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Photosynthesis. The Dark and Light Reactions. Energy is essential to all living things. All energy on earth originates in nuclear reactions in the sun. Producers plants and other organisms capable of carrying out photosynthesis. 6C0 2 + 6H 2 0+ energy C 6 H 12 0 6 + 60 2. - PowerPoint PPT Presentation
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PHOTOSYNTHESISThe Dark and Light Reactions
ENERGY IS ESSENTIAL TO ALL LIVING THINGS.
All energy on earth originates in nuclear reactions in the sun.
PRODUCERS PLANTS AND OTHER ORGANISMS CAPABLE OF CARRYING OUT PHOTOSYNTHESIS
6C02+ 6H20+ energy C6H1206 + 602
PHOTOSYNTHESIS:6 CO2 + 6 H2O + light energy C6H12O6 + 6O2
PHOTOSYNTHESIS TAKES PLACE IN THE CHLOROPLAST
LIGHT REACTIONS: OCCUR ON THE THYLAKOID MEMBRANES
•convert light and water into chemical energy •produce O2 as a waste product
HOW LIGHT WORKS Visible radiation drives the light reactions Light is a type of energy called
electromagnetic energy. Different pigments embedded in thylakoid
membranes
DIFFERENT PIGMENTS ABSORB LIGHT OF DIFFERENT WAVELENGTHS. The wavelengths absorbed by the light harvesting
pigments are mainly in the blue and red range This is why most plants appear green
The light harvesting pigments of chloroplasts are1. chlorophyll a: absorbs in blue and red2. chlorophyll b: absorbs in blue and orange3. carotenoids: absorbs mainly blue-green range
Having all these different pigments broadens the range of visible light that is usable for photosynthesis.
Only chlorophyll a passes electrons to the electron transport chain and thus is directly involved in the light reactions.
The other pigments convey the light energy to chlorophyll a.
THE LIGHT REACTIONSPhotosystems I and II
STEP 1: Pigments in photsystems II absorb light Energy from the light is absorbed by electrons
(increasing energy level) High-energy electrons are passed on to the
electron transport chain H2O molecules provide new electrons to the
chlorophyll to replace the ones that were lost Enzymes on the inner surface of the thylakoid
membrane break up each H2O molecule into 2 high-energy electrons
Oxygen is released into the air as oxygen gas 2 H+ ions are released inside the thylakoid
membrane
STEP 2: High-energy electrons move through the
electron transport chain from photosystem II to photosystem I
b.Energy is used from the electrons to transport the H+ from the stroma into the inner thylakoid
STEP 3: Pigments in photosystem I use energy from
light to reenergize the electrons b.NADP+ picks up high-energy electrons on
the outer surface of the thylakoid membrane plus a H+ ion and becomes NADPH
STEP 4: H+ ions released during water-splitting and
electron transport the inside of the thylakoid membrane becomes positively charged and the outside negatively charged
b.The difference in charges provides the energy to make ATP
STEP 5: H+ ions CANNOT directly cross the
membrane b.ATP synthase (protein) allows H+ ions to
pass through it c.As H+ ions pass through this protein, the
protein rotates and ATP synthase binds to ADP and a phosphate group – producing ATP
Water splits into H+ ions electrons and Oxygen
Electrons
H+ ions
Oxygen
WATER
PHOTOLYSIS: the splitting of water
PHOTOSYNTHESIS: THE DARK REACTIONS
ATP + NADPH2 + CO2C6H12O6
DARK REACTIONS: OCCUR IN THE STROMA
Carbon dioxide is split, providing carbon to make sugars.
The ultimate product is glucose. While this system depends on the products from
the light reactions, it does not directly require light energy.
CARBON FIXATION 3 CO2 molecules attach to 3, 5 carbon
sugars (RuBP) A 6 carbon sugar is formed and O2 is
released This reaction is catalyzed by the enzyme
Rubisco. This 6 carbon sugar rearranges and splits
into 2, 3 carbon sugars (PGA)
REDUCTION 6 ATP contribute phosphate groups 8 NADPH drop off electrons These are used to make the high energy
compound G3P
REGENERATION 1 G3P is used to form glucose The others are used to regenerate the original
5 carbon sugar 9 ATP and 6 NADPH are used per turn of the
calvin cycle These are regenerated by Light Reactions 2 G3P = Glucose