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AP Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Photosynthesis

A

Process by which light energy is converted to chemical bond energy and carbon is fixed into organic compuounds

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2
Q

Light dependent reactions

A

● Use light energy directly to produce ATP that powers hte light-independent reactions
● Occur when light is present

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3
Q

Light independnet reactions

A

● Consist of hte Calvin cycle, which produces sugar

● Occur when light is present

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4
Q

Photosynthetic pigments

A

● Absorb light energy and use it to provide energy to carry ou t photosynthesis
● Plants contain two major groups of pigments, the cholorophylls, and carotenoids

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5
Q

Chlorophyll a

A

● A type of chlorophyll
● Green
● Absorb all wavelengths of light in the red, blue, and violet range
● Participate directly in the light reactions of photosynthesis
● Large molecule with a porphyrin ring and long hydrocarbon tail

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6
Q

Chlorophyll b

A

● A type of chlorophyll
● Green
● Absorb all wavelengths of light in the red, blue, and violet range

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7
Q

Carotenoids

A

● A type of photosynthetic pigments
● Yellow, orange, and red
● Absorb all wavelengths of light in the blue, green, and violet range

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8
Q

Xanthophyll

A

● A type of carotenoids (with slight chemical variation)
● Yellow, orange, and red
● Absorb all wavelengths of light in the blue, green, and violet range

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9
Q

Phycobilins

A

● Pigments found in red algae
● Reddish
● Absorb light in the blue and green range

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10
Q

Antenna pigments

A

● Chlorophyll b, the carotenoids, and the phycobilins
● Capture light in wavelengths other htan those captured by chlorophyll a
● Absorb photons of light and pass hte enrgy along to chlorophyll a, which is directly invovled in the transformation of light energy to sugars

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11
Q

Action spectrum

A

A spectrum with wavelengths of light plotted against rate of photosynthesis

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12
Q

Porphyrin ring

A

● Chlorophyll a’s head
● with a single magnesium atom in it surrounded by alternating double and single bonds
● Attached to a long hydrocarbon tail

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13
Q

Chloroplast

A

● Contains photosynthetic pigments that carry ou tphotosynthesis
● Contains grana, and stroma
● Enclosed by a double membrane

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14
Q

Grana

A

● Where te light-dpendent reactions occur

● A set of thylakoid

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15
Q

Stroma

A

● Where the light-independent reactions occur

● The space outside of grana but inside of chloroplast

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16
Q

Thylakoids

A

● The site of photosystems I and II

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17
Q

Photosystmes

A

● Light-harvesting complexes in the thylakoid membranes of chloroplasts
● Each photosystem consists of a reaction center and a region containing several hundred antenna pigment molecules
● Two types of photosystmes: PSI and PSII

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18
Q

Reaction center

A

● Within each photosystem

● Contains chlorophyll a that receives energy from antenna pigment molecules

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19
Q

PSI

A

● Absorbs light best in the 700 nm range
- Also called P700
● Operates after PSII

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20
Q

PSII

A

● Operates first
● Absorbs light best in the 680 nm
- Also called P680

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21
Q

Noncyclic flow

A

● Electrons enter two elecron trnasport chains

● The products are ATP and NADPH

22
Q

Cyclic photophosphorylation

A

Only produces ATP; no NADPH is produced and no oxygen is released

23
Q

Primary electron acceptor

A

First cytochrome to capture the electrons moving out of reaction centre

24
Q

Photolysis

A

THe splitting of water to provide electron to replace those lost from chlorophyll a in P680

25
Q

Chemiosmosis

A

Process by which ATP is formed during the light reactions of photosynthesis

26
Q

Thylakoid space / lumen

A

Where protons were pumped into to provide a proton gradient

27
Q

NADP

A

Becomes reduced when it picks up the two protons that were released from water in P680

28
Q

NADPH

A

Carries hydrogen to the Calvin cycle to make sugar in the light-independent reactions

29
Q

Calvin Cycle

A

● Light-independent reactions
● Takes place in the stroma
● Cyclical process that produces the 3-carbon sugar PGAL
● Uses the products of the light reactions: ATP and NADPH

30
Q

Carbon fixation

A

● Reduction reaction since carbon is gaining protons and electrons
● CO2 enters the Calvin cycle and becomes attached to a 5-carbon sugar, ribulose biphosphate (RuBP), forming a 6-carbon molecule
● The 6-carbon molecule is unstable and immediately breaks down into two 3-carbon molecules of 3-PGA

31
Q

Rubisco

A

Then enzyme that catalyzes this first step is ribulose biphosphate carboxylase

32
Q

Photorespiration

A

● this process diverts the process of photosynnthesis when Rubisco binds with O2 instead of CO2
● It diverts it in two ways
- Unlike normal respiration, no ATP is produced
- Unlike normal photosynthesis, no sugar is formed

33
Q

C-3 plants

A

● The first step of Calvin Cycle produces the compound 3-PGA that contains three carbon
● This is not very efficient because rubisco binds with O2 as well as with CO2
- When rubisco binds with O2 instead of CO2, photorespiration occurs

34
Q

Peroxisomes

A

Breaks down the products of photorespiration

35
Q

C-4 plants

A

● Modification for dry environments
● Exhibit modified anatomy and biochemical pathways taht enable them to minimize excess water loss and maximize sugar production
● Thrive in hot and sunny environments where C-3 plants would wilt and die
● Corn, sugar cane, and carbgrass

36
Q

CAM plants

A

● Live in desert

● Special photosynthesis

37
Q

What is the general formula for photosynthesis?

A

6 CO2 + 12 H2O -> C6H12O6 + 6 H2O + 6 O2

38
Q

What are the two main processes of photosynthesis?

A

● Light-dependent reactions

● Light-independent reactions/Calvin cycle

39
Q

How do the double bonds in porphyrin ring play a critical role in the light reactions?

A

● They are the source of the electrons that flow through the electron transport chains during photosynthesis

40
Q

Why happens in photosystem II - P680 in the light-dependent reaction?

A

● Energy is absorbed by P680
● Electrons from the double bonds in the head of chlorophyll a become energized and move to a higher energy level
● They are captured by a primary electron acceptor

41
Q

What is the reaction in photolysis?

A

2 H2O -> 4 H+ + 4 e- + O2

42
Q

What happens in the ETC in noncylcic photophosphorylation?

A

● Electrons from P680 pass along an electron transport chain consisting of several molecules including cytochromes and several other proteins, and ultimately end up in P700 (PSI)
● This flow of electrons is exergonic, and provides energy to produce ATP by chemiosmosis

43
Q

Why is the ETC called photophosphorylation?

A

The ATP synthesis is powered by light

44
Q

What happens in chemiosmosis?

A

● Protons that were released from water during photolysis are pumed by the thylakoid membrane from the stroma into the thylakoid space/lumen
● ATP is formed as these protons diffuse down the gradient from the thylakoid space, through the ATP synthase channels, and into the stroma
● The ATP produced here provides the energy that powers hte Calvin cycle

45
Q

What happens in Photosysten I - P700?

A

● Energy is absorbed by P700
● Electrons from the head of chlorophyll a become energized and are captured by a primary electron recetor
● Electrons that escape from chlorophyll a are replaced with electrons from photosystem II, P680, instead of from water
●This ETC produces NADPH, not ATP

46
Q

What does noncyclic photophosphorylation look like in short?

A

light -> P680 oxygen released -> ATP produced -> P700 -> NADPH produced and carries H+ to the Calvin cycle

47
Q

Why does chloroplast sometimes carry out cyclic photophosphorylation?

A

● THe production of sugar that occurs during the Calvin cycle consumes enormous amounts of ATP
- Periodically, the chloroplast runs low on ATP
● THe Chloroplast will then carry out cyclic photophosphorylation to replenish the ATP levels
● Also occures when NADP+ is not available

48
Q

What happens in the cyclic photophosphorylation?

A

Electrons travel from the P680 ETC to P700, to a primary electron acceptor, and then back to the cytochrome complex in the P680 ETC

49
Q

Why does the problem of photorespiration happen?

A

It is probably a vestige from ancient Earth billions of years ago when the atmosphere had little or no free oxygen to divert rubisco and sugar production

50
Q

How is C-4 photosynthesis different from C-3 photosynthesis?

A

● PEP carboxylase enzyme is used to help PEP (3-Carbon molecule) to bind with CO2 to form 4-Carbon molecule oxaloacetate
● Oxaloacetate becomes malate and is tranported to bundle sheath cell in the leaf where Oxygen level is extremely low
● Malate then breaks apart and CO2 binds with RuBP and the rest of Calvin cycle will resume

51
Q

How is CAM photosynthesis different from C-3 photosynthesis?

A

● PEP + CO2 -> Malate -> Malic acid
● Malic acid is stored in the vacuole
● CAM plants open their stomata during night time to prevent H2O loss
- Obtains CO2 at night
● Malic acid breaks apart in the morning and completes the Calvin cycle with the presence of light
● Temporal adaptation

AP Biology (15 decks)

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