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LGS A-Level OCR Biology > Unit 5 - Photosynthesis > Flashcards

Unit 5 - Photosynthesis Flashcards

1
Q

Autotrophs

A

An organism that makes their own food (complex organic compounds) from inorganic molecules using energy (chemical/ light)
Producers in an ecosystem

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2
Q

Chemosynthesis

A

Making food using chemical energy

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3
Q

Photoautotrophs

A

Organisms that photosynthesise using sunlight

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4
Q

Relationship between respiration and photosynthesis

A

All organisms respire but not all photosynthesise

Reverse processes

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5
Q

When do plants photosynthesise

A

In the day but always respire

The intensity of light has to be sufficient to allow photosynthesis to replenish carbs used in respiration

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6
Q

Compensation point

A

The rate of photosynthesis is equal to the rate of respiration
No net loss or gain of mass (carbs)
CO2 uptake in Ps = CO2 production is R

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7
Q

Compensation period

A

Time it takes to reach the compensation point

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8
Q

Photosystems

A

Particles attached to thylakoid membranes

Contain photosynthetic pigments which carry out the absorption of light in two distinct chlorophyll complexes

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9
Q

Photosystem I (PSI)

A

Funnel-shaped
Absorption wavelength is 700 nm
Found in intergranal lamellae

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10
Q

Photosystem II (PSII)

A

Funnel-shaped
Absorption wavelength is 680 nm
Found on the grana

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11
Q

Chlorophyll a

A

Reflects blue-green
Primary pigments
Found at reaction centre of both photosystems
2 forms absorb light at wavelength 680 (PSII) and 700nm (PSI) - red light
Can also absorb some blue (400nm)

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12
Q

Chlorophyll b

A

Reflects yellow - green
An accessory pigment
Absorbs light wavelengths 400-500nm (blue) and 640 (red)

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13
Q

Accessory pigments

A

Carotenoids
Xanthophyll
Chlorophyll b

Pass emitted electrons to the primary pigments which are then emitted (light harvesting pigments)
This drives photosynthesis

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14
Q

Carotenoids

A 
Reflect yellow
Absorb blue (400-500nm)
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15
Q

Xanthophyll

A

Reflects yellow

Absorbs blue/green (375-550)

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16
Q

Absorption spectrum

A

Results of the calorimeter test plotted on a graph

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17
Q

Action spectrum

A

Combined absorption spectra of pigments

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18
Q

Structure of chlorophyll molecule

A

Porphyrin head - hydrophilic, flat head lies parallel to thylakoid membrane for maximum absorption
Lipid soluble tail - hydrophobic, lies in thylakoid membrane
Side chains - determines which wavelengths are absorbed

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19
Q

Excitation of pigments by light

A

Chlorophyll pigments absorb light, electrons enter an ‘excited state’
This is unstable and electrons return to ‘ground state’
Lost excitation energy gets trapped during photosynthesis

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20
Q

Chlorophyll excitement equation

A

chlorophyll –> chlorophyll^+ + e^-

Reduced —-> oxidised + excited elctron

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21
Q

Chloroplast membrane

A

Both inner and outer membrane

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22
Q

Integranal lamellae

A

Extension of thylakoid membrane

Acts as skeleton

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23
Q

Intermembrane space

A

Space between membranes (10-20nm)

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24
Q

Granum

A

Stack of thylakoids

Plural grana

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25
Stroma
Contains enzymes needed for photosynthesis, DNA and ribosomes
26
Thylakoids
Where the green pigment is found | Site of light absorption and ATP synthesis
27
Chromatogrophy table
Pigment Distance travelled by compound Distance travelled by solvent Rf value
28
Paper chromatogrophy to seperate pigments
Dissolve pigments in solvent (propan-2-ol) Using chromatography paper Allow the solvent to move up the paper and seperate the pigments Diff pigments would move at diff speeds up the paper Calculate Rf values
29
Why do plants contain a mixture of diff pigments
Light is made up of many diff wavelengths | To allow plants to absorb maximum light for photosynthesis
30
Photophosrylation
Production of ATP in the presence of light from ADP and Pi
31
ATP
Adenosine tri-phosphate | Formed from inorganic phosphate and ADP during photophosphorylation
32
NADP
Co.enzyme reduced to NADPH by the addn. of protons and electrons at the end of the light dependent stage
33
Photolysis
2H2O ---> 4 H+ and 4 e- and O2 H+ and e- used in photophosphorylation O2 used in respiration and/or released
34
Non cyclic photophosphorylation
Involves PSII and PSI | Produces ATP, oxygen and reduced NADP
35
Cyclic photophosphophorylation
Involves PSI | Produces ATP in smaller amounts. No photolysis involved so no protons or oxygen produced
36
Process of cyclic photophosphorylation
Light hits a chlorophyll molecule in PSI and e- in primary pigment is raised to a higher energy level until it leaves Passed along electron transport chain and energy is released in small amounts to pump H^+ into the thylakoids disc Builds up conc. gradient Diffuse back out through specialised channels attached to ATP synthase Movement provides energy to combine ADP and Pi (chemiosmosis)
37
Non-cyclic vs cyclic photophsophophorylation
The electrons from the chlorophyll a aren't passed onto NADP but are passed back to PSI via electron carriers
38
Role of chlorophyll in photolysis
It is the lost electrons from photolysis that go to the chlorophyll after absorbing light Causes more water to dissociate
39
How is energy of light converted into chemical energy in the LDR
Electrons excited Use of electrons carriers Production of ATP
40
Calvin cycle
6 CO2 (+ RuBisCO) ---> 12 GP (+ 12 ATP) ---> 1,3 biphosphate (+12 NADPH) ---> 12 TP ---> 10 TP (5 ATP) ---> 6 RuBP
41
Light Independent Stage
Only happens during the day as it needs continuous supply of products from LDR (ATP/ NAPDH)
42
Where does the CO2 needed in LIS come from
CO2 from respiration and other organisms (people) enter leaf through stomata Diffuses to palisade layer then into cells then into stroma
43
Reactions in LIS
Carbon fixation Reduction Regeneration
44
Carbon fixation in LIS
CO2 combines w/ a CO2 acceptor (RuBP) Reaction is ctalysed by RuBisCO By accepting carboxylate group RuBP forms an unstable intermediate 6C compounds that immediately breaks down into GP compounds CO2 is now fixed
45
Reduction in LIS
ATP reacts w/ GP to form 1,3 biphosphate which is reduced using H from NADPH into TP
46
Regeneration in LIS
10/12 TP molecules are rearranged into 6 RuBP using phosphate groups from ATP. Remaining 2 TP are products and can be used to synthesise organic compounds
47
Use of triose phosphate
2 TP can be used to synthesise glucose Glucose can then be converted into sucrose, starch and cellulose (or used immediately in respiration) Synthesis of fatty acids, glycerol and amino acids Regeneration of RuBP
48
Factors affecting photosynthesis
Light Intensity CO2 conc. Temp Water stress
49
Light intensity as a factor of photosynthesis
Provides power to produce ATP and NADPH Light allows stomata to open, enabling gas exchange Transpiration occurs, allowing water from the roots
50
Molecules from Calvin Cycle in bright light
RuBP - high TP - high GP - low
51
Molecules from Calvin Cycle in dim light
RuBP - low TP - low so RuBP cannot be regenerated GP - high as cannot be reduced to TP
52
CO2 conc. as a factor of photosynthesis
CO2 levels in the atm. and aquatic habitats usually high enough to not become a limiting factor
53
Molecules from Calvin Cycle in high CO2
TP - High RuBP - low GP - high
54
Calvin Cycle in low CO2
RuBP - High as nothing for to acccept so it accumulates GP - low as cannot be made TP - low; cannot be made
55
Temp as factor of photosynthesis
25 - 30 degrees: rate increases 30 - 45 degrees: O2 more successfully competes w/ CO2 for active site of RuBisCO > 45 degrees: Enzymes denature
56
Calvin cycle as temp increases
CO2 not accepted by RuBP (denaturing/ O2 filling binding sites) Less GP therefore less TP RuBP initially accumulates but doesn't regenerate due to lack of RuBP
57
Non - cyclic photophosphorylation
Light is absorbed by PS2, e- in primary pigment raised to a higher energy level until it leaves PS Travels down etc releasing energy to pump H+ into thylakoid space Photolysis of H2O replaces e- lost from reaction centre in PS2 Light absorbed by PS1, excites e-, accepted by NADP and combines w/ excess H+ from ATP synthase Protons accumulate in thylakoid space, membrane impermeable to H+ so diffuse down channels associated w/ ATP synthase
58
Measuring the rate of photosynthesis
Use a photosynthometer, measures volume of O2 produced Use NaHCO3 as source of extra carbon Change temp, CO2 conc. (by adding NaHCO3 to aerated water), LI (moving lamp) Allow apparatus to equilibrate for 5 mins
59
Chemiosmosis
Uses an electrochemical gradient | Moving down a conc.gradient using a proton motive force
60
How many times does the Calvin cycle need to occur to produce 1 glucose molecule
6

LGS A-Level OCR Biology (42 decks)

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