Unit 2: Photosynthesis

Question 1

What are chloroplasts?

Answer 1

Convert light energy into glucose (sugar)

Question 2

Photosynthesis reaction equation…

Answer 2

6CO2+12H2O—) C6H12O6+6O2+6H2O

Question 3

What stages do photosynthesis occur in?

Answer 3

• Light reactions (thylakoid of chloroplast)
• Calvin cycle
  (stroma of chloroplast)

Question 4

Where is the thylakoid?

Answer 4

Is the membrane system

Question 5

Where is the stroma?

Answer 5

Surrounding system

Question 6

What are photosynthetic pigments?

Answer 6

Photosynthetic pigments capture energy from photons of sunlight

Question 7

What are photons?

Answer 7

They are packets of energy that have properties of particles and waves (have characteristic wavelength; distance covered in one cycle of wave); most energetic photons travel at shorter wavelengths

Question 8

What type of wavelength does red light have?

Answer 8

Long wavelength; less energy

Question 9

What type of wavelength does blue light have?

Answer 9

Short wavelength; more waves per unit of time for blue light; more energy

Question 10

Why are leaves green?

Answer 10

Because chlorophylls are the most abundant pigments; but other pigments are hidden beneath this overpowering green colour

Question 11

Why do leaves turn red in autumn

Answer 11

Chlorophylls breakdown revealing the presence of other pigments

Question 12

What light do chlorophyll a and b absorb?

Answer 12

They absorb both blue and red light wavelengths while reflecting and transmitting wavelengths in the middle of the visible spectrum (green and yellow)

Question 13

What wavelengths do carotenoids absorb and what colours do they give off?

Answer 13

Absorb some blue and green wavelengths turn orange

Question 14

What wavelengths do phycobilins absorb and give off?

Answer 14

They absorb most of the green, yellow, and orange wavelengths they give up purple light

Question 15

Where do light reactions take place?

Answer 15

In the thylakoid of chloroplast (location in chloroplasts)

Question 16

What are the 3 steps of light reactions?

Answer 16

1. Pigments embedded in thylakoid membrane absorb energy from sunlight and give up electrons to membrane proteins; pigments are organized into 2 photosystems (take light get excited and move electrons and H+ ions
2. Movement of electrons and H+ ions leads to the production of NADPH and ATP
3. Electrons released by pigments are replaced by the splitting of H20, (photolysis) producing O2

The overall result is the formation of ATP + NADPH used in the Calvin cycle to construct glucose

Question 17

What is the process of light reactions?

Answer 17

• Light energy of a wavelength excites chlorophyll a in photsystem II causing release of electrons
• photolysis (splitting of water by light) provides electrons to replace those lost by chlorophyll a and oxygen gas
• electrons released by chlorophyll a transferred through series of proteins in the thylakoid membrane until they reach photosystem 1
• just as with the etc, the movement of electrons through the thylakoid membrane results in the build of H+ ions within the thylakoid space
• H+ ion concentration used to power the synthesis of ATP
• Coenzyme NADP+ is the final electron acceptor; it is reduced to form NADPH
• ATP and NADPH are used in Calvin Cycle to build organic molecules like glucose

Question 18

What did Melvin Calvin work out?

Answer 18

• Worked out the biochemical pathways of the light-independent reaction in experiments that used green algae called Chlorella

Question 19

How does the Calvin Cycle begin?

Answer 19

• The first step in carbon fixation is catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO)

1. Rubisco attaches to carbon to RuBP
2. NADPH and ATP convert 3-PGA to G3P
3. 5 G3P and 3 ATP regenerates 3 RuBP

Phase 1:
- Rusbisco cataylses the reaction of 3 CO2 with 3 RuBP to form 6 PGA

Phase 2:
- 6 PGA are “reduced” to form 6 1,3-BPG which is the “reduced” to 6 G3P
- These reactions require 6 ATP and 6 NADPH

Phase 3:
- 5 G3P molecules are used to regenerate the 3 RuBP we began with
- 3 ATP are required
- 1 G3P can go towards making glucose