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 energy6 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.