lec 17- photosynthesis I

Question 1

what is in the chloroplast and where do the light reactions take place in them?

Answer 1

the chloroplast has thylakoid membranes that form pancake like stacks called grana, the light reactions take place in and around the thylakoid membrane while the dark reaction/calvin cycle takes place in the stroma

Question 2

what wavelengths stimulate oxygen production according to Engelmann?

Answer 2

blue and red wavelengths attract cyanobacteria, making oxygen

Question 3

how does Engelmann’s discovery of the bacteria liking red and blue light (action spectrum) relate to the absorption spectrum of chlorophyll?

Answer 3

the absorption spectrum and action spectrum both overlap, meaning that chlorophyll is the primary pigment in photosynthesis

Question 4

why do leaves appear green?

Answer 4

cause chlorophyll absorbs red and blue light while the most reflected light is green, hence the coloration

Question 5

how many genes and proteins does the chloroplast genome have?

Answer 5

100 genes, 3000 proteins, 95% encoded by nuclear genome

Question 6

where do the chloroplast genes move to?

Answer 6

the nuclear genome inside the cytosol, where they produce proteins (endosymbiotic gene transfer)

Question 7

what do transit peptides do?

Answer 7

import nuclear encoded proteins into the chloroplasts

Question 8

how is the transit peptide removed?

Answer 8

it is cleaved off at the end of import

Question 9

what forms a super complex with one another in the thylakoid membrane?

Answer 9

Light harvesting Complex II (LHCII) and photosystem II

Question 10

does photosystem I also form a super complex?

Answer 10

No

Question 11

what are the three complexes in the thylakoid membrane?

Answer 11

LHCII, photosystem II, and photosystem I

Question 12

what are the pigments inside the three complexes?

Answer 12

chlorophyll A, chlorophyll B, and carotenoids (neoxanthin and violaxanthin)

Question 13

what are PS I and PS II designed to do?

Answer 13

1. harvest many photons in an antenna complex
2. transfer energy to a central reaction center

Question 14

what energy levels do the pigments have highest to lowest?

Answer 14

carotenoids, chlorophyll B, chlorophyll A,, chlorophyll P680

Question 15

where does all the energy transfer too?

Answer 15

the reaction center

Question 16

what is the reaction center?

Answer 16

chlorophyll P680

Question 17

what are carotenoids also known as?

Answer 17

accessory pigments

Question 18

how are the photons in chlorophyll used in photosynthesis?

Answer 18

chlorophyll absorbs blue and red photons, going from ground to excited state, blue excitation state is reduced to the red state releasing heat in the process, red excitation state is used for photosythesis

Question 19

what are the steps to photosystem II?

Answer 19

1. light excites chlorophyll in PSII
2. PSII gives off electron to electron transport chain
3. void electron is filled by electron from water oxidation
4. water oxidation also generates protons and oxygen
5. As plastoquinone (PQ) gains electrons (2), it takes 2 protons from stroma

Question 20

what are the steps to the cytochrome b6f complex ?

Answer 20

1. As PQ passes electrons to cytochrome b6f complex, protons are released in the lumen
2. The cytochrome b6f complex passes electrons to plastocyanin, a small copper-containing protein

Question 21

what are the steps to photosystem I?

Answer 21

1. light excites chlorophyll in PS I
2. chlorophyll gives off electrons to ferredoxin (Fd)/ ferredoxin NADP reductase (FNR)
3. void is filled by electrons from plastocyanin
4. FNR reduces NADP+ and H+ to NADPH

Question 22

what happens in ATP synthase- phosphorylation?

Answer 22

1. proton diffuse from lumen to stroma via ATP synthase
2. diffusion is down chemical gradient
3. energy is used to phosphorylation ADP into ATP in stroma

Question 23

explain zigzag method and division of labour between PSII and PSI:

Answer 23

PSII:
1. PSII P680 is a strong oxidizer , strong enough to oxidize water, splitting it into oxygen , hydrogen protons and electrons for PSI
2. the released protons stay in the lumen
3. the electron transport chain brings protons into the stroma and provide low energy electrons to PSI P700
4. the proton gradient fuels an ATPase that generates ATP
PSI:
5. When P700 electron is excited, it becomes strong reductant, strong enough to reduce NADP+ to NADPH

Question 24

what is a high-pressure sodium (HPS) light and what are the drawbacks?

Answer 24

a light used in greenhouses that have many drawbacks because most of the energy is not used due to producing light that is mostly not blue or red and it is energy inefficient

Question 25

what are the steps taken to determine light recipe for plants?

Answer 25

intensity, R:B ratio, additional wavelengths for best shape and taste, daylength to supress or enhance flowering