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Questions and Answers
What is the primary pathway for electron transport in photosynthesis?
What is the primary pathway for electron transport in photosynthesis?
Which substance is produced as a byproduct of non-cyclic electron flow?
Which substance is produced as a byproduct of non-cyclic electron flow?
During the light reactions, what directly excites chlorophyll a?
During the light reactions, what directly excites chlorophyll a?
What is the role of NADP+ in photosynthesis?
What is the role of NADP+ in photosynthesis?
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Where does electron transport occur within the chloroplast?
Where does electron transport occur within the chloroplast?
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What is the main function of ATP synthase in the light reactions?
What is the main function of ATP synthase in the light reactions?
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Which molecule is created from the high concentration of H+ ions in the thylakoid space?
Which molecule is created from the high concentration of H+ ions in the thylakoid space?
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What initiates the Calvin Cycle after the light reactions?
What initiates the Calvin Cycle after the light reactions?
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What is the low concentration of H+ ions found in the stroma associated with?
What is the low concentration of H+ ions found in the stroma associated with?
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Which process is primarily involved in generating the proton gradient during electron transport?
Which process is primarily involved in generating the proton gradient during electron transport?
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What is the role of NADP+ in the light reactions?
What is the role of NADP+ in the light reactions?
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What does cyclic electron flow primarily produce?
What does cyclic electron flow primarily produce?
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In the Calvin Cycle, which molecule is primarily synthesized?
In the Calvin Cycle, which molecule is primarily synthesized?
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What is the main purpose of chemiosmosis during the light reactions?
What is the main purpose of chemiosmosis during the light reactions?
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Which statement is true about the electron transport chain in the light reactions?
Which statement is true about the electron transport chain in the light reactions?
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Which component of the light reactions helps pump protons from stroma to lumen?
Which component of the light reactions helps pump protons from stroma to lumen?
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What is the primary function of the light reactions in photosynthesis?
What is the primary function of the light reactions in photosynthesis?
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Which statement accurately describes the relationship between ATP and NADPH in the Calvin Cycle?
Which statement accurately describes the relationship between ATP and NADPH in the Calvin Cycle?
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What is the main product of the Calvin cycle?
What is the main product of the Calvin cycle?
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In which part of the chloroplast does the light-dependent reaction occur?
In which part of the chloroplast does the light-dependent reaction occur?
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Which process describes the creation of ATP powered by the diffusion of H+ ions?
Which process describes the creation of ATP powered by the diffusion of H+ ions?
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Where do protons have a high concentration during chemiosmosis?
Where do protons have a high concentration during chemiosmosis?
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Which electron transport complex is involved in transferring electrons from water to NADP+?
Which electron transport complex is involved in transferring electrons from water to NADP+?
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What is formed as a result of the excitation of electrons in photosystem II?
What is formed as a result of the excitation of electrons in photosystem II?
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What connects the electron transport processes to ATP synthesis in chloroplasts?
What connects the electron transport processes to ATP synthesis in chloroplasts?
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During non-cyclic electron flow, what is the final electron acceptor?
During non-cyclic electron flow, what is the final electron acceptor?
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What is the main function of ATP synthase during photosynthesis?
What is the main function of ATP synthase during photosynthesis?
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Study Notes
Photosynthesis: An Overview
- Photosynthesis is the process by which plants create sugar using light energy.
- The general equation for photosynthesis is: 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂.
- Photosynthesis takes place in chloroplasts.
Photosynthesis in Chloroplasts
- Chloroplasts contain an internal membrane system of connected disc-shaped structures called thylakoids.
- Thylakoids stack to form grana.
- The region between the thylakoid membranes is the thylakoid space.
- The major pigment in chloroplasts is chlorophyll a.
- Chlorophyll a, along with other pigments, captures light energy from visible light and uses this energy to convert CO₂ and H₂O into glucose.
Leaf Structure
- Leaves are the photosynthetic organs of plants.
- Mesophyll cells perform photosynthesis.
- Mesophyll cells contain the largest number of chloroplasts.
- Stomata are pores in leaves that allow CO₂ in and O₂ out.
Stomata
- Stomata perform three functions:
- Allowing CO₂ in
- Allowing O₂ out
- Evaporative cooling: When water exits through stomata, leaves cool.
Stomata Regulation
- Stomata regulate their size to maximize CO₂ uptake and minimize water loss.
- Stomata typically reduce in size under sunny, warm, dry, and windy conditions.
- Guard cells control the opening and closing of stomata.
- When water is scarce, guard cells lose water and close stomata.
- When water is abundant, guard cells swell and open stomata.
Photosynthesis: Why are Plants Green?
- Visible light is electromagnetic radiation with wavelengths between 400 and 700 nm.
- Plants appear green because green wavelengths of light are reflected.
- Other wavelengths are absorbed.
- Chlorophyll absorbs light most strongly in the blue and red portions of the visible spectrum.
Pigments
- Pigments are substances that absorb visible light.
- The reflected and transmitted light include the colors we see.
- Absorbed light is important in driving photosynthesis.
- Chlorophyll a is the main photosynthetic pigment
- Chlorophyll b is an accessory pigment.
Two Types of Reactions in Photosynthesis
- Photosynthesis involves two main processes:
- Light-dependent reactions (light reactions)
- Require light
- Excite electrons and split H₂O
- Light-independent reactions (dark reactions)
- Do not directly require sunlight
- Including Carbon fixation, the Calvin cycle
- Light-dependent reactions (light reactions)
Light Reactions
- Occur in the grana.
- Split water, release oxygen, produce ATP, and form NADPH.
Dark Reactions (Calvin Cycle)
- Occur in the stroma.
- Forms sugar from carbon dioxide, using ATP and NADPH.
- A cyclic process that fixes carbon, utilizes energy molecules, and regenerates molecules.
Stages of Photosynthesis
- Light reactions produce NADPH and ATP.
- Dark reaction uses NADPH and ATP to form glucose from carbon dioxide.
The Light Reactions (Light-Dependent Reactions)
- The light reactions begin when light energy is trapped by chloroplasts.
- This light energy is absorbed by a complex cluster of chlorophyll molecules.
- This complex is called a photosystem.
- The first photosystem involved in the light reactions is photosystem II (or P680).
- Electron transport chain components transport lost electrons from photosystem II.
- Electrons are passed down a chain of electron acceptors to photosystem I (or P700)
- Photosystem II replenishes lost electrons from water; oxygen is produced as a by-product.
- This energy is used to produce ATP through chemiosmosis.
- The electrons reach photosystem I , which excites the electrons and passes them to NADP+, creating NADPH.
Photosystems
- Photosystems I and II are complexes containing chlorophyll a and other pigments
Electron Transport
- Electron transport occurs in the thylakoid membrane.
- Two mechanisms of electron transport:
- Non-cyclic electron flow.
- Cyclic electron flow.
Non-Cyclic Electron Flow
- The primary pathway.
- Process starts with Photosystem II (or P680) which is energized by light and releases electrons to an electron transfer chain
- Electrons pass through Cytochrome Complex
- The energy from the electron transport allows the active transport of hydrogen ions into the thylakoid space
- The final electron acceptor NADP+ is reduced to NADPH as it picks up a hydrogen ion giving NADPH.
Cyclic Electron Flow
- Cyclic electron flow generates more ATP using only Photosystem I.
ATP Synthase
- Protons pass through ATP synthase by facilitated diffusion.
- ATP is produced in the stroma.
Factors Affecting Photosynthesis
- Light intensity
- Carbon dioxide concentration
- Temperature
C3 Plants
- Stomata open during day and close at night.
- When stomata close in hot, arid conditions, O2 builds up within the cells and Rubisco binds to O2 rather than CO2, resulting in photorespiration.
C4 Plants
- Adaptation to hot, arid environments
- Mesophyll cells create 4-carbon molecules.
- Bundle sheath cells perform Calvin cycle.
- Allows Rubisco to have sufficient CO₂ to prevent binding with O₂
CAM Plants
- Adaptation to hot, arid environments.
- Stomata are closed during the day, and open at night.
- Carbon fixation happens during the night, and the Calvin cycle happens during the day.
Homework
- Read Chapter 3.1
- Do page 145 problems 4, 5, 6, and 7.
- Read Section 3.2 questions (page 154-155) Questions 1-3, 11.
- Read Section 3.3 Questions (page 166-167) Questions 1-4, 6, 8a(i-iii), 8b.
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