8. Photosynthesis

Question 1

What is the photic zone?

Answer 1

surface layer of the ocean, about 100 m deep
- where photosynthesis is able to occur

Question 2

What are the two stages of photosynthesis?

Answer 2

• light capture: capture energy from sunlight into useable chemical forms
• carbon fixation: convert CO2 into organic molecules

Question 3

What type of reaction is photosynthesis? what is its end goal?

Answer 3

redox reaction

Use CO2 and sunlight to from high energy carbohydrate molecules

Question 4

What is the electron donors in the photosynthesis reaction? What are the products?

Answer 4

Water

After oxidation, water becomes:
- electrons
- protons
- O2

Question 5

Name the parts of a chloroplast

Answer 5

• outer membrane
• inner membrane
• thylakoid: highly folded flattened membrane sacks
• lumen: space inside the thylakoid membrane
• grana: the orderly stacks of thylakoids
• stroma: space surrounding thylakoids (where carbon fixation occurs)

Question 6

What are pigments? What is the principle pigment in photosynthesis?

Answer 6

pigments: molecules that absorb some or all wavelengths of visible light

photosynthetic pigments:
- absorbs photons and transitions to a higher energy state
- transfers energy to anther molecule to reestablish ground state

chlorophyll is the principle pigment in photosynthesis
- reflects green wavelengths

Question 7

What is the light dependent reaction in photosynthesis?

Answer 7

• chlorophyll absorbs light energy
• energy is used to power the movement of electrons
• movement of electrons through the photosynthetic electron transport chain creates NADPH and ATP

Question 8

What is the light independent reaction in photosynthesis?

Answer 8

Calvin cycle

Question 9

What is the molecule getting oxidized/reduced in the reaction for photosynthesis?

Energy + 6CO2 + 12H2O
->
Glucose C6H12O6 + 6O2 + 6H2O

Answer 9

CO2 reduced to glucose
H2O oxidized to Oxygen

Question 10

What is the structure of chlorophyll?

Answer 10

Porphyrin ring for light absorption
- Magnesium surrounded by alternating double/single bonds

Phytol side chain
- insertion of chlorophyll in the lipid bilayer (thylakoid membrane)
- positioned within integral membrane proteins

Question 11

Does the oxygen resulting from photosynthesis come from water or CO2?

Answer 11

water

Question 12

What is a photosystem

Answer 12

Protein + pigment complexes that absorb light energy and drive electron transport

Question 13

What are accessory pigments?

Answer 13

Additional pigments other than chlorophyll that photosystems have

• etc. carotenoids (yellow/orange)

Question 14

What is the difference in the behaviour of chlorophyll absorbing light in the lab vs in a chloroplast

Answer 14

in the lab:
- remits energy as heat
- small amount of fluorescence

in chloroplast:
- transfers energy to adjacent chlorophyll (very efficient!)

Question 15

What is an antenna chloropyll

Answer 15

the initial chlorophyll molecule that absorbs the light energy (and then passes it on)

Question 16

T/F antenna chlorophylls transfer electrons

Answer 16

F

they transfer energy

Question 17

What is the reaction center

Answer 17

• end destination of the chlorophyll’s energy
• at the reaction center, the electron itself (along with energy) is transferred to an adjacent molecule

so the reaction center becomes oxidized and the adjacent electron acceptor becomes reduced

Question 18

Where does the reaction center get its electron from, after it has donated it?

Answer 18

H2O

Question 19

What are the roles of the two photosystems?

Answer 19

Photosystem II: Takes in energy to allow electrons to be pulled from water

Photosystem I: Takes in energy to allow electrons to be transfered from NADP+ to NADPH

Question 20

What is the Z scheme?

Answer 20

The energy trajectory as the electron moves through and between the two photosystems resembles a Z turned on its side (CCW)

• moving through: increase in energy
• moving between: decrease in energy

Question 21

What are the parts of the photosynthetic electron transport chain?

Answer 21

• Photosystem II
• Pq (plastoquinone)
• b6f complex
• Pc (pastocyanin)
• Photosystem I
• Fd
• NADP reductase

Question 22

How does the proton gradient get produced in the photosynthetic electron transport chain?

Answer 22

• In photosystem II, by breaking H2O into H+ + O2
• Using the b6f complex to pump H+ from outside the thylakoid membrane (stroma) to inside the lumen

Question 23

How many molecules of NADPH and ATP are required for each CO2 incorporated into carbohydrates (calvin cycle)?

Answer 23

2 molecules of NADPH

3 molecules of ATP

Question 24

What is cyclic electron transport?

Answer 24

Electrons from photosystem I are redirected back into the electron transport chain

Question 25

What has the higher proton concentration - Lumen - Stroma

Answer 25

Lumen

Question 26

What are the three main steps of the calvin cycle?

Answer 26

Carboxylation - Addition of CO2 to 5-carbon compound RuBP - Catalyzed by the enzyme rubisco - Outputs are two 3-carbon compounds (3-phosphoglycerate, PGA) Reduction - Increases the potential energy of the PGA - Energy inputs from ATP and NADPH lead to the synthesis of triose phosphates (G3P) - NADPH transfers two electrons and one proton - Outputs are 3-C Regeneration - 3-Carbon compounds are reorganized and combined to produce RuBP - Requires energy (ATP)

Question 27

What are extra carbohydrates from the Calvin cycle stored as?

Answer 27

starch - If the carbohydrates were in the form of soluble sugars, it would cause water to enter the cell by osmosis

Question 28

What are the main inputs and outputs to the carbon cycle?

Answer 28

Main inputs: - CO2 (from the atmosphere), ATP and NADPH (from the photosynthetic electron transport chain) Main outputs: - carbohydrates (triose phosphates, G3P) - ADP and NADP+

Question 29

The Calvin cycle requires both ATP and NADPH. Which of these molecules provides the major input o f energy needed to synthesize carbohydrates?

Answer 29

NADPH

Question 30

What are two hypotheses for why there are two photosystems?

Answer 30

1. Horizontal gene transfer (organism 1 gives a gene to organism 2) 2. Duplication and divergence (mutation during duplication of the gene)

Question 31

What were the first organisms to use water as the electron donor?

Answer 31

cyanobacteria