1. CELLS
Structure

2. Cell Membrane
Surrounds the cell to separate it from its external environment
Composed of a phospholipid bilayer that has proteins embedded in it
Cholesterol is also an important component of cell membranes since it keeps the membrane intact yet fluid
The membrane acts as a selective barrier by controlling what substances enter and leave the cell

3. Membrane Structures
Microvilli (microvillus): extensions of the cell membrane used to increase the surface area of the cell
Cilia (cillium): short, hair-like extensions on the cell membrane used for movement
Flagella (Flagellum): long, whip-like structures used for movement

4. Cell Interior Cytoplasm:
A semi-fluid substance in which all of the cell’s organelles are suspended
Located between the nucleus and the cell membrane
Contains the cytoskeleton
Cytoskeleton: a network of microtubules that support the cell and give it shape

5. Nucleus
Nucleus: the control center of the cell and where the cell’s DNA is located
Nuclear Membrane:
Separates the nucleus from the cytoplasm
Contains pores so that substances may enter or leave the nucleus
Nucleolus: structure within the nucleus that is responsible for making rRNA
Nucleoplasm: similar to the cytoplasm, it is a semifluid substance in which the DNA and nucleolus are suspended

6. Organelles Endoplasmic reticulum (ER): Extensive network of membranes
There are 2 types:
Rough ER: contains ribosomes that make proteins destined to leave the cell
Smooth ER: makes lipids, steroids, and is involved in detoxification; important in cells that are responsible for ridding the body of toxic substances (i.e. liver)

7. Organelles (cont.) Ribosomes:
Structures involved in protein synthesis
Found attached to the RER or suspended in the cytoplasm
Mitochondria: structures used to make ATP (energy compound)
Golgi complex (apparatus):
Series of flat membrane-bound sacs
Packages proteins made from the RER and sends them in membrane-bound vesicles to their destination

8. Organelles (cont.) Vacuole:
Membrane-bound compartment that serves many functions (i.e. absorbs water, stores proteins, stores wastes, etc.)
Plant cells have one large central vacuole whereas animal cells contain several small vacuoles

9. Organelles (cont.) Lysosome:
Membrane-bound organelles filled with hydrolytic enzymes
These enzymes are used to break down substances (i.e. carbohydrates, proteins, lipids, old organelles, etc.)