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A-Level Biology - OCR A > 5.2.1 Photosynthesis > Flashcards

5.2.1 Photosynthesis Flashcards

1
Q

What is the name of the theory that suggests that chloroplast are derived from single celled organisms?

A

Endosymbiont Theory

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2
Q

What is the endosymbiont theory?

A

That chloroplast used to be unicellular organisms that, at one time, were taken up by a eukaryotic cell, e.g. cyanobacterium, to provide energy. This stayed in the cell and passed on through asexual reproduction.

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3
Q

Why is photosynthesis important?

A

It creates a source of energy for nearly all living organisms.

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4
Q

What is the classification of organisms that don’t use light energy get chemical energy?

A

Chemoautotrophs

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5
Q

What is the classification of organisms that use light energy to produce chemical energy?

A

Photoautotrophs

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6
Q

Where in the food chain are photoautotrophs found?

A

Producers in the first trophic level

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7
Q

What is the equasion for photosynthesis?

A

6CO2 + 6H20 –CHLOROPLAST+PHOTON–> C6H12O6 + 6O2

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8
Q

What is a photon?

A

A particle of light. Each photon contains an amount of quantum energy

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9
Q

What is the main product of photosynthesis?

A

A monosaccharide sugar, which can be converted to disaccharides for transport and then to starch for storage.

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10
Q

What is the role of photosynthesis?

A

Carbon fixation

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11
Q

How does photosynthesis facilitate carbon fixation?

A

Takes carbon dioxide from the atmosphere and converts it to sugar.

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12
Q

Is carbon fixation endothermic or exothermic?

A

Endothermic.
This means that energy is required.

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13
Q

How is carbon fixation benificial?

A

Regulates the concentration of carbon dioxide in the atmosphere and oceans

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14
Q

How does plants rate of respiration change over time?

A

It doesn’t. Respiration rates stay fairly constant

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15
Q

How does a plants rate of photosynthesis change over time?

A

Only photosynthesis during daylight

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16
Q

What is the compensation point?

A

When the rate of photosynthesis and resperation are the same. There is no loss or gain of carbohydrates.

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17
Q

Why is the compensation point important?

A

Light intensity has to be great enough to allow photosynthesis to take place at the same rate as respiration. This allows it to replenish the carbohydrate stores that are used up during respiration.

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18
Q

What is the compensation period?

A

The time it takes for a plant to reach the compensation point.

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19
Q

How does the compensation period change with different plants?

A

Shade plants utilise a lower light intensity so adjust to reach heir compensation point sooner than sun plants which receive a greater light intensity

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20
Q

What is the general structure of a chloroplast?

A

Disk shaped organelles around 2-10um long.

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21
Q

What is the structure of the membranes of the chloroplast?

A

A double membrane. The outer membrane is highly permiable.
The intermembrane space (10-20nm) is between the two membranes.

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22
Q

What fills the Chloroplast?

A

A Fluid-filled matrix called the stroma.

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23
Q

What is found within the stroma?

A

Grana

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24
Q

What is the role of grana?

A

The site of the light-dependent stage of photosynthesis.

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25
Q

What is the grana made up of?

A

Stacks of thilacoids.

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26
Q

What is the structure of thylakoids within the grana?

A

Stacked together. Stackss can be connected to other thilacoids in other granum by intergranular lamelle (intergranal Thilacoids)

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27
Q

How many thilacoids make up a granum?

A

up to 100

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28
Q

How are thilcoids adapted to their role?

A

They have a permiable membrane that are folded into flattened disc like sacks.

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29
Q

How do thilacoids and grana assist with photosynthesis?

A

With lots of thylakoids in grana and lots of grana in chloroplast and lots of chloroplast in cells, it gives a large surface area for:
* The distribution of photo stems that contain photosystems that trap sunlight.
* Electron carriers and ATP synthase enzymes needed to convert light to ATP

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30
Q

How are photosystems held in place?

A

Held in the thilacoid membrane by proteins

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31
Q

How does the position of the Grana help the LIS of photosynthesis?

A

Grana is surrounded by the stroma so products of the LDS can easily pass to the stroma to be used in the LIS.

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32
Q

What is the stroma?

A

A fluid-filled matrix containing the enzymes needed to catalyse the light Independent Stage of photosynthesis.

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33
Q

What is found within the stroma?

A

Enzymes,
Starch Grains,
Oil droplets,
Small ribosomes,
DNA

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34
Q

Why is there DNA found in the stroma?

A

It codes for some of the proteins needed for photosynthesis.
The proteins are assembled in the chloroplast ribosomes.

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35
Q

What are photosystems?

A

Funnel shaped structures that are found within the thylakoid membranes of chloroplast. They contain photosynthetic pigments.

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36
Q

How do photosystem pigments work?

A

Each pigment absorbs light of a particular wavelength and reflects the other wavelengths. The colour we see is the colour of the reflected wavelength.

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37
Q

What is the structure of a photosystem?

A

Funnel shapped with a primary pigment at the base. The walls contain accessory pigments that funnel the light to the primary pigment.

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38
Q

How many types of photosystems are there?

A

2.
photosystem I and photosystem II

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39
Q

What is chlorophyll?

A

A mixture of pigments, all with a similar molecular structure consisting of a porphyrin group (ring shape), in which is a magnesium atom, and a long hydrocarbon chain.

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40
Q

What are the two types of chlorophyll?

A

chlorophyll a and chlorophyll b

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41
Q

What is found in the primary pigment?

A

chlorophyll a

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42
Q

What is found in the acceessory pigments?

A

chlorophyll b and cartenoids

43
Q

What colours does chlorophyll a absorb?

A

red light

44
Q

What colour does chlorophyll appear?

A

blue-green

45
Q

Where is chlorphyll a found?

A

Centre of the photosystem

46
Q

What are the two types of chlorophyll a?

A

P680 and P700

47
Q

Where is P680 fund?

A

Photosystem II

48
Q

What wavelength is absorbed by P680?

A

Peak absorbtion at 680nm

49
Q

Where is P700 found?

A

Photosystem I

50
Q

What wavelength of light does P700 absorb?

A

Peak absorption at 700nm

51
Q

What other light is absorbed by both types of chlorophyll a?

A

Some blue light at wavelengths around 440nm

52
Q

What colour does chlorophyll b appear?

A

Yellow-green

53
Q

What wavelengths of light does chlorophyll b absorb?

A

400-500nm.
Around 640nm

54
Q

What are the other pigments found within the accesssory pigments?

A

Caratanoids.
Xanthophylls.

55
Q

What wavelengths of light are absorbed by caratenoids?

A

Absorb blue light of wavelengths 400-500nm and reflect yellow and orange light.

56
Q

What wavelengths of light do xanthophyll absorb?

A

Absorb blue and green light of wavelengths 375-550nm and reflect yellow light.

57
Q

What is the first stage of photosynthesis?

A

Light Dependent Stage

58
Q

Where does the light dependent stage of photosynthesis take place?

A

In the grana (thylakoids) of the chloroplast.

59
Q

What are the main stages of the LDS of photosynthesis?

A

*Light harvesting at photosystems,
*Photolysis of water,
*Photophosphorylation,
*Forming reduced NADP.

60
Q

What happens in the light harvesting stage?

A

A photon of light is absorbed by the chlorophyll in a photosystem which excites a pair of electrons.

61
Q

What is the photolysis of water?

A

The splitting of water by light producing protons, electrons and oxygen.

62
Q

What is the equation for the photolysis of water?

A

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

63
Q

How are the products of photolysis used?

A

The electrons replace those lost from PSII when they become excited and leave the chlorophyll.
The protons reduce NADP.
Oxygen diffuses out of the chloroplast as a waste product.

64
Q

What happens to oxygen after photolysis?

A

Some of the oxygen is used by the plant for respiration. During periods of high light intensity, photosynthesis happens at a greater rate than respiration so oxygen is in excess. So oxygen diffuses out of the leaves through the stomata and into the atmosphere.

65
Q

Why is water important to plants?

A

*Source of protons for photophosphorylation
*Donates electrons to chlorophyll to replace those lost
*The source of the oxygen bi-product
*Keeps the plant turgid so it can function

66
Q

What is photophosphorylation?

A

The process of generating ATP from ADP and an inorganic phosphate group (Pi) in the presence of light.

67
Q

What are the types of photophosphorylation?

A

Non-Cyclic and Cyclic

68
Q

What is non-cyclic photophosphorylation?

A

Uses PSI and PSII to produce ATP, NADPH and O2

69
Q

What is cyclic photophosphorylation?

A

Using only PSI to produce only ATP.
ATP is produced in smaller amounts than non-cyclic

70
Q

What does photophosphorylation involve?

A

iron-containing proteins imbedded in the thylakoid membrane that accept and donate electrons. This forms part of the electron transfer chain.

71
Q

What are the steps of non-cyclic photophosphorylation?

A

Light absorption in PSII.
ATP Synthesis.
Pass to PSI.

72
Q

What happens during absorption and excitation?

A

A photon of light strikes PSII and the energy is channeled down to the primary pigment. The light energy is used to excite a pair of electrons in the chlorophyll a molecule by giving them energy so they move to a higher energy level. The energized electrons leave the chlorophyll molecule.

The electrons are replaced by electrons produced from the photolysis of water.

73
Q

Where do the electrons go from the chlorophyll molecule?

A

Electrons are captured by an electron carrier/acceptor.

74
Q

What are electron carriers/acceptors?

A

Proteins with an iron at its center that’s found within the thylakoid membrane that picks up a free pair of electrons.

75
Q

After being accepted where do the electrons pass to?

A

The electron transfer chain

76
Q

What is the electron transfer chain?

A

Series of carrier proteins embedded in the thylakoid membrane.

77
Q

What happens in the electron transport chain and how dos this produce ATP?

A

The electrons pass through the proteins of the electron transfer chain in the thylakoid membrane that perform a series of oxidation and reduction reactions, releasing energy in the process.
At the end of the chain there is an ATP synthase molecule that that uses this energy to combine a molecule of ADP and an inorganic Phosphate group (Pi) to produce a molecule of ATP.

78
Q

After ATP is produced, where do the electrons pass to in non-cyclic photophosphorylation?

A

The electrons pass into photosystem I where they are excited again to produce reduced NADP

79
Q

What happens to electrons in PSI?

A

Light energy from photons is transferred to the electrons. This excites the electrons and moves them to an even higher energy level. This causes them to leave the Chlorophyll a molecule.

80
Q

What happens to electrons once they leave PSI?

A

They are picked up by an electron carrier, called ferredoxin, which takes the electrons to NADP found in the stroma.

81
Q

How does NADP form NADPH?

A

The electrons and protons (produced from the photolysis of water) are transferred to NADP which gets reduced to form NADPH/reduced NADP.

82
Q

What Happens to the NADPH produced?

A

It passes onto the light independent stage of photosynthesis.

83
Q

What happens in cyclic photophosphorylation?

A

Only uses photosystem I.
The electrons are continually cycled to produce ATP and do not form NADP.

84
Q

What happens in the absorption of light by Photosystem I during cyclic-photophosphorylation?

A

A photon hits photosystem I and the energy is transferred to a pair of electrons which become excited and leave the chlorophyll molecule.
They are picked up by an electron carrier but are not taken to NADP, they are put into an electron transfer chain.

85
Q

What happens in the electron transfer chain?

A

The electrons are passed between electron carriers, releasing small amounts of energy through oxidation and reduction reactions. The energy is used by ATP synthase molecules to produce a molecule of ATP by combining a ADP molecule with an inorganic phosphate group (Pi).

86
Q

Where do the electrons go after they pass out of the electron transfer chain in cyclic photophosphorylation?

A

They go back into Photosystem I where they get re-excited and repeat the cycle.
No NADPH is produced as the electrons are not added with the protons.

87
Q

What is the Light Independent stage of Photosynthesis?

A

It takes place in the stroma of chloroplast. It utilises the ATP and NADPH produced in the LDS as well as CO2 from the atmosphere to fix carbon to be used in sugars (glucose).

88
Q

What is the Light Independent stage also known as?

A

The Calvin Cycle.

89
Q

What molecules are reused in the Calvin cycle?

A

Triosephosphate - TP.
Glycerate-3-phosphate - GP.
Ribulose bisphosphate - RuBP

90
Q

How is carbon dioxide used in the Calvin Cycle?

A

CO2 from the air is combined with RuBP (a CO2 acceptor). This reaction is catalysed by the enzyme Rubisco.
When the RuBP accepts the carboxyl group (COO-) it becomes carbonylated and forms an unstable 6-carbon molecule.

91
Q

Why is a 6-carbon molecule produced?

A

RuBP contains 5 carbons.
CO2 contains 1 carbon.
When they combine they produce a molecule with 6 carbons.

92
Q

What happens to the 6-carbon molecule?

A

Immediately breaks down to form two molecules of GP with 3 carbons each.
At this stage the carbon is fixed.

93
Q

What happens to the GP?

A

It gets reduced by hydrogen from NADPH (from the LDS) to form two molecules of TP.
Two molecules of ATP are used to provide the energy for the reaction.

94
Q

What happens to the NADP and ADP once it is done in the LIS?

A

It returns to the thylakoid membrane to be used in the LDS

95
Q

What happens to the TP?

A

ATP is used to regenerate it into RuBP. The two molecules of TP (combined 6 carbons) are used to make RuBP (with 5 carbons) this leves 1 carbon that is not returned to the cycle. This is used to make a hexose sugar.

96
Q

How many times must the Cavin Cycle happen for a sugar to be produced?

A

6 times. Therefore 6 carbons can be released to make the hexose sugar.

97
Q

What are the factors affecting the rate of photosynthesis?

A

Light Intensity.
CO2 Concentration.
Temperature.
Water Stress.
Wavelengths of Light.
Chlorophyll Availability.

98
Q

How does Light Intensity affect the rate of photosynthesis?

A
99
Q

How does CO2 Concentration affect the rate of photosynthesis?

A
100
Q

How does temperature affect the rate of photosynthesis?

A
101
Q

How does water stress affect the rate of photosynthesis?

A
102
Q

How does the wavelength of light affect the rate of photosynthesis?

A
103
Q

How does chlorophyll availability affect the rate of photosynthesis?

A

A-Level Biology - OCR A (16 decks)

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