Photosynthesis

Question 1

What is chlorophyll? Where is it located

Answer 1

A specialized light absorbing green pigment - located inside chloroplasts inside mesophyll cells

Question 2

Is photosynthesis efficient?

Answer 2

Not very - only 4% of sunlight is used

Question 3

Define photosynthesis

Answer 3

The process of transforming light energy into usable energy (ATP/NADPH) which is then stored in chemical bonds of carbohydrates

Question 4

Describe why leaves are optimal organs for light absorption

Answer 4

They have a thin cross section and flat surface which allow for a cell organization that maximizes light capture/gas exchange and take little energy to produce

Question 5

How much of the light spectrum can plants use?

Answer 5

The visible light spectrum only

Question 6

What portion of the light spectrum is absorbed by chlorophyll?

Answer 6

Blue and red (400-450/650-700)

Question 7

What pigments absorb the rest of the light if chlorophyll doesnt?

Answer 7

Bacteriochlorophyll
Chlorophyll a
Chlorophyll b
phycoerythin
beta-carotene

Question 8

What are the 2 groups of pigments other than chlorophyll, and briefly summarize them

Answer 8

Carotenoids- accessory pigments that absorb between 400-500, anti-oxidant properties and prevent light damage (photo-protective role)
Bilin pigments
Accessory pigments
absorb between 400-500

Question 9

How does chlorophyll absorption work?

Answer 9

It absorbs light photons which changes its energy state
Blue light excites chlorophyll more than red light
the excited state makes the pigment unstable

Question 10

After absorption by chlorophyll what are the routes the energy may go

Answer 10

Heat-energy loss
Re-emittance of longer wavelength - fluorescence
Energy transfer- resonance transfer
Photochemistry- absorption with electron transfer

Question 11

Summarize chloroplast anatomy

Answer 11

Relatively large
One circular chromosome
Arise from pre-existing chloroplasts or precursor proplastids
3 Membranes

Question 12

What are the 3 membranes in chloroplasts

Answer 12

Outer- relatively permeable & contains porins
Inner - Very impermeable, requires transporters
Thylakoid- site of light reactions, contains integral proteins and pigments

Question 13

What are the four protein complexes within the thylakoid membrane and what is their arrangement?

Answer 13

Photosystem 2
Cytochrome b6f complex
Photosystem 1
ATP synthase
They have a vectorial arrangement

Question 14

Define resonance transfer

Answer 14

Vibrational transfer which passes energy down the energy gradient from pigments to reaction center chlorophyll - used for light absorbed by accessory pigments

Question 15

What is the importance of P680+?

Answer 15

It is the strongest oxidizing agent in biological systems

Question 16

Quickly summarize the difference between PS 1 and PS 2

Answer 16

in PS 2 Water is split and oxygen is released, it is a part of non cyclic electron flow
Cyclic electron flow uses only PS1

Question 17

Summarize non cyclic electron flow

Answer 17

Z- scheme
5 steps
photo absorbtion
oxidation of water
ETC p1
ETC p2
Photophosphorylation
Uses both photosystems
Splits H20

Question 18

What does the non-cyclic pathway produce?

Answer 18

Equal amounts ATP and NADPH

Question 19

Briefly summarize cyclic electron flow

Answer 19

No water and no oxygen used
ATP produced
Electron from P700 moves to ferredoxin and is then transfered into PQ and CYTb6f
transferred into lumen and replace with plastocyanin
then generates ATP through ATP synthase in protein gradient

Question 20

What are carbon reactions?

Answer 20

Reactions indirectly regulated by light
Allows photoautotrophic organisms to reduce CO2 to CH2O
Converts chemical energy to stored energy within carbohydrates
Occur in chloroplast stroma

Question 21

What are the 3 phases of the carbon reactions?

Answer 21

Carboxylation
Reduction
RuBp regeneration

Question 22

What are the products of the carbon reaction?

Answer 22

6 G3P molecules/ 3CO2 used

Question 23

Where do the 6 G3P molecules from carbon reactions go?

Answer 23

5 are used for RuBP regeneration
1 is used to produce sugars and starch