alveolus A microscopic air sac in the lungs that is lined with epithelial cells. The plural of alveolus is alveoli.
amino acid Any one of many acids that occur naturally in living things and that include some which form proteins.
autotrophic Needing only carbon dioxide or carbonates as a source of carbon and a simple inorganic nitrogen compound for metabolic synthesis.
cell The smallest unit of living matter that can exist by itself.
cell wall A rigid wall outside the cell membrane of plant cells. Composed mostly of cellulose, it provides support and protection.
cellular respiration The process by which organisms use oxygen to break down food molecules to get chemical energy for cell functions.
chloroplast A plastid that contains the pigment chlorophyll; it provides the site of photosynthesis.
chromoplast A plastid that contains carotenoid pigments.
cytoplasm A jellylike material that fills all the spaces in a cell between the plasma membrane and the nucleus.
cytoskeleton A meshlike network in the cytoplasm that provides internal support for the cells, anchors internal cell structures, and functions in cell movement and division.
deoxyribonucleic acid A substance that carries genetic information in the cells of plants and animals. Generally known by its abbreviation, DNA.
endoplasmic reticulum Long, stringy structures in eukaryotic cells where some proteins and lipids are synthesized and detoxification happens.
epithelial tissue Tissue that covers a free surface or lines a tube or cavity of an animal body and serves especially to enclose and protect the other parts of the body, to produce secretions and excretions, and to function in assimilation.
eukaryotic Having a distinct nucleus and intracellular membranes. All protists, fungi, plants, and animals are eukaryotic.
Golgi complex An organelle that handles protein processing and transport.
hemoglobin The part of blood that contains iron, carries oxygen through the body, and gives blood its red color
lysosome An organelle full of enzymes that enables a cell to break down certain molecules for recycling and disposal.
mitochondrion An organelle that serves as the site for the reaction of oxygen and glucose to produce energy used for the cell. The plural of “mitochondrion” is “mitochondria.”
neuron A very long, thin, wirelike cell, along which nerve signals pass from one part of the body to another.
nucleolus A round body inside the nucleus, which produces RNA that is sent out of the nucleus to other parts of the cell. The plural of “nucleolus” is “nucleoli.”
nucleus A part of a cell containing DNA and RNA and responsible for growth and reproduction. The plural of “nucleus” is “nuclei.”
organelle A structure inside a cell’s cytoplasm that carries out a particular function in the life of the cell.
organism An individual living thing.
phloem tissue Cells of the vascular system in plants that transport food from leaves to other areas of the plant.
photosynthesis A chemical reaction in which energy from sunlight is harnessed and used to convert carbon dioxide and water into organic compounds—namely sugar molecules—and oxygen.
plasma membrane A thin, semipermeable double layer of fatty molecules that surrounds every cell.
plastid A kind of organelle in the cytoplasm of a plant cell.
prokaryotic Possessing no distinct nucleus, such as bacteria and cyanobacteria.
protein Any of various naturally occurring extremely complex substances that consist of amino-acid residues joined by peptide bonds and include many essential biological compounds (as enzymes, hormones, or antibodies).
ribosome An organelle, usually found on the surface of the endoplasmic reticulum, that functions in the synthesis of proteins.
stimulus Something that causes something else to happen, develop, or become more active. The plural of stimulus is stimuli.
tissue A group of similar cells that work together to carry out a specific function.
transpiration The process in which water passes through a plant.
vacuole A large sac in the inside of plant cells that removes waste products and stores food.
xylem tissue Tissue in the vascular system of plants that moves water and dissolved nutrients from the roots to the leaves.