1. Chapter 8 Section 2 - Photosynthesis

2. Photosynthesis
Light energy is trapped and converted into chemical energy during photosynthesis.

4. Overview of Photosynthesis
Cellular Energy
Overview of Photosynthesis
Purpose of Photosynthesis
To convert light energy into an energy that organisms can use.

5. Overview of Photosynthesis
Cellular Energy
Overview of Photosynthesis
Purpose of Photosynthesis
Plants make sugars through photosynthesis, an energy that all life on earth can use.
Protists such as algae and certain bacteria can use photosynthesis as well.
Without photosynthetic organisms, there would be no life on earth!

6. The Reactants of Photosynthesis are: Light – from the sun
Cellular Energy
Photosynthesis
The Reactants of Photosynthesis are:
Light – from the sun
Carbon Dioxide (CO2) – from the air
Water (H2O) – from the roots
The Products of Photosynthesis are:
Glucose (C6H12O6) - sugar
Oxygen (O2)

7. Overview of Photosynthesis
Cellular Energy
Overview of Photosynthesis
Photosynthesis occurs in two phases:
Light-dependent reactions (Light reactions)
Light-independent reactions (sometimes called dark reactions or Calvin cycle)

8. Overview of Photosynthesis
Occurs in the chloroplasts of plant cells.

9. Takes place in the thylakoids.
Cellular Energy
Photosynthesis
Phase One: Light Reactions
Takes place in the thylakoids.
Chloroplasts
Chloroplasts are the organelles that capture light energy.
Disk-shaped

10. Chloroplasts Photosynthesis Phase One: Light Reactions 2 compartments:
Cellular Energy
Chloroplasts
2 compartments:
Thylakoid: membranes that contain stacks called grana; where light reactions take place.
Photosystems I and photosystems II contain light-absorbing pigments and protein complexes important in the light reactions.
Stroma: Fluid-filled space outside grana.
Where light-independent reactions take place.

13. Light absorbing molecules found in thylakoid membranes.
Cellular Energy
Photosynthesis
Phase One: Light Reactions
Pigments
Light absorbing molecules found in thylakoid membranes.
Different pigments absorb different wavelengths of light and reflect others.
Chlorophylls are the major light-absorbing pigments in plants.
Chlorophylls absorb most in blue-violet region of visible light spectrum and reflect light in green spectrum.

14. Chloroplast Pigments Chloroplasts contain several pigments:
Chlorophyll a
Chlorophyll b
Carotenoids

15. Basics of the Light Reactions
Cellular Energy
Photosynthesis
Basics of the Light Reactions
The absorption of light is the first step of photosynthesis.
When light strikes a thylakoid in a chloroplast, energy is transferred to and excites electrons in chlorophyll.

17. Basics of the Light Reactions
Section 2
Cellular Energy
Photosynthesis
Basics of the Light Reactions
Energized electrons are used to break down (split) water molecules.
Oxygen is released through openings on the underside of the leaf called stomata.
Activated electrons are passed along a series of molecules along the thylakoid membrane, the electron-transport chain. This generates energy in the form of NADPH.
Energy produced from protons (H+) is used to synthesize ATP.

19. Basics of the Light Reactions
Cellular Energy
Photosynthesis
Basics of the Light Reactions
Energy stored is stored temporarily in energy carrying molecules, ATP and NADPH that will be used in the Calvin cycle (light-independent reaction)

20. Review: ATP CYCLE + Occurs continuously in cells
About 10 million new ATP molecules are made in every cell every second!!!
2. Releasing Energy Energy released by breaking bonds – used to power cells
Stored Energy Energy stored in chemical bonds.
4. Making ATP
Energy released by other chemical reactions and processes can be used to bond a phosphate to ADP to make ATP
3. Energy Depleted ADP has less chemical energy than ATP
ADP + P

21. Phase Two: The Calvin Cycle (Light-Independent Reactions)
A series of enzyme-assisted reactions in which chemical energy stored in ATP and NADPH is used to synthesize carbohydrates such as glucose.

24. Phase Two: The Calvin Cycle (Light-Independent Reactions)
Does not require light.
Occurs in the stroma of chloroplast.
Requires CO2.
Uses ATP and NADPH as fuel to run.
Makes glucose sugar from CO2 and hydrogen.
Plants use sugars formed during the Calvin cycle as a source of energy and to form starch, which stores energy, and cellulose for structure of cell wall.

26. https://www.youtube.com/watch?v=E_XQR800AgM Chloroplast Light Stroma
NADP
Stack of
thylakoids
ADP
+ P
Light
reactions
Calvin
cycle
Sugar used for
 Cellular respiration
 Cellulose
 Starch
 Other organic compounds

27. Factors That Affect The Rate Of Photosynthesis
Cellular Energy
Photosynthesis
Factors That Affect The Rate Of Photosynthesis
Light intensity
If you increase the amount of light, then photosynthesis will increase up to a point.
Temperature
CO2 concentrations
Water

28. Cellular Energy
Alternative Pathways
Many plants in extreme climates have alternative pathways for photosynthesis.
C4 plants
In hot, dry environments where light energy is plentiful but water is scarce.
Sugarcane
Corn
Some grasses

29. Water conserving plants. Open their stomata at night. Thick cuticle.
Cellular Energy
Alternative Pathways
CAM plants
Water conserving plants.
Open their stomata at night.
Thick cuticle.
Cacti
Orchids
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