Q: During photosynthesis, which equation correctly represents the overall reaction?

$$6 \mathrm{CO}_2 + 6 \mathrm{H}_2\mathrm{O} \xrightarrow{\text{light, chlorophyll}} \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6 \mathrm{O}_2$$

Question 1

Which of the following best describes the role of differential centrifugation in the isolation of chloroplasts from spinach leaves?

Accepted Answer

It separates chloroplasts from other organelles based on their density and size by spinning at progressively higher speeds.

Question 2

During photosynthesis, which equation correctly represents the overall reaction?

Accepted Answer

$$6 \mathrm{CO}_2 + 6 \mathrm{H}_2\mathrm{O} \xrightarrow{	ext{light, chlorophyll}} \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6 \mathrm{O}_2$$

Question 3

In the experiment, DCPIP is used to measure photosynthetic activity. What property of DCPIP allows it to serve this function?

Accepted Answer

DCPIP changes color when it is reduced by accepting electrons from the light-dependent reactions.

Question 4

Which statement best explains why the absorption spectrum of chloroplasts is important for understanding photosynthesis?

Accepted Answer

It shows which wavelengths of light are most efficiently absorbed by chlorophyll and accessory pigments, indicating which colors drive photosynthesis.

Question 5

If you expose isolated chloroplasts to red, blue, and green light, which color would you expect to result in the highest rate of DCPIP reduction, and why?

Accepted Answer

Blue light, because chlorophyll absorbs blue wavelengths most efficiently, leading to higher photosynthetic activity.

Question 6

Why is it necessary to keep isolated chloroplasts on ice during the experiment?

Accepted Answer

To slow down enzymatic activity and prevent degradation of chloroplasts before measurement.

Question 7

Which of the following best describes the function of ATP and NADPH produced during the light-dependent reactions of photosynthesis?

Accepted Answer

They provide energy and reducing power for the synthesis of carbohydrates in the Calvin cycle.

Question 8

A student wraps a test tube containing chloroplasts in black paper during the experiment. What is the most likely effect on the rate of DCPIP reduction?

Accepted Answer

The rate of DCPIP reduction will decrease because the chloroplasts are not exposed to light.

Question 9

Which process in photosynthesis is most directly responsible for the production of oxygen gas ($$\mathrm{O}_2$$)?

Accepted Answer

The splitting of water molecules during the light-dependent reactions.

Question 10

In the experiment, why is it important to use a blank solution when measuring absorbance in the spectrophotometer?

Accepted Answer

To account for the absorbance of solvents and reagents, ensuring only the change due to DCPIP reduction is measured.

Question 11

Which of the following best explains why the rate of DCPIP reduction is used as a proxy for photosynthetic activity in isolated chloroplasts?

Accepted Answer

DCPIP accepts electrons from the light-dependent reactions, so its reduction reflects the rate of electron transport.

Question 12

If a group forgets to take the '0' reading (initial absorbance) before exposing their samples to light, what is the most likely consequence for their data analysis?

Accepted Answer

They will not be able to accurately determine the change in absorbance due to photosynthesis.

Question 13

Which of the following is a correct sequence of steps for isolating chloroplasts by differential centrifugation?

Accepted Answer

Homogenize spinach leaves, spin at low speed to pellet cell debris, decant supernatant, spin at higher speed to pellet chloroplasts.

Question 14

Which of the following statements about the light-dependent reactions of photosynthesis is TRUE?

Accepted Answer

They occur in the thylakoid membranes and produce ATP and NADPH.

Question 15

A researcher wants to compare the photosynthetic rates of chloroplasts exposed to different wavelengths of light. Which experimental variable should be kept constant to ensure valid results?

Accepted Answer

The concentration of chloroplasts in each test tube.

Question 16

Which of the following best describes the purpose of using cold buffer solution during the isolation of chloroplasts?

Accepted Answer

To maintain the integrity of chloroplasts by slowing down enzymatic degradation.

Question 17

If the absorbance of DCPIP in a test tube decreases rapidly after exposure to light, what does this indicate about the photosynthetic activity of the chloroplasts in that tube?

Accepted Answer

The chloroplasts are highly active, rapidly reducing DCPIP as electrons are transferred during photosynthesis.

Question 18

Which of the following is a direct product of the light-dependent reactions that is used in the Calvin cycle?

Accepted Answer

$$\mathrm{NADPH}$$

Question 19

A student claims that all plant cell organelles are capable of photosynthesis. Based on the experiment and your knowledge, which organelle is responsible for photosynthesis?

Accepted Answer

Chloroplast

Isolation of Chloroplasts and Measurement of Photosynthetic Activity Lab 16

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