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 CO H 2 O  C 6 H 12 O 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 CO H 2 O  C 6 H 12 O 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.