Photosynthesis - PP Exam 2

Question 1

What is the absorption spectrum of chlorophyll? (Chlorophyll a & b)

Answer 1

The absorption spectrum describes the range of wavelengths of light that chlorophylls a & b absorb, showing what wavelengths are best absorbed. (400-700 nm).
Peaks of Chlorophyll a: 410-430 nm & 660-680 nm.
Peaks of Chlorophyll b: 450-470 nm & 640-660 nm.

Question 2

What is an action spectrum?

Answer 2

An action spectrum shows how effective different wavelengths of light are at fueling a biological process.

Question 3

What is the relationship between the action spectrum for photosynthesis and the absorption spectrum of chlorophyll?

Answer 3

The action spectrum for photosynthesis coincides with the absorption spectrum for photosynthesis. This is because it shows the wavelengths of light at which photosynthesis exhibits the most activity, and this would be the same as what wavelengths of light are absorbed the most by chlorophyll.

Question 4

Describe Photosystem II (PSII).

Answer 4

on grana lamella; ETC: P680 (chlorophyll a molecules in PSII) to plastoquinones to cytochrome b6f to plastocyanin; similar to PS in purple photosynthetic bacteria; water is oxidized

Question 5

Describe Photosytem I (PSI)

Answer 5

on stroma lamella; ETC: plastocyanin to P700 (chlorophyll a molecules in PSI), from PSI to ferredoxin to NADP+, then gets electron and becomes NADPH; similar to anoxygenic green sulfur bacteria

Question 6

Why is chlorophyll a the type of chlorophyll in the electron transfer chain?

Answer 6

cuz chlorophyll a is the type that gets excited and gets the electron

Question 7

Give two pieces of experimental evidence that led to the two photosystems.

Answer 7

______elaborate_______
green algae spyrogyra experiments

Question 8

What is the role of electron transport in oxygen-evolving photosynthesis?

Question 9

Name the final electron donor and final electron acceptor in photosynthesis.

Question 10

Describe the path traveled by an electron in the electron transport process.

Question 11

Describe the process of ATP synthesis at the thylakoid membrane (make sure to identify reactants, the energy source, and the role of light).

Question 12

What is the enhancement effect in photosynthesis?

Answer 12

It states that the rate of photosynthesis when red and far-red light are
given together is greater than the addition of individual rates

Question 13

What is the red drop in photosynthesis?

Answer 13

It is when the quantum yield (amount of oxygen produced per
quantum of light) drops in the far-red region of the spectrum. It is the reason wavelengths below 680 nm are necessary for maximum photosynthetic efficiency.

Question 14

What is the proper electron chain in PSII?

Answer 14

P680 (chlorophyll a molecules in PSII) -> plastoquinone -> cytochrome b6f -> plastocyanin

Question 15

What is the proper electron chain in PSI?

Answer 15

plastocyanin (from the end of ETC in PSII) -> P700 (chlorophyll a molecules in PSI) -> ferredoxin -> NADP+ & NADPH

Question 16

What is the combined ETC for both photosystems?

Answer 16

P680 -> plastoquinones -> cytochrome b6f -> plastocyanin -> P700 -> ferredoxin -> NADP+ (acceptor)

Question 17

How is the enzyme RuBisCo regulated by light?

Answer 17

1) light activates transcription of small Ru subunit in nucleus
2) light allows higher translation of large Ru subunit in chloroplast
3) light controls RuBisCo being active, which requires ferredoxin reduction and carbamylation

Elaboration:
RuBisCo is regulated by light because it is only active in the presence of light. It is regulated in a few ways: 1) light activates transcription of the gene encoding the small subunit of RuBisCo in the nucleus, 2) light results in higher translation of the mRNA encoding the large subunit of RuBisCo in the chloroplast (post-transcriptional regulation), 3) RuBisCo is activated the binding of the enzyme ‘RuBisCo activase’ and carbamylation; RuBisCo activase is only active when ferredoxin is reduced in the ferredoxin-thioredoxin system, which is only possible when the ETC is occurring in the thylakoid membranes, which only happens in the presence of light, also carbamylation occurs in higher pH levels and high Magnesium (Mg+2) concentrations in the stroma, which happens when the ETC is occuring, which only occurs in the presence of light.

Question 18

What kind of cells are RuBisCo in?

Answer 18

Bundle sheath cells.

Question 19

When do CAM plants carry out the Calvin cycle, day or night?

Answer 19

During the day.

Question 20

When is PEP Carboxylase active in C4 plants? When is it active in CAM plants?

Answer 20

C4 Plants: active in day
CAM Plants: active in night

Question 21

Describe the process of acquiring atmospheric CO2 in C3, C4, and CAM plants.

Answer 21

C3: acquire atmospheric CO2 during the day in mesophyll, CO2 binds to rubisco and calvin cycle takes place in mesophyll in C3

C4: acquire atmospheric CO2 during the day in the mesophyll cells, hten it becomes a four carbon compound, this compound moves to bundle sheath, CO2 concentrated and released and calvin cycles takes plac

CAM: acquire atmospheric CO2 at night when they keep their stomata open to prevent water loss, and then store it in the form of malate stored and in the plants vacuoles. When daytime comes, malate releases CO2 and then it is used in the Calvin cycle, calvin takes place in mesophyll.

The Calvin cycle is the same in all 3 plants.

Question 22

What is the Kranz anatomy?

Question 23

What units are used to measure light intensity?

Answer 23

umol/m^2/s (micromoles / square meter / second)

Question 24

What is photosynthetic saturation?

Answer 24

When the photosynthetic rate stops increasing, even as light intensity continues increasing.

Question 25

What causes photosynthetic saturation at a certain light intensity

Answer 25

When a certain light intensity is reached, the enzymes used in the Calvin cycle cannot fix any more carbon dioxide.

Question 26

What is the dark respiration rate?

Answer 26

When more carbon dioxide is being produced than consumed. This happens when there is more aerobic respiration occurring than photosynthesis.
On the graph, this would be the part of each line that is under the x-axis, these are in the negative.

Question 27

What is the light compensation?

Answer 27

When the amount of carbon dioxide being produced by respiration is the exact same as the amount being consumed by photosynthesis.
On the graph, this is when the line intersects the x-axis, y=0.

Question 28

Is photosynthesis taking place at the light compensation?

Answer 28

Yes, but it is only 0 because aerobic respiration is producing carbon dioxide at the same time, so the respiration and photosynthesis essentially cancel each other out.

Question 29

What is photochemical efficiency?

Answer 29

When the photosynthetic rate increases as the light intensity increases.
On the graph, this is the slope of the line.

Question 30

What type of plant achieves photosynthetic saturation at lower light intensity, C3 or C4?

Answer 30

C3

Question 31

What type of plant has a higher maximum photosynthetic rate, C3, or C4?

Answer 31

C4

Question 32

How does the color of light affect the photosynthetic rate?: order the colors from best to worst on their ability to stimulate photosynthesis

Answer 32

Best to Worst:
White -> Blue -> Red -> Green

White light is the best at stimulating photosynthesis because it has all of the colors of the spectrum, so chlorophyll can absorb everything.

Blue and red are both absorbed by chlorophyll on the peaks of their absorption spectrum, and blue is just a bit better than red.

Green is not able to be absorbed by chlorophyll, so it does not stimulate photosynthesis.

Question 33

Which plants have a higher maximum photosynthetic rate, those adapted to the sun or the shade?

Answer 33

The plants adapted to the sun because they get more light, and increased light leads to increased photosynthesis.

Question 34

Which plants achieve photosynthesis saturation at lower light intensities, those adapted to the sun or the shade?

Answer 34

The plants adapted to the shade because they would not be able to process as much light as the sun plants without experiencing photosynthetic saturation.

Question 35

Which plants show higher light compensation points, those adapted to the sun or the shade?

Answer 35

The plants adapted to the sun because they produce more CO2 in the dark than the shade plants.

Question 36

Which plants have higher dark respiration rates, those adapted to the sun or the shade?

Answer 36

The plants adapted to the sun because they produce more CO2 in the dark than the shade plants.

Question 37

What type of plant has a higher photosynthetic rate at a low CO2 concentration, C3 or C4?

Answer 37

C4 because they do not experience photorespiration, but C3 could experience photorespiration at a low CO2 concentration.

Question 38

What type of plant acheives photosynthetic saturation at a low CO2 concentration, C3 or C4?

Answer 38

C4 because as CO2 increases, the C3 photosynthesis rate steadily increases but the C4 photosynthesis rate experiences a plateau.

Question 39

What is the CO2 compensation point?

Answer 39

The concentration of CO2 of when the photosynthetic rate is 0.

Question 40

What type of plant will have a higher CO2 compensation point?

Answer 40

C3

Question 41

What effect does temperature have on the photosynthetic rate in a C3 plant?

Answer 41

As temperature increases, the photosynthesis rate increases as well, and this is because the CO2 assimilation rate is increasing.

Question 42

What effect does temperature have on the photosynthetic rate in a C4 plant?

Answer 42

As temperature increases, the photosynthesis rate is increasing because the CO2 assimilation rate is increasing. The photosynthesis rate is increasing more than that of a C3 plant.

Question 43

Which between C3 and C4 would have the highest optimal temperature for photosynthesis? Why?

Answer 43

C4 plants because they are better adapted to hotter environments.

In C3 plants, at 30 degrees they will experience stomatal closure from photorespiration, but this doesn’t happen until a higher temperature in C4 plants.

Question 44

Why can’t dark reactions actually happen in the dark?

Answer 44

_________