Energy is transferred between reactions
- Cells use energy released from exergonic reactions to fuel endergonic reactions – they happen simultaneously (at the same time).
- Energy is transferred within a molecule called adenosine triphosphate (ATP).
- Energy is stored in ATP between the bonds holding the second and third phosphates together.
- The benefit of ATP is that it is a small molecule (easily transportable) and has a high amount of stored energy for its size.
- ATP becomes adenosine diphosphate (ADP) and energy is released.
- ATPase enzyme catalyses ATP to ADP.
- ATP synthase enzyme catalyses ADP back to ATP.
Photosynthesis
First let's recall chloroplast structure:
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Photosynthesis is actually a series of steps!
The equation you've been taught in previously is the net reaction of all steps:
Light Dependent Stage:
Occurs in the thylakoids.
Light Independent Stage:
Occurs in stroma (liquid that fills the chloroplast).
Occurs in the thylakoids.
- Light energy from the sun ‘excites’ electrons within the thylakoid membrane.
- Light energy splits H2O into H+ and O2.
- Oxygen is released as a waste product.
- Electron energy and H+ ions are used to synthesise ATP and an important molecule called NADPH.
- ATP and NADPH will be used in the next stage to build glucose.
Light Independent Stage:
Occurs in stroma (liquid that fills the chloroplast).
- NADPH, CO2, H+, and ATP move into the stroma.
- The Calvin cycle begins.
- The Calvin cycle transforms these raw materials into glucose using energy from H+ and NADPH.
- Glucose is then converted into sucrose.
- Sucrose is then easily transported to the parts of the plant that need it (e.g. roots, flowers, etc.).
You should now complete...
Question Set 9.3 on page 230.
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