4.1 Light-Dependent Reactions (CQ - exam)

Question 1

What is anaerobic respiration? Explain when it would occur.

Answer 1

Anaerobic respiration is a metabolic pathway in which an inorganic molecule other than oxygen is used as the final e’ acceptor during the chemiosmotic synthesis of ATP.

Question 2

Why is the balanced chemical equation for photosynthesis referred to as an overall equation, and why is it an oversimplification?

Answer 2

There are more reactions needed to occur for the reactants to become products. Hence, it being considered an oversimplification.
6CO2 + 6H2O –light→ C6H12O6 + 6O2

Question 3

What are thylakoids, and why are they important to photosynthesis?

Answer 3

Thylakoids are the disks that stack to create the grana. It is the site of the light-dependent reactions, contains chlorophyll—a coloured compound that absorbs light.

Question 4

Plants are green, but a plant provided with only green wavelengths of light will barely survive. Explain why.

Answer 4

• Chlorophyll does not absorb green light
• if only provided w green wavelengths of light, would not be able to absorb any energy from the light (aka photons).
• They absorb red and blue light
• Only reflect green light

Question 5

What is the role of pigments in photosynthesis?

Answer 5

Photosynthetic pigments is a compound that traps light energy and passes it on to other compounds. Light energy, aka photons, are essential for the photosystem to work.

Question 6

What is the advantage of plant leaves having a variety of photosynthetic pigments, rather than just chlorophyll?

Answer 6

The advantage of plant leaves having a variety of photosynthetic pigment is so they are able to absorb a range of different wavelengths than just blue and red.

Question 7

What is the function of the splitting of water in the light-dependent reactions?

Answer 7

The water splitting enzyme releases oxygen and donates 2 electrons per water molecule.

Question 8

What two events are linked in chemiosmosis?

Answer 8

1. Proton has to be going through the channel (diffusion of hydrogen)
2. Energy from the proton moving with the concentration gradient, allows for phosphorylation (creation of ATP)

Question 9

Compare and contrast the thylakoid membrane in plant cells to the inner mitochondrial membrane.

Answer 9

Thylakoid
- Uses light photons start e’ moving
- 1 proton pump
- Final e’ acceptor is NADPH

Both
- Have Electron Transport Chain
- Have ATP synthase
- Create proton [H+] gradient
- Lipid bilayer

Mitochondria
- Uses NADH and FADH2 start e’ moving
- 3 proton pumps
- Final e’ acceptor is oxygen

Question 10

Distinguish between cyclic and noncyclic photophosphorylation. How are they different? How are they the same? When would one be used over the other? What are the final products of each?

Answer 10

Cyclic photophosphorylation
- After P700 to b6-f complex
Different
- Noncyclic make NADPH and ATP
- Cyclic only make ATP
Uses
- Cyclic when ATP levels is low

Question 11

In both the mitochondria and chloroplast, energy for the phosphorylation of ADP comes from the hydrogen ion gradient. Why is a gradient formed with ions more effective than a gradient of neutral molecules?

Answer 11

Hydrogen ions carry a charge which allows for it to create an electrochemical gradient. An electrochemical gradient is created by the difference of electric charges. With a neutral charge, this cannot be made.

Question 12

Does light cause the oxidation or reduction of chlorophyll? Explain your reasoning.

Answer 12

Light oxidizes chlorophyll because it causes the photon to excite the electron and then breaks off.

Question 13

Since cyclic photophosphorylation uses components that are also used in noncyclic photophosphorylation, why does a plant require cyclic photophosphorylation? Think about how the products of cyclic and non cyclic photophosphorylation differ?

Answer 13

Cyclic
- No longer pass it to the NADH reductase
- Passes it back to the b6-f complex
- Skips NADH creation

Non cyclic
- Passes it to the NADH reductase
- Creates NADH

Question 14

Differentiate between phosphorylation and photophosphorylation.

Answer 14

• Phosphorylation is the addition of a phosphate.
• Photophosphorylation is the conversion of ADP to ATP using photon energy by activation of photosystem II.

Question 15

What are the two sources of hydrogen ions that accumulate in the thylakoid space?

Answer 15

1. When H2O is split by the water splitting enzyme
2. Hydrogen ions pumping by b6-f complex