| A | B |
|---|
| Mitochondria | Rodlike, double-membrane structures |
| Ribosomes | Dense particles consisting of two subunits, free or attached to rough ER |
| Rough Endoplasmic Reticulum | Membrane systems enclosing a cavity, externally studded with ribosomes |
| Smooth Endoplasmic Reticulum | Membranous system of sacs and tubules, free of ribosomes |
| Golgi Apparatus | Stack of smooth membrane sacs and associated vesicles close to the nucleus |
| Lysosomes | Membrane sacs containing acid hydrolases |
| Peroxisomes | Membranous sacs of oxidase enzymes |
| Microtubules | Cylindrical structures made of tubulin proteins |
| Microfilaments | Fine filaments of the contractile protein actin |
| Intermediate filaments | Protein fibers, composition varies |
| Centrioles | Paired cylindrical bodies, each composed of nine triplets of microtubules |
| Cilia | Short, cell surface projections, each cilium composed of nine pairs of microtubules surrounding a central pair |
| Flagella | Like cilium but longer, only example in humans is the sperm tail |
