 Biology is defined as “the study of the living world”.  One of the most important base concepts of biology is deciding what is living, and what is not.

 Biologists agree that something is alive if it shows several common traits. Anything that is alive is called an organism.  All living organisms have all of these traits. There may be things that show some of these traits, but they are NOT alive, because they do not show all those traits.

 If something is alive, it is made up of cells.  Cells are considered the smallest living units of matter.

Unicellular Multicellular  Unicellular organisms are made up of only ONE cell.  “Uni-” means one  Multicellular organisms are made up of MORE than one cell.  “Multi-” means many or several

 All living organisms can reproduce.  This means that living organisms can create new organisms.

Asexual Reproduction Sexual Reproduction  Asexual reproduction only requires ONE parent.  Includes fission and budding.  Sexual reproduction requires TWO parents.  Two different cells combine to form a new organism.

 All living organisms use a genetic code.  This code is the reason why many traits can be inherited, or passed on.

 All living organisms grow.  Many multicellular organisms develop special tissues.  However, unicellular organisms do NOT exhibit development.

 All living organisms require materials and energy.  This is because both materials and energy are required for growth and development!  Metabolism : the building or breaking of materials to support life.

 All living organisms can sense and respond to changes in the environment.  These changes are called stimuli.  Stimuli can be external or internal.

 Living organisms have to maintain internal conditions to live.  We call these conditions homeostasis.

 Homeostasis is the state of balance that an organism can exist at.  For instance, we must maintain our water content to live. › Too much or too little water and we die!  We also have to maintain our internal temperature, or we will die!