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A-level Biology Longridge Towers School > Chapter 11 Photosynthesis > Flashcards

Chapter 11 Photosynthesis Flashcards

1
Q

Where does most photosynthesis take place in a plant? (Organ and organelle)

A

In the chloroplasts (organelle) of the leaf (plant organ).

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2
Q

Give 9 adaptations of leaves for photosynthesis.

A

1 - Large surface area to absorb as much light as possible.
2 - Leaves are arranged to avoid overlapping and shadowing each other.
3 - Thin as light absorbed in the first few micrometres, also reduces diffusion distance.
4 - Transparent cuticle and epidermis to let light through.
5 - Long narrow upper (palisade) mesophyll packed with chloroplasts to absorb sunlight.
6 - Many stomata to allow gas exchange, all mesophyll cells are close to a stomata
7 - Stomata open and close in response to light intensity
8 - Many air spaces in lower (spongy) mesophyll for rapid diffusion of gases
9 - Network of xylem (water to) and phloem (sugars away) from leaf.

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3
Q

What is the basic word equation for photosynthesis?

A

Carbon dioxide and Water —> Glucose and Oxygen

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4
Q

What is the overall symbol equation for photosynthesis?

A

6CO2 + 6H2O —> C6H12O6 + 6O2

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5
Q

Photosynthesis at A-Level is more complex than GCSE. What stages is it split into?

A

1 - Capturing light energy -photoionisation
2 - The light dependent reaction - photolysis
3 - The light independent reaction - Calvin cycle

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6
Q

Give an overview of the light dependent reaction

A

Light is absorbed by chlorophyll, which in turn releases a pair of electrons at high energy.
Light energy is also used to break water. Through a series of reactions ATP, reduced NADP (NADPH) and oxygen are made.

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7
Q

Give a brief overview of the light independent reaction

A

The reduced NADP and ATP from the LDR are used to produce sugars and other organic molecules.

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8
Q

How is a chloroplast adapted for photosynthesis

A

1 - The thylakoid membranes have a large surface area.
2 - Proteins in the grana hold the chlorophyll in a position to absorb maximum light.
3 - The stroma contains DNA and proteins needed for the light independent reactions.

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9
Q

What are the components of a chloroplast?

A

Double membrane. Flattened membrane sacs called thylakoids, stacked to make grana, starch grains and lipid droplets. Fluid called stroma.

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10
Q

What is a stack of thylakoids called?

A

Granum

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11
Q

What is the fluid in chloroplasts called?

A

Stroma

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12
Q

What is held by the membrane of the grana?

A

Pigments, enzymes and electron carriers.

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13
Q

Why is it important that there are a lot of membranes in the chloroplast?

A

They provide a large surface area for pigment molecules to be held so that they can absorb light for the light dependent reaction.

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14
Q

Where do the light dependent reactions take place?

A

Thylakoids

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15
Q

Where do the light independent reactions take place?

A

Stroma

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16
Q

What is oxidation?

A

Oxidation is the loss of electrons. It also refers to the gain of oxygen or the loss of hydrogen.

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17
Q

What is reduction?

A

Reduction is the gain of electrons. It also refers to the loss of oxygen or gain of hydrogen.

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18
Q

How does energy change during oxidation?

A

Energy is given out

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19
Q

How does energy change during reduction?

A

Energy is take in

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20
Q

What is the first step of the light dependent reaction?

A

Light is absorbed by chlorophyll, this excites a pair of electrons to leave the molecule. The chlorophyll is now ionised. This is called photoionisation.

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21
Q

What is photoionisation?

A

Photoionisation is when light causes a pair of electrons to become excited and leave chlorophyll, ionising it. Electrons are taken in by an electron carrier.

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22
Q

What happens to the chlorophyll molecule and the electron carrier during photoionisation?

A

The chlorophyll is oxidised (loses energy) the electron carrier is reduced (gains energy).

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23
Q

What happens to the pair of electrons after photoionisation?

A

They move through a series of electron carriers, gradually losing energy. This energy is used to transport protons (H+ ions) and to generate ATP.

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24
Q

Where are the electron carriers used in the light dependent reaction?

A

In the thylakoid membrane, they are known as the electron transport chain.

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25
Q

What happens to the pair of electrons at the end of the light dependent reaction?

A

They are used alongside a pair of protons (H+ ions) to reduce NADP.

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26
Q

What 4 substances are required for the light dependent reaction?

A

NADP, ADP, Pi and water

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27
Q

What is the photolysis of water?

A

Light splits water creating H+ ions, electrons and oxygen. These electrons replenish those lost from chlorophyll during photoionisation..

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28
Q

What is the equation for photolysis?

A

H20 -> 2H+ + 2e- + 1/2 O2

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29
Q

What is chemiosmosis?

A

Protons are pumped into the thylakoid space; they can only cross back (following their concentration gradient) through an ATP synthase channel protein. As the protons pass through, this catalyses the formation of ATP.

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30
Q

How are protons pumped into the thylakoid space?

A

The excited pair of electrons transfers energy to a proton pump which moves the protons (H+ions) into the thylakoid space.

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31
Q

Why do we want a greater concentration of protons (H+ ions) in the thylakoid space?

A

The concentration gradient means they diffuse out through a channel protein. This is called ATP synthase. This causes the enzyme to catalyse the combination of ADP and inorganic phosphate to ATP.

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32
Q

Where does the energy for chemiosmosis to take place come from?

A

Photolysis and the release of electrons.

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33
Q

How does the light dependent reaction create ATP?

A

A proton concentration gradient is set up. High in the inner space of the thylakoid, low in the stroma. Protons move through the enzyme ATP synthase which binds ADP and Pi to form ATP

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34
Q

What is Pi?

A

Inorganic phosphate molecule. A component of ADP and ATP.

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35
Q

What is an electron carrier, hydrogen carrier or coenzyme molecule?

A

A non-protein molecule which binds loosely to an enzyme to help catalyse reactions.

36
Q

Which electron carrier molecule is used in photosynthesis?

A

NADP

37
Q

What happens to NADP in the light dependent reaction?

A

NADP is converted to reduced NADP by the addition of 2H+ ions and 2 electrons. It carries this to the light independent reaction.

38
Q

Why is NADP important?

A

It is a source of chemical energy for the light independent reaction.

39
Q

Where do the hydrogen ions and electrons for the reductions of NADP come from?

A

Photolysis and photoionisation.

40
Q

Describe the light dependent reaction (detailed)

A

1 - Light hits chlorophyll and excites electrons.
2 - These electrons are lost from chlorophyll. This is called photoionisation.
3 - Electrons are accepted by an electron carrier and move from carrier to carrier in a series of redox-reactions.
4 - Protons are pumped into thylakoid space using energy from the electrons.
5 - Protons move back through the thylakoid membrane through ATP synthase generating ATP.
6 - Electrons and protons reduce NADP to make NADPH.
7 - Photolysis of water occurs to replace lost electrons in the chlorophyll.

41
Q

What happens to reduced NADP in the light independent reaction?

A

NADP alongside ATP from the light dependent reaction reduce GP (glycerate-3-phosphate) to 2 molecules of TP (triose phosphate).

42
Q

What are the 2 products of the light dependent reaction which are needed in the light independent reaction?

A

ATP and reduced NADP (NADPH)

43
Q

At what stage of photosynthesis is ATP produced?

A

The light dependent reaction.

44
Q

Give an overview of the light independent reaction.

A

1 - The reduced NADP and the ATP from the light dependent reaction are used to reduce Glycerate 3-phosphate(GP) into triose phosphate (TP).
2 - This in turn is either continued through the cycle, or converted to glucose.
3 - RuBP (5 carbon) joins with CO2 to make 2 lots of GP (3 carbon).
4 - The GP is reduced into TP (3 carbon). This uses energy from ATP and hydrogen from reduced NADP.
5 - The TP can be used to reform RuBP (uses energy from ATP) (5 out of 6). The TP can also be used to form glucose (carbohydrate). GP can also be used to form amino acids (proteins) and fatty acids. TP can also be used to form glycerol

45
Q

What are the 5 components required for the Light Independent Reaction ?

A

Carbon Dioxide, Ribulose Bisphosphate (RuBP), RuBisCo, Reduced NADP, ATP.

46
Q

Where does the light independent reaction take place?

A

In the stroma.

47
Q

What are the adaptations of the chloroplast for the light independent reaction?

A

1 - The stroma contains enzymes to carry out the light independent reaction.
2 - The stroma is membrane bound in the chloroplast, this ensures the chemical environment is maintained (high concentration of enzymes and substrates).
3 - Stroma surrounds the grana, so products of the light dependent reaction readily diffuse into the stroma.
4 - Chloroplasts contain DNA and ribosomes to quickly produce proteins required for the light independent reaction.

48
Q

What is another name for the light independent reaction?

A

The Calvin Cycle.

49
Q

Where do you find RuBisCo?

A

The stroma.

50
Q

What role does carbon dioxide have in the light independent reaction?

A

Carbon dioxide reacts with Ribulose bisphosphate (RuBP) to generate 2 molecules of glycerate 3-Phosphate (GP).

51
Q

How many carbons in RuBP?

A

5

52
Q

How many carbons in GP?

A

3

53
Q

Which enzyme catalyses the reaction between CO2 and RuBP?

A

Ribulose bisphosphate carboxylase (RuBisCo)

54
Q

What happens to the glycerate 3-phosphate (GP) in the light independent reaction (Calvin Cycle)?

A

Reduced NADP reduces GP to triose phosphate (TP) using energy from ATP.

55
Q

What happens to the ATP and the NADP as GP is converted to TP?

A

Reduced NADP is oxidised, then returns to the light dependent reaction to be reduced again by accepting more protons. ATP is converted to ADP and Pi.

56
Q

What happens to triose phosphate (TP) generated in the light independent reaction (Calvin Cycle)?

A

Some is converted to organic substances required by the plant such as glucose, fatty acids, glycerol and amino acids. Most converted to RuBP.

57
Q

What is required to convert triose phosphate (TP) to ribulose bisphosphate (RuBP)?

A

ATP

58
Q

What are the 3 limiting factors of photosynthesis?

A

Light intensity, carbon dioxide concentration and temperature

59
Q

Why does light limit the light independent stage?

A

No ATP or NADPH can be made from the light dependent stage if there is low or no light, therefore GP cannot be converted to TP. RuBP will not be regenerated from TP as ATP needed for this.

60
Q

Why does carbon dioxide limit the light independent stage?

A

RUBP can not be converted into GP without carbon dioxide.

61
Q

What is the name given to the point at which photosynthesis and respiration balance out the production and absorption of oxygen and carbon dioxide?

A

The compensation point.

62
Q

What is in the chloroplasts which absorb light?

A

Pigments

63
Q

Why are there different pigments in the chloroplasts

A

Different pigments absorb different wavelengths of light.

64
Q

What technique can be used to separate out the different pigments in a sample of leaf tissue?

A

Chromatography

65
Q

How does chromatography separate out the different pigments present in a solution?

A

Different pigments have different solubilities. This means they will move at different rates up filter paper. They are drawn up as a solvent moves up the filter paper.

66
Q

How are the pigments released from a leaf to allow chromatography?

A

The leaf must be broken down using a pestle and mortar.

67
Q

How are the pigments separated from the broken up leaf to allow for chromatography?

A

They are dissolved in a solvent (propan-2-ol) and then filtered.

68
Q

How is the chromatography paper prepared to separate out the pigments present in a leaf?

A

The chromatography paper has a line drawn 1cm from the bottom in pencil. It has a cross drawn on the centre. Solution of dissolved pigment is dotted on the cross using a capillary tube.

69
Q

Why is the line drawn on the chromatography paper done in pencil?

A

Pencil graphite is not soluble in propan-2-ol (our solvent). This means that it remains in place and can be used to calculate Rf values.

70
Q

How do we ensure enough pigment is on the chromatography paper?

A

Multiple dots of the pigment solution are placed on the pencil cross. This builds up the concentration of pigment.

71
Q

Why is time given between the dotting of pigments?

A

To ensure the pigment doesn’t spread too far.

72
Q

How is the paper set up to allow the chromatography to take place?

A

The paper is suspended over a beaker, the base submerged in the solvent (propan-2-ol). The pencil line and the pigment above the solvent.

73
Q

What can affect the time taken for the solution to travel up the paper?

A

The temperature and the concentration of the solvent vapour inside the beaker.

74
Q

What is done with the results of the chromatography practical?

A

The distance travelled by the solvent and the pigments is measured. From this the Rf value can be calculated.

75
Q

How is the Rf value calculated?

A

Rf value = distance travelled by compound / distance travelled by solvent.

76
Q

If a 30cm ruler was used to measure the distance travelled, how many decimal points can the Rf value have?

A

Measuring in cm will give answers to 1 decimal point. Therefore all results calculated can also only be accurate to 1 decimal point.

77
Q

Why do some pigments move further than others during chromatography?

A

They are more soluble than others.

78
Q

What is the enzyme dehydrogenase used for in photosynthesis?

A

This is an enzyme which reduces NADP in the light dependent reaction. It allows the movement of electrons down the electron chain.

79
Q

What is DCPIP?

A

DCPIP is a redox indicator. It turns from blue to colourless in the presence of a reducing agent. Blue when oxidised, colourless when reduced.

80
Q

What happens to DCPIP in the presence of actively photosynthesising material?

A

DCPIP turns from blue to colourless as it accepts electrons released from chlorophyll.

81
Q

What does DCPIP take the place of in the LDR?

A

DCPIP accepts electrons in the place of NADP.

82
Q

What effect does ammonium hydroxide have on dehydrogenase?

A

Ammonium hydroxide stops dehydrogenase from working.

83
Q

If dehydrogenase does not work, what happens to the light dependent reaction?

A

The electron chain will not be able to transfer electrons, so NADP or DCPIP will not be reduced.

84
Q

If dehydrogenase does not work, what effect will there be on DCPIP?

A

If dehydrogenase doesn’t work, DCPIP can’t be reduced, and will stay blue.

85
Q

If there is no light shining on the chloroplasts what does this mean for the LDR?

A

If there is no light source, the electrons will not be excited and released, so NADP and DCPIP will not be reduced.

A-level Biology Longridge Towers School (37 decks)

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