Phototrophy

Question 1

What is photosynthesis?

Answer 1

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose.

Question 2

What is the difference between photoautotrophs and photoheterotrophs?

Answer 2

Photoautotrophs use light energy to convert carbon dioxide into organic compounds, while photoheterotrophs use light energy but require organic compounds for growth.

Question 3

What are genera or groups of prokaryotes representing the six different photosynthetic systems that evolved within the Bacteria?

Answer 3

The six groups include cyanobacteria, green sulfur bacteria, purple sulfur bacteria, purple non-sulfur bacteria, heliobacteria, and green non-sulfur bacteria.

Question 4

How did photosynthesis evolve in eukaryotes?

Answer 4

Photosynthesis in eukaryotes evolved through endosymbiosis, where a eukaryotic cell engulfed a photosynthetic prokaryote.

Question 5

What is the overall purpose of the light reactions of photosynthesis?

Answer 5

The light reactions convert solar energy into chemical energy in the form of ATP and NADPH.

Question 6

What is the overall purpose of the dark reactions of photosynthesis?

Answer 6

The dark reactions, or Calvin cycle, use ATP and NADPH to convert carbon dioxide into glucose.

Question 7

What two energy sources are required for the reduction of carbon dioxide?

Answer 7

ATP and NADPH are required for the reduction of carbon dioxide.

Question 8

What three groups of organisms use water as their electron donor for photosynthesis?

Answer 8

Cyanobacteria, green plants, and algae use water as their electron donor.

Question 9

What groups of prokaryotes cannot use water as their electron donor for photosynthesis? What do they use instead?

Answer 9

Green sulfur bacteria and purple sulfur bacteria cannot use water; they use hydrogen sulfide instead.

Question 10

What is oxygenic photosynthesis? What groups of organisms perform this?

Answer 10

Oxygenic photosynthesis is the process that produces oxygen as a byproduct, performed by cyanobacteria, algae, and green plants.

Question 11

What is anoxygenic photosynthesis? What groups of organisms perform this?

Answer 11

Anoxygenic photosynthesis does not produce oxygen and is performed by green sulfur bacteria, purple sulfur bacteria, and heliobacteria.

Question 12

What are chlorophylls? What groups of organisms contain them?

Answer 12

Chlorophylls are green pigments essential for photosynthesis, found in plants, algae, and cyanobacteria.

Question 13

What are bacteriochlorophylls? What groups of organisms contain them?

Answer 13

Bacteriochlorophylls are pigments used in anoxygenic photosynthesis, found in purple and green bacteria.

Question 14

How are chlorophylls and bacteriochlorophylls similar to and different from cytochromes?

Answer 14

Chlorophylls and bacteriochlorophylls are involved in light absorption, while cytochromes are involved in electron transport; they differ in structure and function.

Question 15

What are the two major absorption peaks for chlorophyll a?

Answer 15

The two major absorption peaks for chlorophyll a are around 430 nm and 662 nm.

Question 16

What are the two major absorption peaks for bacteriochlorophyll a?

Answer 16

The two major absorption peaks for bacteriochlorophyll a are around 800 nm and 870 nm.

Question 17

What is the ecological significance of the existence of different forms of chlorophyll and bacteriochlorophyll?

Answer 17

Different forms allow organisms to utilize various light wavelengths, enhancing survival in diverse environments.

Question 18

What are photocomplexes? What groups of organisms possess these?

Answer 18

Photocomplexes are structures that contain pigments and proteins for light harvesting, found in plants, algae, and some bacteria.

Question 19

What is the major function of photocomplex reaction centers?

Answer 19

The major function is to convert light energy into chemical energy.

Question 20

What is the primary function of photocomplex antenna (light-harvesting) pigments?

Answer 20

The primary function is to capture and funnel light energy to the reaction center.

Question 21

What is a chloroplast? What are its major components? What group of organisms possesses them?

Answer 21

A chloroplast is an organelle where photosynthesis occurs, containing thylakoids, stroma, and chlorophyll, found in plants and algae.

Question 22

What is a chromatophore? What is a lamella? What group of organisms possesses these structures?

Answer 22

A chromatophore is a photosynthetic membrane structure found in purple bacteria, while a lamella is a membrane layer within chromatophores.

Question 23

What photosynthetic structure is present in cyanobacteria?

Answer 23

Cyanobacteria possess thylakoid membranes for photosynthesis.

Question 24

What is a chlorosome? What are its major components? What groups of organisms possess them?

Answer 24

A chlorosome is a light-harvesting structure found in green bacteria, composed of bacteriochlorophyll and proteins.

Question 25

How are chlorosomes different from the photosynthetic structures in other prokaryotes?

Answer 25

Chlorosomes are more efficient at capturing light in low-light environments compared to other prokaryotic structures.

Question 26

What are carotenoids? carotenes? xanthophylls?

Answer 26

Carotenoids are pigments that include carotenes (orange pigments) and xanthophylls (yellow pigments), involved in light absorption and protection.

Question 27

What is the primary function of carotenoids?

Answer 27

The primary function of carotenoids is to protect against photooxidative damage and assist in light harvesting.

Question 28

How can bright light harm cells?

Answer 28

Bright light can cause photooxidative damage, leading to the production of reactive oxygen species.

Question 29

What are phycobiliproteins? In what groups of organisms are they present?

Answer 29

Phycobiliproteins are light-harvesting proteins found in cyanobacteria and red algae.

Question 30

What are three examples of phycobilins? What is the absorbance peak for each one?

Answer 30

Examples include phycoerythrin (around 495 nm), phycocyanin (around 620 nm), and allophycocyanin (around 650 nm).

Question 31

What are phycobilisomes? Where are they located?

Answer 31

Phycobilisomes are complexes of phycobiliproteins located on the thylakoid membranes of cyanobacteria and red algae.

Question 32

What advantage do phycobilisomes provide to the organisms that contain them?

Answer 32

Phycobilisomes enhance light absorption, allowing organisms to thrive in low-light conditions.

Question 33

What is the overall purpose or goal of the photosynthetic light reactions? How is this accomplished?

Answer 33

The goal is to convert light energy into chemical energy, accomplished through the generation of ATP and NADPH.

Question 34

What is the general structure of a photosynthetic reaction center?

Answer 34

The reaction center consists of a complex of proteins and pigments that facilitate the conversion of light energy.

Question 35

How do the photosynthetic light reactions generate high-potential electrons?

Answer 35

High-potential electrons are generated through the excitation of pigments by light energy.

Question 36

What happens to these high-potential electrons?

Answer 36

They are transferred through an electron transport chain, leading to the production of ATP and NADPH.

Question 37

What are the two types or classes of reaction centers used in anoxygenic photosynthesis?

Answer 37

The two types are Type I and Type II reaction centers.

Question 38

What type of photosynthetic reaction center is used by purple sulfur bacteria?

Answer 38

Purple sulfur bacteria use Type II reaction centers.

Question 39

What is photophosphorylation?

Answer 39

Photophosphorylation is the process of generating ATP from ADP and inorganic phosphate using light energy.

Question 40

What is reverse electron transport?

Answer 40

Reverse electron transport is the process where electrons are moved back against their gradient to generate reducing power.

Question 41

Which type of photosystem requires reverse electron transport and why?

Answer 41

Photosystem I requires reverse electron transport to generate NADPH.

Question 42

What is ferredoxin? How is it used in anoxygenic photosynthesis?

Answer 42

Ferredoxin is a protein that carries electrons and is used in anoxygenic photosynthesis to transfer electrons to NADP+.

Question 43

What is the difference between cyclic and noncyclic photophosphorylation?

Answer 43

Cyclic photophosphorylation recycles electrons back to the reaction center, while noncyclic photophosphorylation transfers electrons to NADP+.

Question 44

How do oxygenic phototrophs differ from anoxygenic phototrophs with regards to their respective reactions center?

Answer 44

Oxygenic phototrophs have two photosystems (PSI and PSII), while anoxygenic phototrophs typically have only one.

Question 45

What is the most distinctive step in oxygenic photosynthesis? Where (and how) does this occur?

Answer 45

The most distinctive step is the splitting of water to release oxygen, occurring in Photosystem II.

Question 46

How does PSII generate a proton motive force?

Answer 46

PSII generates a proton motive force by pumping protons into the thylakoid lumen during electron transport.

Question 47

What is the function of plastocyanin?

Answer 47

Plastocyanin is a copper-containing protein that transfers electrons from the cytochrome b6f complex to Photosystem I.

Question 48

What is the major purpose of PSI?

Answer 48

The major purpose of PSI is to generate NADPH for the Calvin cycle.

Question 49

How many protons are translocated for every molecule of oxygen produced in oxygenic photosynthesis? Where do these protons come from?

Answer 49

Four protons are translocated for every molecule of oxygen produced, coming from the splitting of water.

Question 50

Oxygenic photosynthesis typically involves what type of photophosphorylation? Under what circumstances would the other type of photophosphorylation be used?

Answer 50

Oxygenic photosynthesis typically involves noncyclic photophosphorylation; cyclic photophosphorylation is used when ATP is needed without NADPH.

Question 51

What is unusual about the cyanobacterium Oscillatoria limnetica?

Answer 51

Oscillatoria limnetica is unusual because it can perform both oxygenic photosynthesis and nitrogen fixation.

Question 52

What evidence supports a close evolutionary relationship between anoxygenic and oxygenic phototrophs?

Answer 52

Genetic and biochemical similarities in their photosynthetic pathways suggest a close evolutionary relationship.

Question 53

What two key evolutionary inventions were made by cyanobacteria?

Answer 53

Cyanobacteria invented oxygenic photosynthesis and the ability to fix atmospheric nitrogen.