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CHAPTER 2 – SEC. 1: PHOTOSYNTHESIS I. WHAT IS PHOTOSYNTHESIS? • Every living organism on this planet needs energy to function. For example, cells need energy to make proteins or bring substances in and out of the cell. • Most of the energy used to perform life functions comes directly from the sun. • Some organisms such as plants capture the sun’s energy through its light to make its own food. This is called PHOTOSYNTHESIS. II. PHOTOSYNTHESIS IS A TWO–STAGE PROCESS • Stage 1 - Plants take sunlight, carbon dioxide (from the air), and water (through the plant’s roots) into a plant’s leaf. • Stage 2 - Once in the leaf, sunlight, carbon dioxide, and water react to make food for the plant (which is the glucose sugar) and a by-product which is released into the air (oxygen). Diagram of the two-steps in Photosynthesis Stage One - CAPTURING THE SUN’S ENERGY • The first stage in photosynthesis is to capture the sun’s light in the plant organelles called CHLOROPLASTS. • Chloroplasts are found in the leaf of a plant. • The sun’s light is actually absorbed by the pigments found inside a chloroplast. • The main pigment doing the light absorption is CHLOROPHYLL. • As the sun’s light is accepted into the chloroplast, all the colors of the visible spectrum are absorbed except the color green. • It is reflected back out causing you to see the plant’s color as green. Stage 2 - USING ENERGY TO MAKE FOOD • In the second stage of photosynthesis, the captured sunlight reacts with two raw materials inside the plant: water and carbon dioxide. • Water comes from a plant’s roots and carbon dioxide comes from the air in through the stomas of the underside of a leaf. • A stoma is an opening on the underside of a leaf that allows in certain air molecules such as carbon dioxide. • Once the water and carbon dioxide are in the plant, they make their way to the inside of a chloroplast. • In the chloroplast, they undergone a chemical reaction with the sun’s light to make glucose sugars (the plant’s food) and oxygen (expelled through the stoma into the air we breathe). III. THE PHOTOSYNTHESIS EQUATION • Light energy • 6 CO2 + 6 H2O C6H12O6 + 6 02 • Carbon dioxide water glucose oxygen • The raw materials needed for photosynthesis are carbon dioxide, water, and the sun’s light. • Their reactions make or yields glucose (sugar) and oxygen. Light energy 6 CO2 + 6 H2O C6H12O6 + 6 02 Carbon dioxide water glucose oxygen • The number before a molecule is how many molecules are involved. • The subscript number tells you how many atoms of a certain element are involved. • The number of atoms must be equal or balanced on both sides of the equation. What is the glucose sugar used for? • Plants use the glucose sugar for food by breaking it down for its energy content. • Plants also use the glucose sugar to make cell parts such as cellulose. • Plants can also store glucose sugar for later use (ex. a potato). IV. PHOTOSYNTHESIS AND LIFE • Def. of AUTOTROPH – an organism that can make its own food such as a plant • Autotrophs get their energy directly from the sun. • Def. of HETEROTROPH – an organism that cannot make its own food such as animals • Heterotrophs get their energy indirectly through the food they eat such as plants.