GRE Subject Test: Biology : Understanding Photosynthesis

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

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Example Question #1 : Photosynthesis

Which of the following is not part of the Calvin cycle?

Possible Answers:

Fixation of carbon dioxide

oxidation of NADPH

addition of light

ATP production

Regeneration of RuBP

Correct answer:

ATP production

Explanation:

ATP is produced during the light-dependent reactions of photosynthesis by photosystem II. Carbon dioxide is fixed by combining with RuBP during calvin cycle. NAPDH donates electrons causing it to be oxdized to NADP+.

Example Question #1 : Understanding Photosynthesis

Photosynthesis is a __________ process, while cellular respiration is a __________ process.

Possible Answers:

anabolic . . . anabolic

anabolic . . . catabolic

catabolic . . . catabolic

spontaneous . . . nonspontaneous

catabolic . . . anabolic 

Correct answer:

anabolic . . . catabolic

Explanation:

Anabolic processes are those that make complex macromolecules out of simple reagents. Photosynthesis is an anabolic process because it converts carbon dioxide, water, and energy into sugars and oxygen. Catabolic processes break down larger macromolecules into simpler ones which can then be oxidized to produce usable energy. This energy can then be used to drive anabolic processes. Cellular respiration is a catabolic process because it breaks down sugar and oxygen into carbon dioxide, water, and energy. Since photosynthesis requires the net input of energy (sunlight) it is a nonspontaneous reaction. The opposite is true for cellular respiration, however the energy is in the form of ATP, not sunlight.

Example Question #2 : Understanding Photosynthesis

Plants are known as __________ because they derive the chemical energy necessary for life from the sun.

Possible Answers:

Auxotrophs

Lithotrophs

Autotrophs

Detritivores

Heterotrophs

Correct answer:

Autotrophs

Explanation:

Plants are autotrophs capable of producing complex molecules from the suns energy and other simple substances such as water, carbon dioxide, and minerals. Heterotrophs cannot fix their own carbon and must use organic molecules as their carbon sources. Auxotrophs are organisms that are unable to synthesize a particular compound required for its growth/survival. Lithotrophs use inorganic substrates to obtain their energy (often from dissolved minerals in rocks). Detritivores are a type of heterotroph that feed on dead animal and plant matter, and the waste products of each.

Example Question #3 : Understanding Photosynthesis

Plants undergo which of the following processes:

I. Photosynthesis

II. Cellular respiration

III. Lactic acid metabolism

Possible Answers:

I and II

I only

I and III

II only

I, II, and III

Correct answer:

I and II

Explanation:

Plants undergo both photosynthesis and cellular respiration. Glucose is made during photosynthesis and then this glucose is used to generate ATP in cellular respiration. This ATP can then be used to drive the complex anabolic processes of plants. Lactic acid metabolism commonly occurs in muscle tissue under anaerobic conditions but is not found to occur in plants.

Example Question #4 : Understanding Photosynthesis

Which of the following are photosynthetic inputs?

I. 

II. 

III. 

IV. Light

Possible Answers:

I, III, and IV

I, II, III, and IV

I and IV

I, II, and IV

II and IV

Correct answer:

I, II, and IV

Explanation:

Carbon dioxide, water, and light are the photosynthetic inputs. Oxygen gas is an output product of photosynthesis, not an input.

In the light reactions of photosynthesis the energetic intermediates NADPH and ATP are generated through chlorophyll pigments excited by sunlight. These then provide the energy and reducing power necessary for the generation of glucose in the Calvin cycle.

Example Question #5 : Understanding Photosynthesis

Which of the following are photosynthetic outputs?

I. 

II. 

III. 

IV. Sugar

Possible Answers:

I, II, and IV

II, III, and IV

I, and II

I, II, and III

II, and III

Correct answer:

I, II, and IV

Explanation:

 is the molecular formula for a monosaccharide (sugar). This sugar can then be used in cellular respiration to create chemical energy to drive the various anabolic processes of the plant. The oxygen that is produced through photosynthesis provides the oxygen that we breathe in order to undergo our own cellular respiration. Water is an input of photosynthesis.

Example Question #6 : Understanding Photosynthesis

Chlorophyll absorbs many different wavelengths of visible light, but __________ light is absorbed the least.

Possible Answers:

Red 

Ultraviolet

Blue 

Yellow

Green

Correct answer:

Green

Explanation:

Chlorophyll is green because it absorbs all wavelengths of visible light except it reflects, not absorbs green. This green light reflected and is therefore the color that we perceive. The wavelengths of red and blue light work well to excited the two different photosystems involved in photophosphorylation. While ultraviolet light is found on the electromagnetic spectrum, it is not considered to be visible light. Ultraviolet light is more energetic and has a shorter wavelength than that of visible light.

Example Question #7 : Understanding Photosynthesis

Where in the chloroplast is the pH the lowest?

Possible Answers:

Cytosol

Matrix

The thylakoid lumen

The stroma

The pH is the same in both the thylakoid lumen and the stroma

Correct answer:

The stroma

Explanation:

The pH is lowest in the thylakoid lumen. During photophosphorylation, protons are pumped into the thylakoid lumen from the stroma. The more protons found in the thylakoid space results in its lower pH. This lumen can have a pH of as low as 4. Protons then move down there concentration gradient out into the stroma in a process that produces ATP.

The stroma of the chloroplast has a pH of approximately 8, while the pH of the cytosol is closer to 7.

Example Question #8 : Understanding Photosynthesis

In the Calvin cycle, carbon is reduced to ultimately form glucose. Where does this carbon come from?

Possible Answers:

Mineralized rock

Soil

Sun

Water

Air

Correct answer:

Air

Explanation:

The carbon fixed in the Calvin cycle comes from the air in the form of . This carbon is reduced through the usage of NADPH and ATP, produced in the light reactions of photosynthesis, in order to make glucose.

The soil provides valuable water and mineral nutrients for the plant. The sun provides the energy necessary to drive photosynthesis. And pure water contains only hydrogen and oxygen. Lithotrophs utilize inorganic carbon, usually from rocks.

Example Question #9 : Understanding Photosynthesis

Plants such as corn are capable of C4 respiration. In order to undergo C4 respiration, which additional enzyme must the plant utilize?

Possible Answers:

PEP carboxylase

Alkaline phosphatase

RUBISCO

Phosphofructokinase

Kinase

Correct answer:

PEP carboxylase

Explanation:

Plants that undergo C4 respiration must also utilize the enzyme PEP carboxylase. This enzyme allows for carbon dioxide to be fixed to PEP to produce oxaloacetate. C4 respiration allows for lower levels of photorespiration, which can cause a decrease in photosynthetic efficiency.

Rubisco is the enzyme that adds carbon dioxide to ribulose bisphosphate to produce two molecules of 3-phosphoglycerate. Alkaline phosphatase is an enzyme that hydrolyzes phosphates from a variety of substrates under alkaline conditions. Kinases are enzyme which add phosphate groups to specific targets, such as fructose-1-phosphate.

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