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Photosynthesis. The History of Discovery (350 b.c.). Aristotle and the Greeks believed plants derived all food from soil. The History of Discovery (1600 a.d.). Belgian physicist Jan Baptista van Helmont grew a willow tree in a pot for 5 years, adding only water. Willow grew 74.4 kilograms
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The History of Discovery (350 b.c.) • Aristotle and the Greeks believed plants derived all food from soil
The History of Discovery (1600 a.d.) • Belgian physicist Jan Baptista van Helmont grew a willow tree in a pot for 5 years, adding only water. • Willow grew 74.4 kilograms • Soil lost 57 grams • Conclusion => plant absorbs resources from water and not from soil
How do plants grow? Van Helmont - 1648
The History of Discovery (1771 a.d.) • English clergyman Joseph Priestley ‘restored air’ by putting a live sprig of mint into air in which a wax candle had burned out; discovering another candle could be burned in the same air 10 days later • “For these discoveries we are assured that no vegetable grows in vain…..but cleanses and purifies our atmosphere”
The History of Discovery (1796) • Dutch physicist Jan Ingenhousz showed air was ‘restored’ on in presence of sunlight and only by the green parts of plants • => suggested CO2 split to yield carbon and oxygen
The History of Discovery (1941) • Using a radioactive oxygen isotope (18O), investigators traced route of oxygen from water to air, in strong support of van Neil’s hypothesis. YOU KNOW IT AS:
Our Primary Energy Source • What is the primary energy source for life on this planet? • The sun! • What are the two different types of autotrophs? • Photoautotrophs • Source of energy = sun • Source of carbon = carbon dioxide • Chemoautotrophs • Source of energy = inorganic chemicals • Source of carbon = carbon dioxide
The role of pigments • A pigment is any substance that absorbs visible light - most absorb only certain wavelengths and reflect or transmit the wavelengths they don't absorb • Chlorophyll absorbs light primarily in the violet, blue and red wavelengths and reflects green wavelengths, and thus appears green • Absorption spectrum - the light absorption pattern of a pigment • Action spectrum - the relative effectiveness of different wavelengths for a specific light-requiring process • Chlorophyll is implicated as the principle pigment in photosynthesis because its absorption spectrum is the same as the action spectrum for photosynthesis
When pigments absorb light, electrons are temporarily boosted to a higher energy level One of three things may happen to that energy: 1. the energy may be dissipated as heat 2. the energy may be re-emitted almost instantly as light of a longer wavelength - this is called fluorescence 3. the energy may be captured by the formation of a chemical bond - as in photosynthesis
An Overview of Photosynthesis • What is the photosystem and where is it found? • The photosystem is found within the thylakoid membrane and it contains all of the photosynthetic pigments. • What is the reaction center? • It is an area of the photosystem where chl a resides
Reaction center with chl a What is the chemical equation for photosynthesis? 6CO2 + 6H2O ---> C6H12O6 + 6O2
How do plants get the light needed for photosynthesis? • Pigments in the thylakoid membranes • How do plants get the water they need for photosynthesis? • From their roots. • How do plants get the carbon dioxide they need for photosynthesis? • From their stomata.
The Two Stages of Photosynthesis • What are the two stages of photosynthesis? • The light reactions (light-dependent) • The Calvin Cycle (light-independent)
What would chloroplasts in the dark need in order to produce sugar from carbon dioxide? • ATP and NADPH
The Light Reactions Chemiosmosis
Summary of the Light Reactions • Input: • Light • Water • ADP + Pi • NADP+ • Output: • ATP • NADPH • Oxygen What do you need for more light reactions to occur?
Summary of the Light Reactions • Input: • Light • Water • ADP • NADP+ • Output: • ATP • NADPH • Oxygen ADP, and NADP+
Summary of the Light Reactions • Input: • Light • Water • ADP • NADP+ • Output: • ATP • NADPH • Oxygen What is the waste product of photosynthesis?
Summary of the Light Reactions • Input: • Light • Water • ADP • NADP+ • Output: • ATP • NADPH • Oxygen Oxygen
NADP+ • NADP+ is an electron carrier that combines with 2 electrons and one hydrogen ion. • Reduction = receiving an electron • Oxidation = giving up an electron • NADP+ becomes reduced into NADPH, when it receives the electrons
What is the role of the water? • To donate low energy (weak) electrons to the reaction center chlorophyll • What is the role of NADPH? • To carry mighty electrons to the sugar that will be made in the Calvin Cycle
Calvin Cycle • Where does the Calvin Cycle occur? • In the stroma • What goes into the Calvin Cycle? • ATP, NADPH, Carbon Dioxide • What comes out of the Calvin Cycle? • Sugar, ADP, NADP+
Rate of Photosynthesis • What is a rate? • It is the activity per unit of time. • What factors affect the rate of photosynthesis?
