Chapter 8: Photosynthesis

Question 1

What happens during Photosynthesis? What is released as a byproduct?

Answer 1

Light energy is converted to chemical energy in the form of sugars (glucose molecules).

Glucose molecules are constructed from water and carbon dioxide, and OXYGEN is released as a byproduct.

Question 2

What are the reactants and products of Photosynthesis? (What is the equation?)

Answer 2

6CO2 + 12H2O -> C6H12O6 = 6O2 + 6H2O

• Because oxidation and reduction are happening side-by-side, this is known as a REDOX reaction

Question 3

What is another difference between “Oxidation” and “Reduction”? What are “Oxidizing Agents” and “Reduction Agents”?

Answer 3

Oxidation is gain of oxygen.
Reduction is loss of oxygen.

Oxidizing Agent: something that GIVES OXYGEN to another substance (“electron ACCEPTOR”)
Reduction Agent: something that TAKES OXYGEN from another substance (“electron DONOR”)

Question 4

What is being oxidized and what is being reduced in photosynthesis?

Answer 4

H2O is oxidized into O2
CO2 is reduced into C6H12O6

(water is oxidized into oxygen, and
carbon dioxide is reduces into glucose)

Question 5

What substance is the “Oxidizing Agent” or “Electron Acceptor” in Photosynthesis?

Answer 5

CARBON DIOXIDE (CO2)
- 6CO2 gives oxygen away and accepts electrons (H12) to become C6H12O6 (glucose)

Question 6

What substance is the “Reduction Agent” or “Electron Donor” in Photosynthesis”?

Answer 6

Water (H2O)
- water replaces the reaction center electron, and oxygen is formed as a byproduct.

Question 7

What are “Pigments” and what do they do?

Answer 7

COLORED SUBSTANCES that reflect only certain wavelengths of visible light

• The color that they are is the color that is reflected!

Question 8

What are two types of pigments in plants?

Answer 8

Chlorophyll: green substance that only reflects green light. (make up photosystems and absorb photons of light)

Carotenoid: red, orange, and yellow substance that only reflects red, orange, and yellow light

Question 9

What do “Reaction Center Chlorophylls” do?

Answer 9

Reaction Center Chlorophylls TRANSFER ABSORBED LIGHT ENERGY (from “Antenna Chlorophylls”) AND an “Excited Electron” to electron acceptors. Once the electron acceptor is reduced, the reaction center is oxidized. The oxidized reaction center cannot absorb any more light energy until it pulls an electron away from an electron donor.

Question 10

What are “Chloroplasts” and what do they do?

Answer 10

PLANT CELL ORGANELLES that convert light energy into relatively stable chemical energy

Question 11

What are “Thylakoid Membranes” and why are they important?

Answer 11

“Thylakoid Membranes” that stack themselves into “Grana” to increase surface area
* More surface area = More photosynthesis = MORE GLUCOSE

Question 12

What does the “Photosynthetic Electron Transport Chain” produce? Where is it located and where are the high and low proton gradients located?

Answer 12

ATP and NADPH (both are required for the Calvin Cycle to build carbohydrates using CO2)

• Located on the “Thylakoid Membrane” and creates a HIGH concentration of protons within the LUMEN, leaving a LOW concentration in the STROMA

Question 13

What are “Photosystems” and what do they do?

Answer 13

THE FUNCTIONAL UNITS for photosynthesis made up of Chlorophyll molecules that are precisely spaced apart. (Power the ETC)

• Take in light energy and energize electrons

Question 14

What do Photosystems II and I do?

Answer 14

Photosystem II: (comes before Photosystem I) Supplies high energy electrons to the electron transport chain. When it loses an electron it can pull more electrons from water.

Photosystem I: Energizes the electrons with more light energy so they have enough energy to reduce to NADP+

Question 15

What is meant by “Z-Scheme” in the Photosynthetic Electron Transport Chain?

Answer 15

The electron loses energy as it travels through the electron transport chain.

Photosystem I is not a sufficiently strong oxidant to split water, and Photosystem II cannot produce electrons with enough energy to form NADPH

• BOTH PHOTOSYSTEMS ARE NEEDED to bridge the energy difference between water and NADPH

Question 16

What happens during the “Calvin Cycle”?

Answer 16

CO2 used to make SUGARS
requires ATP and NADPH (created in the Photosynthetic Electron Transport Chain)

Question 17

What are the 4 steps of the Calvin Cycle and what happens in each step?

Answer 17

1) Carbon Fixation (Carboxylation)
- The addition of CO2 to the 5-carbon compound, RuBP, is catalyzed by the enzyme “Rubisco”

2) Reduction Phase
- NADPH transfers high energy electrons

3) Carbohydrate Formation
- Carbs exit as two 3-carbon compounds

4) Regeneration Phase
- 3-carbon compounds are reorganized and combined to produce RuBP

Question 18

What are “Oxygen Radicals” or “Free Radicals” or the “Reactive Oxygen Species”? How are they formed? Why are they bad?

Answer 18

Highly reactive oxygens due to their uneven number of electrons.

When not enough NADP+ is available in the ETC, the high-energy electrons will reduce O2 instead of NADP+

• They can cause large chain chemical reactions that react with lipids and proteins in the cell causing damage

Question 19

What are the 3 solutions to the creation of Reactive Oxygen Species (ROS)?

Answer 19

1) XANTHOPHYLLS reduce the amount of ROS by converting excess light energy into heat, thereby slowing down the ETC

2) ANTIOXIDANTS detoxify reactive oxygen species

3) CYCLIC ELECTRON TRANSPORT

Question 20

What is “Cyclic Electron Transport”?

Answer 20

When the cell is overwhelmed by excess light and lack of NADP+, the electron is sent back to Photosystem II to avoid damaging the cell and still results in some ATP production

Question 21

What can plants do to defend themselves?

Answer 21

Grow thorns or hairs. Some plants are also poisonous.

Question 22

What other organelles, besides chloroplasts, are found only in plants?

Answer 22

(Cell walls) and Vacuoles

Question 23

What is “Photorespiration?” Is it helpful or harmful?

Answer 23

A process that occurs in the Calvin Cycle during plant metabolism. In this process, the key enzyme Rubisco that is responsible for Carbon Fixation REACTS WITH O2 RATHER THAN CO2.

• HARMFUL: Because it produces 2PG, a compound “toxic” to many enzymes in photosynthetic metabolism, and oxidizes organic carbon without seemingly generating ATP, photorespiration is generally considered a wasteful process. PRODUCES NO CHEMICHAL ENERGY OR FOOD.