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Quizzes > High School Quizzes > Science

Calvin Cycle Practice Quiz

Sharpen your Calvin cycle skills with practice

Difficulty: Moderate
Grade: Other
Study OutcomesCheat Sheet
Colorful paper art promoting The Calvin Cycle Challenge high school biology quiz.

Where in the plant cell does the Calvin cycle occur?
Chloroplast stroma
Thylakoid membrane
Mitochondrial matrix
Cytoplasm
The Calvin cycle takes place in the stroma of the chloroplast where all necessary enzymes and substrates are present. This environment supports the carbon fixation process efficiently.
What is the primary purpose of the Calvin cycle?
To split water molecules
To convert CO2 into sugars
To break down glucose for energy
To produce ATP from sunlight
The primary function of the Calvin cycle is to fix carbon dioxide and convert it into organic molecules like sugars. This process is essential for converting light energy into chemical energy used by the plant.
Which enzyme initiates carbon fixation in the Calvin cycle?
Rubisco
ATP Synthase
Phosphofructokinase
Cytochrome c
Rubisco is the enzyme that catalyzes the fixation of CO2 by combining it with RuBP. It is the most abundant enzyme in chloroplasts and is crucial for initiating the Calvin cycle.
How many molecules of CO2 must be fixed to net produce one molecule of G3P for biosynthesis?
Six
One
Two
Three
In the Calvin cycle, three CO2 molecules are fixed to eventually yield one net molecule of glyceraldehyde-3-phosphate (G3P) that can be used for synthesizing sugars. The remaining intermediates are recycled to regenerate RuBP.
The Calvin cycle is also referred to as which type of reaction?
Dark reactions
Light-dependent reactions
Light-independent reactions
Photorespiration
The Calvin cycle does not require light directly and is therefore known as the light-independent reactions. It utilizes ATP and NADPH produced during the light reactions to drive carbon fixation.
Which molecule functions as the initial carbon acceptor in the Calvin cycle?
3-phosphoglycerate (3-PGA)
Fructose-6-phosphate
Ribulose-1,5-bisphosphate (RuBP)
Glyceraldehyde-3-phosphate (G3P)
Ribulose-1,5-bisphosphate (RuBP) is the molecule that accepts CO2 at the start of the Calvin cycle. This step is critical for initiating the process of carbon fixation.
During the reduction phase, which cofactor is essential for converting 3-phosphoglycerate to G3P?
ATP
Coenzyme A
FADH2
NADPH
NADPH serves as the reducing agent that converts 3-phosphoglycerate into glyceraldehyde-3-phosphate (G3P) during the reduction phase. Its role is indispensable for the successful completion of this step.
What is the main objective of the regeneration phase in the Calvin cycle?
Regenerating RuBP to continue carbon fixation
Generating ATP
Producing NADPH
Absorbing light energy
The regeneration phase converts glyceraldehyde-3-phosphate (G3P) back into ribulose-1,5-bisphosphate (RuBP), enabling the cycle to continue. This step is vital for maintaining a continuous supply of RuBP for CO2 fixation.
How many ATP molecules are used in the Calvin cycle per three CO2 fixed?
9
3
6
12
For every three molecules of CO2 fixed, the Calvin cycle uses 9 ATP molecules. This energy is necessary for the phosphorylation steps and the regeneration of RuBP.
What is the net output of the Calvin cycle in terms of molecules available for biosynthesis?
Six molecules of G3P
Two molecules of G3P
Three molecules of G3P
One molecule of G3P
Although the cycle generates multiple G3P molecules, only one molecule is net available per three CO2 fixed for further synthesis of carbohydrates. The remaining molecules are recycled to regenerate RuBP.
Which pigment is crucial for absorbing light energy that ultimately supports the Calvin cycle?
Anthocyanin
Chlorophyll
Xanthophyll
Carotenoids
Chlorophyll is the primary pigment that absorbs light energy in photosynthesis, which is then used to generate ATP and NADPH during the light reactions. These products are essential for driving the Calvin cycle.
What role does ATP play in the Calvin cycle?
It fixes carbon dioxide directly
It transports electrons
It acts as a reducing agent
It supplies energy for reactions
ATP provides the necessary energy to drive the endergonic reactions in the Calvin cycle. It is particularly important for the conversion of 3-phosphoglycerate to G3P and the regeneration of RuBP.
Which molecule exits the Calvin cycle to contribute to the formation of glucose?
Pyruvate
Glyceraldehyde-3-phosphate (G3P)
Phosphoenolpyruvate (PEP)
Acetyl-CoA
Glyceraldehyde-3-phosphate (G3P) is the key three-carbon sugar produced by the Calvin cycle that exits for use in various biosynthetic pathways, including the production of glucose. This intermediate links the cycle to the broader metabolic network of the plant.
Why is Rubisco deemed inefficient despite its abundance?
It also catalyzes oxygenation, leading to photorespiration
It requires a high concentration of NADPH
It operates only at low temperatures
It tends to denature quickly under normal conditions
Rubisco is not very efficient because it can catalyze both carboxylation and oxygenation reactions. The oxygenation reaction leads to photorespiration, a process that diminishes the overall efficiency of photosynthesis.
How does a limitation in NADPH availability impact the Calvin cycle?
It increases the regeneration of RuBP
It directly converts CO2 into glucose
It enhances ATP production
It causes a slowdown in the reduction phase
NADPH is a critical reducing agent required for transforming 3-phosphoglycerate into G3P. When NADPH is limited, the reduction phase of the Calvin cycle slows, resulting in decreased efficiency of carbon fixation.
What is the ATP:NADPH ratio required by the Calvin cycle for fixing three molecules of CO2?
3:1
2:3
3:2
1:1
For each set of three CO2 molecules fixed, the Calvin cycle uses 9 ATP and 6 NADPH, which simplifies to an ATP:NADPH ratio of 3:2. This ratio is critical in ensuring that the energy supplied from the light reactions meets the demands of carbon fixation.
Which metabolic pathway shares intermediates with the Calvin cycle, influencing photosynthetic regulation?
Beta-oxidation
Pentose phosphate pathway
Citric acid cycle
Glycolysis
The pentose phosphate pathway shares several intermediates with the Calvin cycle, such as ribose-5-phosphate. This interconnection plays an important role in synchronizing carbon flow and regulating photosynthetic activity based on cellular needs.
Under which conditions does Rubisco favor oxygenation over carboxylation, leading to photorespiration?
High light intensity and low temperature
High CO2 and low oxygen
Low oxygen and high water availability
High oxygen and low CO2
Photorespiration is more likely when oxygen levels are high and CO2 concentrations are low. Under these conditions, Rubisco is more prone to bind oxygen, leading to the less efficient oxygenation reaction.
How does an increase in temperature affect the efficiency of the Calvin cycle?
It increases ATP synthesis
It decreases enzyme specificity, increasing photorespiration
It enhances the specificity of Rubisco for CO2
Temperature does not affect the Calvin cycle
Increased temperatures reduce Rubisco's ability to differentiate between CO2 and O2, leading to greater rates of photorespiration. As a result, the overall efficiency of the Calvin cycle in carbon fixation decreases under high temperature conditions.
In experimental conditions, what effect does an elevated atmospheric CO2 concentration have on the Calvin cycle?
It enhances carbon fixation by increasing substrate availability
It decreases NADPH production
It has no impact on carbon fixation
It reduces ATP consumption
Higher CO2 levels increase the likelihood of Rubisco binding CO2 over O2, which enhances the rate of carbon fixation. This results in a more efficient Calvin cycle and improved synthesis of sugars.
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Study Outcomes

  1. Understand the key phases of the Calvin cycle, including carbon fixation and reduction.
  2. Analyze the role of enzymes and molecules involved in the cycle.
  3. Apply knowledge to solve problems related to carbon assimilation in photosynthesis.
  4. Evaluate the differences between the Calvin cycle and light-dependent reactions.
  5. Synthesize information to identify and address knowledge gaps in the Calvin cycle process.

Calvin Cycle Practice Cheat Sheet

  1. The Calvin Cycle's carbon magic - Imagine turning CO₂ into sugar like a botanical wizard! In the chloroplast stroma, the Calvin Cycle uses ATP and NADPH from light reactions to stitch carbon atoms into glucose. It's the sugar factory that keeps plants - and us - fed. OpenStax Biology
  2. Three-stage superstar - The cycle rolls through carbon fixation, reduction, and regeneration to keep the party going. RuBisCO grabs a CO₂ and bonds it to RuBP, creating two 3‑PGA molecules like a carbon appending pro. OpenStax Biology
  3. Reduction: from 3‑PGA to G3P - ATP and NADPH swoop in to convert 3‑phosphoglycerate into the sugar G3P, the building block for glucose. Think of it as the cycle's molecular makeover moment, turning simple molecules into valuable three‑carbon treasures. OpenStax Biology
  4. Regeneration: rewind and repeat - G3P doesn't get to chill long - it's largely sent back to regenerate RuBP, powered by more ATP. This recharge step ensures the cycle never stops, like a musical loop that keeps carbon grooving. OpenStax Biology
  5. Six spins for one glucose - To build a single glucose (C₆H₝₂O₆), the cycle turns six times, grabbing six CO₂, spending 18 ATP, and burning through 12 NADPH. It's like a carbon carousel: ride six loops to collect enough sugar bits for that sweet six‑carbon prize. OpenStax Biology
  6. RuBisCO: protein superstar - RuBisCO is so common it's the most abundant protein on Earth, making CO₂ fixation its daily gig. Without this enzyme's carbon-collecting prowess, life as we know it would run out of sugar fuel. Wikipedia
  7. Powered by the sun (indirectly) - The Calvin Cycle itself doesn't catch light, but it breathes in ATP and NADPH produced by light reactions. It's solar-powered in spirit - a dark-process dependent on day-time energy harvest. OpenStax Biology
  8. Photorespiration pitfall - When RuBisCO grabs O₂ instead of CO₂, it starts photorespiration, releasing CO₂ and wasting energy. This quirk is more common in hot conditions, making photosynthesis less efficient on sunny scorchers. Wikipedia
  9. C4 & CAM adaptations - Some plants outsmart photorespiration: C4 species separate fixation and the Calvin Cycle by space, while CAM plants do it by time - fixing CO₂ at night. These clever strategies keep photosynthesis humming even when heat wants to sabotage it. Wikipedia
  10. Mnemonic magic: Fix, Reduce, Regenerate - Remember the cycle's three acts with "Fix, Reduce, Regenerate" - it's like a catchy study jingle for your memory. Sing it in your mind next time you review to lock down those phases! TopperLearning
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