & reactions in an organism
Molecules breaking apart (releasing energy)
Molecules forming (to store energy)
Enzymes – molecules that help reactions occur

4. All living organisms are composed of cells
Characteristic #2
All living organisms are composed of cells
Some have many cells
Some have only one cell
Humans have ~100 trillion cells

5. All life can obtain and use energy from the environment
Characteristic #3
All life can obtain and use energy from the environment
Energy = the ability to do work
Organisms need energy to feed, grow, reproduce
Plants get energy from sun (photosynthesis)
Animals get energy from plants
Some organisms get energy from chemicals in the earth

6. All living things reproduce using the same genetic mechanism (code)
Characteristic #4
All living things reproduce using the same genetic mechanism (code)
Each organism reproduces its own species
Offspring inherit genetic instructions from their parents through a molecule called DNA
Offspring can differ from their parents (genetic variation)

7. All living organisms grow and develop
Characteristic #5
Most change form and capabilities as they grow older
Growth requires energy

8. Characteristic #6
All organisms respond to changes in external environment while maintaining constant internal environment.
Inside is controlled chemically and physically.
External responses:
Skin tans in response to sunlight
Roots change direction moving towards water
Dogs pant in the heat