Ch. 2 How Cells Function 2.1 Chemical reactions take place inside cells. 1. All cells are made of the same elements. A. There are about 100 elements; 25 of them are necessary for life. B. The smallest unit of an element is the atom. C. Atoms bond together in chemical reactions to form molecules. 2. Large molecules support cell function. A. All large molecules in living things contain carbon. B. Carbon atoms can form long chains, leading to a huge number of possible compounds. C. There are four types of large molecules: a. Carbohydrates are sugar, starch, and cellulose. They provide cells with energy and structural support. b. Lipids are fats, oils, and waxes that cannot mix with water. Lipids often provide cells with energy. c. Proteins are made of smaller molecules amino acids. Proteins control chemical reactions, support growth and repair of tissue, allow movement, fight infections, and deliver oxygen. d. Nucleic acids hold the instructions for maintenance, growth, and reproduction of the cell. The two types are DNA and RNA. 3. About two thirds of every cell is water. A. A water molecule, which consists of two hydrogen atoms and one oxygen
atom, is a polar molecule. B. Because its two sides have slightly different charges, water is an excellent solvent. C. Cell membranes are composed of special lipids that have one end that repels water. D. Cell membranes have double layers of lipids. E. Both sides of a membrane have water repellent ends facing out. 2.1 Key Terms 1. chemical reaction The process by which chemical changes occur. In a chemical reaction, atoms are rearranged, and chemical bonds are broken and formed. 2. Carbohydrate A type of carbon based molecule in living things. Carbohydrates include sugars and starches used for energy or as structural materials. Carbohydrate molecules contain carbon, hydrogen, and oxygen atoms. 3. Lipid A type of carbon based molecule in living things. Lipids include fats, oils, and waxes used for energy or as structural materials. Lipids are made up of subunits of fatty acids. 4. Protein A macromolecule in living things that is made up of smaller molecules called amino acids. Proteins control the chemical activity of a cell and support growth and repair. 5. nucleic acid One of several carbon based molecules that carry an organism s genetic code. One of the nucleic acids (DNA) contains the information needed to construct proteins. RNA, a second type of nucleic acid, translates the information into proteins. 2.2 Cells capture and release energy 1. All cells need energy.
A. Molecules store chemical energy in the bonds between their atoms. B. Glucose is the energy source for most cells. 2. Some cells capture light energy. A. Plants capture light energy from the sun through photosynthesis. a. This process takes place in plant cells that have chloroplasts. B. Plants take water from the soil and carbon dioxide from the air. C. In chloroplasts a pigment called chlorophyll absorbs light. D. The cell uses the energy to break water into hydrogen and oxygen the freed hydrogen and the carbon dioxide from the air are combined to make glucose. a. Most of the oxygen from water is released into the air. 3. All cells release energy. A. All cells, plant and animal, break down glucose for energy. B. In cellular respiration, the mitochondria in cells convert small glucose molecules into energy, carbon dioxide, and water. a. This process is the other half of the energy cycle. C. Photosynthesis and cellular respiration are the two processes in the energy cycle.
D. Fermentation allows cells to release energy without oxygen. a. It releases small amounts of energy and can produce either carbon dioxide and alcohol or lactic acid. b. When you run out of oxygen while exercising, your muscles use fermentation to break down sugar. c. This results in lactic acid build up, which makes muscles sore.
2.2 Key Terms 1. Chemical Energy Energy that is stored in the chemical composition of matter. The amount of chemical energy in a substance depends on the types and arrangement of its atoms. 2. Glucose A sugar molecule that is a major energy source for most cells, produced by the process of photosynthesis. 3. Photosynthesis The process by which green plants and other producers use simple compounds and energy from light to make sugar, an energy rich compound. 4. Chlorophyll A light absorbing chemical that traps the energy in sunlight and converts it to chemical energy. Found in chloroplasts of plant cells and the cells of other photosynthetic organisms. 5. Cellular Respiration A process in which cells use oxygen to release energy stored in sugars. 6. Fermentation A chemical process by which cells release energy from sugar when no oxygen is present. 2.3 Materials move across the cell s membranes 1. Some materials move by diffusion. 2. Diffusion occurs when molecules spread out until they are evenly mixed. A. Molecules move from a higher concentration to a lower one. a. Small molecules diffuse through membranes during passive transport. b. The diffusion of water through a membrane is called osmosis. 6. Some transport requires energy. A. Cells use chemical energy for active transport. This type of transport is
necessary for two puroposes: a. Cells need to move materials from lesser concentrations to greater. Example: Our kidneys use active transport to remove excess salt from our bodies. b. Cells need to move large molecules. Molecules move into the cell through endocytosis and out of it through exocytosis. In both cases, the cell membrane encloses the molecule in a pocket, which pinches off the pocket, and moves it. 7. Cell size affects transport. A. All materials needed by the cell must move across the cell membrane. If the ratio of volume to surface area is too large and the cell doesn t change have, there will not be enough membrane area to transport materials into and out of the cell. B. Cells avoid this problem by one of three adaptations: a. staying small b. dividing c. changing shape