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Plant Physiology > Photosynthesis: Light reaction > Flashcards

Photosynthesis: Light reaction Flashcards

1
Q

Does a longer wave length of higher or lower energy?

A

Lower

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2
Q

What is the connection between wave length and amount of energy?

A

Longer wave length –> lower energy

Shorter wave length -> higher energy

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3
Q

Which has longer wave length/energy: blue light (ultra violet) or red (infrared)?

A

Blue or violet - shorter wave length, higher energy

Red - longer wave length, lower energy

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4
Q

When chlorophyll absorbs light it goes to a higher energy state. What are the four possible option that the chlorophyll has to dispose of the available energy?

A
  1. Re-emit the photon (fluorescence)
  2. Convert the energy to heat, with no emission of a photon
  3. Energy transfer - transfer the energy to another molecule
  4. Photochemistry - the energy causes a chemical reaction
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5
Q

Pigments (what and where?)

A

They absorb the energy of the light and are found in the chloroplast. Serve as an antenna complex

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6
Q

Structure of pigments

A
  1. A ring shaped complex (porphyrin like groups found in hemoglobin)
  2. Long hydrocarbon tail that anchors it downs in the photosynthetic membrane
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7
Q

Carotenoids (where are they found and what do they do?)

A

Carotenoids are found in almost all photosynthetic organisms. They absorb light energy and pass it to the chlorophyll. They also help protect the organism from the light damage.

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8
Q

Antenna

A

Many pigments serve as an antenna: collecting light and transferring it to the reaction center

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9
Q

Where does the oxygen in photosynthesis originate from?

A

Water, not CO2

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10
Q

What are the steps of the thylakoid reactions?

A
  1. Water ix oxidized to oxygen
  2. NADP+ is reduced to NADPH
  3. ATP is formed
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11
Q

What links the two photosystems?

A

An electron transport chain

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12
Q

Difference between PS1 and PS2 (photosystem 1 and 2)

A

PS1:
* Absorbs light with a wave length greater than 680nm
* Produces a strong reductant (“loser of electron”), capable of reducing NADP+
(A reducing agent is an element or compound that loses an electron to another chemical species in a redox chemical reaction)

PS2:
* Absorbs light with a wave length greater of 680nm
* Produces a very strong oxidant, capable of oxidizing water
(an oxidizing agent is a substance that has the ability to oxidize other substances — in other words to accept their electrons.)

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13
Q

Oxidant

A

An oxidizing agent is a substance that has the ability to oxidize other substances — in other words to accept their electrons.

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14
Q

Reductant

A

A reducing agent is an element or compound that loses an electron to another chemical species in a redox chemical reaction

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15
Q

מחמצן

A

החומר שמקבל אלקטרונים עובר חיזור (דרגת החמצון שלו יורדת) והוא נקרא מחמצן

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16
Q

מחזר

A

החומר שמוסר אלקטרונים עובר חמצון (דרגת החמצון שלו עולה) והוא נקרא מחזר.

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17
Q

חיזור באנגלית

A

רֵדוּקְציה (Reduction)

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18
Q

חימצון באנגלית

A

אוֹקְסִידַצְיָה (Oxidation)

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19
Q

Where does the light reaction take place?

A

In the thyloakoids

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20
Q

Where does the carbon reaction take place?

A

In the stroma (the region of the chloroplast outside the thylakoids)

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21
Q

What’s the interior space of the thylakoid called?

A

The Lumen

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22
Q

What are stacked membranes called?

A

Grana Lamellae

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23
Q

Grana Lamellae

A

The stacked membranes in the chloroplast

PSII, antenna chlorophylls and associated electron transport proteins is mostly located in the grana lamellae

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24
Q

The Lumen

A

The interior space of the thylakoid

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25
Q

Stroma lamellae

A

Exposed membranes in which there isn’t stacking

PSI and its associated antenna pigments and electron transfer proteins, and ATP synthase enzyme are almost exclusively in the stroma lamelle and edges of the grana lamellae

26
Q

What are the two main roles of the pigments?

A

Antioxidants and for photosynthesis (“capture” the light.)

27
Q

Which pigments are in a higher energy state? Closer to the reaction center or farther away from it?

A

Pigments closer to the reaction center are lower in energy than those farther from it.

28
Q

Why are pigments closer to the reaction center in a lower energy state than those farther from it.?

A

Pigments closer to the reaction center are lower in energy than those farther from it. This energy gradient ensures that excitation transfer toward the reaction center is energetically favorable and that transfer back out to the peripheral portions of the antenna is energetically unvavorable.

29
Q

What percentage of the light that hits the leaf is absorbed in photosynthesis?

A

About 56% is absorbed

30
Q

מתי נראה עליה בפלורוסנציה?

A

אם אי אפשר לעשות פוטוסינטזה (לדוג’ פיוניות סגורות בגלל חוסר מים) אז הפיגמנטים ממשיכים לספק את האור אבל בגלל שאין פוטוסינטזה זה נפלט בפלורוסנציה

31
Q

מתי הפלורוסנציה תהיה נמוכה יותר?

A

כאשר הפוטוסינטזה גבוה יותר

וגם הפוך: אם הפוטוסינטזה נמוכה יותר יש יותר פלורוסנציה

32
Q

באמצעות מה נעשה ביקוע מולקולת המים?

A

הביקוע של מים נעשת ע”י
Mn
החמצן נקשר אליו והמנגן “מותח” אותו ככה שאפשר לשלוף את האלקטרון החוצה.

33
Q

Where does plastoquinone carry protons?

A

Plastoquinone carries protons to the inside of thylakoids, creating a proton-motive force.

34
Q

What direction on the protons pumped?

A

From stroma to tyhlakoid lumen

Passage of electrons along the chain involves a series of reduction-oxidation reactions that results in protons being pumped from stroma to thylakoid lumen

35
Q

Where are there more protons: Stroma or thylakoid lumen?

A

Thylakoid lumen (protons are pumped form stroma into the thylakoid lumen)

36
Q

Where is there a lower PH: Stroma or thylakoid lumen?

A

Lumen, since there are more protons there.

37
Q

למה גורמת כניסה של פרוטון ל

ATP סינטז?

A

לסיבוב של היחידה התחתונה וזה גורם לציר להסתובב שמוביל לשינו קונפורמציה בתוך הראש של ה
ATP סינטז

38
Q

כמה ממברנות יש לכלורופלסט?

A

2: ממברנה חיצונית ופנימית

הממברנה הפנימית מזכיר ממברנה של פרוקריוטי והחיצוני מזכיר ממברנה של אוקריוט

39
Q

איך קוראים לאזור שכלוא בתוך הממברנה הפנימית בכלורופלסט?

A

Stroma

40
Q

Lamella

A

הממברנות שמחברות בין ה

Granum

41
Q

איך קוראים לממברנות שמחברות בין ה
Granum
השונים?

A

Lamella

42
Q

Why is it important for the pH to not change in the stroma?

A 
חשוב לא לשנות את ה
PH
ב
stroma
כי שם נעשה קיבוע הפחמן והחלבונים צריכים 
PH
ספציפי
43
Q

What does the light reaction supply to the dark reaction?

A

ATP and NADPH

44
Q

Where are the ATP synthases located?

A

Only in the stroma lamella and edge of grana stacks

45
Q

Are the pigments closer to the reaction center lower or higher in energy than pigments further away from the reaction center?

A

Pigments closer to reaction center are lower in energy. This insures that the energy gradient is going in the right direction (towards the reaction center and not backwards).

46
Q

What is the ultimate electron donor?

A

Water

47
Q

What is the ultimate electron acceptor?

A

NADP+

48
Q

What traits does Plastohydroquinone have that help it do its job?

A

It is a small, non polar molecule that can defuse readily in the nonpolar core of the membrane bilayer.

49
Q

What does the cyclic electron flow through the cytochrome and plastoquinone gain?

A

The cyclic electron flow through the cytochrome and plastoquinone increases the number of protons pumped into the lumen

50
Q

What connects the two photosystems (and transfers electrons between them)?

A

Plastoquinone or plastocyanin (or both) are the mobile carries between PSI and PSII

51
Q

Why would there sometimes be cyclic electron flow (that instead of a linear flow from water to NADP+)?

A

The cyclic flow (through cytochrome b) is couple with proton pumping into the lumen, which can then be used for ATP synthesis.

52
Q

In what plant types is cyclic electron flow important?

A

C4

53
Q

What is DCMU?

A

It’s a chemical that blocks the electron flow (at the quinone acceptors of PSII) by competing with the binding site of platsoquinone.

54
Q

What’s more acidic: the lumen or stroma?

A

Lumen

55
Q

Is the “head” of ATP synthase pointing inot the stroma or lumen?

A

Stroma

56
Q

What are the protection mechanisms from too much light?

A
  • Cartonoids can quench the exicted state of chlorophyll and the energy is released as heat
57
Q

What is photoinhibition

A

The inhibition of photosynthesis because of excess light. The main target is D1 (part of PHII).
The inhibition can be reversed in its early stages

58
Q

What happens if D1 is damaged?

A

It needs to be replaced (synthesized), as opposed to other components which recycled.

59
Q

What will happen to the two PS if there is limited light?

A

Because the two PS absorb light in different lengths, if then if there is limited light, the rate of electron flow will be limited by the PS that is receiving less energy. However, there is a system (based on phosphorylation) that shifts energy between the PS based on external conditions.

60
Q

Where are most chloroplast proteins encoded?

A

Encoded by nuclear genes and imported into the chloroplast from the cytoplasm

Plant Physiology (22 decks)

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