Microscopes were invented in the 1600s. Robert Hooke first looked at a thin slice of cork in 1665; he saw "a lot of little boxes." These little boxes first reminded of the little rooms monks lived in, so he called them cells. Hooke observed the same pattern in the stems and roots of carrots and other plants. What Hooke still did not know, however, was that cells are the basic units of living things. Ten years …showed first 75 words of 1382 total…

…showed last 75 words of 1382 total…pigments, light-absorbing substances such as the chlorophyll of green plants, and the pigment retinal found in your eyes. Proteins are the third major group of macromolecules. The most abundant protein in your body is collagen, a fibrous protein that forms the matrix of your skin, ligaments, tendons, and bones. Proteins also play a vital role in the metabolic (chemical and physical) activities of all living things. Proteins called enzymes assist the chemical reactions of metabolism.