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Alevel Biology OCR > 5.2.1 - Photosynthesis > Flashcards

5.2.1 - Photosynthesis Flashcards

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1
Q

What is photosynthesis?

A

a process that converts light energy into chemical energy

-energy is used to synthesise large organic molecules from inorganic substances

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2
Q

What is the equation for photosynthesis?

A

carbon dioxide + water -> glucose + oxygen

6CO2 + 6H20 -> C6H12O6 + 6O2

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3
Q

What is an autotroph?

A

an organism that uses energy and inorganic molecules to synthesise organic molecules

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4
Q

What is a chemoautotroph?

A

an organism that synthesises complex organic molecules using energy from exergonic reactions

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5
Q

What is a photoautotroph?

A

an organism that can photosynthesise

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6
Q

Describe the structure of a chloroplast

A
  • double membrane
  • stacks of thylakoids (granum) -LDS on thylakoid membrane
  • intergranal lamella join grana together
  • stroma (fluid filled matrix containing enzymes, DNA, ribosomes, starch, etc) -LIS
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7
Q

What are photosynthetic pigments?

A

pigments that absorb light energy

-different pigments absorb different wavelengths

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8
Q

What are the two main types of photosynthetic pigments?

A 
chlorophylls 
-chlorophyll a
-chlorophyll b
carotenoids
-xanthophyll
-carotene
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9
Q

What is a photosystem?

A

a funnel found in thylakoid membrane which light is reflected down (by accessory pigments) to the reaction centre (primary pigment)

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10
Q

What are the accessory pigments?

A
  • xanthophylls
  • carotenes
  • chlorophyll b
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11
Q

What is the primary pigment?

A

chlorophyll a

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12
Q

What is an absorption spectrum?

A

a graph of different wavelengths of light by a pigment
(-chlorophylls absorb red + blue regions and reflect green
-carotenoids absorbs blue/purple region)

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13
Q

What is an action spectrum?

A

a graph of the rate of photosynthesis at different wavelengths of light

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14
Q

What are the two stages of photosynthesis?

A
  • light dependant stage

- light independent stage

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15
Q

Where does the light dependant stage occur?

A

thylakoid membrane

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16
Q

What does the electron transport chain do?

A

makes ATP (needed as energy for the rest of the reactions in photosynthesis)

17
Q

What is the role of water in the light dependent stage?

A

in PSII, an enzyme splits a molecule of water into H+ ions, electrons and oxygen (photolysis)

  • electrons replace the ones previously lost in PSII
  • H+ ions combine with the electrons in PSI and are accepted by NADP to become redNADP
18
Q

What is cyclic photophosphorylation?

A

when some of the electrons lost from PSI return back to PSI

-on the way, these electrons loose energy, which is used to convert ADP into ATP

19
Q

What is the roles of electron carriers in the light dependent stage?

A

transport excited electrons down an electron transport chain

20
Q

What happens in the light dependent stage?

A
  • photon of light reflected down PSII and absorbed by chlorophyll
  • excites 2 e- which then move down an electron transport chain to PSI
  • photon of light hits PSI where e- get excited and move down an electron transport chain
  • electrons lost from PSI are replaced with electrons from PSII
  • some e- lost from PSI return back to PSI (cyclic phosphorylation)
  • these e- loose energy on the way, which is used to convert ADP to ATP
  • in PSII, a molecule of water is split into H+ ions, electrons and oxygen (photolysis)
  • these e- replace the ones lost from PSII
  • H+ ions (from H2O molecule) combine with e- from PSI and are accepted by NADP to form redNADP (aka NADPH)
  • H+ ion gradient is formed across the thylakoid membrane and H+ ions flow down the gradient through channel proteins (chemiosmosis)
  • as they do so, they switch on ATP synthase and ATP is made from ADP (photophosphorlyation)
21
Q

What is the Calvin Cycle?

A

the light independent stage of photosynthesis

22
Q

Where does the the light independent stage occur?

A

stroma of chloroplasts

23
Q

What products of the light dependent stage are used in the light independent stage?

A

ATP

redNADP

24
Q

What happens in the light independent stage?

A
  • CO2 combines with RuBP which is catalysed by Rubisco (CO2 is fixed and RuBP is carboxylated)
  • this forms an unstable 6C intermediate
  • this intermediate splits into 2 GP compounds
  • GP is reduced and phosphorlyated (uses redNADP and ATP from LDS)
  • this forms 2 TP compounds
  • 10 out of every 12 TP produced are used to regenerate RuBP (using ATP from LDS)
  • 2 out of every 12 TP produced are used to make biological molecules
25
Q

What is produced in the light independent stage of photosynthesis?

A
  • GP

- TP

26
Q

How are the products from the light independent stage used?

A
  • GP is used to make amino acids and fatty acids (used to make proteins and lipids)
  • TP is used to make hexose sugars and glycerol (used to make carbohydrates and lipids)
27
Q

What is the role of ribulose bisphosphate carboxylase (Rubisco)?

A

catalyses carbon fixation (RuBP and CO2 combining)

28
Q

What are the limiting factors of photosynthesis?

A
  • light intensity
  • temperature
  • carbon dioxide concentration
29
Q

Why is light intensity a limiting factor?

A
  • needed for stomata to open
  • needed to excite e- in LDS
  • needed for photolysis in LDS
  • e- and H+ are needed in photophosphorylation in LIS
30
Q

Why is temperature a limiting factor of photosynthesis?

A
  • enzymes needed (eg. Rubisco in LIS)
  • when too high, water is lost and stomata close
  • increased oxygen production causes O2 molecules to compete for Rubisco’s active site, preventing Rubisco from accepting CO2 (photorespiration)
31
Q

Why is carbon dioxide a limiting factor of photosynthesis?

A

-needed for LIS

32
Q

What is photorespiration?

A

when oxygen molecules bind to Rubisco’s active site (instead of carbon dioxide) which doesn’t release any ATP

33
Q

What effect does darkness have on the levels of GP, TP and RuBP in the Calvin Cycle?

A
  • GP increases and TP decreases (redNAD and ATP from LDS are needed to convert GP into TP)
  • RuBP decreases (RuBP continues being converted into GP, increasing GP, but less TP is regenerated into RuBP)

Alevel Biology OCR (26 decks)

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