Photosynthesis

Energy needs of life All life needs a constant input of energy Heterotrophs (Animals) get their energy from “eating others” eat food = other organisms = organic molecules make energy through respiration Autotrophs (Plants) produce their own energy (from “self”) convert energy of sunlight build organic molecules (CHO) from CO2 make energy & synthesize sugars through photosynthesis consumers producers

How did we figure out all of these components are what a plant needs?

making energy & organic molecules from ingesting organic molecules How are they connected? Heterotrophs making energy & organic molecules from ingesting organic molecules glucose + oxygen  carbon + water + energy dioxide C6H12O6 6O2 6CO2 6H2O ATP  + oxidation = exergonic Autotrophs making energy & organic molecules from light energy So, in effect, photosynthesis is respiration run backwards powered by light. Cellular Respiration oxidize C6H12O6  CO2 & produce H2O fall of electrons downhill to O2 exergonic Photosynthesis reduce CO2  C6H12O6 & produce O2 boost electrons uphill by splitting H2O endergonic + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  + reduction = endergonic

Willow Soil Initial Mass 5lbs. 200 lbs. Final Mass 169 lbs. 3 oz. Points of understanding What did his experiment show about what contributes to the mass of a plant? Willow Soil Initial Mass 5lbs. 200 lbs. Final Mass 169 lbs. 3 oz. 199 lbs. 14 oz. Change in mass + 164 lbs. 3 oz. - 2 oz.

Early Experiments Van Helmont Showed roots don’t “eat” dirt Plants are made of H20

Early Experiments Joseph Priestly Candles & animals remove oxygen from the air Plants replace oxygen

Early Experiments Senebier Plants use carbon dioxide when they produce oxygen Plants take in CO2, not just water CO2 was a source of “nutrition”

+ water + energy  glucose + oxygen General formula + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  + Notice that oxygen comes solely from water, not from carbon dioxide Shown with isotope experiments

Blackman’s Evidence What he found out… Rate of photosynthesis increases as light intensity increases Photosynthesis increases as temperature increases Something else other than light is needed for photosynthesis, since it can also occur in the dark! Reminder… this is information that was discovered before we knew what the names of proteins, photosystems, etc. were. Evidence for two stages of photosynthesis was presented in 1905 by the English plant physiologist, F.F. Blackman. He measured the individual and combined effects of changes in light intensity and temperature on the rate of photosynthesis. Based on his experiments, Blackman came to the following conclusions: there is a set of LIGHT DEPENDENT reactions which are TEMPERATURE INDEPENDENT; the rate of these reactions in the dim to moderate light range could be accelerated by increasing the light intensity, but they were not accelerated by increase in temperature there is a second set of reactions that are TEMPERATURE DEPENDENT Both sets of reactions are required for photosynthesis. RATE CHANGES When the rate of one set of reactions increases, the rate of the entire process increases until the second set of reactions begins to hold back the first (becomes RATE-LIMITING). Photosynthesis was shown to have a light-dependent stage, the "light reactions," as well as a light-independent stage, the "dark reactions." The so-called dark reactions occur in the light. They require the products of the "light" reaction. Light is NOT directly involved in the "dark" reactions. At low light intensities, light is limiting, temperature and carbon dioxide concentration are not. At high light intensities, the pigment molecules are saturated and the chemical reactions are limited due to changes in temperature and carbon dioxide concentration. Light independent ("dark") reactions increase in rate as temperature increases until about 30-40 degrees C (dependent upon plant in question), after which the rate begins to decrease. Blackman concluded that these (dark) reactions are controlled by enzymes since this is the way enzymes respond to temperature. In the light dependent phase of photosynthesis, light energy is used to form ATP from ADP and to reduce electron carrier molecules. In the light independent phase of photosynthesis, the energy products of the first stage are used to reduce carbon from carbon dioxide to a simple hexose sugar. The conversion of carbon dioxide into organic compounds is known as CARBON FIXATION.

Data/Evidence Conditions Something depends on light Constant temp Increasing light intensity Something depends on light Rate of photosynthesis Increasing light intensity

Data/Evidence Conditions Constant light intensity Increasing temp There must also be a chemical reaction WITHOUT light Rate of photosynthesis Increasing temp expected if ONLY a light rxn is involved

Structures of Photosynthesis Refer to handout…

Chloroplast structure lamellae (thylakoid reservoir) Lumen: thylakoid reservoir; where hydrogen ions accumulate to supply energy for the chemiosmotic synthesis of ATP Thylakoid membranes contain 3 important groups of molecules Photosystems: contain pigments and reaction centers Chloroplasts’s electron transport chain Protein complexes involved in ATP synthesis Stroma: contain enzymes that make carbs; as well as DNA, RNA, and ribosomes Note the large surface area provided by the thylakoid membranes  more surface area allows more photosynthesis to take place

Chloroplast structure Lumen: thylakoid reservoir; where hydrogen ions accumulate to supply energy for the chemiosmotic synthesis of ATP Thylakoid membranes contain 3 important groups of molecules Photosystems: contain pigments and reaction centers Chloroplasts’s electron transport chain Protein complexes involved in ATP synthesis Stroma: contain enzymes that make carbs; as well as DNA, RNA, and ribosomes Note the large surface area provided by the thylakoid membranes  more surface area allows more photosynthesis to take place

Pigments Appear to be colored because they absorb some wavelengths of light than others; reflect a different color to our eyes. Electromagnetic spectrum shows all types of wavelengths Visible light can be separated into waves  wavelength (λ) determines color

Absorption spectrum

Chlorophyll (chloro = green; phyll = leaf) Absorb at blue and red wavelengths (λ) mostly Transmit/reflect the middle λ around green!

Engelmann’s Experiment

Engelmann’s Experiment

Engelmann’s Experiment Observed spirogyra w/ aerobic bacteria under microscope Inserted a prism into beam of light from micrscope Separated light into different wavelengths

Engelmann’s Experiment

Engelmann’s Experiment Aerobic bacteria gathered in a oxygen-rich area meant more photosynthesis action was occurring at those wavelengths Conclusion Chlorophyll played a role in photosynthesis Red and blue light were most effective in photosynthesis