AP Biology : Understanding Photosynthesis, Light Reactions, and Calvin Cycle

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #11 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Photosynthesis is commonly divided into how many primary stages?

Possible Answers:

Two stages

Four stages

Three stages

One stage

Correct answer:

Two stages

Explanation:

The correct answer is two major stages. The first stage is known as the light reactions where solar energy is converted to chemical energy. The second stage is the Calvin cycle that synthesizes sugar.

Example Question #12 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

The light reactions of photosynthesis are responsible for the production of which of the following molecules?

Possible Answers:

Producing sugars

Producing carbon dioxide

Converting solar energy to chemical energy

Producing water

Correct answer:

Converting solar energy to chemical energy

Explanation:

The light reactions are the steps of the photosynthesis that function to convert solar energy into chemical energy that can be used during the Calvin cycle. The light reactions use solar energy to reduce   to  and to convert  to .  

Example Question #11 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Where does the Calvin cycle take place in the chloroplasts?

Possible Answers:

Stroma

Nucleus

Mitochondria

Thylakoid

Correct answer:

Stroma

Explanation:

The Calvin cycle takes place in the stroma area in the chloroplasts. The mitochondria is another organelle, and the nucleus contains the DNA. The thylakoids are in the chloroplasts and contain the pigment chlorophyll in which the light reactions occur.

Example Question #11 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Which of the following is one of the end products of photosynthesis?

Possible Answers:

Glucose

Carbon dioxide

Lipids

Water

Correct answer:

Glucose

Explanation:

Glucose is the six carbon sugar that is the main product of photosynthesis. Water and carbon dioxide are the reactants in photosynthesis. Lipids are fat molecules that store energy in cells.

Example Question #11 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

What is the name of the light-independent reaction of photosynthesis?

Possible Answers:

Krebs cycle

Beta-oxidation

Calvin cycle

Glycolysis

Correct answer:

Calvin cycle

Explanation:

The light-independent reaction in photosynthesis is called the Calvin cycle. Glycolysis and the Krebs cycle are the first and second steps in cellular respiration, respectively. Beta-oxidation is the process by which fatty acids are broken down into acetyl-CoA, which may enter the Krebs cycle, ultimately to produce ATP.

Example Question #24 : Plant Functions

Which of the following is not true regarding photosynthesis?

Possible Answers:

Glucose is a product

It is a nonspontaneous reaction

Carbon dioxide is a reactant

Water is a product

Correct answer:

Water is a product

Explanation:

In photosynthesis, water, carbon dioxide, and energy in the form of sunlight are inputs, and the outputs are glucose and oxygen. A nonspontaneous reaction is one that will not proceed without the net input of energy (in this case, sunlight).

Example Question #12 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Which of the following is an adaptation in plants to prevent water loss in arid climates?

Possible Answers:

Oxidative phosphorylation

Krebs cycle

Calvin cycle

Glycolysis

CAM pathway

Correct answer:

CAM pathway

Explanation:

CAM plants open their stomata only at night, when temperatures are lower and water loss is less severe. This prevents gas exchange during the day thus making them less efficient at photosynthesis, but the water conservation makes it a worthwhile trade off. The processes of glycolysis, oxidative phosphorylation, the Calvin cycle and the Krebs cycle occur in all plants.

Example Question #13 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Where do the light reactions of photosynthesis occur?

Possible Answers:

In the cell wall

In the phospholipid bilayer

In the mitochondrial membrane

In the stroma

In the thylakoid membranes

Correct answer:

In the thylakoid membranes

Explanation:

The light reactions of photosynthesis occur in the thylakoid membranes inside of chloroplasts in plant cells. Photosynthesis depends on the buildup of a proton gradient across a membrane to generate ATP. The thylakoid is an organelle present only in plants. The phospholipid bilayer and cell wall surround plant cells, and are not involved in photosynthesis.

Example Question #14 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Which of the following correctly illustrates how plants undergo photosynthesis?

Possible Answers:

Plants use the energy of the sun to convert carbon dioxide and water into glucose and oxygen

Plants use the energy of the sun to break down glucose for energy

Plants use the energy of the sun to convert glucose and oxygen into carbon dioxide and water

Plants use the energy of the sun to convert ATP into glucose

Plants use the energy of the sun to convert glucose into ATP

Correct answer:

Plants use the energy of the sun to convert carbon dioxide and water into glucose and oxygen

Explanation:

Plants are considered photoautotrophs, meaning that they can use the electromagnetic energy from sunlight to generate organic chemical energy. The process for this conversion is photosynthesis, which takes place in the chloroplasts of the plant cells. Sunlight excites electrons, which donate energy to form NADH and ATP. These compounds enter the Calvin cycle, which converts carbon dioxide to glyceraldehyde-3-phosphate, a sugar that can easily be converted to glucose and used for energy.

The sugars produced from photosynthesis then undergo oxidation via cellular respiration in order to actually produce ATP. Remember that plant cells contain both chloroplasts (to make sugars) and mitochondria (to make ATP).

Example Question #11 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

When a molecule of NAD⁺ gains a hydrogen atom, the molecule becomes?

Possible Answers:

reduced

oxidized

redoxed

hydrolyzed

plasmolyzed

Correct answer:

reduced

Explanation:

The molecule is reduced because when a molecule gains an electron, it is said to be reduced. The answer oxidized would have been chosen if the molecule lost an electron. Plasmolysis has nothing to do with the gain or loss of an electron, and the term redoxed does not fit into this question. Hydrolysis is when a bond is broken using water, so that is incorrect as well.

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