High School Biology : Understanding the Calvin Cycle

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #201 : High School Biology

Which of the following does not show a simplified version of the photosynthesis reaction?

Possible Answers:

Correct answer:

Explanation:

There are several ways that the photosynthesis reaction is often written. A common form shows carbon dioxide and water combining, with the help of energy from the sun, to produce sugar and oxygen.

Often the reaction will be simplified to remove the coefficients of the molecules, or the reaction will be written in words instead of chemical symbols. NADP is converted to NADPH during photosynthesis, but may or may not be included in the reaction.

The incorrect reaction in the answer choices reverses the carbon dioxide and oxygen. Remember that the reaction must contain carbon on both sides of the equation in order to be balanced; carbon dioxide cannot be on the same side as glucose. The overall purpose of photosynthesis is to convert carbon, in the form of carbon dioxide from the air, into usable sugar. In terms of a reaction equation, this means that carbon dioxide is a reactant on the left side and sugar is a product on the right side.

Example Question #5 : Photosynthesis

Which of the following statements about the Calvin cycle is false?  

Possible Answers:

The Calvin cycle releases oxygen as a byproduct

The Calvin cycle occurs within the stroma of the chloroplast

The Calvin cycle binds carbon atoms from carbon dioxide sources into organic compounds

The Calvin cycle is the second set of reactions in photosynthesis

Correct answer:

The Calvin cycle releases oxygen as a byproduct

Explanation:

The Calvin cycle is the second set of biochemical reactions in photosynthesis and follows the light reactions. The light reactions function to use photons and water to generate NADPH, oxygen, and water. The NADPH can then be used to power the Calvin cycle, which uses the energy stored in ATP and NADPH during light reactions to generate organic molecules for energy. The light reactions take place in the chloroplasts, but the Calvin cycle takes place in the stroma and is not dependent on light. The final result of the Calvin cycle is to use energy to bind reactant carbon dioxide to produce glyceraldehyde 3-phosphate (G3P), a three-carbon sugar. G3P is then used to build sucrose, starch, and cellulose for energy storage and metabolism.

Example Question #22 : Cell Functions

What is the function of rubisco during the Calvin cycle?

Possible Answers:

It regenerates RuBP

It produces G3P molecules 

It catalyzes the carboxylation of RuBP

It carries the prepared glucose to surrounding cells

It captures photons and uses them to generate ATP

Correct answer:

It catalyzes the carboxylation of RuBP

Explanation:

Rubisco is an enzyme that helps add carbon dioxide to RuBP molecules. This in turn forms an unstable inermediate compound, which immediately breaks into two 3-PGA molecules. 

Example Question #7 : Photosynthesis

Some plants can fix carbon through an alternative pathway called the C4 pathway. What is the key advantage of the C4 pathway?

Possible Answers:

The combination of both C3 and C4 pathways allows the plant to grow faster

Production of more RuBP to fuel the Calvin cycle

It provides a feedback mechanism to split more water during the light reaction

Fixing carbon with less water loss compared to C3 plants

Correct answer:

Fixing carbon with less water loss compared to C3 plants

Explanation:

The key characteristic of the C4 pathway is that is produces oxaloacetate and four-carbon sugars from carbon dioxide, compared to the Calvin cycle of most plants, which generates glyceraldehyde 3-phosphate and three-carbon sugars.

The Cpathway fixes carbon dioxide into four-carbon compounds, thus the name. Pores on the plant called stomata regulate how much carbon dioxide, oxygen, and water enter and leave the plant and are usually partially closed during the hottest part of the day to conserve water. This yields a low carbon dioxide level and high oxygen level, which inhibits carbon fixation by the Calvin cycle. Plants that use the C4 pathway have an enzyme that can efficiently fix carbon to four-carbon compounds when the carbon dioxide level is low. The four-carbon compounds are then transported to other cells, where carbon dioxide is released and can enter the Calvin cycle.

Plants that use the C4 pathway are better adapted to hot and dry conditions, as they can fix carbon with less loss of water. Examples of C4 plants are corn and crabgrass.

Example Question #8 : Photosynthesis

In the chemical reaction of photosynthesis, photoautotrophs combine carbon dioxide and water to produce sugar and which of the following?

Possible Answers:

Ethyl alcohol

ATP

Methane

Oxygen

Correct answer:

Oxygen

Explanation:

Sugar (glucose) and oxygen are the two products of photosynthesis. Methane is a gas consisting of carbon and hydrogen. ATP is the energy produced in the organelle mitochondria. Ethyl alcohol is the active substance in beer and wine that causes intoxication if too much is consumed.

Example Question #9 : Photosynthesis

Which of the following is an example of an anabolic pathway?

Possible Answers:

Photosynthesis

Fatty acid decarboxylation

All of these

Glycolysis

Citric acid cycle

Correct answer:

Photosynthesis

Explanation:

An anabolic pathway is a pathway in which smaller molecules are combined to form larger ones. This type of pathway usually requires energy to complete the combinations required. Photosynthesis is an example of this, because it combines carbon dioxide molecules to form glucose. The rest of the listed processes are catabolic pathways.

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