acid: A substance which contains an excess of hydrogen ions and has a pH that is less than 7.

amino acids: The basic building blocks of proteins. They contain an amino group and a carboxyl group.

base: A substance which contains an excess of hydroxide ions and has a pH that is greater than 7.

carbohydrate: An organic nutrient made of carbon, hydrogen and oxygen and having a carbon to hydrogen ratio of 2:1.

carbon dioxide: (CO2) An inorganic clear colorless gas released as an end product of respiration; one of the starting materials needed for photosynthesis.

catalyst: A chemical that speeds up the rate of a chemical reaction but is not used up.

chemical bond: A bond that is formed by the simultaneous attraction for electrons by two nuclei.

complex carbohydrates: Polysaccharides or starches such as glycogen which are made of many monosaccharides or simple sugars.

covalent bond: A type of chemical bond formed when atoms share electrons.

digestion: The enzyme-controlled process that changes large insoluble molecules into small soluble molecules.

digestive system: The specialized organs that act on nutrients as they are digested and absorbed by an organism.

DNA (deoxyribonucleic acid): The nucleic acid that stores the hereditary information or genetic material. It is made of repeating units called nucleotides.

environment: All the living and nonliving things that surround a living thing.

enzyme: A protein that speeds up the rate of biochemical reactions; an organic catalyst. excretion: The removal of metabolic wastes.

fat: An organic molecule that is made of three fatty acid molecules and one glycerol molecule; a lipid.

genetic: Pertaining to DNA, the hereditary material.

glucose: A monosaccharide that is the primary source of cellular energy in most organisms. It is one of the basic building blocks of polysaccharide carbohydrates.

graph: A visual comparison of the data from laboratory investigations usually resulting in a line or bars used to observe general trends in the data.

hormone: A secretion that is released directly into the bloodstream by an endocrine gland.

hydrocarbon: A molecule that contains only hydrogen and carbon.

inorganic: A compound that does not contain both carbon and hydrogen.

ionic bond: The force of attraction between two oppositely charged ions.

lipase: The enzyme that breaks down lipids into fatty acids and glycerol.

lipid: An organic molecule that is made of three fatty acid molecules and one glycerol molecule. Examples include fats, oils and waxes.

molecule: Two or more atoms chemically combined. nitrogenous bases Adenine, thymine, uracil, cytosine and guanine.

nucleic acid: An organic compound composed of a phosphate, a 5-carbon sugar and a nitrogenous base. DNA or RNA.

nucleotide: The basic unit of nucleic acids. It consists of a 5-carbon sugar bonded to a phosphate and a nitrogenous base.

optimum: The best.

organic compound: A compound that contains the elements carbon and hydrogen.

organic molecules: Molecules that contain both carbon and hydrogen.

pH: A scale that measures the acidity or basicity of a solution. photosynthesis The process by which green plants (autotrophs) convert light energy to chemical-bond energy stored in organic nutrients.

plasma membrane: The cell membrane; the semi-permeable outer boundary of the cell.

polymer: A large molecule made of repeating units. For example, polysaccharides are made of many monosaccharides.

protein: An organic compound made of amino acids.

protein synthesis: The making of a protein from amino acids by matching the anticodon of the transfer RNA to the codon of the messenger RNA. reaction: The chemical interaction between reactants resulting in products.

respiration: The process which releases chemical bond energy from organic nutrients (food).

small intestine: A long coiled tube that is the site of most of the chemical digestion and absorption that takes place in the digestive tract.

starch:A carbohydrate composed of many glucose molecules; a polysaccharide.

substrate: The molecule that an enzyme acts on.