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

Study concepts, example questions & explanations for AP Biology

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Example Question #1 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Which of the following is not a reactant used in the process of photosynthesis?

Possible Answers:

CO2

Light energy

H2O

O2

Correct answer:

O2

Explanation:

The process of photosynthesis can be summarized by the following equation.

H2O, CO2, and light energy are thus reactants of photosynthesis, while O2 is only a product.

Example Question #1 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

What are the products of photosynthesis?

Possible Answers:

Water and carbon dioxide

Oxygen and carbon dioxide

Glucose and oxygen

Light and glucose

Carbon dioxide and light

Correct answer:

Glucose and oxygen

Explanation:

The photosynthesis equation can be written as:

From this equation, we can see that plants take in carbon dioxide, water, and light energy as reactants and produce glucose and oxygen as products.

Example Question #1 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Some organisms, such as green plants, are capable of obtaining energy directly from photosynthesis. These organisms are termed __________.

Possible Answers:

herbivores

autotrophs

primary consumers

heterotrophs

homotrophs

Correct answer:

autotrophs

Explanation:

Autotrophs are organisms that produce complex organic compounds from substances present in the surroundings. These organisms may do this through the use of energy from light or from inorganic chemical reactions.

In contrast, heterotrophs require organic input in order to generate biological compounds and are unable to use light or inorganic materials for energy.

Example Question #3 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Which of the following is true of photosynthesis? 

Possible Answers:

Electrons decrease in potential energy as they move from water to sugar

Carbon dioxide is reduced

Water is reduced

The process requires no energy

Carbon dioxide is oxidized

Correct answer:

Carbon dioxide is reduced

Explanation:

Photosynthesis occurs in the chloroplasts of plant cells, where carbon dioxide is reduced and water is oxidized to create sugar. During this process electrons demonstrate increased potential energy as they move from water to sugar. The process requires an initial energy input, derived from photons.

Example Question #1 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

What is the first step in photosynthesis?

Possible Answers:

Water is split by chlorophyll

Nutrients from the soil are turned into carbohydrates when combined with water

Light causes oxygen to pair with hydrogen, forming water for the plant

Light reduces sugars present in the plant cells to energized derivatives

Photons present in light strike and excite electrons in chlorophyll

Correct answer:

Photons present in light strike and excite electrons in chlorophyll

Explanation:

Photosynthesis begins with energy from light being converted to chemical energy. The only answer explanation accurately explaining this process describes the conversion of light energy (photons) to chemical energy (excited electrons).

Photons present in light strike and excite electrons in chlorophyll.

The photons are highly energized light particles, which strike chlorophyll and excite and free electrons in the chlorophyll molecule. These excited electrons pass through the electron transport chain and their energy is collected to make ATP.

Example Question #3 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Where does the Calvin Cycle take place?

Possible Answers:

Mitochondrial lumen

Cytoplasm

Stroma

Thylakoid membrane

Chloroplast outer membrane

Correct answer:

Stroma

Explanation:

The Calvin Cycle (dark reactions) take place in the stroma of the chloroplasts, which is the aqueous space inside the organelle. 

Example Question #2 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Organisms that make their organic molecules from inorganic raw materials obtained from the surrounding environment are called __________.

Possible Answers:

autotrophs

auxotrophs

heterotrophs

plants

Correct answer:

autotrophs

Explanation:

Autotrophs create organic material from inorganic materials. Autotrophs are self-feeders in that they do not consume other organic materials but rather create their own organic materials. Plants and other photosynthetic organisms are examples of autotrophs.   

Example Question #4 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Which of the following is a by-product of the light reactions in photosynthesis?

Possible Answers:

Oxygen

Sugar

Carbon dioxide

Water

Correct answer:

Oxygen

Explanation:

During the light reactions water is split and the by-product is oxygen. Oxygen is then released back into the atmosphere. Sugars are produced during the Calvin cycle and are not a direct product of the light reactions.

Example Question #2 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Plants are an example of which of the following categories of organisms?

Possible Answers:

Heterotrophs

Chemoautotrophs

Autotrophs

Biosphere consumers

Correct answer:

Autotrophs

Explanation:

Plants are an example of autotrophs. Autotrophs sustain themselves without consuming other organic material. Instead they create organic material from inorganic materials.

Example Question #6 : Understanding Photosynthesis, Light Reactions, And Calvin Cycle

Which of the following are referred to as the major sites of photosynthesis in most plants?

Possible Answers:

Flowers

Leaves

Stems

Roots

Correct answer:

Leaves

Explanation:

The leaves are the major sites of photosynthesis in most plants. The chloroplasts are located in the mesophyll—interior tissues of the leaves—and are the primary sites of photosynthesis.

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