1. Photosynthesis
Chapter 8

2. Autotrophs vs. Heterotrophs
Autotrophs: Plants and some other types of organisms that use light energy from SUNLIGHT to make their own food. These organisms undergo photosynthesis!!
– EX: Trees, grass, algae, plants
Heterotrophs: Organisms that CANNOT use the sun’s energy to make food– they obtain energy from the foods they consume
– EX: Deer, rabbits, bear, fish, insects, etc…

3. The Photosynthesis Equation
Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high energy sugars and oxygen
6CO2 + 6H2O + light→C6H12O6 + 6O2
(carbon dioxide + water + light → sugars + oxygen)
Plants then use the sugars to produce complex carbohydrates such as starches
Plants obtain CO2 from the air or water in which they grow

4. Photosynthesis
Light Energy
Chloroplast
CO2 + H2O
Sugars + O2

5. Inside a Chloroplast
Chloroplast= Filled with chlorophyll and are where photosynthesis takes place in plants and other photosynthetic eukaryotes
– Thylakoids= saclike photosynthetic membranes arranged into stacks known as grana. Area where light-dependent reactions take place
– Photosystems= clusters of chlorophyll and other pigments that are organized by the thylakoids
– Stroma= Area outside the thylakoid membranes where light- independent reactions

6. Light-dependent Reactions

7. Figure 8-5 Chlorophyll Light Absorption
Section 8-2
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a V B G Y O R

8. Electron Carriers
Electron Transport= The transfer of a pair of high energy electrons & their energy to another molecule
Electron Carriers= The “bucket” or carrier that moves electrons and their energy from molecule to the next
EX: NADP+: Accepts and holds a pair of high-energy electrons and an H+ ion, converting NADP+ into NADPH turning energy from the sun into chemical energy .
An analogy would be a pan carrying hot coals like the NADP+ carries two electrons and a H+ ion.

9. ATP Formation

10. Adenosine Triphosphate (ATP)
Adenine
Ribose
3 Phosphate groups

11. ADP and ATP (Electron Carriers)
Energy
Energy
Adenosine triphosphate (ATP)
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Fully
charged
battery

12. Light-Dependent Reactions
Light-Dependent Reactions: Use energy from sunlight to produce the energy carriers ATP and NADPH and oxygen.
– Reactions occur within the thylakoid membranes of chloroplasts

13. Light-dependent Reactions http://highered. mcgraw-hill

14. Figure 8-10 Light-Dependent Reactions
Section 8-3
Hydrogen
Ion Movement
Photosystem II
Chloroplast
ATP synthase
Inner
Thylakoid
Space
Thylakoid
Membrane
Stroma
Electron
Transport Chain
Photosystem I
ATP Formation

15. Photosynthesis

16. Steps in Photosynthesis
Photosynthesis: Has five major steps that occur within the thylakoid membrane of the chloroplast
– 1. Photosystem II: Light absorbed by photosystem II is used to break up water molecules into energized electrons, hydrogen ions (H+) and oxygen.
– 2. Electron Transport Chain: High-energy electrons from photosystem II move through the electron transport chain into photosystem I.

17. Steps in Photosynthesis
– 3. Photosystem I: Electrons released by photosystem II are energized again in photosystem I. Enzymes in the membrane use these electrons to make NADPH/
– 4. Hydrogen Ion Movement: The inside of the thylakoid membrane is charged with H+ ions. This causes the outside of the thylakoid membrane to be negatively charged and the inside of the membrane to be positively charged.

18. Steps in Photosynthesis
– 5. ATP Formation: As hydrogen ions pass through ATP synthase, their energy is used to convert ADP into ATP. As it rotates ATP synthase (enzyme) binds ADP and P+ group to create ATP. Because of this, light-dependent transport produces high energy electron AND ATP.
SUMMARY:
Light dependent reactions use water, ADP and NADP+ to produce oxygen, ATP and NADPH (Water, ADP, NADP+ Oxygen, ATP, NADPH)
ATP and NADPH then provide energy to build energy containing sugars from low-energy compounds.

19. Light-independent Reactions
Calvin Cycle: Energy stored in the ATP and NADPH formed during photosynthesis, is used to build high-energy sugars that can be stored for a long period of time.
– Does not require light and is called light independent reaction
– Takes place in the stroma of the chloroplasts

20. Calvin Cycle http://highered. mcgraw-hill

21. Steps in the Calvin Cycle
The Calvin Cycle has four major steps:
– 1. C02 Enters the Cycle: 6 CO2 molecules are combined with six 5- carbon molecules to produce three 12-carbon molecules
– 2. Energy Input: Energy from ATP and electrons from NADPH convert the twelve 3-carbon molecules into higher-energy forms
– 3. 6-Carbon Sugar Produced: two 3-carbon molecules are removed to produce sugars, lipids, amino acids, and other compounds

22. Steps in the Calvin Cycle
– 4. 5-Carbon Molecules Regenerated: the 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to start the next cycle : )

23. Figure 8-11 Calvin Cycle Section 8-3 CO2 Enters the Cycle Energy Input
ChloropIast
5-Carbon
Molecules
Regenerated
6-Carbon Sugar
Produced
Sugars and other compounds

24. Concept Map Photosynthesis Light- dependent reactions Calvin cycle
Section 8-3
Photosynthesis
includes
Light-
dependent
reactions
Calvin cycle
takes place in
uses
use
take place in
Thylakoid
membranes
Stroma
NADPH
ATP
Energy from
sunlight
to produce of
to produce
ATP
NADPH O2
Chloroplasts
High-energy
sugars

25. Figure 8-7 Photosynthesis: An Overview
Section 8-3
Light O2
Sugars
CO2
Chloroplast
Chloroplast
NADP+
ADP + P
Light-
Dependent
Reactions
Calvin
Cycle
ATP
NADPH

26. Factors Affect Photosynthesis
Various Factors Affect the Rate of Photosynthesis.
Some of these factors are:
1. Amount of available water
– EX: Plants in dry areas have waxy leaves to prevent water loss
2. Temperature
– EX: Enzymes work best between 0° and 35°C. Temps above or below this range may slow down photosynthesis or stop it entirely
3. Light Intensity
1. EX: The higher the intensity the higher the rate of photosynthesis. There is a maximum limit however. This varies from plant to plant