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Life is difficult to defineBiologists focus on how life worksLife is determined by a set of characteristics
that distinguish all living organisms from inanimate objects
ALL LIVING THINGS ARE MADE UP OF
CELLS
• Cells are the smallest unit of life
• Cells are the smallest unit capable of sustaining life
• Organisms range from unicellular to multicellular
ALL LIVING THINGS CONTAIN
DNA
• Organisms store, use, and transmit information to live, grow, and reproduce
• Universal genetic code
ALL LIVING THINGS
OBTAIN AND USE ENERGY
• Organisms require energy to perform their processes
• Obtained from their environment
• Metabolism:The combination of chemical reactions where an organism builds up and breaks down materials
ALL LIVING THINGS
MAINTAIN HOMEOSTASIS
• Organisms maintain a fairly stable internal environment
• Positive and negative feedback loops
ALL LIVING THINGS
CHANGE OVER TIME
• Populations change over long periods of time
• Each species has characteristics that vary within the population
• Some of these variations are preferred and become more pronounced over time