1. Chapter 2 Section 1 Chemical reactions take place inside cells.

2. A. All cells are made of the same elements: elements - all living and nonliving matter in the universe can be broken down into pure substances - there are about 100 different known elements. -25 elements are necessary for life but only 6 account for 99% of the human body. atom - the smallest unit of an element (or matter) molecule – two or more atoms joined together compound – two or more different atoms joined together to form a molecule examples: water H2O carbon dioxide CO2

3. A. All cells are made of the same elements: chemical reaction - process where chemical changes occur -atoms are rearranged and chemical bonds are either broken or formed. -produces energy that cells use for life activities B. Large molecules support cell function: All large molecules in living things contain carbon (organic compounds). There are four types of large molecules. 1) carbohydrates3) proteins 2) lipids4) nucleic acids

4. B. Large molecules support cell function: 1)carbohydrates – provides the cell with energy and structural support (ex: sugar, starch and glucose) 2)lipids – provide cells with energy and used to build structures (ex: fats, oils and waxes that cannot mix with water) 3)proteins – support growth and repair tissue, control chemical reactions, allow movement, fight infection and deliver oxygen (ex: amino acids – building blocks of proteins) 4)nucleic acids – hold the instructions for maintenance, growth and reproduction of the cell (ex: DNA and RNA)

5. C. About two thirds of every cell is water: 1)A water molecule consists of two hydrogen atoms and one oxygen atom (H2O). 2)Water is a polar molecule, its two sides have slightly different charges. (positive & negative) 3)Like a magnet, the ends of polar molecules attract opposite charges and repel charges that are the same. 4)Most substances dissolve in water because it is a polar molecule. Those that mix attract, most lipids, like oil, repel and do not dissolve in water.

6. C. About two thirds of every cell is water: 5)Cell membranes are made of special lipids that have a “water-loving head” and a “water-hating tail”. The tails repel water molecules. 6)Cell membranes have a double layer of these lipids. They separate the inside of the cell from the outside.