Biosphere: all environments on Earth inhabited by life  (bodies of water)

Ecosystems: all living things and nonliving components with which the living things interact (soil, light, etc) in a particular area (forest)

Communities: array of organisms inhabiting a particular ecosystem (animals, plants)

Populations: all individuals of a species living within the bounds of a specified area (population of black bears)

Organisms: individual living things (squirrel)

Organs and Organ Systems: an organ is a body part consisting of two or more tissues, organ systems are groups of organs that work together (heart)

Tissues: group of similar cells (leaf)

Cells: life's fundamental unit of structure and function, an organism can be a single cell (bacteria) or multicellular (animals)

Organelles: functional components of a cell (chloroplasts)

Molecules: chemical structure consisting of atoms (chlorophyll, a pigment molecule)

an educated postulate

tentative answer to a well-framed question

makes predictions that can be tested

an experimental group is compared with a control group

the experimental and control groups differ only in one factor the experiment is designed to test 

we compare to the control group to see changes caused by a variable factor in the experimental group 

broad scope

general enough to spin off many new hypothesis

explain a great diversity of observations and are supported by an accumulation of evidence