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Cell Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What are catabolic pathways?

A
  • Break down complex molecules into simpler compounds

- Releases energy

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2
Q

Give 2 examples of catabolic pathways

A
  • Glycolysis

- Krebs cycle

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3
Q

What are anabolic pathways?

A
  • Builds complicated molecules from simpler ones

- Consume energy

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4
Q

Give an example of an anabolic pathway

A

Photosynthesis

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5
Q

What is the balanced equation for photosynthesis?

A

6CO2 + 6H2O + ENERGY ——> C6H12O6 + 6CO2

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6
Q

Where does photosynthesis occur?

A

In chloroplasts

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7
Q

Where does the light dependent stage occur?

A

On the thylakoid membranes

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8
Q

What are the organisms that can photosynthesise called?

A

Photoautotrophs

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9
Q

Where are chloroplasts found in leaves?

A

In mesophyll cells

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10
Q

How are electrons excited?

A

Through absorbing sunlight

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11
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 the thylakoid membrane, creating a gradient
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12
Q

How is a proton gradient maintained?

A

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

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13
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)
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14
Q

What is the primary pigment in photosynthesis?

A

Chlorophyll a

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15
Q

What colours does chlorophyll absorb?

A

Red and blue light

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16
Q

What colour does chlorophyll reflect?

A

Green light

17
Q

Name 2 accessory pigments

A

1- Chlorophyll b

2- Carotenoids

18
Q

Where are the accessory pigments located?

A

Thylakoid membrane

19
Q

What is the antennae complex?

A
  • Light harvesting system

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

20
Q

Where is chlorophyll a located?

A

Reaction centre

21
Q

What are photosystems?

A
  • Proteins with pigments attached
  • In thylakoid membrane
  • Made up of antennae complex and reaction centre
22
Q

What are the 2 forms of chlorophyll a?

A

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

23
Q

What are the 2 stages of photosynthesis?

A
  • Light dependent stage

- Light independent stage

24
Q

Where does the light independent stage happen?

A

In the stroma

25
Q

Describe non-cyclic photophosphorylation

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 phosphorylase 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
26
Q

What is photolysis?

A

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

  • The electrons released replace the electrons lost from the reaction centre of PS2
  • O2 = “waste gas”, used in respiration
27
Q

What are the 3 products from the light dependent stage?

A

1- ATP
2- NADPH
3- O2

28
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 storms
  • Proton gradient forms across thylakoid membrane
  • H+ diffuses down gradient through ATP synthase
  • This releases energy
  • Allows ADP + Pi —> ATP
  • Electrons are continuously recycled
29
Q

Describe the light independent stage (Calvin cycle)

A
  • CO2 diffuses into the leaf via the stomata, across spaces of spongy mesophyll into mesophyll cells, then into stroma
  • CO2 is picked up by 5C acceptor molecule = RUBP
  • This is catalysed by the enzyme RuBisCo
  • An unstable 6C molecule us formed
  • Immediately splits into 2x GP
  • GP is converted into 2x TP
  • NADPH acts as a reducing agent, donating H
  • ATP acts as an energy source
30
Q

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

A
  • NADPH acts as a reducing ages to, donating H

- ATP acts as an energy source

31
Q

What is TP and what is it used for?

A
  • 3C sugar
  • 5/6 used to regenerate RUBP
  • 1/6 converted into sugars
32
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
33
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 = photoprespiration - less PHS
34
Q

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

A

Above 30 degrees, causing problems for plants living at high temps

35
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

36
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
37
Q

What is photophosphorylation?

A
  • Synthesis of ATP
  • Addition of phosphate group to ADP
  • Use energy from light
38
Q

What is chemiosmosis?

A
  • Protons diffuse back out of the thylakoids down their concentration gradients
  • Diffuse through the ATP synthase enzyme
  • H+ release energy during this, which allows ADP to join with Pi to form ATP
39
Q

What does chemiosmosis depend on?

A
  • The creation of a proton concentration gradient

- The energy to do this comes from excited electrons

Cell Biology (8 decks)

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