| A | B |
|---|
| Prokaryotes | Cells without nuclei or organelles (Bacteria & Archaea) |
| Eukaryotes | Complex cells with nuclei, and organelles, such as mitochondria and chloroplasts |
| Nucleus | Double-membrane bound organelle that contains chromosomes (DNA) |
| Nucleolus | Region in the nucleus where ribosomal components are synthesized and assembled |
| Ribosomes | Cell organelle made of RNA; site of protein synthesis |
| Rough endoplasmic reticulum (RER) | Membranous system of flattened sacs that is the site of protein synthesis |
| Smooth endoplasmic reticulum (SER) | Membranous system in cytoplasm that is involved in the synthesis of steroid hormones and other lipids; carries out detoxification processes |
| Golgi apparatus | A system of concentrically folded membranes found in the cytoplasm of eukaryotic cells; functions in secretion from cell by exocytosis. |
| Lysosomes | Single-membrane bound organelle that contains hydrolytic enzymes used in intracellular digestion |
| Peroxisomes | Membrane-bound organelle that converts harmful hydrogen peroxide to water |
| Mitochondrion | Site of aerobic respiration; derived from ancient endosymbiosis with proteobacterium |
| Central vacuole | Large vacuole found in plant cells |
| Contractile vacuole | Found in freshwater protists; pumps out excess water that enters cell through osmosis |
| Chloroplast | An organelle bounded by a double membrane containing the enzymes and pigments that perform photosynthesis. Chloroplasts occur only in eukaryotes. |
| Cytoskeleton | The network of microtubules and microfilaments that gives a eukaryotic cell its shape and its capacity to arrange its organelles and to move. |
| Flagellum | Long, whiplike appendage that propels cells. Prokaryotic flagella differ sharply from those found in eukaryotes. |
| Cell wall | A relatively rigid structure that encloses cells of plants, fungi, many protists, and most prokaryotes. Gives these cells their shape and limits their expansion in hypotonic media. |
| Plasma membrane | Phospholipid bilayer that surrounds cell; selectively permeable |
| Tight junctions | Fuse adjacent epithelial cells; prevent leakage between cells |
| Gap junctions | Specialized cell junctions that are involved in cell-to-cell communication |
| Centriole | A paired organelle that helps organize the microtubules in animal and protist cells during nuclear division. |
| Cilium | Hairlike organelle used for locomotion by many unicellular organisms and for moving water and mucus by many multicellular organisms. Generally shorter than a flagellum. |
| Cytoplasm | The contents of the cell, excluding the nucleus. |
| Cytosol | The fluid portion of the cytoplasm, excluding organelles and other solids. |
| Endomembrane system | Endoplasmic reticulum plus Golgi apparatus; also lysosomes, when present. A system of membranes that exchange material with one another. |
| Endoplasmic reticulum | A system of membranous tubes and flattened sacs found in the cytoplasm of eukaryotes. Exists in two forms: rough ER, studded with ribosomes; and smooth ER, lacking ribosomes. |
| Endosymbiosis | Two species living together, with one living inside the body (or even the cells) of the other. |
| Endosymbiotic theory | The theory that the eukaryotic cell evolved via the engulfing of one prokaryotic cell by another. |
| Intermediate filaments | Cytoskeletal component with diameters between the larger microtubules and smaller microfilaments. |
| Microfilament | Minute fibrous structure generally composed of actin found in the cytoplasm of eukaryotic cells. They play a role in the motion of cells. |
| Microtubules | Minute tubular structures found in centrioles, spindle apparatus, cilia, flagella, and cytoskeleton of eukaryotic cells. These tubules play roles in the motion and maintenance of shape of eukaryotic cells. |
| Nuclear envelope | The surface, consisting of two layers of membrane, that encloses the nucleus of eukaryotic cells. |
| Nuclear pore complex | A protein structure situated in nuclear pores through which RNA and proteins enter and leave the nucleus. |
| Nucleoid | The region that harbors the chromosomes of a prokaryotic cell. Unlike the eukaryotic nucleus, it is not bounded by a membrane. |
| Nucleolus | A small, generally spherical body found within the nucleus of eukaryotic cells. The site of synthesis of ribosomal RNA. |
| Organelles | Organized structures found in or on eukaryotic cells. Examples include ribosomes, nuclei, mitochrondria, chloroplasts, cilia, and contractile vacuoles. |
| Plasmodesma | A cytoplasmic strand connecting two adjacent plant cells. |
| Surface area-to-volume ratio | For any cell, organism, or geometrical solid, the ratio of surface area to volume; this is an important factor in setting an upper limit on the size a cell or organism can attain. |
| Thylakoid | A flattened sac within a chloroplast. Thylakoid membranes contain all of the chlorophyll in a plant, in addition to the electron carriers of photophosphorylation. Thylakoids stack to form grana. |
| Vacuole | A liquid-filled, membrane-enclosed compartment in cytoplasm; may function as digestive chambers, storage chambers, waste bins. |
