3.2 -photosynthesis Flashcards
(124 cards)
1
Q
What is the overall equation for photosynthesis?
A
Carbon dioxide + water —> glucose + oxygen
2
Q
Define the term photophosphorylation
A
An endergonic reaction bonding a phosphate Ion to a molecules of ADP using energy from light making ATP
3
Q
What are the two main stages of photosynthesis?
A
The light dependent stage
The light independent stage
4
Q
Describe briefly what energy changes happen in the light dependent stage?
A
- The light dependent stage converts light energy into chemical energy via the photolysis of water which produces 2 protons and 2 electrons.
- the energy carried by electrons establishes a proton gradient across the thylakoid membrane
- the energy is used to phosphorylate ADP, which generates ATP
5
Q
What happens in terms of energy change in the light independent stage of photosynthesis?
A
The ATP and reduced NADP reduce carbon dioxide and produce energy containing glucose
6
Q
Where does photosynthesis take place?
A
In chloroplasts
7
Q
Describe the structure of a chloroplast briefly
A
- chloroplasts are surrounded by a double membrane
- The inner membrane folds inwards to make a thylakoid lamellae
- these combine to form grana
- The stroma is the fluid filled interior bathing the thylakoids and grana
- starch grains
8
Q
Where is the photosynthetic pigment stored in the chloroplast?
A
In the grana
9
Q
Where did the reactions of the light dependent stage of photosynthesis take place?
A
In the grana
10
Q
What do the light independent reactions of photosynthesis take place in a chloroplast?
A
In the stroma
11
Q
Why do the starch grains in the chloroplast appear white in an electron micrograph?
A
Because the stain used for the electron micrograph (osmium tetroxide) binds to lipids and not carbohydrates.
12
Q
What evidence do we have to indicate that chloroplasts are descended from cyanobacteria?
A
The base sequence of the small number of genes in chloroplasts indicate that they are descended from cyanobacteria
13
Q
Where are chloroplasts found in a plant?
A
The leaves and the stem as they are exposed to light, especially in the palisade mesophyll, spongy mesophyll and guard cells.
14
Q
What is the main organ of photosynthesis?
A
The leaf
15
Q
What is the benefit of a leaf having a large surface area?
A
It can capture as much light as possible
16
Q
What is the benefit of a leaf being thin?
A
Light penetrates right through the leaf
17
Q
What is the benefit of a leaf having stomatal pores?
A
Allows carbon dioxide to diffuse into the leaf
18
Q
What is the benefit of a leaf having air spaces in the spongy mesophyll?
A
Allows carbon dioxide to diffuse to the photosynthesising cells
19
Q
What is the benefit of a leaf having space between palisade cells?
A
Allows carbon dioxide to diffuse to the photosynthesising cells
20
Q
What is the benefit of cells having A transparent cuticle and epidermis and thin cellulose cell walls?
A
Light penetrates through to the mesophyll
21
Q
What is the benefit of cells having Palisade cells with a large vacuole?
A
Chloroplasts form a single layer at the periphery of each cell so do not shade each other
22
Q
What is the benefit of cells having palisade cells that are cylindrical, elongated and are right angels to the surface of the leaf?
A
- Can accommodate a large number of palisade cells
- Lights only has to penetrate through two epidermal cell walls and one Palisade cell wall before reaching chloroplasts (unlike if cells were stacked horizontally)
23
Q
What is the benefit of chloroplasts having A large surface area?
A
Maximum absorption of light
24
Q
What is the benefit of chloroplasts Being able to move within palisade cells?
A
- Chloroplasts can move towards the top of the cell on full days for maximum absorption of light
- If the light intensity is very high they move to the bottom of the cell protecting pigments from bleaching
25
What is the benefit of chloroplasts rotating within palisade cells?
Thylakoids maximise the absorption of light
26
What is the benefit of chloroplasts having pigments in the thylakoids forming a single layer at the surface of the thylakoid membrane?
Pigments maximise their absorption of light
27
What is the benefit of leafs having about five times as many chloroplasts in the palisade cells than spongy mesophyll cells?
Palisade cells are at the top of the leaf and they are more exposed to light than the spongy Mesophyll cells so chloroplasts can capture as much light as possible
28
List the structures in a leaf:
- cuticle
- upper epidermis
- palisade mesophyll
- spongy mesophyll
- lower epidermis
- stoma
- guard cells
29
What is a transducer?
It is something that changes energy from one form to another.
30
Why are biological transducers much more efficient than such artificial devices?
They waste less energy in the conversions that they make
31
How are chloroplasts transducers?
They turn energy in the photons of light into chemical energy made available through ATP and incorporated into molecules such as glucose.
32
What did Engelmanns experiment find?
He placed filamentous green alga in a suspension of evenly distributed motile aerobic bacteria and exposed them to a range of wavelengths of light.
He noticed that in blue and red light the bacteria clustered near the chloroplasts
He seduced that these wavelengths resulted in a high rate of photosynthesis which produced a lot of oxygen which attracted the bacteria.
33
Give some other examples of biological transducers
Conversion of heat, light and sound into electrical energy in sense organs.
The conversion of chemical energy into kinetic energy and heat in muscles.
34
What is a pigment?
It’s a molecule that absorbs specific wavelengths of light
35
Why is light energy and a chloroplast trapped by different photosynthetic pigments?
It allows a large range of wavelengths to be absorbed and is consequently more useful than if one pigment was used absorbing a small range of wavelengths
36
What are the two main classes of pigments in flowering plants?
1) chlorophylls
| 2) carotenoids
37
What are the main two forms of Pigment chlorophyll in plants?
1) Chlorophyll a
| 2) Chlorophyll b
38
What is the wavelength (peak) and pigment colour absorbed by pigment chlorophyll a?
Wavelength: 435, 670-680
Pigment colour: yellow-green
39
In what plants is chlorophyll a found?
All plants e.g misses, ferns, conifers, flowering plants
40
What is the wavelength (peak) and pigment colour absorbed by pigment chlorophyll b?
Peak wavelength: 480, 650
Pigment colour: blue-green
41
In what plants is chlorophyll b found?
Higher plants e.g conifers/flowering plants
42
What are the main two divisions of carotenoids found in plants?
1) beta-carotene
| 2) xanthophylls
43
What is the wavelength (peak) and pigment colour absorbed by pigment beta-carotene?
Peak wavelength: 425-480
Pigment colour: orange
44
What is the wavelength (peak) and pigment colour absorbed by pigment xanthophyll?
Peak wavelength: 400-500
Pigment colour: yellow
45
In what form of plants are beta-carotene and xanthophylls found?
Beta-carotene: all
| Xanthophylls: most
46
What is phaeophytin?
It is a grey-blue breakdown product of chlorophyll which does not contain a magnesium ion.
It can absorb light but it’s role is transferring electrons in photo system 2 rather than light absorption.
47
Define the term absorption spectrum
A graph showing how much light is absorbed of different wavelengths.
48
Define the term action spectrum
A graph showing the rate of photosynthesis at different wavelengths.
49
In what regions do chlorophyll a and b absorb light in the absorption spectrum?
What wavelengths do they reflect?
Absorb light in the red and blue-violet regions of the absorption spectra.
Reflect light in green regions giving leaves their colour.
50
In what regions carotenoids absorb light in the absorption spectrum?
Absorb light energy from the blue-green region so they appear yellow.
51
How is the rate of photosynthesis at different wavelengths of light measured in an action spectrum?
It is measured by the mass of carbohydrate synthesised by plants exposed to different wavelengths
52
What does the close correlation between an action spectrum and absorption spectrum show?
Shows that the pigments responsible for absorbing the light are used in photosynthesis
53
Where do photosystems live in a chloroplast?
Photosystems lie in the plane of the thylakoids membrane.
54
What is an antenna complex?
And antenna complex is an array of protein and pigment molecules in the thylakoids membranes of the grana that transfer energy from light of a range of wavelengths to chlorophyll a at the reaction centre.
55
What does each photosystem comprise of?
1) An antenna complex containing photosynthetic pigments
| 2) A reaction centre within the antenna complex
56
Describe in detail what the reaction centre contains.
It contains two molecules of the primary pigment chlorophyll a. When the chlorophyll a molecules absorb light their excitation allows each one to transmit an electron.
57
What are the two types of reaction centre?
1)Photosystem 1 is arranged around the chlorophyll a molecule with an absorption peak of 700 nm.
It is also called P700
2)Photosystem 2 is arranged around a chlorophyll a molecule with an absorption peak of 680 nm.
It is also called P680
58
What happens to the photons of light that are absorbed by accessory pigments chlorophyll b and the carotenoids?
The photons excite the accessory pigments and energy is passed through them to the reaction centre were electrons of chlorophyll a are excited and raised to a higher energy level.
59
Why is chlorophyll ate the most significant molecule of the reaction centre?
Because it passes energy to the subsequent reactions of photosynthesis.
60
What is chlorophyll a also referred to as?
The primary or core pigment
61
What are the products of the light dependent stage of photosynthesis?
What is the significance of each of these products?
1) ATP: Provides the chemical energy transduced from light energy to synthesise energy rich molecules such as glucose
2) NADPH2: provides the reducing power to synthesise molecules such as glucose from carbon dioxide.
3) Oxygen: a byproduct derived from water.
62
How is the oxygen the byproduct of water removed from the plant?
Oxygen defuses out of the chloroplast out of the photosynthetic cells and out of the leaf through the stomata.
63
What cycle of reactions is present in the light independent stage?
What do these products use?
which uses the products of the light dependent stage such as ATP and reduced NADP making molecules such as glucose in the solution of the stroma?
1) the Calvin cycle
2) the Calvin cycle uses the products of the light dependent stage such as ATP and reduced NADP making molecules such as glucose in the solution of the stroma.
64
What are the two pathways of photophosphorylation present in photosynthesis?
1) Cyclic photophosphorylation
| 2) Non cyclic photophosphorylation
65
Define the term cyclic photophosphorylation
ATP can be produced by electrons that take a cyclical pathway and are recycled back into the chlorophyll a in photosystem 1.
66
Define the term non-cyclic photophosphorylation.
ATP can be produced by electrons that take a linear pathway from water, through photosystem 2 and photosystem 1 to NADP which they reduce.
67
Which photosystems do cyclic and non-cyclic photophosphorylation use?
Cyclic: only uses PS1
| Non-cyclic: uses PS1 and PS2
68
Describe the passage of electrons in cyclic photo phosphorylation
1) Photosystem 1 absorbs photons which excites electrons in the chlorophyll a molecules in its reaction centre
2) These are emitted and picked up by an electron acceptor which passes them down a chain of electron carriers back to photosystem 1. The energy released as electrons pass through the electron transport chain phosphorylates ADP to a ATP.
69
Describe the passage of electrons in non-cyclic photo phosphorylation.
1) Photosystem 1 absorbs photons which excites electrons in the chlorophyll a molecules in its reaction centre
2) These are emitted and picked up by an electron acceptor
3) The electrons are then transferred from the electron acceptor to oxidised NADP in the stroma, which with protons from the photolysis of water is reduced
4) The electrons have not been returned to PS1 and :: its chlorophyll a is left with a positive charge
5) The positive charge is neutralised by electrons from PS2. These electrons have been excited to a higher energy by light absorption, picked up by an electron acceptor and passed down the ETC to PS1.
6) Electron passage down the ETC makes energy available for phosphorylation if ADP.
7) The chlorophyll in PS2 is left with a positive charge which is neutralised by the electrons released in the photolysis of water.
70
Define the term photolysis
The splitting of water molecules by light, producing hydrogen ions, electrons and oxygen.
71
Define the term the Z scheme
The pathway taken by electrons in non cyclic photo phosphorylation
72
In what form of photo phosphorylation is oxidised NADP reduced?
In non-cyclic photo phosphorylation only
73
Where does the photolysis of water occur in a chloroplast?
In the thylakoid spaces where water molecules absorb light, indirectly causing them to dissociate into hydrogen, oxygen and electrons.
74
What enhances the photolysis of water in a chloroplast?
A protein complex in PS2 (the only known enzyme that oxidised water)
75
How are the products of the photolysis of water used for photosynthesis?
1) The electrons produced replace those lost from PS2
2) The protons produced are used to reduce oxidised NADP into NADPH2
3) Oxygen diffuses out of the chloroplast and cell, through the stomata as a waste product.
76
What provides the energy for protons to be pumped from the stomata into the thylakoid space?
Electrons passing through the proton pumps in the ETC provide the energy for protons to be pumped from the stomata to the thylakoid spaces.
77
Describe the passage of protons in photo phosphorylation after they have been pumped into the thylakoid spaces.
1) The protons join the H+ ions from the photolysis of water and accumulate forming and electrochemical gradient.
2) This gradient is a source of potential energy.
3) Chemiosmosis occurs where the H+ ions diffuse down their electrochemical gradient through ATP synthase in the thylakoid membrane into the stroma.
4) This makes the energy derived from light available to be carried by the electrons.
5) As they pass through ATP synthase ADP is phosphorylated to ATP
6) Once in the stroma, protons are passed to oxidised NADP reducing it.
78
What maintains the proton gradient across the thylakoid membrane?
1) The proton pump associated with the ETC pushing protons into the thylakoid space
2) the photolysis of water in the thylakoid space
3) the removal of protons from the stroma reducing NADP
79
What can the light dependent stage of photosynthesis be summarised as?
NADP + H2O + 2ADP + 2P —> NADPH2 + 2ATP + 1/2O2 + 2H2O
| The product 2H2O is produced from the condensation of ADP + P —> ATP
80
How many proton pumps are there in the Electron transport chain in photosynthesis compared to respiration?
```
Photosynthesis = 1
Respiration= 3
```
81
Compare the photosystems used in cyclic and non cyclic photo phosphorylation.
Cyclic: PS1 only
| Non-cyclic: PS2 and PS1
82
Compare the chlorophyll at the reaction centre in cyclic and non cyclic photophosphorylation.
Cyclic: P700
Non-cyclic: P680
(Both chlorophyll a variants)
83
Compare the electron flow in cyclic and non cyclic photophosphorylation.
Cyclic: cyclic
| Non-Cyclic: Linear (Z scheme)
84
Compare the ATP production in cyclic and non cyclic photophosphorylation.
Cyclic: ATP produced
| Non-cyclic: ATP produced
85
Compare the photolysis of water in cyclic and non cyclic photophosphorylation.
Cyclic: Not present
| Non-cyclic: present
86
Compare the oxygen production in cyclic and non cyclic photophosphorylation.
Cyclic: not produced
| Non-cyclic: produced
87
Compare the NADP reduction in cyclic and non cyclic photophosphorylation.
Cyclic: not produced
| Non-cyclic: produced
88
Compare what plants cyclic and non cyclic photophosphorylation occur in.
Cyclic: all photosynthetic organisms
| Non-cyclic: plants, algae and cyanobacteria
89
What did Robert Hill find in 1939?
Found that in the cell NADP is the oxidising agent that removes hydrogen from water.
The blue dye DCPIP acts as a substitute for NADP, and in the presence of light loses its colour when it’s reduced.
Light + chloroplasts
Oxidised DCPIP ———————> reduced DCPIP
Dark blue colour Colourless
90
Where does the light dependent stage of photosynthesis occur?
In the stroma of the chloroplast.
91
What products of the light dependent stage of photosynthesis are used in the light independent stage?
1) ATP as a source of energy
| 2) Reduced NADP as a source of reducing power
92
Describe the steps of the Calvin Cycle (light independent stage of photosynthesis)
1) 5C compound ribulose bisphosphate combines with carbon dioxide, catalysed by the enzyme Ribulose Bisphosphate carboxylase (RuBisCo).
2) This forms an unstable 6C compound
3) The 6C compounds splits into 2 molecules of glycerate-3-phosphate (GP)
4) GP is reduced to triose phosphate by reduced NADP.
5) reducing a molecule requires energy, so the ATP formed in the light dependent stage is used producing ADP + P1
6) Some of the triose phosphate is converted to glucose phosphate and then into starch via condensation (1/6)
7) most of the triose phosphate regenerates into Ribulose phosphate (5C) (5/6)
8) Another molecule of ATP is used forming ADP + P. The P is used to phosphorylate Ribulose phosphate into Ribulose Bisphosphate and the cycle continues.
93
For every 6 molecules of triose phosphate formed, how many are used to produce glucose (starch) and how many are used to regenerate RuBp?
For every 6 molecules of triose phosphate, 5 are used to regenerate RuBp and 1 is used to form glucose.
94
How did Calvin and his associates discover the Calvin Cycle?
1) they used radioisotope C14, and incorporated it into hydrogen carbonate ions H14CO3-, as a source of carbon dioxide for photosynthesis by Chlorella.
2) H14CO3- was added to a flat lollipop vessel at the top.
3) The Chlorella photosynthesised and every 5 seconds samples were dropped into hot methanol (to stop further chemical reactions.)
4) The compounds produced were separated by chromatography and identified, mapping out the Calvin cycle.
95
How are carbohydrates made in plants from the 3C compounds in the Calvin cycle?
The first hexose made is fructose phosphate. This is converted to glucose and combined with more glucose to make sucrose.
Sucrose is used for transport around the plant.
The a glucose molecules may be converted to starch for storage, or to beta-glucose which is polymerised into cellulose for cell walls.
96
How are fats made in plants from the 3C compounds in the Calvin cycle?
Acetyl coenzyme A can be synthesised from GP and converted into fatty acids.
Triose phosphate can be converted directly to glycerol.
Fatty acids and glycerol undergo condensation reactions to form triglycerides.
97
How are proteins made in plants from the 3C compounds in the Calvin cycle?
Glycerate-3-phosphate (GP) can be converted into amino acids for protein synthesis.
The amino group is derived from NH4+ ions made from nitrate ions (NO3-) taken in at the roots and transported through the plant.
98
Define the term limiting factor
A factor that limits the rate of a physical process by being in short supply, an increase in a limiting factor increases the rate of the process.
99
What suitable environment to plants require to be efficient at photosynthesis?
1) The reactants carbon dioxide and water
2) Light at a high enough intensity and of suitable wavelengths
3) suitable temperature
100
What happens if the light intensity, reactants or temperature is lacking severely?
What if they are not at their optimum level?
Lacking: photosynthesis won’t take place
| Not at optimum: rate of photosynthesis is reduced
101
Describe the relationship between carbon dioxide concentration and the rate of photosynthesis.
1) As the carbon dioxide Concentration increases from 0, the rate of the light independent reactions increases and so the rate of photosynthesis increases show on the carbon dioxide concentration is a limiting factor.
2) If the concentration is increased above 0.5% the rate of photosynthesis remains constant and the concentration is not affecting rate of photosynthesis and therefore is not a limiting factor.
102
What happens if the concentration of carbon dioxide increases above 1%?
The stomata closes preventing carbon dioxide uptake and therefore the rate of photosynthesis decreases.
103
Why does the stomata close when the carbon dioxide concentration is above 1%?
Carbon dioxide diffuses into leaves and dissolves making carbonic acid. H+ ions formed from its dissociation decrease the pH denaturing proteins. Stomata close to stop this.
104
What is the rate limiting step?
The rate of the slowest reaction in a sequence which determines the overall rate of a process.
105
What is the rate limiting step in the light independent reactions of photosynthesis (Calvin cycle)?
The reaction catalysed by enzyme rubisco producing the unstable 6C compound.
106
In what form of plants is carbon dioxide normally a limiting factor? Why?
In terrestrial plants because the concentration of carbon dioxide in the air is about 0.04% (low).
107
What actions are plant breeders trying to perform to increase the efficiency of the light independent stage of photosynthesis?
They are trying to increase the efficiency of rubisco, increasing the yield of plants?
108
What would be useful to find as global temperatures increase?
Variants of enzyme RuBisCo that continue to function efficiently at a greater range of temperatures.
109
If a light is placed in darkens what parts of photosynthesis are possible and what parts aren’t?
What does this mean?
The light-independent stage is possible but the light dependent stage is not.
This means that no oxygen is evolved!
110
Describe the relationship between the light intensity and rate of photosynthesis.
As light intensity increases, the light dependent reactions occur with increasing efficiency and so overall the rate of photosynthesis increases. Light intensity is controlling the rate of photosynthesis and so it is a limiting factor.
At certain intensity (around 10,000 lux) the reactions of light dependent stage at the maximum rate. Higher light intensity does not produce faster reactions and so the rate of photosynthesis remains constant light intensity is not a limiting factor.
111
When would an increasing light intensity decrease the rate of photosynthesis?
At very high light intensity the photosynthetic pigments may be damaged, they will not absorb light efficiently and so the light dependent stage fails, decreasing the rate of photosynthesis.
112
Give an example of a “Sun plant” and a “shade plant”
Example of sun plant: Salvia
Most efficient at photosynthesis in high light intensities.
Example of shade plant: lily of the valley
Most efficient at photosynthesis in low light intensities.
113
Define the term light compensation point.
The light intensity at which a plant has no net gas exchange as the volume of gas is used and produced in respiration and photosynthesis to equal.
114
Describe think link between photosynthesis and respiration as light intensity decreases (how the light compensation point occurs).
- As light intensity decreases the rate of the light dependent reactions decreases. The route of the light independent reactions also decreases and so the rate of carbon dioxide uptake decreases.
- at a particular light intensity so little carbon dioxide is needed that respiration provides all that is required and none is absorbed.
- similarly, all of the oxygen needed for respiration is provided by photosynthesis.
- There is therefore no gas exchange.
- The light intensity at which this happens is called the light compensation point.
115
In the light compensation point lower or higher for shade plants compared to sun plants.
The light compensation point occurs at a lower light intensity for shade plants then for sun plants so they can grow in more shaded habitats.
116
Describe the correlation between temperature and rate of photosynthesis
Increased temperature increases the rate of photosynthesis because the kinetic energy of the molecules increases above a particular temperature, which is different in different species. The enzymes progressively denature at too high a temperature and the rate of photosynthesis decreases.
Thus, temperature does control the rate of photosynthesis and it is therefore a limiting factor.
117
Describe the effect of low water availability on the rate of photosynthesis.
- When water is scarce a plant cell stomata closes, wilting occurs and many physical functions are affected. -Experiments with water deficient plants show that even slight water deprivation can reduce the carbohydrate made, so water availability is a limiting factor in photosynthesis.
- As so many systems are affected it is not straightforward to see its affect on photosynthesis alone.
118
What is important to note about limiting factors of photosynthesis?
Limiting factors can combine, and the actual rate of photosynthesis is controlled by the factor that is nearest to its minimum value.
E.g if two plants grow at 25 degrees Celsius, one at 0.04% CO2 and the other at 0.01% CO2, the 0.04% plant will have a great rate of photosynthesis as its closer to the optimum.
If two plants grow at a 0.01% CO2 concentration, but one at 15 degrees and the other at 25, the plant at 25 degrees will have a higher rate of photosynthesis.
119
What are the 2 macronutrients we are required to know about in detail?
1) Nitrogen
| 2) Magnesium
120
What are the main roles of inorganic nutrients?
1) Structural e.g calcium in the middle of lamellae walls
2) Synthesis if compounds needed for the the growth of a plant e.g enzyme activators.
3) May form an integral part of a molecule e.g Mg in chlorophyll, Fe in the carriers of the ETC.
121
Give two examples of micronutrients and 4 examples of macronutrients.
Micronutrients: manganese and copper
Macronutrients: nitrogen, magnesium, sodium and calcium.
122
How is magnesium obtained/used in plants?
Magnesium is absorbed as Mg2+ and it is transported in the xylem. It is required by all the shoes but especially leaves.
Magnesium forms part of the chlorophyll molecule and so the main symptom of magnesium deficiency chlorosis.
Magnesium irons are also important and so I’m activated such as for ATPase.
123
How is nitrogen obtained by a plant?
- Most of the nitrogen in the soil is in the humid, organic molecules of decaying organisms.
- Nitrogen is taken up by roots as nitrates, although Rhizobium in root modules delivers ammonium ions to the plant.
- The ions are transported in the xylem and delivered to the cells.
- nitrate is converted into ammonium ions which become the amino groups of amino acids.
- Amino acids are transported in the phloem and used for the synthesis of protein, chlorophylls and nucleotides.
124
What are the symptoms of nitrogen deficiency in plants?
- Reduced growth of the whole plant.
| - Nitrogen is also part of chlorophyll and :: causes chlorosis (yellowing it the leaves).
