Understanding Photosynthesis

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GRE Subject Test: Biology › Understanding Photosynthesis

Questions 1 - 10
1

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

Air

Soil

Sun

Water

Mineralized rock

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.

2

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

PEP carboxylase

RUBISCO

Alkaline phosphatase

Kinase

Phosphofructokinase

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.

3

Which of the following are photosynthetic outputs?

I.

II.

III.

IV. Sugar

I, II, and IV

I, II, and III

II, III, and IV

I, and II

II, and III

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.

4

Plants undergo which of the following processes:

I. Photosynthesis

II. Cellular respiration

III. Lactic acid metabolism

I and II

I, II, and III

I only

I and III

II only

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.

5

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

Green

Blue

Red

Ultraviolet

Yellow

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.

6

Which of the following are photosynthetic inputs?

I.

II.

III.

IV. Light

I, II, and IV

I and IV

I, II, III, and IV

I, III, and IV

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.

7

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

ATP production

Fixation of carbon dioxide

Regeneration of RuBP

oxidation of NADPH

addition of light

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+.

8

Where in the chloroplast is the pH the lowest?

The stroma

The thylakoid lumen

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

Cytosol

Matrix

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.

9

CAM (crassulacean acid metabolism) plants undergo __________ photosynthesis and keep their stomata __________ during the day.

C4 . . . closed

C4 . . . open

C3 . . . closed

C3 . . . open

reverse . . . closed

Explanation

CAM plants utilize C4 photosynthesis and keep their stomata closed during the day. By using the enzyme PEP carboxylase, CAM plants are able to store up enough fixed carbon during the night in order to keep their stomata closed during the day. The closure of the stomata prevents the loss of water from the plant. This is especially important in hot, dry climates.

10

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

Autotrophs

Heterotrophs

Auxotrophs

Lithotrophs

Detritivores

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.

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