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3.5.1 Photosynthesis (A-level only)

3.5.1 Photosynthesis (A-level only)
Subject

Biology

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3.5 Photosynthesis

Light dependant reaction – occurs in THYLAKOID

  1. Photolysis occurs. Water is split into electrons, protons and oxygen.
  2. Chlorophyll absorbs light, becoming photoionised.
  3. Electron’s get ‘excited’ and increase in energy level, they leave chlorophyll and get accepted by a primary electron acceptor.
  4. Some of the energy released from electrons during photoionisation is conserved in the production of ATP and reduced NADP.
  5. The electrons are passed down a series of redox reactions by an electron carrier.
  6. Some energy is lost at this stage to form ATP from ADP + Pi
  7. The process by which this happens is called the Chemiosmotic theory:  Electrons from photolysis are taken up by proteins embedded in the thylakoid membrane and are passed along the proteins [the electron transfer chain]  this releases energy [energy also used from photolysis] which is used to pump protons from stroma to thylakoid space [across membrane]  high proton concentration in the thylakoid  proton's move down an electrochemical gradient from thylakoid into stroma via facilitated diffusion through ATP synthase channels [protein channel/enzyme]  this catalyses the reaction of ADP + Pi ATP
  8. NADP in stroma takes up protons and electrons to form reduced NADP

Products: ATP and NADP reduced

Light independent reaction – occurs in STROMA

Calvin Cycle:

  1. CO 2 from atmosphere diffuses into leaf through stomata  cells  chloroplast membrane  stroma.
  2. CO 2 reacts with RuBP (5C) to form 2 molecules of GP (glycerate 3-phosphate)
  3. Enzyme Rubisco catalyses this reaction.
  4. Reduced NADP and energy from ATP from light-dependant reaction are used to reduce GP to TP (triose phosphate)
  5. NADP is re-formed and goes back to light-dependant reaction
  6. 1 carbon molecule leaves the cycle and some TP molecules converted into organic substances [eg. glucose]
  7. Most TP is used to regenerate RuBP using ATP from light-dependant reaction.

(1 round of the cycle forms 1 carbon so the cycle must happen 6 times to form a hexose sugar, eg. glucose)

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3.5.1 Photosynthesis (A-level only)

Subject: Biology

999+ Documents
Students shared 1274 documents in this course
Degree • Grade:

Sixth Form (A Levels)

• A2 - A Level
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3.5.1 Photosynthesis
Light dependant reaction – occurs in THYLAKOID
1. Photolysis occurs. Water is split into electrons, protons and oxygen.
2. Chlorophyll absorbs light, becoming photoionised.
3. Electron’s get ‘excited’ and increase in energy level, they leave chlorophyll and get
accepted by a primary electron acceptor.
4. Some of the energy released from electrons during photoionisation is conserved in the
production of ATP and reduced NADP.
5. The electrons are passed down a series of redox reactions by an electron carrier.
6. Some energy is lost at this stage to form ATP from ADP + Pi
7. The process by which this happens is called the Chemiosmotic theory:
Electrons from photolysis are taken up by proteins embedded in the thylakoid
membrane and are passed along the proteins [the electron transfer chain]
this releases energy [energy also used from photolysis] which is used to pump
protons from stroma to thylakoid space [across membrane]
high proton concentration in the thylakoid
proton's move down an electrochemical gradient from thylakoid into stroma via
facilitated diffusion through ATP synthase channels [protein channel/enzyme]
this catalyses the reaction of ADP + Pi ATP
8. NADP in stroma takes up protons and electrons to form reduced NADP
Products: ATP and NADP reduced

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