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A2 BIO UNIT3 > 3.2 Photosynthesis > Flashcards

3.2 Photosynthesis Flashcards

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1
Q

Adaptation of the cuticle for photosynthesis

A
  • stops the leaf from losing water
  • transparent so light can penetrate to mesophyll
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2
Q

Adaptation of the epidermis for photosynthesis

A
  • protective layer
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3
Q

Adaptations of palisade cells for photosynthesis

A
  • cylindrical and elongated at right angles to the surface of the leaf
  • enable light to reach the chloroplasts to accommodate large numbers
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4
Q

Adaptations of air spaces for photosynthesis

A
  • create diffusion gradient for gas exchange
  • increase SA to exchange gas
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5
Q

Adaptations of stoma for photosynthesis

A
  • able to let CO2 in and O2 out for gas exchange and photosynthesis
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6
Q

Adaptations of guard cells for photosynthesis

A
  • control the opening and closing of stomata based on external conditions
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7
Q

Adaptations of the vein for photosynthesis

A
  • steady supply of water to leaf
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8
Q

Define an absorption spectrum and an action spectrum

A

Absorption: a graph showing how much light is absorbed at different wavelengths
Action: a graph showing the rate of photosynthesis at different wavelengths
—> rate of photosynthesis at different wavelengths of light as measured by the mass of carbohydrate synthesised by plants exposed to different wavelengths

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9
Q

Rf equation

A

Rf = distance travelled by pigment
——————————————
distance traveled by solvent front

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10
Q

What is meant by saying chloroplasts are transducers?

A
  • they convert light energy to chemical energy in ATP
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11
Q

Name the photosynthetic pigments and the value of having multiple

A
  • chlorophyll a and b, beta carotene, and xanthophylls
  • different pigments absorb light at different wavelengths, utilising most of the visible light spectrum
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12
Q

What is the most significant pigment of the reaction centre?

A
  • chlorophyll a and b
  • they excite electrons
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13
Q

Where are photosystems found?

A

Thylakoid membrane

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14
Q

Describe a photosystem

A
  • antenna complex containing photosynthetic pigments
    —> array of protein and pigment molecules that transfer energy from light to chlorophyll a
    —> harvest energy to pass onto reaction centre for excitation
  • reaction centre that contains 2 molecules of chlorophyll a that get excited, emitting an electron
    —> electrons are passed down electron carriers and gradually lose energy to make ATP
    —> electrons fall back to photosystem or go to diff one to end up making water
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15
Q

Describe the two types of reaction centre

A
  • PSI - two chlorophyll a molecules with an absorption peak of 700nm
  • PSII - two chlorophyll a molecules with an absorption peak of 680nm
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16
Q

Define cyclic photophosphorylation

A

ATP can be produced by electrons that take a cyclical pathway and are recycled back into the chlorophyll a in PSI

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17
Q

Define non-cyclic photophosphorylation

A

ATP can be produced by electrons that take a linear pathway from water, through PSII and PSI to NADP, which they reduce

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18
Q

Explain the light dependant stage and what it produces

A
  • light as energy source and using water
  • produces ATP to synthesise energy rich molecules
  • produces NADP which provides reducing power to produce molecules like CO2
  • oxygen is a byproduct derived from water
19
Q

Explain the passage of electrons in cyclic photophosphorylation

A
  • PSI absorbs photons which excites electrons in the chlorophyll a molecules in its reaction centre
  • these are emitted and picked up by an electron acceptor which passes them down a chain of electron carriers back to PSI
  • energy released phosphorylates ADP to ATP
  • electrons have flowed from PSI to the electron acceptor back to PSI, so this is described as cyclic
20
Q

Explain the passage of electrons in non-cyclic photophosphorylation

A
  • electrons are transferred from the electron acceptor to oxidised NAP in the stroma which is reduced
  • electrons have not been returned to PSI so its chlorophyll is left with a positive charge
  • the positive charge is neutralised by electrons from PSII that have been excited to a higher energy level by light absorption, picked up by an electron acceptor and passed down the ETC to PSI
  • transport down the ETC makes energy available for the phosphorylation of ADP
  • chlorophyll in PSII is left with a positive charge which is neutralised by electrons from the photolysis of water
21
Q

Equation for the photolysis of water

A

2H2O —> 4H+ + 4e- + O2

22
Q

Explain the photolysis of water

A
  • water molecules absorb light which indirectly causes them to dissociate into hydrogen, oxygen and electrons
    —> enhanced by a protein complex in PSII which is the only known enzyme to cause water to be oxidised
  • electrons replace those lost from PSII
  • protons from water and electrons from PSI reduce NADP
  • oxygen diffuses out of stomata
23
Q

Explain the photolysis of water

A
  • water molecules absorb light which indirectly causes them to dissociate into hydrogen, oxygen and electrons
    —> enhanced by a protein complex in PSII which is the only known enzyme to cause water to be oxidised
  • electrons replace those lost from PSII
  • protons from water and electrons from PSI reduce NADP
  • oxygen diffuses out of stomata
24
Q

Explain the passage of protons and phosphorylation

A
  • electrons pass through a proton pump in the thylakoid membrane providing energy to pump protons from stroma into thylakoid space
  • protons join H+ ions from the photolysis of water and accumulate
  • generate an electrochemical gradient which is a source of potential energy
  • chemiosmosis occurs - H+ ions diffuse down electrochemical gradient through ATP synthetase into the stroma which makes energy available
  • ADP is phosphorylated to ATP
  • H+ ions are passed to oxidised NADP
25
Q

What are the 3 factors maintaining the proton gradient?

A
  • proton pump associated with ETC pushes protons into thylakoid space
  • photolysis of water in thylakoid space
  • removal of protons from stroma, reducing NADP
26
Q

Explain the light independent stage / Calvin cycle

A
  • a 5C acceptor molecule ribulose bisphosphate combines with carbon dioxide catalysed by the enzyme ribulose bisphosphate carboxylase
  • produces an unstable 6C compound which immediately splits into two molecules of a 3C compound glycerate-3-phosphate
  • GP is reduced to triose phosphate by reduced NADP
    —> energy provided by ATP made in light dependant stage
  • NADP is reformed
  • some of the triose phosphate is converted to glucose phosphate, then into starch by condensation
  • most of triose phosphate goes through reactions that regenerate RuBP for the cycle to continue
27
Q

3 phases of the Calvin cycle

A
  • carbon fixing
  • reduction
  • regeneration
28
Q

Production of carbohydrates from the Calvin cycle

A
  • fructose bisphosphate
  • converted to glucose and combined with fructose to make sucrose
  • alpha glucose converted to starch
  • beta glucose polymerised to cellulose
29
Q

Production of fats from the Calvin cycle

A
  • AcCoA can be synthesised from glycerate-3-phosphate and converted to fatty acids
  • triose phosphate can be directly converted to glycerol
  • fatty acids and glycerol undergo condensation to make triglycerides
30
Q

Production of proteins from the Calvin cycle

A
  • glycerate-3-phosphate can be converted to amino acids for protein synthesis
31
Q

Name the requirements of plants

A
  • CO2 and H2O
  • light at high intensity and suitable wavelength
  • suitable temperature
32
Q

Define a limiting factor

A
  • 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
33
Q

Explain CO2 as a limiting factor

A
  • limiting until hits >0.5% conc
34
Q

Explain light intensity as a limiting factor

A
  • light dependant stage not possible in dark so no O2 evolved
  • as intensity increases efficiency increases
  • when exceeds max it damages pigments so decreases efficiency
35
Q

Define light compensation point

A
  • light intensity at which a plant has no net gas exchange as the volume of gases used and produced in respiration and photosynthesis are equal to the
36
Q

Draw the Calvin cycle

A
37
Q

Use of nitrogen in plants

A
  • humus, organic molecules, decaying organisms
  • amino acids, protein, chlorophylls and nucleotides
38
Q

Use of magnesium in plants

A
  • major component of chlorophyll
  • enzyme activators for ATPase
39
Q

Magnesium and nitrogen deficiency symptoms

A

Nitrogen: stunted growth and chlorosis
Magnesium: chlorosis

40
Q

Describe how glycerate-3-phosphate is converted to triose phosphate

A
  • reduced using reduced NADP from light dependant reactions
  • NADP reformed
  • formation of TP
41
Q

Explain the effects of Diuron on non-cyclic photophosphorylation and why cyclic is not affected

A
  • blocked reduction of NADP
  • electron emitted by PSII cannot travel down ETC
  • cyclic only involves PSI and the carrier involved is not impacted
42
Q

Why would a plant die when Diuron is sprayed onto it?

A
  • plant cannot generate NADPH
  • Calvin cycle cannot work
  • no glucose so no respiration
43
Q

How does blocking electron transport systems from photosystems lead to the death of a plant?

A
  • destruction of chlorophyll makes unable to absorb light energy
  • no reduced NADP for Calvin cycle
  • no glucose for respiration
  • no ATP for active transport of minerals and nutrients
  • destruction of cell membranes
44
Q

Explain shape of the rate graph for CO2 and RuBP

A
  • initially CO2 and RuBP reaction continues
    -GP cannot be converted to TP as ATP and reduced NADH needed
  • only produced in light dependant reactions which can’t happen if dark
  • less TP to regenerate RuBP
  • rate of reaction decreases

A2 BIO UNIT3 (8 decks)

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