Photosynthesis

Photosynthesis The process by which plants and other producers convert the energy of sunlight into the energy, stored in organic molecules. (Carbon Compounds) Plants and other photosynthetic organisms produce the food that start the food chain.

Pigment Chlorophyll For most plants chlorophyll is the main pigment Gives green color

Types of Chlorophyll Pigments Chlorophyll a – absorbs mainly blue-violet and red light; reflects green light Chlorophyll b – (helper pigment) absorb mainly blue and orange light; reflects yellow-green (looks light frees) Carotenoids – (many types) absorb mainly blue- green light; reflect yellow-orange Xanthophyll - a yellow or brown carotenoid plant pigment that causes the autumn colors of leaves

Electromagnetic Spectrum The range of types of electromagnetic energy; from the very short wavelength (gamma rays) to the very long wavelength (radio waves)

Electromagnetic Spectrum ROYGBIV

Electromagnetic Spectrum Plants use the same part of the electromagnetic spectrum that our eyes are able to see.

Electromagnetic Spectrum Those wavelength that your eyes can see as different colors Make a small fraction of the electromagnetic spectrum Shorter wavelengths (violet/indigo) have more energy than longer wavelengths (red) Actually shorter wavelengths can damage organic molecules like proteins and nucleic acids This is why U.V. rays cause sunburns and can lead to skin cancer

Electromagnetic Spectrum Substances can do one of only 2 things when struck by a particular wavelength of light: Absorbed Reflected Pigments in the leaf’s chloroplast absorb blue-violet and red very well

Wavelength

Chloroplast

Photosynthesis ATP and H2 generated from light dependent stage used to covert CO2 and H2O into organic compounds (like glucose) 6CO2 + 6H2O C6H12O6 + 6O2 This carbon fixation…turning inorganic to organic Fixation requires energy—all comes from sun

Photosynthesis Two Main Stages Stage I Light Reaction (Light Dependent) Convert the energy in sunlight to chemical energy Takes place in the thylakoid membrane 1st – Chlorophyll molecules in the membrane capture light energy 2nd – Chloroplast use energy to remove eˉ (excites) from water (photolysis) This splits H⁺ + O₂ O₂ is the “waste product” for photosynthesis

Photosynthesis Stage 1 Photolysis – when a water molecule is split into its component elements Hydrogen and water Generates electrons in light dependent reaction

Results of Light Reaction – NADPH + ATP Photosynthesis Stage 1 O₂ escape into the atmosphere via the stoma (on leaves) 3rd – Chloroplast use H₂O eˉ and H⁺ ions to (make energy rich molecules) NADH found in cellular respiration. 4th – (finally) ATP is made in chloroplast Excited e⁻ from Photosystem II are used to generate a proton gradient Results of Light Reaction – NADPH + ATP

Photosynthesis Stage 1 Transfer of excited electrons occurs between carriers in the thylakoid membrane

Photosynthesis Stage 1 In photosynthesis light-excited eˉ for the electron transport from chlorophyll travel down the chain. (P680/P700 are pigments)

Photosynthesis Stage 2 Stage II The Calvin Cycle (takes place in Stoma) Makes sugar from the atoms in CO₂ + the H ions and high-energy eˉ carried by NADPH Enzymes for the Calvin Cycle are located outside the thylakoids and are dissolved in the stoma ATP made in Light Reaction provides energy to make sugar (carbohydrates or other carbon compounds) Calvin Cycle AKA “Light Independent Reactions” because it does not require light to begin reaction

Photosynthesis Stage 2 ATP synthase in thylakoids generates ATP using the proton gradient.

Photosynthesis Stage 2 Ribulose biphosphate (RuBP), 5 carbon compound, binds with CO₂ in a process called carbon fixation. Catalyzed by an enzyme called RuBP carboxylase (rubisco). Result: 6 carbon compound The unstable 6-carbon breaks down into 2 3 carbon compounds (Glycerate 3 – phosphate GP) GP = what we called G3P!!!!! Done by reducing NADP and ATP

Photosynthesis Stage 2 The 3 carbon molecules of GP are acted upon by ATP and NADPH from the light-dependent reaction to form 2 other 3-carbon molecules called triose phosphate (TP). This is a reduction reaction. The molecules of TP then do one of 2 things: some leave the cycle to become sugar phosphates that may become more complex carbohydrates. The others continue in the cycle and reproduce RuBP. ATP is used to regain RuBP

Calvin Cycle

The Calvin Cycle

Photosynthesis-rates Photosynthesis does not occur at such a steady rate Greatly affected by intensity of light, temperature, and CO2 levels Can be measured directly via CO2 intake and O2 production amounts IF adjusted to account for respiration Biomass (amount of plant/size) is an indirect method of measuring rate of photosynthesis—indirect b/c a lot of other potential factors

Photosynthesis O2 released + Photosynthesis Respiration O2 taken in -- Respiration O2 taken in -- Day 1 Night 1 Day 2 Night 2

Photosynthesis Light intensity—varies inversely with the square of the distance (farther away, less intense) Enzymes at max rate Rate of photosynthesis intensity

Photosynthesis Temperature Enzymes and other proteins begin to get denatured Rate of photosynthesis Temp

Photosynthesis CO2 concentration Plateaus unless light intensity or temp. go up Rate of photosynthesis CO2

Photosynthesis Summary Light Reaction – takes place in the thylakoid membrane Convert light energy to chemical energy (ATP) and NADPH Calvin Cycle – takes place in the stroma; uses ATP and NADPH to convert CO₂ to sugar.