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BIOLOGY A2 > Topic 13 - Photosynthesis > Flashcards

Topic 13 - Photosynthesis Flashcards

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1
Q

Symbol equation of photosynthesis

A

6CO2 + 6H2O —————–> C6H12O6 + 6O2

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2
Q

Where does the oxygen that’s produced from photosynthesis go?

A

It’s lost from the cells through the stomata or used in respiration in the plant

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3
Q

What is happening in photosynthesis?

A
  1. Carbon dioxide is reduced to make a carbohydrate
  2. Hydrogen in water comes from water
  3. Light energy from sunlight which is absorbed by chlorophyll drives these reactions,
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4
Q

What are the 2 stages in photosynthesis?

A

The light dependent and light independent stages

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5
Q

Give a quick breakdown of what happens in the light dependent stage

A
  1. Pigments in the chlorophyll absorb energy from light
  2. The same energy is used to split water into H and O (Photolysis)
  3. The energy in hydrogen is used to make ATP (Phosphorylation)
  4. Hydrogen is eventually picked up by coenzyme NADP to make reduced NADP
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6
Q

What are the inputs in the light dependent stage? (3 things)

A
  1. Light
  2. Water
  3. Oxidised NADP
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7
Q

What are the outputs in the light dependent stage? (3 things)

A
  1. ATP
  2. Oxygen
  3. Reduced NADP
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8
Q

Give a quick breakdown of what happens in the light independent stage

A

The energy in the ATP and the hydrogens in the NADP are used to reduce CO2 and produce carbohydrates in the Calvin Cycle

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9
Q

Where do the light dependent and light independent stages occur?

A

In the chloroplast

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10
Q

Name all the structures in a chloroplast (9 things)

A
  1. Starch grain
  2. Granum
  3. Lamella
  4. Thylakoid
  5. Stroma
  6. Lipid droplet
  7. Outer membrane
  8. Inner membrane
  9. Chloroplast envelope = outer + inner membrane
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11
Q

Where are chloroplasts mainly found in plant tissue?

A

Palisade and spongy mesophyll

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12
Q

What does the stroma contain? (3 things)

A
  1. Many enzymes and other substances needed for the light independent stage
  2. Small 70S ribosomes and small circles of DNA to synthesise proteins
  3. Starch grains to store some of the carbohydrate made in an insoluble form
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13
Q

What are lamellae?

A

Membranes inside the chloroplast that are arranged so they produce fluid-filled sacs

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14
Q

What are the membranes forming sacs as part of the lamellae called?

A

Thylakoids

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15
Q

What is grana?

A

A group of thylakoids that are stacked up like coins

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16
Q

What do membranes of the lamellae and thylakoids hold and what is the purpose of this?

A

They hold carrier molecules that act as the ETC like cristae in mitochondria

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17
Q

What is embedded into the lamellae and thylakoid membranes?

A

Photosynthetic pigments

Coloured substances that absorb energy from certain wavelengths or colours of light

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18
Q

What are the most abundant pigments in chlorophyll?

A

Chlorophyll a and b

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19
Q

What are the 4 main pigments in chlorophyll?

A
  1. Chlorophyll a
  2. Chlorophyll b
  3. Carotene
  4. Xanthophyll
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20
Q

Explain the reflecting and absorption of light by the pigments

A

Pigments absorb some wavelengths of light and reflect others. The wavelengths that aren’t absorbed are reflected into our eyes

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21
Q

What colour does chlorophyll a and b reflect and absorb?

A

Chlorophyll a and b absorb all colours except green, which they reflect

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22
Q

Does chlorophyll a or b absorb a slightly longer wavelength?

A

Chlorophyll absorbs a slightly longer wavelength than chlorophyll b

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23
Q

What colour light does carotene absorb?

A

Blue light

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24
Q

How are pigments in the thylakoid membrane arranged?

A

They are arranged in clusters called photosystems

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25
Q

What are photosystems made of?

A

Each photosystem is made of a large number of pigment molecules and some proteins

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26
Q

What do photosystems do after absorbing the energy from light?

A

The pigments absorb energy from light then channel it to the reaction centre

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27
Q

How many photosystems are there and what are they called?

A

2: Photosystem I and Photosystem II

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28
Q

What is the main wavelength of light absorbed in photosystem I?

A

700nm

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29
Q

What is the main wavelength of light absorbed in photosystem II?

A

680nm

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30
Q

What do the reaction centres of both photosystems have?

A

Both have 2 molecules of chlorophyll a. The other pigments help channel the energy harvested from light to chlorophyll a molecules.

31
Q

What happens after the other pigments help channel the energy harvested from light to the chlorophyll a molecules?

A

It increases the energy level of electrons in the chlorophyll a molecules and the high energy electrons drive the steps in the light dependent reactions

32
Q

What does an absorption spectra show you?

A

The absorbance at different wavelengths of light

33
Q

What does an action spectra show you?

A

Shows the rate of photosynthesis at different wavelengths of light

34
Q

What is chromatography?

A

A technique that can separate substances in a mixture according to their solubility in a solvent

35
Q

Explain how you would carry out a chromatography test for a leaf

A
  1. Pigments are extracted from the leaf by crushing the leaf in a suitable solvent, e.g a mixture of propanone and petroleum ether
  2. The extract is then filtered, to obtain a dark green solution of the pigments
  3. Use a ruler and pencil to draw a line about 2cm from the base of a rectangular piece of chromatography paper
  4. Use a capillary tube or pipette with a very narrow point to place a small drop of the green filtrate onto this line
  5. Repeat over and over again, trying to produce an intensely freen, very small spot of the filtrate
  6. Can put many spots on ant position on the line
  7. Dry the spots using a hairdryer
  8. Place the paper in a small amount of solvent in a glass vessel, like a gas jar or test tube, with the pencil line above the solvent. This is the SOLVENT FRONT
36
Q

How do you calculate the Rf value?

A

Distance travelled by pigment spot / distance travelled by solvent

36
Q

How do you calculate the Rf value?

A

Distance travelled by pigment spot / distance travelled by solvent

37
Q

What is the typical Rf values of carotenoids, chlorophyll a, and b. Why?

A

Carotenoids travel almost as far as the solvent front so their Rf value is close to 1. Next highest is chlorophyll a and then b.

38
Q

What are the 3 substages in the light dependent stage?

A
  1. Cyclic phosphorylation
  2. Non-cyclic phosphorylation
  3. Photolysis
39
Q

Which photosystem is involved in cyclic phosphorylation?

A

Photosystem i

40
Q

What are the products of cyclic phosphorylation?

A

ATP

41
Q

Describe the stages of cyclic phosphorylation

A
  1. Light energy is absorbed by photosystem I and passed to the reaction centre
  2. The energy excites the electron in the chlorophyll a molecule to a higher level
  3. The energy of the electron is so high that it’s emitted from the chlorophyll molecule (photo-activation)
  4. The excited electron is captured by the electron acceptor in the thylakoid membrane
  5. The electron is passed along a chain of electron carriers and the carriers are alternatively reduced and oxidised
  6. The electrons lose energy as they pass along the chain
  7. The energy is used to actively move protons from the stroma, across the thylakoid membrane, into the thylakoid space
  8. This sets up a proton gradient and the protons move down this gradient by facilitated diffusion through ATP synthase molecules
42
Q

How is ATP synthesised?

A

By adding inorganic phosphate to ADP, a process known as chemiosmosis

43
Q

Which photosystem is involved in non-cyclic phosphorylation?

A

Both

44
Q

Describe the stages that take place in non cyclic phosphorylation

A
  1. Energy from light is absorbed by both photosystems
  2. The excited electrons are emitted from their reaction centres
  3. In both cases, the electrons that are absorbed by electron acceptors pass along chains of electron carriers in the thylakoid membranes
  4. Energy from the electrons emitted from photosystem II is used to form ATP
  5. Energy from the electrons emitted from photosystem I are passed to coenzyme NADP which produces reduced NADP
45
Q

Electrons lost from photosystems need to be replaced. How is this ensured?

A

Photosystem I receives electrons emitted from photosystem II

Photosystem II receives electrons from photolysis

46
Q

Where does photolysis take place?

A

Photosystem II as it has a water splitting enzyme

47
Q

What is the water splitting enzyme called?

A

Oxygen evolving complex or water splitting complex

48
Q

What is the symbol equation for photolysis?

A

H2O —————> 2H+ + 2e- + 1/2O2

where oxygen is a waste product and diffuses out of the chloroplast and lost from cell or is used in aerobic respiration

49
Q

How is reduced NADP produced with the electrons emitted by photosystem I?

Give the symbol equation

A

H+ combines with an electron from photosystem I and coenzyme NADP to give reduced NADP

2H+2e- + NADP —————–> Reduced NADP

50
Q

What products that are produced in the light dependent stage are used in the light independent stage?

A

ATP and Reduced NADP

51
Q

What essentially happens in the light independent stage using ATP and reduced NADP?

A

ATP and reduced NADP are used to convert carbon dioxide to carbohydrate

52
Q

Where does the light independent stage take place?

A

The stroma

53
Q

What is another name for the light independent stage?

A

The Calvin Cycle

54
Q

What does the light independent stage not necessarily need unlike the light dependent stage?

A

Doesn’t need light but also can’t go on for very long without light

55
Q

Describe what happens in the Calvin Cycle

A
  1. Reaction of CO2 with 5C compound ribulose bisphosphate (RuBP)
  2. This is catalysed by the enzyme rubiso
  3. The reaction produces X2 3C compound GP (not a carb)
  4. CO2 is now ‘fixed’ - removed from the environment and is part of the cell
  5. Energy from ATP and H from reduced NADP that was made in the light dependent stage is used to reduce GP to phosphorylate 3C sugar TP (Reduces GP to TP)
  6. Most (5/6) of the TP is used to regenerate RuBP and ATP is needed for this
  7. The rest of the TP is used to produce other molecules needed by the plant
  8. GP can be converted to glycerol and fatty acids to produce lipids for cellular membranes
55
Q

Describe what happens in the Calvin Cycle

A
  1. Reaction of CO2 with 5C compound ribulose bisphosphate (RuBP)
  2. This is catalysed by the enzyme rubiso
  3. The reaction produces X2 3C compound GP (not a carb)
  4. CO2 is now ‘fixed’ - removed from the environment and is part of the cell
  5. Energy from ATP and H from reduced NADP that was made in the light dependent stage is used to reduce GP to phosphorylate 3C sugar TP (Reduces GP to TP)
  6. Most (5/6) of the TP is used to regenerate RuBP and ATP is needed for this
  7. The rest of the TP is used to produce other molecules needed by the plant
  8. GP can be converted to glycerol and fatty acids to produce lipids for cellular membranes
56
Q

Some TP condense to become hexose phosphates which can be used to produce ____________ (3 things)

A
  1. STARCH for storage
  2. SUCROSE for translocation
  3. CELLULOSE for cell walls
57
Q

How do plants produce all 20 amino acids needed for protein synthesis?

A

Using ammonium ions absorbed from the soil and carbohydrates produced in light independent reactions

58
Q

What are the factors needed for photosynthesis? (5 things)

What does a shortage of these factors result in?

A
  1. Presence of photosynthetic pigments
  2. Supply of CO2
  3. Supply of H2O
  4. Light energy
  5. Suitable temperature

A shortage reduces the rate of photosynthesis below the maximum rate

59
Q

What are the main external factors affecting the rate of photosynthesis? (4 things)

A
  1. Light intensity
  2. Light wavelength
  3. Temperature
  4. CO2 concentration
60
Q

Why isn’t water one of the main external factors affecting the rate of photosynthesis?

A

A shortage of water usually affects other processes in plants before photosynthesis

61
Q

What does a higher light intensity result in?

A

Higher light intensity means more energy is supplied so there’s a faster light dependent stage which means more ATP and reduced NADP will be supplied to the Calvin cycle resulting in a faster Calvin Cycle

62
Q

What does temperature have a significant effect on in plants?

A

Metabolic reactions

63
Q

What does temperature not have a significant effect on and why?

A

No significant effect on light dependent reactions as it is driven by light energy rather than the kinetic energy of the reacting molecules

64
Q

Why is the Calvin cycle affected by temperature?

A

Because the Calvin Cycle has enzyme controlled reactions

65
Q

Draw the graph of concentration against time for RuBP, GP, and TP in carbon dioxide percentage

A

Check 13P 13.5 Notes

66
Q

Draw the graph of concentration against time for RuBP, GP, and TP in levels of light intensity

A

Check 13P 13.5 Notes

67
Q

What redox indicator dyes can you use to test for photosynthesis in plants?

A

DCPIP and Methylene Blue

68
Q

How do the redox indicators work?

A

The indicator takes up the electrons that are usually picked up by electron acceptors and passed along the ETC

69
Q

How do the redox indicators work?

A

The indicator takes up the electrons that are usually picked up by electron acceptors and passed along the ETC

70
Q

If photosynthesis is taking place how does the redox indicator show this?

A

Turns from blue to colourless

71
Q

What are the steps for using a redox indicator to test for photosynthesis?

A
  1. Crush some leaves in a liquid called an isolation medium to produce a concentrated leaf extract containing a suspension of chloroplasts
  2. Medium must have around same water potential as lead cells and contain a buffer to keep the pH constant and should be ice cold to avoid damage to chloroplasts
  3. Add redox indicator

BIOLOGY A2 (8 decks)

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