• All energy on earth comes from the sun.
• Solar energy is converted by: – Plants – Algae (underwater plants) – Cyanobacteria (photosynthetic bacteria – sometimes called blue-green algae)

– draw this diagram

– write this in your notes 1. Carbon dioxide and water are taken in by plants 2. Plants absorb light energy and convert it to cellular energy called “ATP” 3. Energy is used to change carbon dioxide and water into sugar molecules called glucose.
4. Sugar is converted to starch and stored for use by the plant, and by animals when they eat plants.

• Chloroplasts in plant cells are where photosynthesis takes place.
• Chloroplasts look green because they contain the pigment CHLOROPHYLL.
• Chlorophyll reflects green light and absorbs the other colors of visible light.

Photosynthesis is a Chemical Change • It changes carbon dioxide and water into two new substances – oxygen and sugar.

Photosynthesis is a Chemical Change Chemical Changes can be written using words in a CHEMICAL EQUATION • carbon + water makes dioxide oxygen + glucose

Photosynthesis is a Chemical Change Chemical changes can also be written with symbols instead of words • carbon + water makes dioxide oxygen + glucose • CO
2 + H 2
O 
O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change When we use numbers and symbols to represent a chemical change, this is called a CHEMICAL EQUATION
CO 2 + H 2
O 
O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change On the left side of an equation are the REACTANTS , or the ingredients needed for the chemical reaction to happen.
CO 2 + H 2 O

O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change On the right side of an equation are the PRODUCTS , or the substances that are produced as a result of the reaction.
CO 2 + H 2
O 
O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change The ARROW always goes left – to – right and shows how the reaction happens.
CO 2 + H 2 O O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change In any chemical reaction, the atoms in the ingredients have to be the same as the atoms in the products, just re-arranged.
What 3 kinds of atoms are involved in photosynthesis?

Photosynthesis is a Chemical Change There are only carbon, hydrogen, and oxygen atoms in the reactants and in the products.
CO 2
Reactants Products
+ H 2 O O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change But count the NUMBERS of each atom. Are they the same on both sides of the equation?
CO 2
Reactants Products
+ H 2 O O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change 2 3 Carbon 6 Hydrogen 12 3 Oxygen 8
CO 2
Reactants Products
+ H 2 O O 2 + C 6 H 12 O 6

CO 2
Photosynthesis is a Chemical Change 2 1 Carbon 6 Hydrogen 12 3 Oxygen 8 THIS CAN’T BE – ATOMS CAN’T BE CREATED!
Reactants Products
+ H 2 O O 2 + C 6 H 12 O 6

CO 2
Photosynthesis is a Chemical Change 2 3 Carbon 6 Hydrogen 12 3 Oxygen 8 THERE MUST BE MORE THAN ONE MOLECULE OF SOME OF THESE Reactants Products
+ H 2 O O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change We need to “balance” the chemical equation to make the same numbers and kinds of atoms on each side.
CO 2
Reactants Products
+ H 2 O O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change We need to “balance” the chemical equation to make the same numbers and kinds of atoms on each side.
(Adding a number in front of the molecule is like multiplying every atom by that number)
6 CO 2
Reactants Products
+ 6 H 2 O 6 O 2 + C 6 H 12 O 6

Photosynthesis is a Chemical Change ___ Carbon ___ ___ Hydrogen ___ ___ Oxygen ___ Now count the atoms on each side…
6 CO 2
Reactants Products
+ 6 H 2 O 6 O 2 + C 6 H 12 O 6