Chapter 4 Photosynthesis
RECAP Autotrophs Organisms that make their own food Heterotrophs cannot make their own food get energy from other organisms Photoautotroph use the suns energy Chemoautotroph use inorganic substances (chemicals)
The Photosynthesis Equation 4
Photosynthesis Reaction Involves the Use Of light Energy to convert Water (H 2 0) and Carbon Dioxide (CO 2 ) into Oxygen (O 2 ) and High Energy Carbohydrates (sugars, e.g. Glucose) & Starches
Light Energy from the sun travels to Earth in the form of light Sunlight is a mixture of different wavelengths Our eyes see the different wavelengths of the visible spectrum as different colors: red, orange, yellow, green, blue, and violet.
Visible light is only 1.5% of the entire spectrum
If this image is made up of the whole electromagnetic spectrum This is how much we would actually see (1.5%)
Outside the visible spectrum UV Infrared
Pigments Gather sun s energy Principal pigment in plants is chlorophyll Chlorophyll absorbs light in the blue and red regions but NOT green Green is most reflected so that s what we see
Light absorbed/reflected
Fall - Pigments As temperatures drop and chlorophyll molecules break down/die the red and orange pigments may be seen.
Main types Chlorophyll a and b 14
Chlorophyll a Found in all plants, algae, cyanobacteria Makes photosynthesis possible Participates directly in the Light Reactions (only one of the reactions of photosynthesis) Absorbs red & blue light and REFLECTS GREEN Can accept energy from chlorophyll b 15
Chlorophyll b Chlorophyll b is an accessory pigment Chlorophyll b acts indirectly in photosynthesis by transferring the light it absorbs to chlorophyll a Like chlorophyll a, it absorbs red & blue light and REFLECTS GREEN 16
Structure of the Chloroplast Inner membrane forms stacks of connected sacs called thylakoids Thylakoid stack is called the granum (grana-plural) Gel-like material around grana called stroma 18
Inside A Chloroplast 19
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Thylakoid membranes Light reactions occur in thylakoid membranes Photosystems are made up of clusters of chlorophyll molecules & embedded in the thylakoid membranes Two types Photosystem I Photosystem II 21
Function of the Stroma Dark reactions or the Calvin Cycle occurs here ATP is used here to make carbohydrates like glucose (where does the ATP come from)? 22
Photosynthesis Overview 23
Two Reactions of Photosynthesis Light dependent reactions, light reactions Calvin Cycle, Light independent reactions, Dark reactions
Energy Carriers NADP+ takes on/picks up high-energy electrons and H + ions from the Light Reactions to form NADPH NADPH carries energy to be passed on to the Calvin Cycle NADP+ = Nicotinamide Adenine Dinucleotide Phosphate NADPH = Reduced Form 25
NADPH 26
Light Reactions Occur in the thylakoid membranes Use light energy Produce Oxygen from water Convert ADP to ATP Convert NADP + into the energy carrier NADPH 28
Light Dependent Reaction 29
Light Dependent Reaction 30
Photosystem I Discovered First Active in the final stage of the Light Dependent Reaction Made of 300 molecules of Chlorophyll Almost completely chlorophyll a 31
Photosystem II Discovered Second Active in the beginning stage of the Light Reactions Contains about equal amounts of chlorophyll a and chlorophyll b 32
Photosynthesis Begins Photosystem II absorbs light energy Electrons are energized and passed to the Electron Transport Chain Lost electrons are replaced from the splitting of water into 2H +, free electrons, and Oxygen 2H + pumped across thylakoid membrane 33
Photosystem I High-energy electrons are moved to Photosystem I through the Electron Transport Chain Energy is used to transport H + from stroma to inner thylakoid membrane NADP+ converted to NADPH when it picks up 2 electrons & H+ 34
Phosphorylation -There is an enzyme in the thylakoid membranes called ATP Synthase -As H+ ions pass through thylakoid membrane, enzyme binds them to ADP -Forms ATP 35
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Light Reaction Summary Reactants: H 2 O Light Energy Energy Products: ATP goes to calvin cycle NADPH goes to calvin cycle Oxygen exits into atmosphere 38