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AS/A-Level Biology > EN: Photosynthesis > Flashcards

EN: Photosynthesis Flashcards

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1
Q

Where does photosynthesis take place?

A

Chloroplasts.

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2
Q

Chloroplasts

A

Flattened organelles surrounded by a double membrane.

Found in plant cells.

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3
Q

Thylakoids

A

Fluid-filled sacs stacked up in the chloroplast into structures called grana.

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4
Q

Grana

A

Stacks of thylakoids.

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5
Q

Lamellae

A

Thylakoid membranes that link together the grana.

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6
Q

What photosynthetic pigments do chloroplasts contain?

Where are they found?

A
  • Chlorophyll A
  • Chlorophyll B
  • Carotene

Found in the thylakoid membranes - attached to proteins.

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7
Q

Flattened organelles surrounded by a double membrane.

Found in plant cells.

A

Chloroplasts

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8
Q

Fluid-filled sacs stacked up in the chloroplast into structures called grana.

A

Thylakoids

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9
Q

Stacks of thylakoids.

A

Grana

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10
Q

Thylakoid membranes that link together the grana.

A

Lamellae

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11
Q

What is the use of photosynthetic pigments in chloroplasts?

A

They are coloured substances that absorb light energy needed for photosynthesis.

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12
Q

Photosystem

A

Protein and pigment that are attached in the chloroplast.

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13
Q

What are photosystems used by plants for?

How many are there?

What wavelength do they best absorb light at?

A

To capture light energy.

There are 2 : photosystem I (PSI) or photosystem II (PSII).

PSI = 700nm

PSII = 680nm

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14
Q

Stroma

A

Gel-like substance, contained in the inner membrane, surrounding the thylakoids.

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15
Q

Protein and pigment that are attached in the chloroplast.

A

Photosystem

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16
Q

Gel-like substance, contained in the inner membrane, surrounding the thylakoids.

A

Stroma

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17
Q

What does the stroma contain?

A

Enzymes, sugars and organic acids.

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18
Q

What happens to carbohydrates produced by photosynthesis?

A

Most is not used straight away and is stored as starch grains in the stroma.

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19
Q

What are the stages of photosynthesis?

A
  1. Light-dependent reaction
  2. Light-independent reaction
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20
Q

Briefly describe the light-dependent reaction stage of photosynthesis:

A
  1. Light energy is absorbed by chlorophyll in the photosystems.
  2. Light energy excites the electrons in the chlorophyll, leading to eventual releases from the molecule - chlorophyll has been photoionised.
  3. Some energy from the released electrons is used to add a phosphate group to ADP to form ATP, and some is used to reduce NADP to reduced NADP.
  4. ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction.
  5. H2O is oxidised to O2.
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21
Q

Where does the light-dependent stage of photosynthesis occur?

A

Thylakoid membranes of the chloroplasts.

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22
Q

What is produced in the light-dependent stage of photosynthesis?

A

ATP and reduced NADP.

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23
Q

In the light-dependent stage of photosynthesis, what does each product do?

A

ATP = transfers energy to light-independent reaction

Reduced NADP - transfers hydrogen to light-independent reation.

24
Q

What is the light-independent stage of photosynthesis also called?

A

The Calvin cycle

25
Q

Where does the light-independent stage occur?

A

In the stroma

26
Q

Briefly, what happens in the light-independent stage of photosynthesis?

A

ATP and reduced NADP from the light-dependent reaction supply the energy and hydrogen to make simple sugars from CO2

27
Q

How is ATP made in the light-dependent reaction?

A

Photophosphorlyation

28
Q

In the light-dependent reaction, the energy produced from the photoionisation of chlorophyll is used for what?

A
  1. Making ATP from ADP and inorganic phosphate - phosphorylation.
  2. Making reduced NADP from NADP.
  3. Splitting water into protons, electrons and oxygen - photolysis.
29
Q

What types of phosphorylation does the light-dependent stage include?

What is the difference?

A

Non-cyclic and cyclic.

Each has different products.

30
Q

What are photosystems linked by?

A

Electron carriers - proteins that transfer electrons.

31
Q

Electron transport chain

A

Chain of proteins through which excited electrons flow.

Formed from photosystems and electron carrier chains.

32
Q

What 4 processes happen during non-cyclic phosphorylation?

A
  1. Light energy excites electrons in chlorphyll
  2. Photolysis of water produces protons, electrons and O2
  3. Energy from excited electrons makes ATP
  4. Also generates reduced NADP.
33
Q

Describe the first stage of non-cyclic phosphorylation:

A
  1. Light energy is absorbed by PSII.
  2. The light energy excites electrons in chlorophyll.
  3. Electrons move to a higher energy level.
  4. High-energy electrons are released from chlorophyll and move down the electron transport chain to PSI.
34
Q

Describe the second stage of non-cyclic phosphorylation:

A
  • Excited electrons from chlorophyll leave PSII to move down the electron transport chain, they must be replaced.
  • Light energy splits water into protons, electrons and oxygen - photolysis.
  • Reaction is: H2O —> 2H+ + 1/2O2
35
Q

Describe the third stage of non-cyclic photophosphorylation:

A
  1. Excited electrons lose energy as they move down the chain.
  2. Energy used to transport protons into the thylakoid, so that thylakoid has a higher concentration of protons than stroma - forms proton gradient across thylakoid membrane.
  3. Protons move down concentration gradient, into stroma, via ATP synthase, which is embedded in thylakoid membrane.
  4. Energy combines ADP and inorganic phosphate to form ATP.
36
Q

Briefly describe what happens during the light-dependent stage of photosynthesis:

A
  • Light energy absorbed by chlorophyll in the photosystems.
  • Excites electrons - leads to their release from chlorophyll.
  • Energy released is used to add a phosphate group to ADP to ATP and also to reduce NADP to form reduced NADP.
  • H2O is oxidised to O2
37
Q

Draw a diagram to show how the light dependent reactions and the calvin cycle are linked:

A
38
Q

What does non-cyclic phosphorylation produce?

What is it?

A

ATP, reduced NADP and O2

One of the two sections of the light-dependent stage of photosynthesis.

39
Q

Describe the 4th and final stage of non-cyclic phosphorylation:

A
  1. Energy from excited electrons generates reduced NADP.
  2. Light energy is absorbed by PSI - excites electrons to even higher level.
  3. Electrons are trasnferred to NADP, long with a proton from the stroma, to form reduced NADP.
40
Q

Chemiosmosis

A

Process of electrons flowing down the ETC and creating a proton gradient across the membrane to drive ATP synthesis.

41
Q

What does cyclic photophosphorylation produce?

A

Only ATP.

42
Q

What photosystem does cyclic phosphorylation use?

A

PSI

43
Q

Why is cyclic phosphorylation ‘cyclic’?

A

Because electrons aren’t passed onto NADP but are passed back to PSI via electron carriers.

Electrons are recycled and repeatedly flow through PSI.

44
Q

What does the Calvin Cycle make?

What does it make this from?

A

A molecule of triose phosphate.

Made from CO2 and ribulose bisphosphate.

45
Q

How many carbons does ribulose bisphosphate have?

A

5 carbons.

46
Q

What is triose phosphate used for?

A

To make glucose and other organic substances.

47
Q

Briefly describe the steps of the calvin cycle:

A
  1. Carbon dioxide is combined with ribulose bisphosphate to form two molecules of glycerate 3-phosphate.
  2. ATP and reduced NADP are required for the reduction of GP to triose phosphate.
  3. Ribulose bisphosphate is regenerated.
48
Q

What happens in the 1st stage of the Calvin Cycle?

A
  • CO2 enters leaf through stomata and diffuses to stroma.
  • Combined with RuBP - 5 carbons.
  • Catalysed by enzyme rubisco.
  • Gives an unstable 6-carbon compound called glycerate 3-phosphate (GP).
49
Q

What happens in the 2nd stage of the calvin cycle?

A
  • Hydrolysis of ATP (light-dependent) provides energy to turn GP into TP.
  • Also requires H+ ions from reduced NADP (LD).
  • Reduced NADP is recycled to NADP.
  • Some triose phosphate is converted to useful organic compounds - some continues in calvin cycle to regenerate RuBP.
50
Q

In the Calvin cycle, what does reduced NADP from the light dependent reactions do?

A

Reduces GP to TP.

51
Q

What happens in the 3rd stage of the calvin cycle?

A
  • Five out of 6 moleculed of TP aren’t used to make hexose sugars, but to regenerate RuBP.
  • Regenerating RuBP uses the rest of the ATP produced by the light-dependent reaction.
52
Q

The light-independent reaction/the calvin cycle, can also be known as what?

A

Carbon dioxide fixation because carbon from CO2 is ‘fixed’ into an organic molecule.

53
Q

Draw a diagram of the Calvin Cycle:

A
54
Q

What are TP and GP used to make after the calvin cycle?

Explain in detail.

A
  • Carbohydrates - hexose sugars made by joining two TP molecules.
  • Lipids - made using glycerol, which is synthesised from TP, and fatty acids, which are synthesised from GP.
  • Amino acids - some are made from GP.
55
Q

How many times does the Calvin cycle need to turn to make one hexose sugar?

A

6 times.

56
Q

Why does the calvin cycle need to turn 6 times to make one hexose sugar?

How much ATP and reduced NADP does this need?

A
  • 3 turns of the cycle produces 6 molecules of TP, as 2 molecules of TP are made for every CO2 molecule used.
  • 5/6 of these TP molecules are used to regenerate RuBP.
  • So, for 3 turns of the cycleonly 1 TP produced is used for a hexose sugar.

​

  • Hexose has 6 carbons, so two TP molecules are needed to form one.
  • Therefore, cycle has to turn 6 times to produce 2 x TP.
  • 18 ATP and 12 reduced NADP from light-dependent reaction are needed for this.*

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