bioch5.txt

All organisms are composed of one or more cells, within which the processes of life occur

Cells are the smallest living things. Nothing smaller than a cell is considered alive

Cells arise only by division of a previously existing cell. Although life likely evolved spontaneously in the environment of the early earth, biologists have concluded that no additional cells are originating spontaneously at present. Rather, life on earth represents a continuous line of descent from those early cells

as cell size increases, volume grows much more rapidly than surface area

lipid bilayer membrane encasing cells

• polar head w/ two non-polar tails
• form the basic structure of the plasma membrane

float within the lipid bilayer

act as markers to identify particular types of cells, or as beacons to bind specific hormones or proteins to the cell

provide pasageways for ions and polar molecules to pass into and out of the cell

• simplest cellular organisms; small, single-celled, most have cell wall and plasma membrane
• no organelles
• no nucleus
• uniform cytoplasm (no subdivision)

examples: bacteria and archaea

long, threadlike structures, made of protein fibers that project from the surface of a cell

used for feeding and locomotion

small flagella

specialized structure within which particular cell processes occur