Cell membrane: a thin layer of lipid and protein separating the cell's contents from the outside environment.
Phospholipid: a structural substance found in cell membranes.
Cytoplasm: a jellylike substance made up primarily of water and the organelles suspended in it; the center for most of the cell's metabolic activity.
Cytoskeleton: a network of fibers and tiny tubes throughout the cytoplasm; gives a cell support and helps it to maintain or change its shape.
Nucleus: the control center of a cell.
Chromosomes: a structure within a cell that contains a cell's genetic information.
Nucleolus: a specialized organelle in the nucleus of cells; the site of ribosome production.
Prokaryotes: an organism whoe cells do not contain a nucleus or membrane-bound organelles.
Eukaryotes: an organism whoe cells have a nucleus surrounded by a nuclear membrane.
Ribosomes: an organelle that helps to assemble proteins from amino acids.
Endoplasmic reticulum: an extensive network of membranes that transports materials through a cell.
Golgi apparatus: a membrane-bound organelle that packages and secretes products of the endoplasmic reticulum from the cell.
Mitochondria: an organelle that changes energy found in food compounds into energy, or ATP, necessary to power the cell's functions; the site of cellular respiration.
Lysosomes: a small saclike organelle that contains digestive enzymes that help the cell break down large molecules of carohydrates, proteins, and lipids.
Cilia: short, hairlike projections that usually occur in large numbers on the surface of certain cells.
Flagella: long, tail-like projections.
Cell wall: a tough, rigid outer convering that provides a cell with protection and maintenance of its shape.
Chloroplasts: an organelle common in plants and algae that converts sunlight, carbon dioxide, and water into sugars during the process of photosynthesis; contains chlorophyll.
Vacuole: a membrane-bound compartment that absorbs water, store proteins, ions, and waste products of metabolism.
Semipermeable: allowing only certain molecules to pass through membrane.
Passive transport: the movement of a substance across a cell membrane without the use of ATP energy.
Active transport: transport of a substance across a cell membrane requiring the use of enegrgy; usually occurs against a concentration gradient.
Diffusion: the random movement of molecules from an area of higher concentration (more molecules) to an area of lower concentration (fewer molecules).
Osmosis: the diffusion of water molecules across a semipermeable membrane.
Endocytosis: a form of active transport in which a portion of the cell membrane surrounds outside particles and moves them into the cell.
Exocytosis: a process in which wastes and cell products are secreted out of a cell through the cell membrane.