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-5.2.1 Photosynthesis Flashcards

1
Q

What is photosynthesis?

A

Light energy is transformed into chemical energy - trapped in the bonds of complex organic molecules which can be produced in the process.

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2
Q

What type of organisms perform photosynthesis?

A

Autotrophs

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3
Q

What is the word equation for photosynthesis?

A

Carbon dioxide + water -> glucose+ oxygen

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4
Q

What is the symbol equation for photosynthesis?

A

6CO2 + 6H2O -> C6H12O6 + 6O2

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5
Q

Is photosynthesis endo or exothermic?

A

Endothermic

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6
Q

What can glucose be converted into by plants?

A

Glucose combines with nitrogen compounds to form amino acids. Glucose monomers can form large molecules such as starch. Nucleic acids have a sugar portion.

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7
Q

What is a photon?

A

It is a particle of light. Each photon contains a quantum/amount of energy.

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8
Q

What is the waxy cuticle on a leaf?

A

It is a non-cellular layer on the surface of the leaf that limits water loss.

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9
Q

What is the upper epidermis on a leaf?

A

It protects the leaf from injury and reduces water loss, it is transparent. It is the layer below the waxy cuticle.

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10
Q

What are the palisade cells on a leaf?

A

They are part of the parenchyma tissue making up the internal tissue of a leaf. They contain a large number of chloroplasts and are adapted for efficient photosynthesis.

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11
Q

What is the lower epidermis on a leaf?

A

Some of the cells of the lower epidermis are modified to form guard cells (stomata) which control the movement of water and gases into and out of the leaf. The lower epidermis also protects the leaf.

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12
Q

What is the spongy mesophyll layer in the leaf?

A

It forms part of the parenchyma tissue. Contain chloroplasts but are in smaller abundance than palisade cells. Air spaces between the cells play a role in gaseous exchange.

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13
Q

What do photosynthesis and aerobic respiration together in a plant allow?

A

Cycling of oxygen and carbon dioxide. Products of one process are the raw materials for the next.

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14
Q

What is the compensation point in respiration and photosynthesis?

A

It is where respiration and photosynthesis occur at the exact same rate and there is no net loss or gain of carbohydrate. The time taken to reach this point (where respiration occurs at a faster rate) is called the compensation period.

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15
Q

What are thylakoids?

A

They are pigment-containing flattened discs. The first part of photosynthesis, the light-dependent reaction takes place in the thylakoid membrane.

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16
Q

What are granum?

A

They are plural grana which is a stack of thylakoids. A single chloroplast can contain around 50 grana. Granum stacks provide the chloroplast with an increased surface area for photosynthesis to occur in limited spaces.

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17
Q

What are the inter-granal thylakoid/lamella?

A

They are extensions of the membrane that form thylakoids. They connect one granum to another. They are the site of the light-dependent reaction.

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18
Q

What is the stroma and what does it contain?

A

It is an amorphous, gel-like material. Contains enzymes. The light-independent reaction takes place here using enzymes.

It also contains starch grains to store glucose. Oil droplets to provide raw materials for making new membranes. Small ribosomes to produce the proteins coded for by chloroplast DNA.

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19
Q

What is the double membrane in a chloroplast?

A

The double membrane or envelope controls molecular traffic into and out of the chloroplast. The inner membrane is extensively folded to form the thylakoids.

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20
Q

What do pigments do in chloroplasts?

A

They absorb specific wavelengths of light and reflect others.

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21
Q

What does chlorophyll a do in plants?

A

It is the primary pigment in photosynthesis and absorbs mainly red and blue light and reflects green light. This is why most plants appear green.

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22
Q

What are the accessory pigments in chloroplasts?

A

Chlorophyll b, carotenoids, xanthrophylls.

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23
Q

What do carotenoids absorb and reflect?

A

Absorb blue-green light and reflects red, orange and yellow light.

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24
Q

Study the diagram to do with absorbance of wavelenths by pigments

A

…

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25
Where does the light-dependent reaction take place?
The thylakoid membranes.
26
What is the role of the photosystem?
To absorb light energy of different wavelengths and transfer this energy efficiently and quickly to the reaction centre (RC).
27
What does the antenna complex of the photosystem consist of?
Carotenoids, chlorophyll a and b and xanthrophyll.
28
What does the reaction centre consist of?
1 of 2 types of chlorophyll a.
29
What is the p680 reaction centre?
Found in photosystem II and has a peak absorption wavelength of 680nm.
30
What is the p700 reaction centre?
Found in photosystem I and has a peak absorption rate of 700nm.
31
What do accessory pigments do?
They pass energy to the primary pigments in the reaction centres.
32
What wavelength does cholorphyll b absorb?
400-500 nm and around 640nm. It reflects yellow green.
33
What wavelengths do xanthrophylls absorb?
Blue and green light of wavelength 375-550nm. They reflect yellow light.
34
What is the advantage of having a range of pigments?
The plant uses a range of pigments absorbing different wavelengths to harvest the maximum amount of energy.
35
How does light energy travel down the photosystem?
Accessory pigments absorb different wavelengths of light. This light energy arrives in the form of photons which excite electrons in the pigments. There is a transfer of energy from one accessory pigment to the next until the energy reaches the reaction centre where there is an electron acceptor to commence the two stages of photosynthesis.
36
Why do leaves change colour in autumn?
The pigment chlorophyll is broken down into colourless compounds. This process allows other pigments of the photosystem to be seen. Anthocyanins, carotenes, xanthophylls - produce the reds, yellows and oranges seen in autumn leaves. The leaf is also drained of all useful substances before abscission.
37
What is phosphorylation?
The addition of an inorganic phosphate group to a molecule like ADP.
38
What are the two stages of photosynthesis?
Light dependent stage and light independent stage.
39
Where does the light dependent stage take place and what does it involve?
Thylakoid membranes. Non-cyclic phosphorylation. Photolysis. Cyclic phosphorylation.
40
Where does the light-independent stage take place and what does it involve?
This occurs in the stroma. Calvin cycle. Regeneration of RuBP.
41
What is OILRIG?
Oxidation Is Loss, Reduction Is Gain (of electrons)
42
What does it mean when a molecule is reduced?
It has gained electrons and may have lost oxygen or gained hydrogen.
43
What does it mean when a molecule is oxidised?
It has lost electrons and may have lost hydrogen or gained oxygen.
44
What is NADP?
It is a coenzyme involved in photosynthetic reactions. A coenzyme aids the function of enzymes - usually by transferring a chemical group from one molecule to another.
45
What is NADP+ and what happens when it turns to NADPH?
NADP+ is the oxidised form. It gains an electron to form neutral NADP and then a hydrogen (electron and proton) to form NADPH or reduced NADP.
46
What does NADPH do?
It can transfer hydrogen to another molecule - this means it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule. When hydrogen is transferred between molecules, electrons are transferred too.
47
Where does the light dependent stage of photosynthesis occur?
In the thylakoid membranes of the chloroplasts.
48
What are the processes of the light dependent reaction?
Non-cyclic photophosphorylation and cyclic photophosphorylation and photolysis.
49
What are the 2 photosystems in the light dependent reaction?
Photosystem I and photsystem II. They each have chlorophyll in their reaction centres.
50
What occurs in the light-independent stage?
Calvin cycle and the regeneration of RuBP?
51
Where does the light-independent stage of photosynthesis occur?
In the stroma
52
Write the complete process of non-cyclic photophosphorylation in the light dependent reaction.
Light strikes PS II exciting 2 electrons in the p680 reaction centre and they leave the PS - they are accepted by an electron acceptor. 2 electrons passed down the ETC made up of proteins embedded in the plasma membrane, this is done by oxidation/reduction reactions. Electrons release energy with each reaction that is used to drive H+ ions across the membrane via a proton pump into the intermembrane space. The 2 electrons react PS I and enter the reaction centre p700. PS II is still deficient in electrons and photolysis provides the electrons to replace the ones lost. Light strikes PS I, exciting the 2 electrons that leave, and pass along the ETC, releasing energy which is used to reduce NADP to NADPH. H+ ions accumulate in thylakoid lumen, concentration gradient set up, H+ ions from photosynthesis and uptake of H+ on stroma side of the membrane to form NADPH. H+ ions move down their concentration gradient into the stroma via ATP synthesise which drives phosphorylation to form ATP (chemiosmosis).
53
Outline the process of cyclic photophosphorylation in the light dependent reaction?
It occurs within PS I only. Light strikes PS I and 2 electrons are excited and leave. They are passed along the ETC releasing energy but this time no NADPH is formed. Instead, energy is used to drive H+ ions across the membrane so that ATP can be formed. Therefore, non-cyclic and cyclic photophosphorylation occur in PS I.
54
What are the products of non-cyclic photophosphorylation?
ATP and NADPH. These are used in the light independent reaction.
55
What happens in photolysis?
As the electrons from PS II get excited and leave they need to be replaced. Light energy and enzymes split water into oxygen, protons and electrons. The hydrogens reduce NADP, the electrons replace those lost, and the oxygen is released as a waste gas.
56
What is the reaction for photolysis?
H20 ---> 2H+ + 1/2 O2 + 2e-
57
What are the 5 products of the light-dependent reaction?
NADPH ATP Oxygen Protons / H+ ions Electrons
58
What is the PAG that can be used to separate pigments in photsynthesis?
Thin-layer chromatography
59
Where does the light-independent stage of photosynthesis occur?
In the stroma of chloroplasts.
60
What can the light-independent stage also be called?
The calvin cycle
61
What is the process of the light-independent stage?
RuBP (5C) combines with carbon dioxide, carboxylation. Catalysed by ribulose bisphosphate carboxylase. RuBP and CO2 produce a highly unstable 6C molecule that immediately breaks down into 2 3C glycerate-3-phosphate molecules. GP is reduced by ATP and NADPH, forms triose phosphate 3C. TP is a carbohydrate, some of it used to produce glucose and other molecules such as amino acids and lipids. Glucose stored as starch. Most of the TP is recycled to make more RuBP. ATP is converted to ADP and Pi in the process. For every 1 molecule of glucose, 10 molecules of RuBP are produced.
62
How many times does the calvin cycle need to turn to make 1 hexose sugar?
6 times. This is because 3 turns of the cycle produces 6 molecules of TP, but only 1/6 molecules of TP go to producing a hexose sugar.
63
How much ATP and NADPH is required for 6 turns of the calvin cycle?
18ATP and 12 NADPH.
64
How can triose phosphate be used?
Can combine to form hexose sugars such as glucose, some of which can isomerise to form fructose. These molecules can convert to form disaccharides such as cellulose and starch. TP can be converted to glycerol and this may be combined with fatty acids to make lipids.
65
Which factors can limit the rate of photosynthesis?
Light intensity. Carbon dioxide concentration. Temperature.
66
How would you investigate the effect of light intensity on the rate of photosynthesis?
Position a lamp a certain distance away from the plant and switch it on. Measure the volume of oxygen given off in 5 minutes. Repeat with the lamp at different distances away from the pondweed. A graph of volume against distance of the lamp can be plotted from the results.
67
What happens to photosynthesis when you increase light intensity?
The higher the light intensity, the more energy is available for the light-dependent reaction. Only certain wavelengths of light are used in photosynthesis. Accessory pigments such as chlorophyll b and carotene assist by absorbing light at different wavelengths to chlorophyll a.
68
What will happen to GP, TP and RuBP if there is little to no light?
GP cannot be reduced to TP (due to a lack of ATP and NADPH). TP levels fall and GP accumulates. If TP levels fall, RuBP cannot be regenerated.
69
Why is carbon dioxide a limiting factor in photosynthesis?
Carbon dioxide is used during the light-independent stage to carboxylate ribulose bisphosphate. When it is limited, the rate of the reactions in the light-independent stage will decrease in a given time. Carbon dioxide makes up 0.04% of the gases in the atmosphere. Increasing the concentration of the CO2 around the plant produces a higher rate of photosynthesis, but any higher than 0.4% will cause the stomata to close.
70
What can you add to water to increase carbon dioxide concentration?
Sodium hydrogencarbonate.
71
What will happen to RuBP, GP and TP if CO2 falls below 0.01%?
RuBP cannot accept CO2 and so RuBP accumulates. GP cannot be made. TP cannot be made.
72
Describe and explain the effect of temperature on rate of photosynthesis.
The light independent reaction is controlled by enzymes, as temperature increases the enzyme and substrate gain kinetic energy, the collision frequency between reactant and enzyme increases. More ES complexes form leading to the formation of more EP complexes, which leads to more product formation. This increases the rate of reaction up to the optimum temperature.
73
What is the effect of temperature on the Calvin cycle?
All reactions in the Calvin cycle are catalysed by enzymes eg rubisco. At low temperatures, reactions will proceed slowly meaning levels of RuBP, GP and TP will fall. At high temperatures, enzymes will denature and the Calvin cycle will halt.
74
How can farmers manipulate the limiting factors of photosynthesis?
Carbon dioxide concentration - added to the air eg by burning a small amount of propane in a carbon dioxide generator. Light - Light can get in through glass and lamps can be used at night. Temperature - Glasshouses trap heat energy from sunlight which warms the air. Heaters and cooling systems can also be used to keep a constant optimum temperature.
75
What happens to an enzyme's structure when it is denatured?
Their tertiary structure breaks down as hydrogen and ionic bonds are disrupted, changing the shape of the active site so that reactant molecules no longer fit.
76
What is the effect of water stress on photosynthesis?
When the roots are no longer able to take up as much water as is lost by transpiration this is called water stress. Cells lose water and become plasmolysed. Plant roots produce abscisic acid that, when translocated to leaves causes stomata to close, reducing gaseous exchange. The rate of photosynthesis greatly reduces.
77
What is a photosynthometer?
It measures the production of oxygen. The gas collects in the flared end of the capillary tube. The air bubble can be moved to the capillary tube and its length measured and if the radius of the tube is known then the volume can be calculated.
78
What are the limitations of a photosynthometer?
Rate of photosynthesis is determined by volume of oxygen produced, this only measures volume of oxygen released. Respiration is not taken into account. There also may be some dissolved nitrogen in the gas collected.
79
What does the Hill reaction measure?
Investigates the light-dependent reactions of photosynthesis.
80
How is the Hill reaction performed?
A chloroplast extract is prepared by grinding spinach leaves with ice cold sucrose solution, straining the liquid into a cooled centrifuge tube and centrifuging. The sediment (containing the chloroplasts) is then added to a buffer solution. DCPIP is added to all the tubes. The tubes are left until the DCPIP in tube A becomes colourless and then they're compared.
81
Why does the sucrose solution in the Hill reaction have to be ice cold?
It is necessary to slow enzyme action and prevent damage to the chloroplasts before the experiment begins.
82
Why does DCPIP in tube A turn colourless?
The DCPIP takes place of NADP+. This allows photolysis to continue (supplying protons and electrons). DCPIP accepts the electrons from the electron transport chain rather than NADP+. DCPIP becomes colourless as it is reduced (gains electrons).
83
How is a qualitative indication produced by DCPIP?
DCPIP is blue when oxidised and colourless when reduced, so it is possible to monitor the loss of blue colour as an indication that DCPIP has accepted electrons.
84
Why does the lack of light stop DCPIP from turning colourless?
The reaction can only occur if the chloroplasts are illuminated as the light-dependent stage stops in the dark.
85
Why does boiling the contents of the tube stop the DCPIP from turning colourless?
It disrupts the thylakoid membranes and denatures the membrane proteins so that the electron transport chain can no longer function. THIS IS NOT TO DO WITH ENZYMES as DCPIP is bypassing the oxidation of coenzyme NADPH.

Biology (26 decks)

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