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biology topic 8 > 8.3 - metabolism, cell respiration and photosynthesis > Flashcards

8.3 - metabolism, cell respiration and photosynthesis Flashcards

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1
Q

what is photosynthesis?

A
  • when cells synthesise organic molecules (glucose) from inorganic molecules (water and CO2) in the presence of sunlight
  • process requires the chloroplast that contains photosythetic pigments called chlorophyll
  • 2 step process, light dependant and light independant
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2
Q

what is the light-dependent reaction of photosynthesis?

A
  • light energy into chemical energy (ATP) by light-harvesting areas called photosystems
  • needs continual light supply
  • in thylakoid space (lumen) and across thylakoid membranes
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3
Q

what is the light-independant reaction of photosynthesis?

A
  • in stroma of chloroplast
  • also called Calvin cycle
  • stroma has many enzymes needed to carry out Calvin cycle
  • use ATP, NADPH and hydrogen ions with CO2 are used to produce sugars
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4
Q

what is the light-dependent reaction process?

A
  • light energy is used to split water mols hydrogen ions, oxygen and electrons
  • the H+ ions and electrons are used to produce ATP and NADPH
  • oxygen is a by-product and is considered a waste and diffuses out of chloroplast
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5
Q

what are the products of light-dependent reactions?

A
  • Forms ATP and reduced NADP+
  • reduced NADP+ is called NADPH
  • NADP+ is a phosphorylated version of the electron carrier NAD+, used in cell respiration
  • both ATP and NADPH are energy sources for light-independent reactions
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6
Q

what are photosystems?

A
  • large light-harvesting areas in thylakoids that contain chlorophyll and accessory pigments
  • photosystems l and photosystems ll
  • have a reaction centre
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7
Q

what is photo activation?

A
  • both have many moles of chlorophyll for the absorption of light energy, then passed to 2 special chlorophyll moles in the reaction centre.
  • when special chlorophyll moles absorb the light energy an electron within the molecule becomes excited
  • now the chlorophyll is photo-activated
  • chlorophylls at the reaction centre give excited elecs to an elec acceptor
  • photosystem ll is the first involved.
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8
Q

what happens in photosystem ll?

A
  • 2 excited elecs are accepted by Plastoquinone (Pq) which moves to another spot on the thylakoid mem
  • the absorption of 2 photos on light produces 1 reduced plastoquinone and one of the chlorophylls in the reaction centre lost 2 electrons
  • photosystem ll repeats this process so that 2 reduced plastoquinone moles are produced and 4 elecs lost from chlorophyll
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9
Q

what is photolysis?

A
  • the splitting of water mols caused by reduced Pq at photosystem ll
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10
Q

what is the process of photolysis?

A
  • when Pq is reduced the chlorophyll in reaction centre becomes a powerful oxidising agent that causes water mols to split and donate electrons
    2H2O –> O2 + 4H+ + 4e-
  • photolysis makes oxygen as a waste product that diffuses out chloroplast
  • the reduced Pq is useful product pf Photosystem ll as it carries the pair of elecs and most energy from absorbed light which is needed in photosynthesis
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11
Q

what is the electron transport chain?

A
  • reduced Pq is needed to carry a pair of excited electrons from the reaction centre of photosystem II to the start of the chain of electron carriers in the thylakoid membranes
  • electrons are passed from one carrier to another, releasing energy
    don’t confuse with cell metabolism in mitochondria
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12
Q

what does the proton gradient do?

A
  • when Pq transfers its e- they are passed down the e- transport chain in thylakoid mem
  • as e- are passed energy is released
  • energy is taken pump proteins (H+) across thylakoid mem into thylakoid space (lumen)
  • makes a concentration gradient of H+ to store potential energy
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13
Q

what is chemiosmosis?

A

-occurs in mitochondria during aerobic respiration
- when e- reaches end of chain of carriers they are passed to plastocyanin for next stage of photosynthesis

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14
Q

what happens when protons move down their gradient?

A
  • the protons can travel back across thy mem into stroma by passing through enzyme ATP synthase
  • energy relased from protons when moving down their gradient is used to make ATP from ADP and Pi
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15
Q

what is plastocyanin?

A
  • an electron acceptor in the fluid inside thylakoid
  • reduced plastocyanin is needed for the next stage of photosynthesis.
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16
Q

Reduction of NADP in photosystem I.

A
  • remainder of light-dependant reactions involve photosystem I.
  • product of reaction is reduced NADP, NADPH, which is used in light-independent reactions
  • NADPH carries a pair of e- to be used in reduction reactions
  • in photosystem I chlorophyll mols absorb and harness light energy that is then passed to 2 special chlorophyll moles in reaction centre.
  • this increases 1 e- in the chloro mol to a higher energy level leading to photoactivation
  • the excited e- is passed along chain and passed to ferredoxin
  • 2 reduced mol of ferredoxin are used to reduce NADP+ to NADPH
17
Q

what is cyclic photophosphorylation?

A
  • sometimes the supply of NADP+ can run out and the e- are passed back into the e- chain rather than passed to NADP+
  • as electrons flow back along the chain to photosystem I, it causes protons to be pumped for more ATP production
18
Q

what is non-cyclic photophosphorylation?

A

when both photosystems II and I are linked as electrons excited in photosystem II is passed along chains of carriers to plastocyanin that donates it to photosystem I

19
Q

what is feradoxin?

A

a protein found outside the thylakoid

20
Q

how do light-dependent reactions require carboxylation?

A
  • the first stage of the reaction involves fixation of carbon dioxide
  • this happens in stroma of chloro and involves the reaction of CO2 with a 5- carbon molecule called ribulose bisphosphate (RuBP) to make t moles of a 3-carbon mol called glycerate-3-phosphate (GP)
  • reaction is catalysed by enzyme ribulose busphosphate carboxylase (RuBisCo) in the stroma
21
Q

how is glycerate-3-phosphate reduced?

A
  • for it to become a carbohydrate, hydrogen must be added
  • this reduction uses ATP and NADPH that were produced in the light-dependant reactions
  • ATP provides energy and NADPH provides hydrogen atoms
  • the product is a 3-carbon compound called triose phosphate

biology topic 8 (3 decks)

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