Cells, Tissues, Organs and Systems
“The smallest units of living matter”
The building blocks for biological form and structure.
Robert Hooke: First person to use the word “cell”
Human cell: 100 microns (just enough for human eyes to see)
How is an organism built?
Chemical level: The very basic level. Including atoms, the smallest units of matter that
participate in chemical reactions and molecules. (two or more atoms joined together)
Cellular level: Molecules combine to form cells, the basic structural and functional units of an
organism that are composed of chemicals.
Tissue level: Tissues are groups of cells and the materials surrounding them that work together
to perform a particular function.
Organs: Structures that are composed of two or more different types of tissues.
Systems: A system consists of related organs working together.
Organism: Any living individual. All the parts of the body functioning together constitute the
Why are cells so small?
Surface area to volume
Need optimal volume to move nutrients such as oxygen, nitrogen and carbon dioxide in
and out of the cell.
How is cellular organization achieved?
1. Plasma Membrane
3. Cytoplasm and organelles PLASMA MEMBRANE
-Defines the cell boundary
-isolates the cytoplasm from the external environment
-regulates flow in and out of the cell
-communication between cells
-It has exceptional biochemistry properties (fluid mosaic model)
Composition of Plasma Membrane: Phospholipids (75%), Glycolipids(5%), Cholestrol (20%). =All
contribute to bilayer.
Lipid Bilayer: Two back-to-back layers made up of three types of lipid molecules (phospholipids,
cholesterol, and glycolipids)
Phospholipids: lipids that contain phosphorous
Cholestrol: steroid with an attached –OH (hydroxyl group)
Glycolipids: lipids with an attached carbohydrate group.
EVOLUTIONARY CONSERVATION: lipids are amphipathic molecules. Which means they have
both polar and nonpolar parts. The polar part is the phosphate-containing, “head”. Which is
hydrophilic. The nonpolar parts are the two long fatty acid “tails”, which are hydrophobic.
(fearing water). Face outwards.
Proteins embedded in membranes serve different functions
Membrane Transport Proteins
Active Processes: Movement of substances against a concentration gradient; requiring cellular
energy in the form of ATP
Active transport: Active process in which a cell expands energy to move a substance
across the membrane against its concentration gradient by trans-membrane proteins
that function as carriers.
-Primary Active transport: Active process in whih a substance moves across the
membrane against its concentration gradient by pumps (carriers) that use
energy supplied by hydrolysis of ATP. -Secondary Active transport: Coupled active transport of two substances across
the membrane using energy supplied by Na+or H+ concentration gradient
maintained by primary active transport pumps. Antiporters move Na+ or (H+)
and other substance in opposite directions across the membrane; symporters
move Na+ or (H+) and other substances in the same direction across the
Transport in vesicles: Active process in which substances move into or out of cells in
vesicles that bud from plasma membrane; requires energy supplied by ATP.
-Endocytosis: Movement of substances into a cell in vesicles.
-Receptor-mediated endocytosis: Ligand-receptor complexes trigger
infolding of a clathrin-coated pit that forms a vesicle containing ligands.
-Phagocytosis: “Cell-eating”; movement of a solid particle into a cell after
pseudopods engulf it to form a phagosome.
-Bulk-phase endocytosis: “Cell-drinking”; movement of extracellular fluid
into a cell by infolding of plasma membrane to form a vesicle.
-Exocytosis: movement of substances out of a cell in secretory vesicles that fuse
with the plasma membrane and release their contents into the extracellular
-Transocytosis: Movement of a substance through a cell as a result of
endocytosis on one side and exocytosis on the opposite side.
Passive Processes: Movement of substances down a concentration gradient until equilibrium is
reached; do not require cellular energy in the form of ATP.
Diffusion: Movement of molecules or ions down a concentration gradient due to their
kinetic energy until they reach equilibrium.
-Simple Diffusion: Passive movement of a substance down its concentration
gradient through the lipid bilayer of the plasma membrane without the help of
membrane transport proteins.
-Facilitated diffusion: Passive movement of a substance down its concentration
gradient through the lipid bilayer by trans-membrane proteins that function as
channels or carriers. Osmosis: Passive movement of water molecules across a selectively permeable
membrane from an area of higher to lower water concentration until equilibrium is
What defines the cell shape?
Cytoskeleton: a network of protein filaments that extends throughout the cytosol.
*Cytoskeleton is composed of three types on filaments. In order of their increasing diameter.
1. Microfilaments: the thinnest elements of the cytoskeleton. They are composed of t