1. USING LIGHT TO MAKE FOOD
Photosynthesis
USING LIGHT TO MAKE FOOD

2. Photosynthesis
Photosynthesis is the process in which plants use energy from the sun to make sugar from carbon dioxide and water.
The reactants are: carbon dioxide and water
The products are: glucose and oxygen
It’s the opposite of cellular respiration!

3. The Equation The overall equation for photosynthesis is:
6CO2 + 6H2O + energy  C6H12O6 + 6O2
In words:
Carbon dioxide plus water and sunlight makes glucose and oxygen.

4. The Equation Where do plants get carbon dioxide from?
The atmosphere and our breathing
Where do plants get water from?
The soil, rain
What do plants produce that we use?
Oxygen (we breathe) and glucose (we eat)

5. Autotrophs vs. Heterotrophs
Autotrophs meaning “self-feeders” they make their own food without eating other things. Autotrophs are producers.
Heterotrophs means “other-feeders” which means they must eat others to get energy. They are also called consumers.
What are plants? What are people?

6. The Reaction Photosynthesis takes place in chloroplasts
They contain chlorophyll, a green pigment that absorbs light energy.
Chloroplasts contain disk-like membranous sacs called thylakoids, which are arranged in stacks called grana.

7. AN OVERVIEW OF PHOTOSYNTHESIS
Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
Carbon dioxide
Water
Glucose
Oxygen gas
PHOTOSYNTHESIS

8. The location and structure of chloroplasts
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Inner membrane
Grana
Stroma
Thylakoid compartment
Stroma
Figure 7.2
Thylakoid

9. The Reaction
Photosynthesis take the carbon from carbon dioxide and uses it to make glucose.
The oxygen from water is used to make oxygen gas, which is considered a waste product.
Plants remove CO2 from the atmosphere and emit O2, which reduces global warming.

10. The Reaction
Photosynthesis occurs in 2 stages: the light reactions and the Calvin cycle (dark reaction).
The light reactions produce ATP
The Calvin cycle uses ATP

11. LIGHT REACTIONS (in grana) CALVIN CYCLE (in stroma)
An overview of photosynthesis
H2O
CO2
Chloroplast
Light
NADP+
ADP + P
LIGHT REACTIONS (in grana)
CALVIN CYCLE (in stroma)
ATP
Electrons
NADPH O2
Sugar
Figure 7.5

12. Step 1: The Light Reactions
The purpose of this step is to convert light energy to chemical energy
The light reactions occur in the grana of the chloroplast.
Water is used to produce oxygen.
ATP and NADPH are also produced.

13. Step 2: The Calvin Cycle
The purpose of the Calvin Cycle is to make sugar molecules (glucose).
It occurs in the stroma, the fluid inside the chloroplasts.
It takes 6 turns of the Calvin Cycle to make 1 glucose molecule.

14. Water Saving Plants
Some plants are adapted to survive in dry climates.
C4 plants keep their stomata (pores) closed to save water. Examples: corn and sugarcane.
CAM plants only open their stomata at night. Examples: pineapples, cactus, jade, aloe.

15. Let’s Review What are the 2 steps of photosynthesis?
Where do the light reactions occur? What goes in and what comes out?
Where does the calvin cycle occur? What goes in and what comes out?