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Biology > 11. Photosynthesis > Flashcards

11. Photosynthesis Flashcards

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1
Q

What is the site of photosynthesis

A
  • leaf (organ)

- chloroplast (organelle)

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2
Q

What 3 substances is the leaf adapted for

A
  • CO2
  • water
  • light
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3
Q

List adaptations of the leaf

A
  • large SA (for light)
  • thin (most light absorbed within first few micrometers, keeps diffusion distance shirt)
  • long narrow upper mesophyll packed with chloroplasts that collects sunlight
  • numerous stomata so all mesophyll cells are a short diffusion from one
  • air spaces in lower mesophyll layer
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4
Q

Write the overall equation for photosynthesis

A

6CO2 + 6H2O ——> C6H12O6 + 6O2

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5
Q

Name the three main stages of photosynthesis

A
  1. capturing of light energy
  2. light dependent reaction
  3. light independent reaction
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6
Q

What is light captured by

A

Chloroplast pigment such as chlorophyll

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7
Q

What occurs in the light dependent reaction

A
  • in which some of the light energy is absorbed and conserved in chemical bonds
  • electron flow is created by photolysis of water into protons, electrons and oxygen
  • products are NADPH ATP and oxygen
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8
Q

What occurs in the light independent reaction

A

-protons (hydrogen ions) are used to produce sugars and other organic molecules

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9
Q

Where does the light dependent reaction take place

A

The grana on structures called thylakoids

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10
Q

Where does the light independent reaction take place

A

The stroma

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11
Q

What is the grana

A
  • stacks of thylakoids
  • where LDR takes place
  • thylakoids contain chlorophyll
  • some have inter-granal lamellae that are tubular extensions that join up with thylakoids in adjacent grana
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12
Q

What is the stroma

A
  • fluid filled matrix
  • light independent stage of photosynthesis takes place
  • in stroma there are another series of structures such as starch grains
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13
Q

What two purposes does the capture of light energy have un the LDR

A
  • to add an inorganic phosphate (Pi) molecule to ADP, producing ATP
  • to split water into H+ ions (protons) and OH- ions (photolysis)
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14
Q

What is the biological definition of oxidation

A
  • when a substance
  • gains oxygen
  • loses hydrogen
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15
Q

What is the biological definition of reduction

A
  • when a substance
  • loses oxygen
  • gains hydrogen
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16
Q

Describe photoionisation

A
  • the ionisation of the chlorophyll molecule
  • as a result of the electrons moving to an excited state
  • caused by the light energy absorbed by the chlorophyll
  • two electrons lost from Mg prosthetic group
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17
Q

If chlorophyll loses a pair of electrons it is said to be…

A

oxidised

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18
Q

What are the two electrons from photoionisation energy taken up by

A

electron carrier

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19
Q

What is the mechanism by which ATP is produced explained by

A

The chemiosmotic theory

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20
Q

Describe the steps in the LDR (up to chemiosmotic theory)

A
  • chlorophyll absorbs light energy, causing the electrons to be promoted to an excited state, ionising the chlorophyll molecule. This is photoionisation.
  • the electrons that leave the chlorophyll are taken up by an electron carrier
  • the electrons pass down along a number of electron carriers in a series of oxidation reduction reactions that happens in the membranes of the thylakoids
  • each new carrier is a slightly lower energy level than the previous so the electrons lose energy at each stage
  • some of the energy released is conserved in the production of ATP (and indirectly NADPH)
  • the replacement of electrons from the chlorophyll molecule is provided by the photolysis of water
  • this can be explained by the chemiosmotic theory
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21
Q

Describe the steps in the LDR (after the chemiosmotic theory)

A
  • each thylakoid is an enclosed chamber in which protons are pumped (active transport) from the stroma to the thylakoid space using protein carriers in the thylakoid membrane
  • the energy of this comes from the photoionization of chlorophyll and the electrons through the electron transport chain
  • photolysis of water also produces protons (further increasing amount of protons in the thylakoid space)
  • this maintains a concentration gradient for the protons meaning the protons from the water crosses the thylakoid membrane through ATP synthase channel proteins
  • the rest of the membrane is impermeable to protons
  • as protons pass through the ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination if ADP with Pi to form ATP
  • these protons are taken up by NADP producing NADPH
22
Q

What are electrons that leave the chlorophyll taken up by

A

Electron carrier proteins in the thylakoid membrane

23
Q

How do electrons lose energy moving down the electron carrier chain

A

Each new carrier level is a slightly lower energy than the previous

24
Q

What is some of the energy conserved from the electron transport chain used in

A

The production of ATP (and indirectly NADPH)

25
Q

How are the electrons replaced in the chlorophyll molecule

A

By the electrons released in the photolysis of water

26
Q

What supplies the energy for the active transport of H+ through electron carrier proteins

A

Photoionisation of chlorophyll causing electrons to flow through these electron carrier proteins.

27
Q

How is the reaction for ATP catalysed in the LDR

A

Protons move through the ATP synthase channels

28
Q

How is the reaction for ATP catalysed in the LDR

A

Protons move through the ATP synthase channel it changes to the structure of the enzyme which then catalyses the combination if ADP with Pi to form ATP

29
Q

Why is it important that NADP accepts protons

A
  • NADPH is needed in the LIR

- H + will cause the pH to decrease harming the cell (e.g denature enzymes)

30
Q

What are chloroplasts adapted for ie. what is their function

A

Capturing sunlight and carrying out LDR

31
Q

How are chloroplasts adapted for their function

A
  • thylakoids provide large surface area for attachment of chlorophyll electron carrier and enzymes that carry out LDR
  • network of proteins in grana hold chlorophyll in very precise manner that allows maximum absorption of light
  • granal membrane have ATP synthase channels which catalyse production of ATP
  • chloroplasts contain DNA and ribosmomes so they can quickly and easily manufacture some of the proteins involved in the light dependent reaction
32
Q

Why must the LDR take place before the LIR

A

LDR produces ATP and NADPH which is necessary in LIR

33
Q

What is the cycle called that takes place in the LIR

A

Calvin cycle

34
Q

Describe the calvin cycle

A
  • CO2 from the atmosphere diffuses into the leaf though stomata and through the cell-surface, cytoplasm and chloroplast membrane of a mesophyll cell into the stroma of the chloroplast
  • CO2 reacts with the 5C compounds RuBP catalysed by rubisco
  • this produces two molecules of 3C GP
  • NADPH from LDR is used to reduce GP to TP using ATP supplied by ATP
  • NADP is reformed and goes back to LDR
  • some TP molecules are converted into organic substances that the plant requires eg. starch
  • most TP are used to regenerated RuBP using ATP from the LDR
35
Q

How does CO2 enter the stroma

A

CO2 from the atmosphere diffuses into the leaf though stomata and through the cell-surface, cytoplasm and chloroplast membrane of a mesophyll cell into the stroma of the chloroplast

36
Q

What does RuBP stand for

A

Ribulose bisphosphate

37
Q

What does GP stand for

A

glycerate 3-phosphate

38
Q

What does TP stand for

A

triose phosphate

39
Q

How many carbons is RuBP

A

5

40
Q

What does Rubisco catalyse

A

The reaction of CO2 with RuBP

41
Q

What are organic molecules required by the plant

A
  • starch
  • cellulose
  • lipids
  • glucose
  • amino acids
  • nucleotides
42
Q

What fraction of carbon is used to make an orgnaic molecule in the LIR

A

1/6

43
Q

What is 5/6 of the carbons used to do in the LIR

A

Used to regenerate RuBP molecules using ATP

44
Q

What is the order of carbons

A

1C + 5C —- 2x 3C —- 2 x 3C —– 1 + 5C

45
Q

Write the three reactions in the LIR

A 
RuBP (5C) + CO2 (1C) ---> 2 GP (3C)
2 GP (3C) + NADPH  + ATP ---> 2 TP (3C) + NADP 
2 TP (3C) + ATP ---> RuBP (5C) + organic molecule (1C)
46
Q

What does CO2 react with in the calvin cycle and what is produced

A

RuBP. 2 GP is produced

47
Q

What does NADPH react with in the calvin cycle and what is produced

A

ATP and 2 GP. 2 TP is produced

48
Q

What does 2TP react with and produce

A

ATP. RuBP is regenerated and 1C organic molecule

49
Q

Why can the calvin cycle not take place without light if light is not required?

A

NADPH and ATP are vital in the Calvin cycle and are produced in the LDR which is dependent on light

50
Q

Why is the Calvin cycle temperature dependent

A

LIR is an enzyme controlled reaction and realises on Rubisco so if temperature too low/high enzymes cant function

51
Q

How is the chloroplast adapted to carry out the light-independent reaction

A
  • stroma contains all enzymes needed to carry out LIR
  • stromal fluid is membrane bound so a high concentration of enzymes and substrates can be maintained within it
  • stroma fluid surrounds grana so the products of LIR can readily diffuse into stroma
  • contains DNA and ribosomes so it can quickly and easily manufactures proteins involved in LIR
52
Q

Name 3 factors than could limit rate of photosynthesis

A
  • light intensity
  • CO2 concentration
  • temperature

Biology (23 decks)

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