Back to AI Flashcard MakerBiology /Biology IB HL - 8.3 Photosynthesis Part 2
Where are the products of the light dependent reactions used?
The products of the light dependent reactions (ATP and NADPH) are used in the light independent reactions
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Key Terms
Term
Definition
Where are the products of the light dependent reactions used?
The products of the light dependent reactions (ATP and NADPH) are used in the light independent reactions
Why is it called photophosphorylation?
Photophosphorylation may be either a cyclic process or a non-cyclic process
What does cyclic phosphorylation involve?
Cyclic photophosphorylation involves the use of only one photosystem (PS I) and does not involve the reduction of NADP+
What happens when light is absorbed by photosystem 1? Cyclic P
When light is absorbed by Photosystem I, the excited electron may enter into an electron transport chain to produce ATP
What happens to the de-energised electrons? Cyclic P
Following this, the de-energised electron returns to the photosystem, restoring its electron supply (hence: cyclic)
What are the 2 differences of cyclic phosphorylation?
As the electron returns to the photosystem, NADP+ is not reduced and water is not needed to replenish the electron supply
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| Term | Definition |
|---|---|
Where are the products of the light dependent reactions used? | The products of the light dependent reactions (ATP and NADPH) are used in the light independent reactions |
Why is it called photophosphorylation? | Photophosphorylation may be either a cyclic process or a non-cyclic process |
What does cyclic phosphorylation involve? | Cyclic photophosphorylation involves the use of only one photosystem (PS I) and does not involve the reduction of NADP+ |
What happens when light is absorbed by photosystem 1? Cyclic P | When light is absorbed by Photosystem I, the excited electron may enter into an electron transport chain to produce ATP |
What happens to the de-energised electrons? Cyclic P | Following this, the de-energised electron returns to the photosystem, restoring its electron supply (hence: cyclic) |
What are the 2 differences of cyclic phosphorylation? | As the electron returns to the photosystem, NADP+ is not reduced and water is not needed to replenish the electron supply |
How many photosystems does non-cyclic phosphorylation involve? | Non-cyclic photophosphorylation involves two photosystems (PS I and PS II) and does involve the reduction of NADP+ |
What happens when light is absorbed? NCP | When light is absorbed by Photosystem II, the excited electrons enter into an electron transport chain to produce ATP |
What does photoactivation of photosystem I do? NCP | Concurrently, photoactivation of Photosystem I results in the release of electrons which reduce NADP+ (forms NADPH) |
What reaction is in NCP and not in cyclic P? | The photolysis of water releases electrons which replace those lost by Photosystem II (PS I electrons replaced by PS II) |
When is cyclic phosophorylation used? | Cyclic photophosphorylation can be used to produce a steady supply of ATP in the presence of sunlight |
Can ATP be stored? | However, ATP is a highly reactive molecule and hence cannot be readily stored within the cell |
What does NCP produce? | Non-cyclic photophosphorylation produces NADPH in addition to ATP (this requires the presence of water) |
What is needed to synthesise organic molecules in light independent? | Both NADPH and ATP are required to produce organic molecules via the light independent reactions |
What is the main advantage of NCP? | Hence, only non-cyclic photophosphorylation allows for the synthesis of organic molecules and long term energy storage |
What is the purpose of the light independent reactions? | The light independent reactions use the chemical energy derived from light dependent reactions to form organic molecules |
Where do the light independent reactions occur? | The light independent reactions occur in the fluid-filled space of the chloroplast called the stroma |
What are the light independent reactions collectively known as? | The light independent reactions are collectively known as the Calvin cycle |
What are the 3 main steps of Calvin cycle? | Carboxylation of ribulose bisphosphate
Reduction of glycerate-3-phosphate
Regeneration of ribulose bisphosphate |
What compound does Calvin begin with? | The Calvin cycle begins with a 5C compound called ribulose bisphosphate (or RuBP) |
What happens to ribulose biphosphate? | An enzyme, RuBP carboxylase (or Rubisco), catalyses the attachment of a CO2 molecule to RuBP |
What happens to the carboxylated RuBP? | The resulting 6C compound is unstable, and breaks down into two 3C compounds – called glycerate-3-phosphate (GP) |
How many RuBP are involved in one cycle? | A single cycle involves three molecules of RuBP combining with three molecules of CO2 to make six molecules of GP |
What is glycerate-3-phosphate converted into? | Glycerate-3-phosphate (GP) is converted into triose phosphate (TP) using NADPH and ATP |
How are hydrogen atoms transferred to the compound and what provides energy? | Reduction by NADPH transfers hydrogen atoms to the compound, while the hydrolysis of ATP provides energy |