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A- Level Biology - Photosynthesis > Light depdent reaction > Flashcards

Light depdent reaction Flashcards

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1
Q

What does a light-dependent reaction involve?

A

Capture of light whose energy is used for two purposes

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2
Q

What are the two purposes of the light-dependent reaction?

(purpose of capturing the light energy)

A
  • To add inorganic phosphate (Pi) molecule to ADP, thereby making ATP
  • Spilt water into H + ions (protons) and OH- ions. As the spiltting is caused by light it is known as photolysis
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3
Q

What is oxidation?

A
  • Loss of electrons
  • Loss of hydrogen
  • Or gain of oxygen
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4
Q

What is the reduction?

A
  • Gain of electrons
  • Gain of hydrogen
  • Or loss of oxygen
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5
Q

What does oxidiation result in terms of energy?

A

Energy being given out

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6
Q

What does reduction result in terms of energy?

A

Results in energy being taken in

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7
Q

What is the first step of light-dependent reaction?

A

The chlorophyll molecule is absorbing light energy, and it boosts the energy of a pair of electrons within this chlorophyll molecule, raising them to a higher energy level. They are in an excited state

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8
Q

What happens to electrons in that excited state?

A

The electrons become so energetic (kinetic enerygy)

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9
Q

What is the second stage of light-dependent reaction?

A

Electrons are so energetic that they leave the chlorophyll molecule all together

As a result the chlorophyl molecule becomes ionised - the process is called photoionisation

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10
Q

What is the third stage of the light-dependent reaction?

A

The electrons that leave the chlorophyll are taken up by a molecule called an electron carrier

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11
Q

What is the fourth step of light-dependent reaction?

A

Having lost a pair of electrons, the chlorophyll molecule has been oxidised

The electron carriers which has gained electrons has been reduced

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12
Q

What is the fifth step of the light-dependent reaction?

A

The electrons are now passing along a number of electrons in a series of oxidation-reduction reaction

Electrons are carried from a transfer chain that is located in the membranes of thylakoids

Each carrier is at a slightly lower level than the previous one in the chain so electrons lose energy at each stage

Some of this energy is used to combine inorganic phosphate molecules with ADP molecules in order to make ATP

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13
Q

What is the sixth stage of light-dependent reaction?

A

The precise mechanisms by which ATP is produced explained by chemiosmotic theory

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14
Q

What is the first step of chemiosmotic theory?

A

Each thylakoid is an enclosed chamber into which protons (H+) are pumped from the stroma using protein carriers in the thylakoid membrane called proton pumps

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15
Q

What is the second step of chemiosmotic theory?

A
  • The energy to drive this process from electrons released from water molecules are spilt by light - photolysis of water
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16
Q

What is the third step of chemiosmotic theory?

A

The photolysis of water also produces protons which further increases their concentration inside the thylakoid space

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17
Q

What is the fourth step of chemiosmotic theory?

A

Overall this creates and maintains a concentration gradient of protons across the thylakoid membrane with a high concentration inside the thylakoid space with a low concentration in the stroma

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18
Q

What is the fifth step of chemiosmotic theory?

A

Protons can only cross the thylakoid membrane through ATP synthase channel proteins - the rest of the membrane is impermeable to protons

These channels form small granules on the membrane surface and so are known as stalked granules

19
Q

What is the sixth step of chemiosmotic theory?

A

As protons pass through these ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination of ADP with inorganic phosphate to form ATP

20
Q

What are the seventh steps of the light-dependent reaction?

A

Photolysis of water

water molecules are spilt using light energy

21
Q

What are the eighth steps of light-dependent reaction?

A

protons pass out of the thylakoid space through the ATP synthase channels and are taken up by an electron carrier called NADP- makes protons reduced

oxygen by-product from the photolysis of water is either used in respiration or diffuses out of leaf as a waste product of photosynthesis

22
Q

Why is photolysis used?

A

loss of electrons when light strikes a chlorophyll molecule leaves it short of electrons

if chlorophyll molecule is to continue absorbing light energy, these electrons must be replaced

Photolysis gives these replacement electrons and yields protons

23
Q

Equation of photolysis of water - chemical

A

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

24
Q

Equation of photolysis of water - word

A

water -> protons + electrons + oxygen

25
Q

Why is reducing NADP used for?

A

it is the main product of the light-dependent reaction and enters into the light-independent reaction taking with it the electrons from chlorophyll molecules

26
Q

Why was reduced NADP important?

A

It is a further potential source of chemical energy to the plant

27
Q

What is grana?

A

Thylakoids are disc-like structures that are stacked up together in groups

28
Q

How are chlorplasts structurally adapted for?

A

Their function of capturing sunlight and carrying out light-dependent reaction of photosynthesis in following ways

29
Q

How are thylakoid membranes adapted for the light-dependent reaction?

A

Provide a large surface area for the attachment of chlorophyll, electron carries and enzymes that carry out this reaction

30
Q

How are network of proteins in grana adapted for the light-dependent reaction?

A

They hold the chlorophyll in a very precise manner that allows maxiumum absorbption of light

31
Q

How are chloroplasts adapted having DNA and ribosomes for the light-dependent reaction?

A

They can easily manufacture some of the proteins involved in this reaction

32
Q

What is oxygen used up as (by-product of photolysis of water)

A

Either used in respiration

or

diffuses out a leaf as a waste product

33
Q
A
34
Q

What is photosystems?

A

Made up of pigments (e.g chlorophyll) plus protein

Function - absorb light

35
Q

What is electron carriers?

A

Proteins that transfer electrons

36
Q

What is a co-enzyme?

A

Proteins that transfer chemical groups

37
Q

What is photo-phosphorylation?

A

Using light energy to add a phosphate

38
Q

What is an electron transport chain?

A

When an electron flows through proteins/electron carriers

39
Q

What is photolysis?

A

Using light energy to spilt a molecule

(Hydrogen uses energy from water to spilt a molecule)

H20 -> light 2H+ + 2e - +0.5 O2 (unbalanced)

40
Q

What type of reaction is photosynthesis?

A

Endothermic (requires/trap energy)

41
Q

What are the two types of photosynthesis? LDP

A

Non-cyclic phosphorylation

Cyclic phosphorylation

42
Q

What happens in both cases of cyclic and non=cyclic

A
  • Photosystems absorb light energy
  • Electrons in chlorophyll become excited
  • A phosphate group is added to ADP to re-synthesise ATP
43
Q

What happens to electrons at each level?

A

Release some energy

Used to transport H+

H+ + e- -> NADPH

44
Q

Diagram of cyclic and non-cylcic

A

A- Level Biology - Photosynthesis (6 decks)

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