1. (1) All organisms are composed of one or more cells. (2) Cells are the smallest living things. (3) Cells arise only from the division of other pre-existing cells.
2. There is an optimal surface-to-volume ratio; a big cell does not have enough surface area to interact properly for all its volume.
3. Prokaryotes contain peptidoglycan in their cell walls while eukaryotes do not; eukaryotic cells are characterized by possessing membrane-bounded organelles while the prokaryotes do not; and prokaryotes contain flagella composed of a simple fibrous protein, while eukaryotic flagella have a more complicated structure involving doublets and triplets of microtubules.
4. The endoplasmic reticulum is a bilayer lipid membrane. It compartmentalizes the cell interior and channels transport of molecules throughout the cell. Rough ER has ribosomes and synthesizes proteins; smooth ER does not have ribosomes and is involved in lipid synthesis and detoxification.
5. The nuclear membrane is bilayered. Proteins move in, and RNA and ribosomal subunits move out through nuclear pores.
6. Ribosomes are aggregates of protein and ribosomal RNA instrumental in protein synthesis. They are manufactured as subunits in the nucleolus and assembled in the cytoplasm.
7. Golgi bodies collect, package, and distribute cell-synthesized molecules. They are closely associated with the ER, which transports material to the Golgi.
8. Microbodies such as peroxisomes contain enzymes that degrade hydrogen peroxide, a dangerous intracellular waste product, into water and oxygen.
9. A mitochondrion has an outer membrane, an outer compartment, an inner folded membrane or cristae, and an inner matrix. It functions in oxidative metabolism. Almost all eukaryotic cells contain mitochondria. In general, the more metabolically active the cell, the more mitochondria it will contain.
10. Chloroplasts are encountered in some bacteria, some protists, and plants, and are the site of photosynthesis.
11. Centrioles form the mitotic spindle between them during cell division (mitosis).
12. The cytoskeleton is composed of actin protein filaments, tubulin microtubules, and intermediate fibers. The first two are changeable and the last is stable.
13. Cilia and flagella have the same structure but cilia are shorter and more numerous. The term "9 + 2 structure" means a circle of 9 pairs of microtubules surrounding 2 central microtubules. This is characteristic of eukaryotes.
14. The endosymbiont theory suggests that eukaryotes arose as a result of specific kinds prokaryotic organisms living in association with one another: a photosynthetic organism perhaps invaded and started living within a non-photosynthetic organism. Evidence for this theory is the fact that chloroplasts and mitochondria have their own DNA.