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USING LIGHT TO MAKE FOOD
Photosynthesis
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!
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.
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)
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?
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.
Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
AN OVERVIEW OF PHOTOSYNTHESIS
Carbondioxide
Water Glucose Oxygengas
PHOTOSYNTHESIS
The location and structure of chloroplasts
Figure 7.2
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outermembrane
Innermembrane
ThylakoidcompartmentThylakoidStroma
Granum
StromaGrana
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.
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
An overview of photosynthesis
Figure 7.5
Light
Chloroplast
LIGHTREACTIONS
(in grana)
CALVINCYCLE
(in stroma)
Electrons
H2O
O2
CO2
NADP+
ADP+ P
Sugar
ATP
NADPH
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.
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.
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.
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?
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