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A-Level Biology > 17.3 Light-dependent reaction > Flashcards

17.3 Light-dependent reaction Flashcards

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1
Q

What is the equation for photosynthesis?

A

6CO2 + 6H2O -> C6H12O6 +6O2

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2
Q

What adaptations do chloroplasts have?

A
  • Network of membranes present within chloroplasts provides a large surface area to maximise absorption of light.
  • contain DNA - code for enzyme (ATP synthase needed in LDR or rubisco in LIDR)
  • ribosome needed for protein synthesis , for example sythesis of pigments, photosystems.
  • high surface area of thylakoids and densely packed with photosystems to maximise light absorbed for photosynthesis in Light dependent reaction
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3
Q

What are thylakoids?

A

Flattened sacs of membranes which are stacked to form grana.

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4
Q

What are lamelle?

A

These are membraneous channels which join the grana.

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5
Q

What is stroma?

A

The fluid enclosed in the chloroplast

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6
Q

What is the primary pigment in photosynthesis?

A

Chlorophyll A

It absorbs red and blue light and reflects green light

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7
Q

What pigments are found in the thylakoid membrane?

A

Chlorophyll B, xanthophylls and carotenoids are embedded in the thylakoid membrane

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8
Q

What is the light harvesting system?

A

When chlorophyll b, xanthophylls, carotenoids and other pigments form together (known as antennae complex) in order to absorb the light energy of different wavelengths and transfer the energy to the reaction centre quickly.

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9
Q

Which pigment is located in the reaction centre?

A

Chlorophyll A

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10
Q

What accessory pigments are responsible for the yellow/orange colours in leaves?

A

Carotenoids (carotene and xanthophyll)

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11
Q

What pigment acts as a sunscreen for plants and how?

A
  • Anthocynanin is a red/purple pigment (the colour is pH dependent)
  • It is produced when the conc of sugars is high and help trees maximise production towards end of growing season.
  • They act as sunscreen by absorbing blue-green and ultraviolet light, thereby inhibiting the destruction of chlorophyll.
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12
Q

How do you calculate Rf value?

A

Rf= (distance traveled by component)/(distance travelled by solute)

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13
Q

What is the mobile phase in TLC?

A

Solution containing a mixture of pigments

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14
Q

What is the stationary phase in TLC?

A

A thin layer of silica gel applied to glass

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15
Q

What are the two stages in photosynthesis?

A

1) Light dependent stage

2) Light independent stage

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16
Q

What is the light dependent stage?

A
  • When energy from the sunlight is absorbed by photosynthetic pigments and converted to chemical energy to form ATP. (By adding an organic phosphate group to ADP)
  • Hydrogen from water is used to reduce the coenzyme NADP to REDUCED NADP.
17
Q

What is the light independent stage?

A
  • Also known as the Calvin Cycle.
  • When hydrogen from reduced NADP and carbon dioxide is used to build organic molecules, such as glucose. ATP supplies the required energy.
18
Q

Where does the light dependent reaction take place?

A

The light dependent reaction takes place in the thylakoid membrane of the chloroplast.

19
Q

Where does the light independent reaction take place?

A

The light independent reaction takes place in the stroma of the chloroplasts.

20
Q

What is the process called when ATP is made from ADP and an inorganic phosphate?

A

Photophosphorylation

21
Q

What is a coenzyme?

A
  • A coenzyme is a molecule that aids the function of an enzyme.
  • They usually work by transferring a chemical group from one molecule to another.
22
Q

What coenzyme is used in photosynthesis?

A

NADP.
- It is used to transfer hydrogen from one molecule to another, and this means it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule.

23
Q

In the light dependent reaction, what is the light energy absorbed used for?

A

1) Making ATP from ADP and inorganic phosphate (Photophosphorylation)
2) Making reduced NADP from NADP
3) Splitting water into protons, electrons and oxygen (photolysis)

24
Q

What is photolysis?

A

The splitting of a molecule using light (photo) energy.

25
Q

What are two types of photophosphorylation in the light dependent reaction?

A

1) Non-cyclic photophosphorylation

2) Cyclic photophosphorylation

26
Q

How are the photosystems in the thylakoid membranes linked?

A

The photosystems are linked by electron carriers.

- Electron carriers are proteins that transfer electrons.

27
Q

What is electron transport chain?

A

A chain of proteins through which excited electrons flow.

28
Q

What wavelength can photosystem II absorb?

A

680nm

29
Q

What wavelength can photosystem I absorb?

A

700nm

30
Q

What are the processes in a non-cyclic photophosphoylation?

A

1) Light energy excites electrons in chlorophyll
2) Photolysis of water produces protons, electrons and oxygen.
3) Energy from the excited electrons makes ATP
4) Energy from the excited electrons generates reduced NADP

31
Q

Detail the process of photophosphorylaton.

A

1) Light energy is absorbed by PSII.
2) The light energy excites electrons in the chlorophyll and the electrons move to a higher energy level.
3) These high-energy electrons move along the electron transport chain to the PSI.
4) As the excited electrons from the chlorophyll leave PSII to move along the electron transport chain, they must be replaced.
5) Light energy splits water into protons, electrons and oxygen.
6) The excited electrons lose energy as they move along the electron transport chain.
7) This energy is used to transport protons into the thylakoid, via membrane proteins called proton pumps, so that the thylakoid has a higher concentration of protons than the stroma.
8) This forms a proton gradient across the membrane and protons move down their concentration gradient into the stroma via an enzyme called ATP synthase.
9) The energy from this movement combines ADP and an inorganic phosphate to form ATP.
10) Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level.
11) Finally the electrons are transferred to NADP, along with a proton from the stroma, to form reduced NADP.

32
Q

What is cyclic photophosphorylation?

A
  • Cyclic photophosphorylation only produces ATP and only uses PSI.
  • It’s called “cyclic” because the electrons from the chlorophyll molecule aren’t passed onto NADP, but passed back to PSI via electron carriers.
  • This means electrons are recycled and can repeatedly flow through PSI.

A-Level Biology (41 decks)

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