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4.3: Photosynthesis. Flashcards

0
Q

What is an autotroph?

A

Organisms that synthesise their own food from simple organic molecules using the energy from sunlight or chemical reactions.

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1
Q

What is the mode of nutrition of plants?

A

Autotrophy (they are autotrophs).

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2
Q

Why is photosynthesis critical to life on this planet?

A

Without plants turning sunlight into glucose, amino acids and starches animals would not be able to survive. It also uses up CO₂ and produces O₂.

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3
Q

What does photosynthesis produce?

A

Glucose and Oxygen(as a waste product).

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4
Q

What is the input for photsynthesis?

A 
Water (provides H and O atoms)
Carbon Dioxide (provides C and O atoms)
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5
Q

What do carnivorous plants use insects for?

A

As a nitrate and phosphate source as they live in poor soil conditions. They still perform photosynthesis.

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6
Q

In what plant cells does photosynthesis take place?

A

Most photosynthesis occurs in palisade cells. However there are also chloroplast present In Mesophyll cells and guard cells.

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7
Q

What is the endosymbiotic theory?

A

This suggests that chloroplasts and mitochondria evolved when a larger bacteria engulfed other bacterium. Chloroplasts are thought to have evolved through the endocytosis of a bacteria related to Cyanobacteria and mitochondria through the endocytosis of bacteria related to rickettsia.

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8
Q

What do chloroplasts contain in the stroma?

A 
Thylakoid membranes
Chloroplast DNA
tRNA
Ribosomes (prokaryotic 70S)
Starch grains and lipid droplets
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9
Q

What is the purpose of the thylakoids and Grana?

A

To increase the surface area for the absorption of light and hence increase the amount of photosynthetic enzymes and therefore the amount of photosynthesis.

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10
Q

What are the two main groups of photosynthetic pigments?

A

Chlorophylls

Carotenoids

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11
Q

What Is the structure (roughly) of chlorophyll?

A

Chlorophyll has a porphyrin head and a hydrocarbon tail which is used to attach them to the thylakoid membranes.

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12
Q

What are the two main chlorophylls in flowering plants?

A

Chlorophyll A (P680 and P700)

Chlorophyll B

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13
Q

What is the main structural difference between chlorophylls A and B?

A

They have one different side chain on the porphyrin head.

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14
Q

Give two examples of carotenoids.

A

Beta carotene

And Xanthophyll (WJEC prefer this)

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15
Q

Why are there different photosynthetic pigments in plants?

A

Because the pigments absorb light at different wavelengths and so having different pigments allows more of the visible spectrum to be used for photosynthesis.

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16
Q

What is the best way to see what wavelengths of light different pigments absorb.

A

By looking at their absorption spectrum.

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17
Q

What is an absorption spectrum.

A

A graph of how well pigments absorb light of different wavelengths. A high absorption means that wavelength is taken in and can be used by that pigment. Low absorption means that the wavelengths are not absorbed and used but are instead reflected or transmitted.

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18
Q

In what region of the visible electromagnetic spectrum do chlorophylls absorb?

A

In the red (650-760nm) and blue-violet (440-510nm).

They do not absorb green light but reflect it.

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19
Q

In what region of the visible electromagnetic spectrum do carotenoids absorb?

A

In the blue-violet regions of the spectrum.

Green light is not absorbed but is reflected and red light is absorbed by chlorophyll so is also not absorbed.

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20
Q

What pigment do plants adapted to shady conditions tend to have more of?

A

They tend to have a higher concentration of chlorophyll. Resulting in dark green leaves.

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21
Q

Why do plants have different combinations of photosynthetic pigments?

A

Because different plants experience different light conditions. This gives rise to different coloured leaves.

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22
Q

What is an accessory pigment?

A

Chlorophyll is the main pigment involved in photosynthesis. The other pigments are accessory pigments - they absorb light energy at extra wavelengths and pass the energy from this on to chlorophyll.

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23
Q

What is an action spectrum?

A

A graph showing how much photosynthesis happens at the different wavelengths of light.

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24
How could you test to see if a plant was performing photosynthesis?
You could test for an increase in the products: Oxygen Glucose-diastix Starch-iodine Or a decrease in the starting materials: CO₂
25
How was the first action spectrum produced?
Filamentous alga (spyrogyra) are put in a suspension of aerobic bacteria. Not much oxygen dissolves in the water and so the bacteria move towards the highest sources of O₂ so that they can respire. He first showed that chloroplasts were the site of photosynthesis by shining white light at the suspension resulting in bacteria accumulating in the area nearest the chloroplasts. He then split the light and as O₂ is produced in the blue and red light the bacteria accumulated there.
26
What does the close correlation between the action spectrum and the absorption spectrum suggest?
It suggests that the pigments are probably responsible for absorbing the light energy used in photosynthesis.
27
What is the role of photosynthetic pigments?
To absorb the light energy to be used in the conversion light energy to chemical energy in the form of chemical energy in chemical bonds
28
How may you test to see what photosynthetic pigments are present in a plant?
You can extract pigments from leaves using ethanol or acetone to disrupt the cell and chloroplast membranes, releasing the photosynthetic pigments. You can then use thin layer chromatography (best solvent 50:50 hexane/ethanol) to separate out the photosynthetic pigments.
29
On what basis does chromatography separate the photosynthetic pigments?
On the basis of molecular mass and solubility in the solvent. I.e lightest pigments travel furthest and the heaviest take longer. Chromatography measures mass by comparing the distance travelled by each pigment and the distance travelled by the solvent line to give you an Rf value.
30
What is an Rf value?
(Distance travelled by component)/(distance travelled by solvent). Lighter molecules will haves larger Rf. Heavier molecules will have a smaller Rf.
31
In what membrane are the photosynthetic pigments found?
In the thylakoid membrane.
32
How are the pigments arranged in the thylakoid membrane?
They are arranged in clusters called photosystems. Each Photosystem contains hundreds of pigment molecules.
33
What are the two main parts of a Photosystem?
The antenna complex The reactions centre.
34
What does the reaction centre consist of?
A molecule of chlorophyll a (P680 in Photosystem II and P700 in Photosystem I)
35
What does the antenna complex consist of?
All the accessory pigments e.g Chlorophyll b and the carotenoids (xanthophyll, carotene, lycopene).
36
How is the Photosystem arranged.
It is arranged so that the accessory pigments are held in the best position to absorb the most light energy and can channel that energy to the reaction centre
37
What is the role of the Photosystem?
To harvest energy from lots of different wavelengths of light and pass it onto the chlorophyll a at the reaction centre.
38
What is the first pigment in the "pigment antenna"?
Chlorophyll b
39
What is the goal of the light dependant reaction in photosynthesis?
To make A.T.P and Hydrogen atoms.
40
What is the first step of the light dependant reaction?
Photosynthetic pigments in the antenna complex of Photosystem II (P680) absorb light energy and pass it on to the reaction centre.
41
What is the second step in the light dependant reaction?
When the energy absorbed by the antenna complex reaches the reaction centre it excites 2 electrons inside chlorophyll a.
42
What is step three of the light dependant reaction in photosynthesis?
The electrons are boosted to a higher energy level and leave the chlorophyll a molecule and enter an electron transport chain. (Cytochrome b6-f complex) where their energy is used in photophosphorylation.
43
Describe the structure of the first electron transport chain (cytochrome b6-f complex).
It consists of three protein subunits. The first of which is purely an electron carrier, the second of which acts like a proton pump and the third of which performs photophosphorylation of ADP to ATP.
44
What is photo phosphorylation?
The production of ATP thought the addition of an inorganic phosphate to ADP using the energy provided by the absorption of light energy.
45
What is the fourth stage of the light dependant reaction?
The electrons coming out of the electron transport chain go to PhotosystemI and are boosted to an even higher energy level using energy absorbed by the antenna complex at the reaction centre. And leave the chlorophyll a molecule and go down another electron transport chain.
46
What is the fifth stage of the light dependant reaction?
The electrons end up forming Hydrogen atoms and their energy is used to produce reduced NADP.
47
How are the electrons lost by chlorophyll a (P680) replaced?
The "energised" P680 molecule causes the photolysis of water producing Protons, Oxygen and electrons to replace the ones that are lost. This produces Oxygen as a waste product (the Hydrogen is used to reduce NADP).
48
What are the products of the light dependant reaction?
Oxygen. Reduced NADP ATP.
49
What molecules are used during the light independant stage?
ADP and Pi Water NADP
50
Give an energy summary of the light dependant reaction.
Light energy gets transduced by the photosynthetic pigments into chemical energy in the bonds of reduced NADP and ATP.
51
How may the energy changes of the light dependant reaction be shown?
They can be shown in a Z scheme.
52
In terms of redox reactions what happens to PSII?
PSII is oxidised.
53
In terms of redox reactions what happens to PSI?
It is neither reduced or oxidised it just acts as an electron carrier.
54
What is cyclic photophosphorylation?
This also happens as part of photosynthesis. Cyclic photophosphorylation occurs when light energy is used to boost electrons from the chlorophyll a (P700) of PSI which then cycle along the first Electron transport chain, producing A.T.P and return to PS1 in a continuous cycle.
55
What does cyclic photophosphorylation produce?
A.T.P only
56
Which Photosystems are used in cyclic photophosphorylation?
Photosystem 1
57
Where is ATP synthetase found in the chloroplasts?
On the inner membranes of chloroplasts and mitochondria.
58
Where is the Concentration of protons highest in chloroplasts?
In the thylakoid lumen.
59
How is the electrochemical gradient across the thylakoid membrane maintained?
By the Hydrogen pumps of the electron transport chain.
60
Where does the energy for pumping the hydrogen ions into the thylakoid lumen come from?
From the electrons passing between Photosystem II and Photosystem I along the electron transport chain.
61
What is the purpose of the light independent reaction?
This uses CO₂ and the products of the light dependant reaction (ATP and reduced NADP) to make glucose.
62
Where does the light Independent reaction take place?
In the stroma
63
What Is ATP used for in the light-independant reaction?
As a source of energy.
64
What is CO₂ used for in the light-independent reaction?
As a source of Carbon atoms.
65
What is Reduced NADP used for in the light-independent reaction?
A source of reducing power (a reducing agent).
66
By what chemical process is glucose synthesised in the light-independent reaction?
The Calvin(Benson) cycle.
67
What is the Calvin Cycle?
A cycle of enzyme catalysed reactions to reduce CO₂ to form glucose using energy from ATP and reducing power from reduced NADP made in the light-dependant reaction.
68
What is the first step in the Calvin cycle?
Carbon Fixation. CO₂ combines with a 5C molecule: Ribulose-Bisphosphate in a carboxylation reaction catalysed by RuBisCo to produce a 6C molecule which is unstable and decomposes to produce two 3C molecules: glycerate-3 phosphate.
69
How efficient is RuBisCo?
Not very; processing 3-10 CO₂ molecules per second. Therefore a large amount of RuBisCo is required by plants which makes it the most abundant protein in nature.
70
What is the second stage of the Calvin cycle?
The two molecules of Glycerate-3 phosphate are reduced (using reduced NADP) in an endergonic reaction requiring energy from ATP to produce Triose phosphate's.
71
What happens to the two Triose phosphates?
One of them is used to make glucose in reverse glycolysis. The other one goes back into the Calvin cycle and is used to regenerate Ribulose Bisphosphate (RuBP) the reactions to regenerate RuBP also require energy and Pi from A.T.P to happen.
73
How many Calvin cycles does it take to make one glucose molecule?
Six.
74
What is the balanced equation for photosynthesis?
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
75
What fraction of the Triose phosphates are made into Glucose from 6CO₂ molecules?
1/6.
76
What is Calvin's lollipop?
This is an experiment created by Calvin which looked at what molecules are made during photosynthesis and when. Chlorella algae were made to photosynthesise under controlled CO₂ and light conditions. Radioactive CO₂ was added and a sample of algae was killed by dropping them into boiling ethanol after set intervals: 2s, 7s, 60s. He then analysed the products that were made using 2D chromatography with X-ray film to see compounds containing the radioactive Carbon. This allowed them to figure out there were several steps to the photosynthesis reaction, some of which were light dependant and some which weren't.
77
What is the glucose produced in the Calvin cycle used for?
~50% is used directly for respiration in mitochondria. The rest is converted into starch, cellulose, proteins and lipids.
78
What are the limiting factors of photosynthesis?
Carbon dioxide concentration. Availability of inorganic nutrients (phosphate, nitrate) Sunlight Temprature.
79
What are the macro-inorganic-nutrients (most importantinorganic nutrients) for plants?
``` Potassium Sodium Magnesium Nitrate Phosphate ```
80
What are the micro-inorganic-nutrients for plants?
Manganese | Copper.
81
What is Mg used for in plants?
Mg is absorbed as Mg²⁺ from water in the soil and transported through the plant in water in the xylem. Mg is used in chlorophyll production and is the electron donor in the Photosystems. It is also important for the activation of A.T.P synthetase.
82
What does lack of Mg lead to in plants?
Lack of Mg leads to chlorosis (yellowing if the leaves). Chlorosis often happens in older leaves as the Mg²⁺ is stripped from them to be given to new young leaves.
83
What is Nitrogen used for in plants?
Nitrogen absorbed as nitrate or ammonium ions from water in the soil are transported as nitrate in water in the xylem and as amino acids in the phloem. It is important for the synthesis of all proteins and nucleic acids so it is required by all tissues and deficiency will seriously affect growth.
84
What does lack of nitrate lead to?
Reduced growth of all organs | Can cause Chlorosis as N is also in chlorophyll.

Biology - BY4 (6 decks)

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