name ____________________ Principles of Biology – Photosynthesis Study Guide Obtain a Glencoe Biology book. Read pages 242 through 248 to complete the following. Carbohydrates, in the form of simple sugars, like glucose are broken apart by organisms to make ATP. Heterotrophs must consume sugars, but autotrophs can make their own. They do this by trapping energy from sunlight to make carbohydrates in a process called photosynthesis. Most plants are green because they contain chlorophyll, chlorophyll found in chloroplasts of some cells. The first step in photosynthesis is trapping energy from the sun. sun This energy is then converted into chemical energy. Besides energy, these two things are needed for photosynthesis to occur: H2O & CO2. Write the balanced chemical equation for photosynthesis here: Light Energy + 6CO2 + 6H2O C6H12O6 + 6O2 How many molecules of carbon dioxide are required? 6 How many molecules of carbohydrates are produced? One (1) What gas is produced as a waste? Oxygen The “light reactions” are the photo part of photosynthesis; during the light reactions, H2O is split into H & energy (or O). O) The Calvin cycle is the synthesis part of photosynthesis, during which carbon dioxide and the H from water are combined to form glucose/sugars. glucose/sugars Complete the 3 main steps for the light reactions: (see fig. 10.8) 1. Electrons from chlorophyll lose energy, which is used to make ATP (used in Calvin Cycle. Cycle 2. Water breaks up into H & O. 3. Additional electrons, along with H+ form another energy molecule, called NADPH. NADPH Complete the steps to the Calvin cycle: (see fig. 10.9) 1. The C from carbon dioxide is “fixed” to a 5-Carbon molecule to form a 6-carbon molecule. 2. This 6-carbon molecule splits into 2 33-carbon molecules, molecules called PGA. 3. The PGA is changed to PGAL (2 33-Carbon sugars) sugars), rs) using NADPH and ATP energy. 4. Some PGAL are left in the Calvin cycle, some are used to form other carbohydrates. carbohydrates In summary, the light reactions make energy molecules, and split water. The Calvin cycle combines CO2 with H to make carbohydrates. carbohydrates Predict what would happen to the rate of photosynthesis if we could increase the concentration of CO2. The rate will go up. up What if we could decrease the concentration of CO2? The rate would decrease. (as long as plenty of light and water are present) How do photosynthetic plants enable us to use the energy from the sun? Convert sun’ sun’s energy into food energy What would happen to animal life on earth if all plants suddenly died? All animals die, due to decrease in O2 and food. food Compare the chemical reaction of photosynthesis to the chemical reaction of respiration: They are opposites (as different kinds of energy). The reactants reactants of one is/are the products of the other.