$$\text{Energy} + 6CO_2 + 12H_2O \rightarrow C_6H_{12}O_6$ + 6O_2 + 6H_2O$$

Question 1

Which of the following best represents the overall chemical equation for photosynthesis?

Accepted Answer

$$	ext{Energy} + 6CO_2 + 12H_2O ightarrow C_6H_{12}O_6$ + 6O_2 + 6H_2O$$

Question 2

During photosynthesis, which molecule is oxidized and what is the by-product of this oxidation?

Accepted Answer

H$$_2O is $$oxidized, producing O$$_2 as a by-$$product.

Question 3

What experimental evidence demonstrated that the oxygen produced during photosynthesis comes from water and not from carbon dioxide?

Accepted Answer

Plants grown in H$$_2O $$with $$^{18}O $$produced $$^{18}O in O$_2.$$

Question 4

Why do leaves appear green to our eyes?

Accepted Answer

Chlorophyll reflects green wavelengths, which are poorly absorbed.

Question 5

What is the primary function of accessory pigments in the thylakoid membrane?

Accepted Answer

To absorb light from regions of the spectrum not efficiently absorbed by chlorophyll.

Question 6

In the context of the photosynthetic electron transport chain, why are two photosystems required?

Accepted Answer

Photosystem I alone cannot split water, and Photosystem II alone cannot reduce NADP$$^+.$$

Question 7

What would be the immediate effect on ATP synthesis if a toxin made the thylakoid membrane permeable to protons?

Accepted Answer

The proton gradient would be eliminated, stopping ATP synthesis.

Question 8

At what point do electrons have the greatest potential energy during photosynthesis?

Accepted Answer

After capturing photon energy in the reaction center of Photosystem I.

Question 9

Which phase of the Calvin cycle would be impacted first by the absence of light energy?

Accepted Answer

Reduction of 3-phosphoglycerate.

Question 10

How many turns of the Calvin cycle are required to produce one molecule of a 3-carbon triose phosphate?

Accepted Answer

3

Question 11

What is the first stable product formed when CO$$_2 is $$incorporated into the Calvin cycle?

Accepted Answer

3-phosphoglycerate (3-PGA)

Question 12

How do plant cells protect themselves from harmful reactive oxygen species generated during photosynthesis?

Accepted Answer

By producing antioxidants.

Question 13

Why are plants with high levels of xanthophylls better suited to growth in bright sunlight?

Accepted Answer

Xanthophylls dissipate excess light energy as heat, protecting the plant.

Question 14

Which enzyme catalyzes the carboxylation step in the Calvin cycle?

Accepted Answer

Rubisco

Question 15

What is the main evolutionary advantage of having two photosystems in oxygenic photosynthesis?

Accepted Answer

It enables the use of water as an electron donor and the reduction of NADP$$^+.$$

Question 16

What is the fate of excess carbohydrates produced during the Calvin cycle?

Accepted Answer

They are converted to starch and stored in the chloroplast.

Question 17

Which of the following best describes the role of cyclic electron transport in photosynthesis?

Accepted Answer

It increases the production of ATP while bypassing NADPH formation.

Question 18

What is the main reason rubisco is not highly selective for CO$$_2$$ over O$$_2$$?

Accepted Answer

It would require more energy to be more selective, slowing its catalytic rate.

Question 19

According to the endosymbiotic theory, what is the evolutionary origin of the chloroplast?

Accepted Answer

It evolved from a cyanobacterium engulfed by a eukaryotic cell.

Question 20

Which of the following is a direct result of the absorption of light by chlorophyll in the reaction center?

Accepted Answer

The elevation of an electron to a higher energy state, which is then transferred to an electron acceptor.

Photosynthesis: Using Sunlight to Build Carbohydrates

Study Guide - Practice Questions