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OCR A level Biology > 5.2.1 - Photoynthesis > Flashcards

5.2.1 - Photoynthesis Flashcards

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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
Q

Stroma

A

Contains enzymes needed for photosynthesis, DNA and ribosomes

26
Q

Thylakoids

A

Where the green pigment is found

Site of light absorption and ATP synthesis

27
Q

Chromatogrophy table

A

Pigment
Distance travelled by compound
Distance travelled by solvent
Rf value

28
Q

Paper chromatogrophy to seperate pigments

A

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
Q

Why do plants contain a mixture of diff pigments

A

Light is made up of many diff wavelengths

To allow plants to absorb maximum light for photosynthesis

30
Q

Photophosrylation

A

Production of ATP in the presence of light from ADP and Pi

31
Q

ATP

A

Adenosine tri-phosphate

Formed from inorganic phosphate and ADP during photophosphorylation

32
Q

NADP

A

Co.enzyme reduced to NADPH by the addn. of protons and electrons at the end of the light dependent stage

33
Q

Photolysis

A

2H2O —> 4 H+ and 4 e- and O2
H+ and e- used in photophosphorylation
O2 used in respiration and/or released

34
Q

Non cyclic photophosphorylation

A

Involves PSII and PSI

Produces ATP, oxygen and reduced NADP

35
Q

Cyclic photophosphophorylation

A

Involves PSI

Produces ATP in smaller amounts. No photolysis involved so no protons or oxygen produced

36
Q

Process of cyclic photophosphorylation

A

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
Q

Non-cyclic vs cyclic photophsophophorylation

A

The electrons from the chlorophyll a aren’t passed onto NADP but are passed back to PSI via electron carriers

38
Q

Role of chlorophyll in photolysis

A

It is the lost electrons from photolysis that go to the chlorophyll after absorbing light
Causes more water to dissociate

39
Q

How is energy of light converted into chemical energy in the LDR

A

Electrons excited
Use of electrons carriers
Production of ATP

40
Q

Calvin cycle

A

6 CO2 (+ RuBisCO) —> 12 GP (+ 12 ATP) —> 1,3 biphosphate (+12 NADPH) —> 12 TP —> 10 TP (5 ATP) —> 6 RuBP

41
Q

Light Independent Stage

A

Only happens during the day as it needs continuous supply of products from LDR (ATP/ NAPDH)

42
Q

Where does the CO2 needed in LIS come from

A

CO2 from respiration and other organisms (people) enter leaf through stomata
Diffuses to palisade layer then into cells then into stroma

43
Q

Reactions in LIS

A

Carbon fixation
Reduction
Regeneration

44
Q

Carbon fixation in LIS

A

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
Q

Reduction in LIS

A

ATP reacts w/ GP to form 1,3 biphosphate which is reduced using H from NADPH into TP

46
Q

Regeneration in LIS

A

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
Q

Use of triose phosphate

A

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
Q

Factors affecting photosynthesis

A

Light Intensity
CO2 conc.
Temp
Water stress

49
Q

Light intensity as a factor of photosynthesis

A

Provides power to produce ATP and NADPH
Light allows stomata to open, enabling gas exchange
Transpiration occurs, allowing water from the roots

50
Q

Molecules from Calvin Cycle in bright light

A

RuBP - high
TP - high
GP - low

51
Q

Molecules from Calvin Cycle in dim light

A

RuBP - low
TP - low so RuBP cannot be regenerated
GP - high as cannot be reduced to TP

52
Q

CO2 conc. as a factor of photosynthesis

A

CO2 levels in the atm. and aquatic habitats usually high enough to not become a limiting factor

53
Q

Molecules from Calvin Cycle in high CO2

A

TP - High
RuBP - low
GP - high

54
Q

Calvin Cycle in low CO2

A

RuBP - High as nothing for to acccept so it accumulates
GP - low as cannot be made
TP - low; cannot be made

55
Q

Temp as factor of photosynthesis

A

25 - 30 degrees: rate increases
30 - 45 degrees: O2 more successfully competes w/ CO2 for active site of RuBisCO
> 45 degrees: Enzymes denature

56
Q

Calvin cycle as temp increases

A

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
Q

Non - cyclic photophosphorylation

A

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
Q

Measuring the rate of photosynthesis

A

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
Q

Chemiosmosis

A

Uses an electrochemical gradient

Moving down a conc.gradient using a proton motive force

60
Q

How many times does the Calvin cycle need to occur to produce 1 glucose molecule

A

6

OCR A level Biology (25 decks)

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