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Photosynthesis Flashcards

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1
Q

How does all energy enter ecosystems?

A

Sunlight

Captured by photoautotrophs

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2
Q

How does all energy leave ecosystems?

A

As heat

from respiration

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3
Q

What does exothermic mean?

A

Releases energy

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4
Q

What does endothermic mean?

A

Takes in energy

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5
Q

What is the balanced equation for photosynthesis?

A

6CO2 + 6H20 + ENERGY - - -> C6H12O6 + 6O2

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6
Q

What does compensation point mean?

A
  • The point at which the rate of PHS is equal to the rate of respiration
  • There is no net change in the mass of carbohydrate in the plants
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7
Q

Explain the changes in the rates of respiration and photosynthesis over the course of a day

A 
- Morning: 
RESP > PHS - low level light intensity
Net loss of carbohydrate by the plant 
(more used than made) 
NET RELEASE OF CO2
  • Afternoon:
    PHS > RESP - higher level light intensity
    Net production of carbohydrate by the plant
    (made faster than used)
    NET UPTAKE OF CO2
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8
Q

Is the breakdown of glucose (resp) exothermic or endothermic?

A

Exothermic

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9
Q

Why is the breakdown of glucose exothermic?

A
  • There is a net release of energy as the total energy required to break all the bonds in glucose is less than the total energy released when the bonds in CO2/H2O are formed
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10
Q

Is the formation of glucose (PHS) exothermic or endothermic?

A

Endothermic

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11
Q

Why is the formation of glucose endothermic?

A
  • Takes in energy from the sun
  • The energy needed to make the bonds in the glucose is more than the energy released when breaking the bonds in CO2 and H2O
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12
Q

What is an oxidation reaction?

A

Gain of O2, loss of electrons/hydrogen

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13
Q

What is a reduction reaction?

A

Loss of O2, gain of electrons/hydrogen

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14
Q

What are organisms that can photosynthesise called?

A

Photoautotrophs

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15
Q

What are photoautotrophs?

A

Organisms that can photosynthesise

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16
Q

Where does photosynthesis occur?

A

In chloroplasts

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17
Q

Where are chloroplasts found in leaves?

A

In mesophyll cells

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18
Q

How are palisade mesophyll cells adapted for photosynthesis?

A
  • Tall and thin rectangle cells, packed together tightly, creating a bigger SA for light absorption
  • Lots of chloroplasts that move around constantly to absorb max sunlight
  • Large vacuole pushes chloroplasts to side of cell so can absorb sunlight easier
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19
Q

Why is ATP the universal energy currency in cells?

A
  • Energy in ATP is used to drive essential metabolic processes
  • It’s small, soluble, readily available within cells and is released in manageable amounts
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20
Q

What is chemiosmosis?

A
  • Protons diffuse back out of the thylakoids down their conc gradient
  • Diffuse through the ATP synthase enzyme
  • H+ release energy during this, which allows ADP to join with Pi to form ATP
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21
Q

How are electrons excited?

A

Absorbing sunlight

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22
Q

What does chemiosmosis depend on?

A

The creation of a proton concentration gradient

The energy to do this comes from excited electrons

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23
Q

How is a proton gradient generated?

A
  • As high energy electrons pass from carrier to carrier, energy is released
  • This energy is used to move H+ across thylakoid membrane, creating a gradient
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24
Q

How is a proton gradient maintained?

A

As a result of the impermeability of the membrane to H+

25
Q

What is the only way that protons can move back through the membrane, down their concentration gradient?

A
  • Through hydrophilic membrane channels (facilitated diffusion)
  • Linked to ATP synthase
  • Flow of protons through channels provides energy to synthesise ATP (ADP + Pi)
26
Q

What is the primary pigment in photosynthesis?

A

Chlorophyll a

27
Q

What colours does chlorophyll absorb?

A

Red and blue light

28
Q

What colour does chlorophyll reflect?

A

Green light

29
Q

Give 2 accessory pigments

A

1- Chlorophyll b

2- Carotenoids

30
Q

Where are the accessory pigments located?

A

Thylakoid membrane

31
Q

What is an antennae complex?

A
  • Light harvesting system

- Absorbs light energy of different wavelengths and transfers it efficiently to reaction centre

32
Q

Where is chlorophyll a located?

A

Reaction centre

33
Q

What are photosystems?

A
  • Proteins with pigments attached
  • In thylakoid membrane
  • Made up of antennae complex and reaction centre
34
Q

What are the 2 forms of chlorophyll a?

A

1- P700 found in photosystem 1 (peak absorption of light is at wavelength 700nm)
2- P680 found in photosystem 2 (peak absorption of light is at wavelength 680nm)

35
Q

What is the formula for calculating Rf value?

A

Distance travelled by component / Distance travelled by solvent

36
Q

What are the 2 stages of photosynthesis?

A

1- The light dependent stage

2- The light independent stage

37
Q

Where does the light dependent stage happen?

A

On the thylakoid membranes

38
Q

Where does the light independent stage happen?

A

In the stroma

39
Q

Describe non-cyclic photophosphorylation in the light dependent stage

A
  • Photosystems arranged in pairs, PS2 first, then PS1
  • Chl-a in PS2 absorbs light, excited e- to a higher energy level
  • Passed along ETC via a protein carrier, as they do they lose energy
  • Energy released as the e- pass along is used to phosphorylate ADP = photophosphorylation
  • The e- that left PS2 are replaced by splitting of nearby water molecules (photolysis)
  • PS1 is also absorbing light and e- are excited
  • e- pass along ETC via carriers
  • Ferredoxin (iron-protein complex) passes the e- and H+ from the water to NADP
  • Causes NADP to become reduced = NADPH
40
Q

What is photolysis?

A

Water molecules are split into hydrogen ion, electrons and oxygen molecules using energy from the sun

  • The electrons released replace the electrons lost from the reaction centre of PS2
  • O2 = “waste gas” , used in respiration
41
Q

What are the 3 products from the light dependent stage?

A

1-ATP
2- NADPH
3- O2

42
Q

Describe cyclic photophosphorylation in the light dependent stage

A
  • Only involves PS1
  • Chlorophyll in PS1 absorbs light energy, exciting e- so they rise to a higher energy level
  • High energy e- pass down ETC through protein carriers
  • As e- pass down, energy is released
  • H+ is pumped into thylakoids from stroma
  • Proton gradient forms across thylakoid membrane
  • H+ diffuses down gradient through ATP synthase
  • This releases energy
  • Allows ADP + Pi —> ATP (chemiosmosis)
  • Electrons are continuously recycled
43
Q

Describe the light independent stage (Calvin cycle)

A
  • CO2 diffuses into the leaf via the stomata, across spaces of spongy mesophyll into meslphyll cells, then into stroma
  • CO2 is picked up by 5C acceptor molecule = RUBP
  • This is catalysed by the enzyme RuBisCo
  • An unstable 6C molecule is formed
  • Immediately splits into 2x GP
  • GP is converted into 2 x TP
  • NADPH acts as reducing agent, donating H
  • ATP acts as an energy source
44
Q

How are the useful products from the light dependent stage used in the Calvin cycle?

A
  • NADPH acts as reducing agent, donating H

- ATP acts as an energy source

45
Q

What is TP and what is it used for?

A
  • 3C sugar
  • 5/6 used to regenerate RUBP
  • 1/6 converted into sugars
46
Q

How is RuBP regenerated?

A
  • For 1 glucose molecule to be produced, 6 CO2 molecules have to enter cycle = 6 turns of cycle
  • 12 TP molecules made
  • 2 removed to make glucose
  • 10 TP molecules are recycled to regenerate 6 RuBP
  • 10 x 3carbon TP = 30 carbons shuffled
  • 6 x 5carbon RuBP = 30 carbons
  • Energy is supplied by ATP for the reactions involved in regeneration of RuBP
47
Q

Why is the RuBisCo enzyme not very efficient?

A
  • The reaction between RuBisCo and CO2 is competitively inhibited by O2
  • RuBisCo can also react with O2 = photorespiration = less PHS
48
Q

When is RuBisCo more likely to react with O2 instead of CO2?

A

Above 30°C, causing problems for plants living at high temps

49
Q

Why is it less likely that RuBisCo will react with O2 instead of CO2?

A

RuBisCo has a higher affinity for CO2 than O2

50
Q

What is the role of water in PHS?

A
  • Photolysis in light dependent stage
  • Source of e- to replace those from PS2
  • Source of H+, used in chemiosmosis to make ATP and join with NADP at the end
  • Source of O2, reused in plant cell respiration
  • Keeps plant cells turgid, which is necessary for cellular reactions to take place
51
Q

What is photophosphorylation?

A
  • Synthesis of ATP
  • Addition of phosphate group to ADP
  • Use energy from light
52
Q

What does the “law of limiting factors” state?

A

The rate of a physiological process is limited by the factor that is in the shortest supply

53
Q

What 3 factors can limit photosynthesis?

A
  • Light intensity
  • CO2 concentration
  • Temperature
54
Q

How does light intensity affect the rate of photosynthesis?

A
  • Light is needed as an energy source
  • Low light intensity = NADPH & ATP in short supply
  • Conversion of GP to TP is slow
  • GP will rise as it’s still being made & TP and RuBP will fall as they’re used to make GP
  • High light intensity = more ATP and NADPH produced = more energy
55
Q

How does carbon dioxide concentration affect the rate of photosynthesis?

A
  • Source of carbon
  • Low CO2 = conversion of RuBP to GP is slow as there is less CO2 to combine with RuBP
  • RuBP will rise as it’s still being made
  • GP & TP will fall as theyre being used to make RuBP
  • High CO2 = more GP & TP
56
Q

How does temperature affect the rate of photosynthesis?

A
  • Affects the rate of enzyme- controlled reactions
  • All reactions in calvin cycle are catalysed by enzymes, e.g. RubIsCO
  • Lower temperatures = slower reactions if enzymes are inactive (below 10°C)
  • RuBP, GP & TP will fall
  • Higher temperatures = rate of enzyme activity increases
  • More KE
  • More successful collisions
  • Increases the rates of carbon fixation - more GP, TP and RuBP
  • Until they denature (above 45°C)
  • However, the rate of photorespiration also increases above 25°C, meaning higher photosynthetic rates may not be seen at higher temps even if enzymes aren’t actually denatured
57
Q

Why is water never considered a limiting factor in photosynthesis?

A

For water potential to have become low enough to limit rate of PHS, the plant will already have closed its stomata and ceased PHS

58
Q

What other factors could potentially limit the rate of PHS?

A
  • Availability of pigment molecules
  • Number of chloroplasts in a cell
  • Mineral ion availability

Biology (19 decks)

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