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A-level biology component 1 (+immunology) > Photosyntheis > Flashcards

Photosyntheis Flashcards

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1
Q

What is photosynthesis?

A

a process that synthesises large organic molecules form simple inorganic molecules using energy from sunlight

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2
Q

Where are photosynthates produced?

A

at the source (the leaves)

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3
Q

What is the main photosynthetic tissue in a leaf?

A

palisade mesophyll

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4
Q

What are stomata essential for?

A

gas exchange in a leaf, without this photosynthesis would not occur

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5
Q

In the lab, how can the density of stomata be studied?

A
  1. Apply clear nail polish to the lower epidermis of a leaf between the veins and allow it to dry.
  2. Using forceps, peel the nail polish from the leaf to produce a replica of the lower epidermis.
  3. Place the replica on a microscope slide and count the number of stomata using the microscope.
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6
Q

What are four adaptations of the leaf for photosynthesis?

A

•large SA
•Thin so light penetrates photosynthetic tissues
•densely packed palisade layer, palisade cells contains chloroplasts, air spaces to allow carbon dioxide to diffuse to photosynthesising cells
•Air spaces between spongy mesophyll to allow CO2 to diffuse photosynthetic cells (maintains O2 conc grad)

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7
Q

Why is it important that biochemical reactions in cells often involve cyclic metabolic pathways which occur in compartments (such as chloroplasts) inside cells?

A

•Reactions occurring in small volume/isolation of enzymes/reactants.
•Keeping products separate from cytoplasm by use of membranes to isolate reactions within organelles.
•Can use mitochondria close to areas needing ATP/movement of organelles within cytoplasm.

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8
Q

What does the LDS make that the LIS uses?

A

ATP and NADPH

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9
Q

Where does the LDS take place?

A

Thylakoid membrane and thylakoid cavity of chloroplast

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10
Q

What is the function of the LDS?

A

Involves the conversion of light energy into chemical energy (ATP and NADPH)

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11
Q

What is the location of the LID?

A

Stroma of chloroplast

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12
Q

What is the function of the LIS?

A

Uses the products of the light dependent reaction to produce organic molecules such as glucose

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13
Q

where are photosynthetic pigments located?

A

within the thylakoid membranes of the chloroplasts

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14
Q

What is the role of photosynthetic pigments?

A

To capture energy from the sun and convert it to chemical energy

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15
Q

What are the two main types of photosynthetic pigment in flowering plants?

A

Primary pigment
Accessory Pigments

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16
Q

What is the primary pigment?

A

Chlorophyll a (absorbs blue and red wavelengths of light)

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17
Q

What are the accessory pigments?

A

catenoids (xanthophyll and carotene)- absorb blue/violet light

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18
Q

why are accessory pigments important?

A

as they absorb wavelengths of light not absorbed by the primary pigments- this ensures a wider range of wavelengths are absorbed, increasing the efficiency of photosynthesis

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19
Q

what macronutrient is needed to produce chlorophyll a?

A

magnesium- one electron is energised from each mg2+ to a higher energy level (when absorbed), the fatty acid tail holds chlorophyll molecule in the thylakoid membrane

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20
Q

What can chromatography be used to separate?

A

photosynthetic pigments

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21
Q

How does chromatography work?

A
  1. Tear up leaves and grind with aetone to form a dark green pigment solution. 2. Use a capilary tube to spot the pigment on to chromatography paper
  2. Place the chromatography paper into a solvent (such as acetone/petroleum)
  3. Remove the chromatography paper once the solvent has travelled to the top of the strip. Observe the different distances the pigments have travelled.
  4. Calculate the Rf value for each pigment (distance travelled by the pigment divided by the distance travelled by the solvent).
  5. Identify each pigment by comparing the Rf values to known values (but must use same solvent for the known and unknown pigment)
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22
Q

Why do we add acetone when grinding the leaves (chromatography)?

A

Acetone (organic solvent) dissolves the phospholipid membrane to extract the pigments from the thylakoid membranes in the chloroplasts

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23
Q

Why do we need a solvent (chromatography)?

A

The running solvent dissolves the pigments (solutes) and carries the pigment up the chromatography filter paper

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24
Q

why do the pigments travel different distances?

A

The more soluble a substance (pigment) is in that solvent, the further it moves up the chromatography paper

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25
Q

Why must the pencil line be drawn above the the solvent?

A

other wise dissolves in the solvent (off the paper)

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26
Q

How is the Rf value calculated?

A

distance travelled by pigment (from the origin)/distance travelled by solvent

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27
Q

What is the absorption spectrum?

A

Graph that shows the amount of light absorbed by chlorophyll a and the accessory pigments at each wavelength

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28
Q

Why is so little light absorbed between 530nm and 640nm?

A

530-640 of the range of light wavelengths at which green light is reflected by chlorophyll pigments

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29
Q

what wavelengths does chlorophyll a absorb?

A

425nm + 675nm (red and blue)

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30
Q

What are the wavelengths absorbed by chlorophyll b?

A

450 and 640nm (blue and orange)

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31
Q

What wavelengths are absorbed my carotenoids?

A

475nm (blue)

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32
Q

What is the action spectrum?

A

A graph that shows the rate of photosynthesis at different wavelengths of light

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33
Q

What experiment could be conducted to measure the rate of photosynthesis?

A

count the number of bubbles (oxygenated) produced by pond weed (an underwater plant) over a certain period of time

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34
Q

What is the relationship between the absorption spectrum and the action spectrum?

A

There is a close correlation between greater light absorption and after faster rate of photosynthesis suggesting that the two the two pigments are responsible for absorbing the wavelengths of light used in photosynthesis to make glucose

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35
Q

Where are photosystems located?

A

in the thylakoid membranes of chloroplasts

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36
Q

what is the role of photosystems?

A

-absorb photons of light energy.
-act as transducers by transferring this light energy to high energy electrons.
-this energy can then be used to fuel proton pumps and the synthesis of ATP.

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37
Q

What is the photo system structure?

A

-accessory pigments are grouped into clusters with associated proteins, forming an antenna complex.
-These pigments absorb photons of light energy and funnel this energy down the antenna complex to the reaction centre below.
-Chlorophyll a molecules are found in the reaction centre below the antenna complex.
-When photons of light energy reach chlorophyll a in the reaction centre, electrons are excited to become high energy electrons

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38
Q

What are the two photosystems involved in the LDR?

A

-PHOTOSYSTEM I (PSI) or P700 - best absorbs light at 700nm wavelength
-PHOTOSYSTEM II (PSII) or P680 - best absorbs light at 680nm wavelength

39
Q

What does the LDR include?

A

•Requires light energy
•Takes place in the thylakoid membranes and thylakoid cavity.
•ATP is synthesised from ADP and Pi.
•This is photophosphorylation as light energy is involved.
•The splitting of water using light is involved and is known as photolysis
•NADP is reduced to form NADPH/H+ (reduced NADP).
• Oxygen gas is released as a by product.

40
Q

What are the two LDR’s in higher plants?

A

•Non-Cyclic Photophosphorylation
•Cyclic Photophosphorylation

41
Q

Where does non-cyclic photophosphorylation start and what happens?

A

PHOTOSYSTEM II-
-Photons of light are absorbed by PSIl and passed to chlorophyll a in the reaction centre.
-This excites two electrons in chlorophyll a to a higher energy level, causing them to be emitted, passed to electron acceptors and then transferred along a chain of carriers (which includes a proton pump) to photosystem I.
-As the electrons move along the chain, they release energy, which is used to pump hydrogen ions (protons) from the stroma across the thylakoid membrane into the thylakoid space.
-This creates an electrochemical gradient due to the high H+ concentration in the thylakoid space and low H+ concentration in the stroma.
-H+ flow down this proton gradient through a proton channel connected to ATP synthase (in a stalked particle providing energy for the formation of ATP from ADP and Pi.

42
Q

What happens at photosystems I in non-cyclic photophosphorylation?

A

-Photons of light are absorbed by PSI, causing two electrons in chlorophyll a to be raised to a higher energy level, emitted, and passed to another electron acceptor.
-The electron acceptor transfers the electrons to protons outside the thylakoid membrane into the stroma, which then reduce NADP to NADPH.
-The use of H+ to reduce NADP lowers their concentration in the stroma, helping to maintain the electrochemical gradient between the thylakoid space and the stroma.
-The emitted electrons do not return to their original source, so this process is known as non-cyclic photophosphorylation.

43
Q

What is the effect of the high concentration of H+ ions in the thylakoid space?

A

Becomes acidic- low pH

44
Q

What is photolysis?

A

the splitting of water using light It occurs in the thylakoid cavity

45
Q

What happens during photolysis?

A

-Water splits into oxygen hydrogen ions and electrons.
-The electrons replace those lost by photosystem II, making the chlorophyll molecule stable.
-The protons help maintain the electrochemical gradient between the thylakoid cavity and the stroma .

46
Q

Where does cyclic photophosphorylation occur?

A

in bacteria and primitive plants

47
Q

Why does higher plants use the pathway cyclic photophosphorylation?

A

to provide extra ATP, especially when CO2 is in short supply

48
Q

What photosystem is involved in cyclic photophosphorylation?

A

Only photosystem I-
-light energy is absorbed at PSI and channelled to chlorophyll a
-Electrons in the chlorophyll a become excited, energised and released. They are accepted by an electron acceptor and eventually passed along the same transfer chain as that used by the electrons from PSIl.
-Protons are pumped into the thylakoid space and ATP is produced from ADP + Pi.
-The same chemiosmotic theory as that used to describe the Z scheme is believed to be involved in the production of ATP.
-The electrons excited and released from PSI return to PSI.

49
Q

What type of photophosphorylation involves photolysis?

A

non-cyclic

50
Q

Where do the electrons and up in cyclic photophosphorylation?

A

Return to PSI

51
Q

Where do the electrons and up in non cyclic photophosphorylation?

A

NADPH

52
Q

What is the product in cyclic photophosphorylation?

A

ATP

53
Q

What are the products in non cyclic photophosphorylation?

A
54
Q

In non-cyclic photophosphorylation where does PSII obtain replacement electrons from?

A

photolysis of water

55
Q

non-cyclic photophosphorylation where does PSI obtain replacement electrons from?

A

PSII (low energy electrons that have travelled down the ETC)

56
Q

In cyclic photophosphorylation what happens to the electron excited and released from PSI?

A

They pass down an electron transport chain and then return to PSI

57
Q

In non-cyclic photophosphorylation, what happens to the O2 produced from photolysis?

A

Oxygen is released as a waste gas or used during aerobic respiration

58
Q

When might plants shift from non cyclic photophosphorylation to cyclic photophosphorylation?

A

A mechanism of generating some extra ATP in the chloroplast because it is needed in the calvin cycle when the chloroplast is low on ATP

59
Q

What does the LIS (calvin cycle) not require?

A

light

60
Q

What does the LIS/Calvin Cycle do?

A

It uses the products of the light dependent stage of photosynthesis (ATP and reduced NADP) to fix carbon dioxide from the atmosphere to organic molecules.

61
Q

Where does the LIS take place and who was it discovered by?

A

-it takes place in the the stroma of the chloroplast and was discovered by melvin calvin

62
Q

What is the process of the calvin cycle?

A

-CO2 from atmosphere is fixed with RuBP (5C).
-Enzyme RuBisCo catalyses this reaction
-Results in the formation of an unstable 6C compound which splits into two molecules of Glycerate-3-phosphate (3C).
-Glycerate-3-phosphate is then reduced using reduced NADP produced during the light dependent stage.
-ATP from the light dependent stage is also required. ATP is hydrolysed and the phosphate transferred to Glycerate-3-phosphate, resulting in the formation of two molecules of triose phosphate (3C).
-One carbon atom of the 6 available is removed from the Calvin cycle and can be used to produce organic molecules such as glucose.
-Five carbon atoms remain in the Calvin cycle and are used to regenerate RuBP so the cycle can begin again

63
Q

How many times does the calvin cycle go around to make 1 glucose?

A

6x

64
Q

What happens to 1 out of 6 carbon atoms from the 2 triose phosphates in the calvin cycle? 1

A

-They are not recycled
-They leave the Calvin cycle and form hexose phosphates, which ultimately yield sucrose, starch and cellulose.

65
Q

What can sugars produced during carbon metabolism can also act as? 2

A

carbon skeletons and can be used for other metabolic reactions like the production of amino acids and lipids.

66
Q

What are the inorganic nutrients in plant metabolism?

A

Nitrates- Taken up by roots and transported in xylem & amino acids in the phloem
Magnesium- Absorbed as Mg2+ and transported in the xylem.
Phosphates- Absorbed as PO4- by the roots and transported in

67
Q

What is the function of nitrates in plant metabolism?

A

Synthesis of proteins
Synthesis of nucleic acids/DNA/RNA/Nucleotides

68
Q

What are the symptoms of nitrate deficiency in plants?

A

Reduced growth of organs
Chlorosis- yellow leaves due to inadequate chlorophyll production so plant no longer able to absorbs light energy

69
Q

What is the function of Mg2+ in plant metabolism?

A

-for chlorophyll production
-and activation of ATPase

70
Q

What is a symptom of mg2+ deficiency in plants?

A

Pronounced chlorosis between veins of older leaves as existing Mg2+ is moved and transported to new leaves.

71
Q

What is the function of phosphates in plant metabolism?

A

Form phospholipids
Form nucleotides (ATP/DNA/RNA) along with nitrogen.

72
Q

What is a symptom of phosphate deficiency in plants?

A

Stunting of plant growth.

73
Q

What are the limiting factors that affect the rate of photosynthesis?

A

-Temperature
-CO2 conc
-Light intensity

74
Q

What does temperature do?

A

Influences enzyme activity

75
Q

What is the effect of enzyme denaturation on the rate of photosynthesis?

A

Tertiary structure of the active site changes shape (e.g. Rubisco), therefore is no longer complementary to its substrate, no ESC form and the rate of reaction slows down (CO2 fixation).

76
Q

Why does an increase in temp speed up the rate of the LIS more than it speeds up the rate of the LDR?

A

The light dependent stage is much less dependent on enzyme activity than the light independent stage.

77
Q

How does temp affect the overall rate of photosynthesis?

A

-An increase in temp speeds up the LIS more than it speeds up the LDS.
-The supply of products from the LDS (ATP and reduced NADP) will not be able to keep up with the demand from the LIS.
-The overall rate of photosynthesis will become limited by the supply of reduced NADP and ATP.

78
Q

During photosynthesis, what happens to CO2?

A

it is fixed to form carbohydrates

79
Q

Why does the conc of CO2 often limit the rate of photosynthesis?

A

it makes up only 0.035% of atmospheric air

80
Q

What is a physical change that could occur in a leaf that might result in the rate of photosynthesis decreasing at very high CO2 concs?

A

•CO2 diffuses into leaves and dissolves in water
•The enzyme carbonic anhydrase catalyses the reaction
•Carbonic acid is formed which dissociates to form H+ ions and HCO3- ions
•The accumulation of H+ causes cells to become more acidic
•The acidity denatures enzymes in mesophyll cells in the leaves

81
Q

What is the role of light in photosynthesis?

A

-Light = essential for the excitation of electrons and for photolysis in the light dependent reaction.
-As light intensity increases so too does the rate of cyclic and non-cyclic photophosphorylation

82
Q

What affect does light intensity increasing the rate of cyclic and non cyclic photophosphorylation on the yield of photosynthates?

A

-As the light dependent reaction speeds up ATP and reduced NADP are produced at a faster rate.
-They enter the calvin cycle and organic molecules are produced at a faster rate.

83
Q

What are the physical changes that could occur in a leaf that might result in the plateau at high light intensity?

A

At high light intensity temperatures are also high so stomata close to reduce transpiration/wilting

84
Q

What is the compensation point?

A

When the rate of photosynthesis is equal to the rate of respiration

85
Q

What is RuBisCo?

A

Enzyme that fixes carbon dioxide onto ribulose bisphosphate

86
Q

What is Photo-phosphorylation?

A

Phosphorylation of ADP to ATP using light energy.
Can be cyclic or non-cyclic

87
Q

What is the antenna complex?

A

Clusters of associated proteins which absorb photons of light energy and funnel this energy downwards

88
Q

What is the reaction centre?

A

Where chlorophyll a is found, below the antenna complex

89
Q

What are photosystems?

A

Transducers which transfer light energy to high energy electrons.

90
Q

What are pigments?

A

Protein that absorbs light energy from the sun and convert it into chemical energy.

91
Q

What is the LDR?

A

Stage involving the conversion of light energy into chemical energy (ATP and NADPH)

92
Q

What is the LIDR?

A

Stage using the products of the light dependent reaction to produce organic molecules such as glucose.

93
Q

What is the palisade mesophyll?

A

The main photosynthetic tissue in a leaf

A-level biology component 1 (+immunology) (7 decks)

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