The Need for Energy Chapter 9

All living organisms must be able to obtain energy from the environment in which they live. Plants and other green organisms are able to trap the light energy in sunlight and store it in the bonds of certain molecules for later use. Other organisms cannot use sunlight directly. They eat green plants. In that way, they obtain the energy stored in plants. Cell Energy

Active transport, cell division, movement of flagella or cilia, and the production, transport, and storage of proteins are some examples of cell processes that require energy. There is a molecule in your cells that is a quick source of energy for any organelle in the cell that needs it. The name of this energy molecule is adenosine triphosphate or ATP for short. ATP is composed of an adenosine molecule with three phosphate groups attached. Work and the need for energy

Forming and Breaking Down ATP The charged phosphate groups act like the positive poles of two magnets. Bonding three phosphate groups to form adenosine triphosphate requires considerable energy. When only one phosphate group bonds, a small amount of energy is required and the chemical bond does not store much energy. This molecule is called adenosine monophosphate (AMP). When a second phosphate group is added, more energy is required to force the two groups together. This molecule is called adenosine diphosphate, or ADP. An even greater amount of energy is required to force a third charged phosphate group close enough to the other two to form a bond. When this bond is broken, energy is released.

The energy of ATP becomes available to a cell when the molecule is broken down. Forming and Breaking Down ATP Adenosine PPP P P Adenosine triphosphate (ATP) Adenosine diphosphate (ADP)

How cells tap into the energy stored in ATP When ATP is broken down and the energy is released, the energy must be captured and used efficiently by cells. Many proteins have a specific site where ATP can bind. Then, when the phosphate bond is broken and the energy released, the cell can use the energy for activities such as making a protein or transporting molecules through the plasma membrane. When ATP has been broken down to ADP, the ADP is released from the binding site in the protein and the binding site may then be filled by another ATP molecule. ATP ADP Protein P

Section 9.2 Of all the organisms in the natural world, green plants are the only ones that manufacture their own food. This process is called photosynthesis and begins when light strikes the plant's leaves (both sunlight and artificial light can power this process). Cells in the plant's leaves, called chloroplasts, contain a green pigment called chlorophyll which interacts with sunlight to split the water in the plant into its basic components. Carbon dioxide enters the leaf through holes called stomata and combines with the stored energy in the chloroplasts through a chemical reaction to produce a simple sugar. The sugar is then transported through tubes in the leaf to the roots, stems and fruits of the plants. Some of the sugar is used immediately by the plant for energy; some is stored as starch; and some is built into a more complex substance, like plant tissue or cellulose. Fortunately for us, plants often produce more food than they need, which they store in stems, roots, seeds or fruit. We can obtain this energy directly by eating the plant itself or its products, like carrots, rice or potatoes. Photosynthesis is the first step in the food chain which connects all living things. Every creature on earth depends to some degree on green plants. The oxygen that is released by the process of photosynthesis is an essential exchange for all living things. Forests have been called the "lungs of the earth" because animals inhale oxygen and exhale carbon dioxide in the process of breathing, and plants take in carbon dioxide and give off oxygen in the process of photosynthesis. But every year, over 28 million acres of tropical forest are cut and then burned to clear land for farming. Deforestation is also blamed for the "greenhouse effect" (global warming) which results from the build-up of carbon dioxide and other gases.

Activity Without enough sunlight, plants cannot use the process of photosynthesis to produce food. Materials: Small shrub, tree or house plant Cardboard or aluminum foil Scissors Paper clips 1. Pick a shrub, tree or houseplant that you can use for an experiment. 2. Using the cardboard or aluminum foil, cut out some geometrical shapes like a circle, square or triangle. Make sure your shapes are big enough to make a patch that will cover nearly half of the plant leaf. 3. Paperclip each shape on a different leaf. 4. If you use a house plant, place it near a south, west or east window were it will get plenty of sunlight. Make notes about the weather each day and add them to your observations. 5. After four days, remove the shapes from the leaves and observe each of the leaves that had a shape covering it. 6. Compare the areas on the leaf that were covered with the shape to other parts of the leaf.

It is the year 2040 and you are a research scientist. The amount of sunlight that reaches the earth has been reduced because of some major event like pollution, volcanoes or global fires. Farmers are asking you for help to save their failing crops. Figure out ways that you might help.