Biology the Study of Life

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

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

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

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

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)

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

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