1. Chapter 7 Lecture Outline See PowerPoint Image Slides
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2. Photosynthesis and Life
During photosynthesis
Organisms use the energy of light to build high-energy organic molecules.
Plants, algae, and some bacteria can do this.
Can make their own food using light
Called photosynthetic autotrophs
99.9% of all life on earth relies on photosynthesis for their energy.
Heterotrophs eat autotrophs.
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3. An Overview of Photosynthesis
Photosynthesis occurs in
Chloroplasts
Contain the pigment that captures the energy in light
Chlorophyll
Found in membranous sacs called grana
A stack of grana is called a thylakoid.
Grana are suspended in a fluid-filled space called the stroma.
During photosynthesis
The energy in light is used to make ATP.
The energy in ATP is used to make organic molecules such as glucose.
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4. Photosynthesis, Chloroplasts, and the Structure of a Leaf
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5. An Overview of Photosynthesis
The chemical equation of photosynthesis:
Light energy + carbon dioxide + water  glucose and oxygen
The three events of photosynthesis
Light-capturing events
The pigment chlorophyll absorbs certain wavelengths of light and some of its electrons become excited.
Light-dependent reactions
These reactions use the energy in the excited electrons to make ATP and NADPH.
Light-independent reactions
ATP and NADPH from the light reactions is used to reduce carbon dioxide to make glucose.
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6. An Overview of Photosynthesis
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7. Light-Capturing Events: Fundamental Concepts
Visible light
Combinations of different wavelengths of light
Can be seen as different colors
Pigments are molecules that absorb light.
Each pigment absorbs certain wavelengths of light.
The wavelengths that they do not absorb, they reflect.
This is the color we see.
In photosynthesis, only the wavelengths that are absorbed can be used to do work.
Chlorophyll: The main photosynthetic pigment
Two forms: a and b
Absorb light in the blue and red portions of the spectrum
Reflect green wavelengths
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8. The Electromagnetic Spectrum, Visible Light and Chlorophyll
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9. Other Types of Pigments
Accessory pigments
Include carotenoids
Absorb blue and green wavelengths
Reflect orange and yellow
Found in leaves, masked by chlorophyll
In the autumn, when chlorophyll disintegrates, accessory pigments show through (fall colors).
Chlorophyll + accessory pigments
Organized into photosystems that harvest the energy from many wavelengths of light
Found in thylakoids of the chloroplasts
When pigments absorb light
Some of their electrons become “excited”
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10. Light-Dependent Reactions: Fundamental Concepts
The excited electrons from chlorophyll
Are passed through an electron transport chain
The energy released is used to pump protons up their concentration gradient.
When protons diffuse through ATP synthase, ATP is made.
Excited electrons passed to NADP+ to make NADPH
Water is split
Electrons are donated to chlorophyll to replace the donated electrons.
Oxygen is produced.
Occurs in the thylakoid membrane
ATP and NADPH move to the stroma to be used in the dark reactions.
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11. Light-Independent Reactions: Fundamental Concepts
The ATP and NADPH from the light-dependent reactions
Provide the energy and electrons needed to build sugar from carbon dioxide
CO2 is captured by an enzyme called RuBisCO
Combines CO2 with ribulose to form a 6-carbon molecule
This is immediately split into two 3-C molecules.
NADPH is used to reduce these molecules.
Glyceraldehyde-3-phosphate is formed.
Can be used to make sugars, proteins, or fats
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12. Photosynthesis: Fundamental Description
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13. Light-Capturing Events: The Details
Packaged as photons
Each photon has a distinct wavelength.
The energy in a photon is related to its wavelength.
When a photon hits a pigment molecule, electrons are excited.
This means that the electrons jump up to a higher energy level.
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14. Light-Capturing Events: The Details Continued
Photosystems
Structures in which the light-capturing events take place
Found in the thylakoid membranes
Made up of antenna complexes and a reaction center
Networks of chlorophyll and accessory pigments
Capture the energy in many different wavelengths of light and pass it to the reaction center
The reaction center is a special chlorophyll molecule that passes its excited electrons to an electron acceptor.
There are two photosystems, I and II.
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15. Light Dependent Reactions: The Details
Photosystem II (PSII)
Occurs first
Donates its excited electrons to the electron transport chain
Splits water to replace the electrons it donated
O2 is released.
Photosystem I (PSI)
Occurs second
Donates its excited electrons to NADP+ to form NADPH
NADPH released into the stroma
Accepts electrons from the electron transport chain to replace the electrons it donated
PS I and II are in the thlyakoid membrane.
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16. The Electron Transport Chain and ATP Synthesis
Between PSII and PSI
Electrons are passed through an electron transport chain (ETC).
This releases energy.
This energy is used to pump protons from the stroma into the thylakoid space.
This creates a proton concentration gradient.
Protons diffuse through ATP synthase.
ATP synthase makes ATP that is released into the stroma.
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17. PS II and I: How They Interact
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18. Light Independent Reactions: The Details
Takes place in the stroma of the chloroplast
Uses
CO2 (from the atmosphere)
ATP and NADPH (from the light-independent reactions)
Ribulose (recycled)
Also called the dark reactions
Also called the Calvin cycle
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19. Carbon Fixation and Sugar Formation
Carbon dioxide gas is combined with a 5-carbon sugar called ribulose.
Accomplished with an enzyme called ribulose bisphosphate carboxylase (RuBisCO)
Forms a 6-carbon molecule
Immediately broken down into two 3-carbon molecules
These 3-carbon molecules are
Energized by ATP
Reduced by NADPH
Glyceraldehyde-3-phosphate is formed.
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20. The Calvin Cycle
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21. Glyceraldehyde-3-phosphate: The Product of Photosynthesis
Glyceraldehyde-3-phosphate can be used for many things.
Used to make glucose
Used to recycle ribulose for the Calvin cycle
Used to make the sugars needed to build ATP, DNA, and RNA
Can be converted into lipids
Can be converted into amino acids to make proteins
Can be broken down in glycolysis
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22. Other Aspects of Plant Metabolism
Plant cells can use the organic molecules produced in photosynthesis to make
Fats, proteins, and other carbohydrates
Toxins for their protection
Many of these are useful medicines.
Some can be used as natural insecticides.
Vitamins
Molecules that we cannot make, but that we need
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23. Interrelationships Between Autotrophs and Heterotrophs
Autotrophs use the energy in light to make food.
Autotrophs use the food they make in cellular respiration.
Plants use the sugar they make!
Plants use the oxygen they make!
Heterotrophs eat the autotrophs.
Then use the food from the autotrophs to fuel cellular respiration
They also use the excess oxygen given off by autotrophs.
All organisms respire!
The circle of life:
Animals get sugar, oxygen, amino acids, fats, and vitamins from plants.
Plants get carbon dioxide, water, and nitrogen from animals.
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24. The Relationship between Photosynthesis and Cellular Respiration
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