Light-dependent reactions, the Calvin cycle and chloroplast structure: flashcards and practice questions for GCSE, A-level and AP Bio. Free, no sign-up.
Subject: biology
Which statement accurately describes the primary energy conversion during photosynthesis?
Answer: It converts light energy into chemical energy stored in organic molecules.
Photosynthesis is an endothermic process that captures light energy and stores it in the chemical bonds of glucose, making it the entry point for energy in most ecosystems.
How does the internal structure of a chloroplast facilitate the Calvin cycle?
Answer: The stroma contains the necessary enzymes for carbon fixation and sugar synthesis.
The Calvin cycle, also known as the light-independent reactions, takes place in the fluid-filled stroma of the chloroplast, where its specific enzymes, like RuBisCO, are located.
What is the direct source of the oxygen gas released as a byproduct during photosynthesis?
Answer: Water molecules (H₂O)
Oxygen gas is released during the light-dependent reactions through a process called photolysis, where light energy splits water molecules (2H₂O → 4H⁺ + 4e⁻ + O₂).
Which statement accurately distinguishes non-cyclic photophosphorylation from cyclic photophosphorylation?
Answer: Non-cyclic photophosphorylation produces ATP, NADPH, and oxygen, while cyclic produces only ATP.
Non-cyclic photophosphorylation involves both photosystems, splits water, and produces ATP, NADPH, and oxygen. Cyclic photophosphorylation uses only Photosystem I, does not split water, and produces only ATP.
Why is the regeneration phase of the Calvin cycle crucial for its continuous operation?
Answer: It remakes the CO₂ acceptor molecule, RuBP, allowing the cycle to continue.
The regeneration phase uses G3P and ATP to reform RuBP (ribulose bisphosphate), which is the five-carbon molecule that accepts CO₂ in the carbon fixation step. Without RuBP, the cycle cannot continue to fix carbon.
Leaves appear green because chlorophyll primarily reflects green light. What does this imply about the effectiveness of green light for photosynthesis?
Answer: Green light is largely unused by chlorophyll for photosynthesis.
Chlorophyll absorbs mainly red and blue light, reflecting green light. Since reflected light is not absorbed, green light contributes least to the energy captured for photosynthesis, as shown by the trough in the absorption spectrum for chlorophyll in the green region.
A plant is exposed to increasing light intensity, but its rate of photosynthesis eventually plateaus. Which factor is most likely limiting the rate at this point?
Answer: The concentration of carbon dioxide in the atmosphere.
According to the law of limiting factors, if light intensity is no longer increasing the rate, another factor is in shortest supply. Carbon dioxide is often a limiting factor for well-lit plants because its atmospheric concentration is low (0.04%), directly affecting the carbon fixation step of the Calvin cycle.
What is the role of the outer membrane of a chloroplast?
Answer: It is freely permeable to small molecules such as CO₂.
The outer membrane encloses the chloroplast and is described as freely permeable to small molecules like CO₂.
What is the primary function of the inner membrane of a chloroplast?
Answer: To control which substances enter and leave the stroma.
The inner membrane of the chloroplast regulates the passage of substances into and out of the stroma, acting as a selective barrier.
What is the role of the stroma within a chloroplast?
Answer: It contains the enzymes of the Calvin cycle, plus DNA and ribosomes.
The stroma is the fluid interior of the chloroplast where the light-independent reactions (Calvin cycle) occur, containing the necessary enzymes, as well as the chloroplast's own DNA and ribosomes.
What is the function of a thylakoid in a chloroplast?
Answer: It is a flattened membrane sac where the light-dependent reactions occur.
Thylakoids are the flattened membrane sacs within the chloroplast where the light-dependent reactions of photosynthesis take place.
What is the thylakoid lumen?
Answer: The space inside a thylakoid where protons accumulate during the light reactions.
The thylakoid lumen is the internal space within a thylakoid, which is crucial for the buildup of a proton gradient during the light-dependent reactions.
What is the role of a granum in a chloroplast?
Answer: It is a stack of thylakoids that increases membrane surface area for light capture.
Grana are stacks of thylakoids, and this stacking arrangement significantly increases the membrane surface area available for the light-dependent reactions and efficient light capture.
What is the function of a lamella in a chloroplast?
Answer: It is a membrane connecting one granum to another.
Lamellae are membrane structures that connect individual grana within the chloroplast, ensuring communication and structural integrity.
What is the role of chlorophyll in photosynthesis?
Answer: It is a green pigment embedded in thylakoid membranes that absorbs light energy.
Chlorophyll is the primary photosynthetic pigment, located in the thylakoid membranes, responsible for absorbing light energy to initiate the light-dependent reactions.
What is photolysis?
Answer: The light-driven splitting of water into protons, electrons, and oxygen.
Photolysis is the specific process during the light-dependent reactions where light energy is used to split water molecules, releasing electrons, protons, and oxygen.
What is a photosystem?
Answer: A cluster of pigments and proteins in the thylakoid membrane that captures light energy.
Photosystems are organized units within the thylakoid membrane, composed of chlorophyll and other pigments along with proteins, designed to capture light energy and initiate electron flow.
What is photophosphorylation?
Answer: The process of making ATP using light energy via the proton gradient across the thylakoid membrane.
Photophosphorylation is the specific term for ATP synthesis that is driven by light energy, utilizing the proton gradient established across the thylakoid membrane through chemiosmosis.
What is chemiosmosis?
Answer: ATP synthesis driven by protons flowing through ATP synthase down their gradient.
Chemiosmosis is the mechanism by which ATP is synthesized, powered by the flow of protons (H⁺) down their electrochemical gradient through the enzyme ATP synthase.
What is the primary role of RuBisCO in the Calvin cycle?
Answer: To attach CO₂ to RuBP in carbon fixation.
RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) is the enzyme responsible for catalyzing the first step of the Calvin cycle, where CO₂ is fixed by combining with RuBP.
What is RuBP?
Answer: A five-carbon molecule that accepts CO₂ in carbon fixation.
RuBP (ribulose bisphosphate) is the initial five-carbon sugar that combines with CO₂ during the carbon fixation step of the Calvin cycle, catalyzed by RuBisCO.
What is G3P (triose phosphate)?
Answer: The direct product of the Calvin cycle, used to build glucose.
G3P (glyceraldehyde 3-phosphate), also known as triose phosphate, is the three-carbon sugar that is the immediate output of the Calvin cycle, from which glucose and other organic molecules are synthesized.
What is the role of NADPH in photosynthesis?
Answer: It is a reduced electron carrier that delivers electrons from the light reactions to the Calvin cycle.
NADPH is an electron carrier molecule that is reduced during the light-dependent reactions and then provides the high-energy electrons needed for the reduction phase of the Calvin cycle to synthesize sugars.
What is carbon fixation?
Answer: The incorporation of inorganic CO₂ into an organic molecule.
Carbon fixation is the initial step of the Calvin cycle where the inorganic carbon from CO₂ is attached to an organic molecule (RuBP), making it available for sugar synthesis.
What is the palisade mesophyll?
Answer: The leaf tissue layer packed with chloroplasts where most photosynthesis occurs.
The palisade mesophyll is a layer of elongated cells located near the upper surface of leaves, densely packed with chloroplasts, making it the primary site of photosynthesis.
What are stomata?
Answer: Pores, mostly on the lower leaf surface, through which CO₂ enters and O₂ and water vapor leave.
Stomata are small pores on the surface of leaves, primarily on the underside, that regulate gas exchange, allowing CO₂ to enter for photosynthesis and O₂ and water vapor to exit.
What does an absorption spectrum represent?
Answer: A graph of how strongly a pigment absorbs light across wavelengths.
An absorption spectrum is a graphical representation showing the extent to which a particular pigment absorbs light at different wavelengths of the electromagnetic spectrum.
What does an action spectrum represent?
Answer: A graph of photosynthetic rate across wavelengths of light.
An action spectrum plots the rate of a biological process, such as photosynthesis, against the different wavelengths of light, showing which wavelengths are most effective.
What is a limiting factor in the context of photosynthesis?
Answer: The single factor in shortest supply that sets the rate of a process.
A limiting factor is the environmental condition or resource that is in the shortest supply relative to the plant's needs, thereby restricting the rate of photosynthesis, even if other factors are optimal.
The process by which plants, algae, and some bacteria use light energy to build glucose from carbon dioxide and water is called {0}.
Answer: Photosynthesis
Photosynthesis is the fundamental process of converting light energy into chemical energy in organic molecules.
In plants and algae, photosynthesis takes place inside organelles called {0}.
Answer: chloroplasts
Chloroplasts are the specific organelles where photosynthesis occurs in plants and algae.
The flattened membrane sacs where the light-dependent reactions occur are called {0} membranes.
Answer: thylakoid
Thylakoid membranes are the site of the light-dependent reactions within the chloroplast.
The fluid interior of the chloroplast, containing the enzymes of the Calvin cycle, is known as the {0}.
Answer: stroma
The stroma is the fluid-filled space within the chloroplast where the Calvin cycle takes place.
The stage of photosynthesis that converts light energy into chemical energy in the form of ATP and NADPH is called the {0}.
Answer: light-dependent reactions
The light-dependent reactions are the first stage of photosynthesis, producing ATP and NADPH.
The light-independent reactions, which use ATP and NADPH to build sugar from CO₂, are also known as the {0}.
Answer: Calvin cycle
The Calvin cycle is the second stage of photosynthesis, where CO₂ is fixed into sugar.
Protons flow back into the stroma through the enzyme ATP synthase, which uses the flow to join ADP and inorganic phosphate into {0}.
Answer: ATP
ATP (adenosine triphosphate) is an energy-carrying molecule produced during the light-dependent reactions.
At the end of the electron transport chain, re-energized electrons, together with H⁺, reduce the carrier NADP⁺ to {0}.
Answer: NADPH
NADPH is a reduced electron carrier that delivers electrons from the light reactions to the Calvin cycle.
The enzyme {0} attaches a molecule of CO₂ to RuBP in the carbon fixation phase of the Calvin cycle.
Answer: RuBisCO
RuBisCO is the enzyme responsible for carbon fixation, the initial step of the Calvin cycle.
The three-carbon sugar that is the true direct product of the Calvin cycle is {0}.
Answer: G3P
G3P (glyceraldehyde 3-phosphate) is the direct sugar product of the Calvin cycle, from which glucose is later built.
The splitting of water molecules by light energy to replace electrons lost by photosystem II is called {0}.
Answer: photolysis
Photolysis is the light-driven splitting of water, which releases oxygen as a byproduct.
ATP synthesis driven by protons flowing through ATP synthase down their gradient is a mechanism called {0}.
Answer: chemiosmosis
Chemiosmosis is the process of ATP synthesis using the energy from a proton gradient.
The single factor in shortest supply that sets the rate of a process is known as a {0}.
Answer: limiting factor
A limiting factor is the environmental condition that restricts the rate of photosynthesis.
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