2. cell theory macromolecule nucleic acid protein Cells and Life lipid carbohydrate

3.  English scientist Robert Hooke first identified cells over 300 years ago while looking at cork under a microscope he built.  After Hooke’s discovery, other scientists began to use better microscopes to identify different structures in the cells of plants and animals. Understanding Cells

4.  Matthias Schleiden, a German scientist, used a new microscope to look at plant cells.  Another German scientist named Theodor Schwann used the microscope to observe animal cells.  Schleiden and Schwann realized that plant and animal cells have similar features.  The observations made by Schleiden, Schwann, and Virchow were combined to make one theory.

5. Cell theoryCell theory includes three principles. Getty Images

6.  The main ingredient in any cell is water. A water molecule has two areas:  The negative (–) end can attract the positive part of another substance.  The positive (+) end can attract the negative part of another substance. Basic Cell Substances

7. Water and salt both have positive and negative parts. Basic Cell Substances (cont.) FoodCollection/SuperStock

8. Basic Cell Substances (cont.) MacromoleculesMacromolecules are necessary substances in cells, formed by joining many small molecules together.

9.  There are four types of macromolecules in cells: Nucleic acids are macromolecules that form when long chains of molecules called nucleotides join together. Nucleic acids Proteins are long chains of amino acid molecules. Proteins Basic Cell Substances (cont.)

10. Lipids are large macromolecules that do not dissolve in water. Lipids Carbohydrates store energy, provide structural support, and are needed for communication between cells. Carbohydrates Basic Cell Substances (cont.)

11. Each type of macromolecule has unique functions in the cell.