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Questions and Answers
What substance is oxidized during photosynthesis?
What is the primary function of the light reactions in photosynthesis?
During the Calvin cycle, what is the initial step that occurs?
Which of the following wavelengths is most effective in driving photosynthesis?
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What by-product is released during the light reactions?
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What type of process is photosynthesis categorized as?
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The thylakoids are primarily responsible for which part of photosynthesis?
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What is the role of NADP+ in the light reactions?
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What is the relationship between the wavelength of light and the energy per photon?
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What is the primary reason leaves appear green?
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Which pigment is the key light-capturing pigment that directly participates in light reactions?
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What does a spectrophotometer measure?
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Which wavelengths of light are most effective for photosynthesis according to the absorption spectrum of chlorophyll a?
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What is the action spectrum of photosynthesis?
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Who first demonstrated the action spectrum of photosynthesis?
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What happens to wavelengths of light that are absorbed by pigments?
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What is the primary function of the Calvin cycle?
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Which of the following molecules is directly fixed to start the Calvin cycle?
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How many molecules of ATP are consumed for the net synthesis of one G3P in the Calvin cycle?
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What occurs during the reduction phase of the Calvin cycle?
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What is the final product of the Calvin cycle that serves as a starting point for other metabolic pathways?
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What role does rubisco play in the Calvin cycle?
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During which phase of the Calvin cycle is RuBP regenerated?
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For every three molecules of CO2 that enter the Calvin cycle, how many molecules of G3P are ultimately produced?
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What is the role of chloroplasts in photosynthesis?
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Where in the plant are chloroplasts primarily located?
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What gas enters the plant's leaves during photosynthesis?
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What is the chemical equation summarizing the process of photosynthesis?
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What is released as a by-product of the splitting of water during photosynthesis?
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What pigment is primarily responsible for capturing light energy in chloroplasts?
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What is the main structural component of a chloroplast that contains the pigment necessary for photosynthesis?
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How do plants primarily transport water to the leaves for photosynthesis?
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What role does PEP carboxylase play in C4 plants?
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How is pyruvate used in C4 plants following its formation?
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What is a primary advantage of C4 photosynthesis over C3 photosynthesis?
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What factors might affect the relative abundance of C3 and C4 plant species?
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What mechanism do CAM plants use to conserve water?
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What is one significant concern regarding the increase in CO2 levels since the Industrial Revolution?
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What is the expected benefit of genetically modifying rice to perform C4 photosynthesis?
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What happens to stomata in CAM plants during the day?
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Study Notes
Photosynthesis: Converting Light Energy to Chemical Energy
- Photosynthesis is the process by which plants and other photosynthetic organisms convert light energy into chemical energy in the form of sugars.
- Chloroplasts are organelles found in plant cells that are the sites of photosynthesis. They are structurally similar to photosynthetic bacteria, suggesting a common evolutionary origin.
- Chlorophyll, the green pigment found in chloroplasts, absorbs light energy and uses it to drive the reactions of photosynthesis.
Chloroplast Structure and Function
- Mesophyll: This is the interior tissue of a leaf where most photosynthesis occurs.
- Stomata: These microscopic pores on the leaf surface allow for gas exchange, with CO2 entering and O2 exiting.
- Veins: Transport water from the roots and sugars to non-photosynthetic parts of the plant.
- Chloroplast Envelope: Two membranes surround a dense fluid called the stroma.
- Thylakoids: Interconnected sacs within the chloroplast that form a third membrane system. Stacks of thylakoids are called grana.
The Photosynthesis Equation
- The overall chemical change during photosynthesis is the reverse of cellular respiration:
- 6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O
The Splitting of Water
- During photosynthesis, chloroplasts split water into hydrogen and oxygen.
- Electrons from hydrogen are incorporated into sugar molecules, while oxygen is released as a byproduct.
Photosynthesis as a Redox Process
- Photosynthesis is a redox process where water is oxidized and carbon dioxide is reduced.
- It is an endergonic process, meaning it requires energy input, which is provided by light.
The Two Stages of Photosynthesis
-
Light Reactions: Occur in the thylakoids and use light energy to:
- Split water, releasing electrons and protons (H+).
- Release oxygen as a byproduct.
- Reduce NADP+ to NADPH.
- Generate ATP from ADP by photophosphorylation.
-
Calvin Cycle (aka the dark reactions): Occurs in the stroma and uses the ATP and NADPH generated by the light reactions to:
- Fix carbon dioxide.
- Reduce fixed carbon to sugar.
The Light Reactions
- Electromagnetic Spectrum: The full range of electromagnetic radiation, including visible light (380-740 nm).
- Photons: Discrete packages of light energy, with shorter wavelengths having more energy per photon.
-
Photosynthetic Pigments: Absorb light energy, with different pigments absorbing different wavelengths.
- Chlorophyll a: The primary pigment involved in light reactions.
- Chlorophyll b: An accessory pigment that captures additional light energy.
- Carotenoids: Accessory pigments that absorb wavelengths not captured by chlorophyll.
The Calvin Cycle
- An anabolic process that builds sugars from smaller molecules using ATP and reducing power from NADPH.
- Carbon Fixation: CO2 binds to a five-carbon sugar named ribulose bisphosphate (RuBP), catalyzed by rubisco.
- Reduction: 3-phosphoglycerate is phosphorylated (using ATP) and reduced (using NADPH) to produce glyceraldehyde 3-phosphate (G3P).
- Regeneration: Five molecules of G3P are rearranged to regenerate three molecules of RuBP.
C4 Photosynthesis
- An adaptation that increases photosynthetic efficiency in hot, dry environments.
- A three-step process:
- CO2 is initially fixed by PEP carboxylase in mesophyll cells.
- Four-carbon compounds are transported to bundle-sheath cells.
- CO2 is released and used in the Calvin cycle.
- C4 plants have higher affinity for CO2 than C3 plants, allowing them to thrive in low-CO2 environments.
CAM Plants
- Plants with crassulacean acid metabolism (CAM), a type of photosynthesis that conserves water.
- Open stomata at night, taking in CO2 and storing it as organic acids in vacuoles.
- Close stomata during the day and release CO2 for use in the Calvin cycle.
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Description
Explore the fascinating process of photosynthesis, where plants convert light energy into chemical energy. This quiz delves into the structure and function of chloroplasts, including the roles of mesophyll, stomata, and thylakoids. Test your knowledge about how plants harness solar energy for growth!