Photosynthesis Honors Biology

Overview of Photosynthesis What is Photosynthesis? What is Photosynthesis? 6 CO H 2 O → C 6 H 12 O O 2 6 CO H 2 O → C 6 H 12 O O 2 light energy light energy Photosynthesis is the process of converting light energy into food energy (glucose, chemical energy stored in chemical bonds). Photosynthesis is the process of converting light energy into food energy (glucose, chemical energy stored in chemical bonds). Photosynthesis carried out by plants and algae. Photosynthesis carried out by plants and algae.

Structures of Photosynthesis Cross-section of a Leaf: Cross-section of a Leaf: 6 CO H 2 O → C 6 H 12 O O 2 6 CO H 2 O → C 6 H 12 O O 2 light energy light energy

Structures of Photosynthesis Cross-section of a Leaf: Cross-section of a Leaf: Palisade Mesophyll Palisade Mesophyll Spongy Mesophyll Spongy Mesophyll Guard cell Guard cell Stomata Stomata Epidermis Epidermis Cuticle Cuticle Vein Vein

What is Solar Energy and Visible Light? Visible Light is made of photons that travel at various wavelengths and frequencies. Visible Light is made of photons that travel at various wavelengths and frequencies. Photons (packets of energy) are formed when an electron is energized and moves to a higher energy level, which is unstable. When the electron falls back to its original energy level, then a photon is released that travels at a particular wavelength. Photons (packets of energy) are formed when an electron is energized and moves to a higher energy level, which is unstable. When the electron falls back to its original energy level, then a photon is released that travels at a particular wavelength. The longer the wavelength, the lower the energy. The shorter the wavelength, the higher the energy.

What is Solar Energy and Visible Light? Visible light is only one form of energy in the Electromagnetic Spectrum. Visible light is only one form of energy in the Electromagnetic Spectrum. Different colors of light have different wavelengths. Different colors of light have different wavelengths. Which color of light contains the most energy? Least energy? Which color of light contains the most energy? Least energy?

How do Plants Capture Solar Energy for use in Photosynthesis? Each plant cell contains chloroplasts. Each plant cell contains chloroplasts. Chloroplasts contain pigments that either absorb or reflect different wavelengths of visible light. Absorbed wavelengths are used for photosynthesis. Chloroplasts contain pigments that either absorb or reflect different wavelengths of visible light. Absorbed wavelengths are used for photosynthesis. Each thylakoid membrane contains chlorophyll pigments Each thylakoid membrane contains chlorophyll pigments

Review Parts of a Chloroplast

Plant Pigments Reaction Center Pigment = Chlorophyll a Reaction Center Pigment = Chlorophyll a Antennae/Accessory Pigments = Chlorophyll b, carotenoids, phycobilins (red algae) Antennae/Accessory Pigments = Chlorophyll b, carotenoids, phycobilins (red algae) What is the absorption spectra for each pigment? (spectrophotometer) What is the absorption spectra for each pigment? (spectrophotometer) Chlorophyll a and b – red, orange, yellow, blue, and violet (reflects green) Chlorophyll a and b – red, orange, yellow, blue, and violet (reflects green) Carotenoids – violet, blue, and green (reflects red, orange, and yellow) Carotenoids – violet, blue, and green (reflects red, orange, and yellow) Phycobilins – violet, blue, green, yellow, and orange (reflects red) Phycobilins – violet, blue, green, yellow, and orange (reflects red)

Photosynthesis is Composed of 2 Reactions: What are the two main reactions of Photosynthesis? Reactants? Products? Where located? What are the two main reactions of Photosynthesis? Reactants? Products? Where located? Light-Dependent reactions = Energy capturing reactions, captures solar energy and traps it as ATP and NADPH. Occurs in Thylakoid membranes. Light-Dependent reactions = Energy capturing reactions, captures solar energy and traps it as ATP and NADPH. Occurs in Thylakoid membranes. Light-Independent reactions = Synthesis reactions, uses the ATP and NADPH and captured CO 2 to make glucose. Occurs in the Stroma. Light-Independent reactions = Synthesis reactions, uses the ATP and NADPH and captured CO 2 to make glucose. Occurs in the Stroma.

What factors affect the rate of photosynthesis? Amount of Visible light and CO 2 : Amount of Visible light and CO 2 : Amount of H 2 O, Minerals, Temperature: Amount of H 2 O, Minerals, Temperature:

Light-Dependent Reactions: 1. Photosystem II absorbs light energy and transfers an excited electron to the Primary electron acceptor.

Light-Dependent Reactions: 2. Primary Electron Acceptor molecule transfers high energy electrons to the Electron Transport System, which establishes a H + ion gradient across the thylakoid membrane.

Light-Dependent Reactions: 3. Energy from the Electron Transport Chain establishing a H + ion gradient is used for Chemiosmotic Phosphorylation production of ATP. (Photophosphorylation)

Light-Dependent Reactions: 4. The electron from the Electron Transport System is accepted by the reaction center chlorophyll of Photosystem I. 5. The Electron Acceptor molecule of Photosystem I sends its electron to ultimately form NADPH.

Light-Dependent Reactions Reviewed Where does the light reaction take place? At the thylakoid membrane At the thylakoid membrane What are the inputs to the light reactions? Light energy, water Light energy, water What are the products of the light reaction? ATP, NADPH, and O 2 ATP, NADPH, and O 2

Light-Independent Reactions (Calvin Cycle) Synthesis reactions that occur in the stroma Synthesis reactions that occur in the stroma CO 2 + ATP + NADPH → Glucose CO 2 + ATP + NADPH → Glucose Carbon dioxide – comes into the leaf via stomata Carbon dioxide – comes into the leaf via stomata ATP and NADPH – from the Light reactions ATP and NADPH – from the Light reactions No light required but typically occurs during the day No light required but typically occurs during the day

Three stages of the Calvin Cycle: 1. Carbon Dioxide Fixation 2. Carbon Dioxide Reduction 3. Regeneration of RuBP

Review Photosyntheis What are the two reactions of photosynthesis? What are the two reactions of photosynthesis? How are the light reactions connected to the Calvin cycle? How are the light reactions connected to the Calvin cycle?

Three Modes of Photosynthesis C 3 Plants C 3 Plants C 4 Plants C 4 Plants CAM Plants CAM Plants The pathways of photosynthesis discussed in this presentation are for C 3 plants. The pathways of photosynthesis discussed in this presentation are for C 3 plants. Examples: wheat, rice, oats Examples: wheat, rice, oats Optimum temperature = 15-25°C Optimum temperature = 15-25°C

C 4 Plants Mesophyll cells fix CO 2 into a C 4 molecule (oxaloacetate) during the day. Mesophyll cells fix CO 2 into a C 4 molecule (oxaloacetate) during the day. Uses PEPCase enzyme instead of Rubisco to fix CO 2 Uses PEPCase enzyme instead of Rubisco to fix CO 2 C 4 molecule pumped to Bundle sheath cells where Calvin Cycle occurs. C 4 molecule pumped to Bundle sheath cells where Calvin Cycle occurs. Examples: sugar cane, corn, bermuda grass, crabgrass Examples: sugar cane, corn, bermuda grass, crabgrass Net photosynthetic rate is greater than C 3 plants. Net photosynthetic rate is greater than C 3 plants. More heat tolerant, optimum temperature = 30-40°C More heat tolerant, optimum temperature = 30-40°C

CAM Plants Like C 3 plants, Mesophyll cells fix CO 2 in the Calvin Cycle, but it occurs at night. Stomata only open at night to bring in CO 2 and reduce water loss. Like C 3 plants, Mesophyll cells fix CO 2 in the Calvin Cycle, but it occurs at night. Stomata only open at night to bring in CO 2 and reduce water loss. Like C 4 plants, CO 2 is fixed into a C 4 molecule and then stored in large vacuoles in mesophyll cells to be used the following day when ATP and NADPH are available from the light reactions. Like C 4 plants, CO 2 is fixed into a C 4 molecule and then stored in large vacuoles in mesophyll cells to be used the following day when ATP and NADPH are available from the light reactions. Uses PEPCase enzyme instead of Rubisco to fix CO 2 Uses PEPCase enzyme instead of Rubisco to fix CO 2 Examples: succulents like cacti that live in deserts (CAM = Crassulacean-acid metabolism) Examples: succulents like cacti that live in deserts (CAM = Crassulacean-acid metabolism) Low photosynthetic rate, variable Low photosynthetic rate, variable Most heat tolerant, optimum temperature = 35°C Most heat tolerant, optimum temperature = 35°C

Review C 3, C 4, and CAM plants What are the differences between C 3, C 4, and CAM plants? What are the differences between C 3, C 4, and CAM plants?

References BIOBK/BioBookPS.html BIOBK/BioBookPS.html