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4.1: Capturing Solar Energy: The Light-Dependant Reactions

McGraw Hill Section 4.1

Ms. Klodt

on 20 September 2014

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Transcript of 4.1: Capturing Solar Energy: The Light-Dependant Reactions

Capturing Solar Energy:
The Light Dependant Reactions

Light-dependant Reaction
Light-independant Reaction
Key Terms
sun energy into chemical energy

2 sets of reactions
light-dependent: light is used to make ATP & NADPH
light-independent: ATP & NADPH make carbohydrates
Photosynthesis takes place in the chloroplasts
thylakoids are the membrane system within
Stacked in piles called grana
Fluid filled interior is called stroma
filled with enzymes
Absorption of Light
Light is absorbed in packets of energy called photons
Pigments absorb specific wavelengths of light and then pass it on
Chlorophyll a & b
A groups of chlorophyll molecules and proteins
reaction centre is made of up chlorophyll a molecules and 'their' protein
Antenna complex transfers energy from light to the reaction centre
e- in the reaction centre becomes excited
e- is passed to an electron accepting molecule, reducing it
2 photosystems:
photosystem I has reaction centre pigment molecules of P700
Photosystem II has reaction centre pigment of P680
The Light Dependent Reactions
P680 molecule in Photosystem II absorbs a photon from light
e- becomes excited, leaves the photosytem and goes to e- acceptor
P680 steals 4 e- from water, passing to an e- acceptor
forms O2
Step 1
Energized e- are transferred across the electron transport system
Energy is released as they are transferred
Energy is used to pump hydrogen ions from the stroma into the thylakoid space, creating hydrogen ion concentration gradient
Step 2
During steps 1 & 2, light energy is also being absorbed by Photosystem I & transferred to P700
e- are excited
Passed to e- acceptor
lost e- are replaced by e- that have reached the end of Photosystem II
Step 3
e- received by electron-acceptor in photosystem I are catalyzed by NADP reductase and used to reduce NADP+, forming NADPH
Step 4
Photophosphorylation is the use of light energy to add phosphate to ADP, forming ATP.
Process is called chemiosmosis
Same process as in respiration
Chemiosmosis & Photophosphorylation
Big Ideas
By the end of the lesson, you should be able to:
use appropriate terminology related to metabolism
explain the chemical changes and energy conversions associated with the processes of photosynthesis
describe, compare, and illustrate the matter and energy transformations that occur during the process of cellular respiration, including the roles of oxygen and organelles such as the mitochondria
Can you?
Explain the purpose of photosynthesis?
Describe the main difference between light dependent and light independent reactions?
Describe the structure of a choloroplast?
Distinguish between the photosystems and describe their structure?
Describe the steps of electrons moving through the photosystems?
Tell what the final products of the reaction are?
Full transcript