Unit 3: Cells

Chapter 8: Photosynthesis

8-2: Photosynthesis: An Overview

Ms. PetrucciBiology

PhotosynthesiPhotosynthesiss

8-2 Photosynthesis: An Overview

History of Photosynthesis History of Photosynthesis & Plant Pigments& Plant Pigments

PhotosynthesisPhotosynthesis

• Involves the Use Of light Involves the Use Of light Energy to convert Energy to convert Water Water (H(H 22 0)0) and and Carbon Dioxide Carbon Dioxide (CO(CO 22 )) into into Oxygen (OOxygen (O 22 )) and and High Energy CarbohydratesHigh Energy Carbohydrates (sugars, e.g. Glucose) & (sugars, e.g. Glucose) & StarchesStarches

Investigating Investigating PhotosynthesisPhotosynthesis

• Many Scientists Have Many Scientists Have Contributed To Contributed To Understanding Understanding PhotosynthesisPhotosynthesis

• Early ResearchEarly Research Focused On Focused On The The Overall ProcessOverall Process

• Later ResearchersLater Researchers Investigated The Detailed Investigated The Detailed Chemical PathwaysChemical Pathways

Early Questions on Early Questions on PlantsPlants

Several Centuries Ago, Several Centuries Ago, The Question Was:The Question Was:

Does the increase in Does the increase in mass of a plant come mass of a plant come

from the air? The soil? from the air? The soil? The Water?The Water?

Van HelmontVan Helmont ’s ’s Experiment 1643Experiment 1643

• Planted a Planted a seedseed into A into A pre-measured amount of pre-measured amount of soil and soil and wateredwatered for 5 for 5 yearsyears

• Weighed Plant & Soil.Weighed Plant & Soil. Plant Was 75 kg, Soil Plant Was 75 kg, Soil The Same.The Same.

• Concluded Mass Came Concluded Mass Came From WaterFrom Water

PriestleyPriestley ’s Experiment 1771’s Experiment 1771

• Burned Candle In Bell Jar Until It Went Out.

• Placed Sprig Of Mint In Bell Jar For A Few Days.

• Candle Could Be Relit And Burn.

• Concluded Plants Released Substance (O 2) Necessary For burning.

IngenhouszIngenhousz ’s Experiment ’s Experiment 17791779

Repeated Priestly experiment with & without sunlightRepeated Priestly experiment with & without sunlight

Results of IngenhouszResults of Ingenhousz ’s ’s ExperimentExperiment

• Showed That PriestleyShowed That Priestley ’s ’s Results Only Occurred In Results Only Occurred In The Presence Of The Presence Of SunlightSunlight ..

• Light Was Necessary For Light Was Necessary For Plants To Produce The Plants To Produce The “Burning Gas” or “Burning Gas” or oxygenoxygen

Julius Robert Mayer 1845Julius Robert Mayer 1845

Proposed That Proposed That Plants can Plants can Convert Convert Light Light Energy Into Energy Into ChemicalChemical EnergyEnergy

Samuel Ruben & Martin Samuel Ruben & Martin KamenKamen19411941

Used Used Isotopes To Isotopes To Determine Determine That The That The OxygenOxygen Given Off In Given Off In PhotosynthePhotosynthesis sis Comes Comes From WaterFrom Water

KAMENKAMEN

RUBINRUBIN

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The Photosynthesis The Photosynthesis EquationEquation

Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.

Photosynthesis is a series of reactions that uses light energy from the sun to convert water and carbon dioxide into sugars and oxygen.

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PigmentsPigments

• In addition to water, carbon dioxide, and light energy, photosynthesis requires Pigments

• Chlorophyll is the primary light-absorbing pigment in autotrophs

• Chlorophyll is found inside chloroplasts

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Light and Light and PigmentsPigments

• Energy From The Sun Enters Earth’s Biosphere As Photons

• Photon = Light Energy Unit

• Light Contains A Mixture Of Wavelengths

• Different Wavelengths Have Different Colors

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Light & PigmentsLight & Pigments

• Different pigmentsDifferent pigments absorb absorb different different wavelengthswavelengths of light of light

• Photons of light Photons of light ““exciteexcite”” electrons in the plantelectrons in the plant’’s pigmentss pigments

• Excited electrons carry the Excited electrons carry the absorbed energyabsorbed energy

• Excited electrons move to Excited electrons move to HIGHERHIGHER energy levels energy levels

• LinkLink

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ChlorophyllChlorophyll

There are 2 main types There are 2 main types of chlorophyll of chlorophyll molecules:molecules:

Chlorophyll aChlorophyll aChlorophyll bChlorophyll b

Magnesium atom at the center of chlorophyll

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Chlorophyll a and bChlorophyll a and b

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Chlorophyll aChlorophyll a

•Found in all Found in all plants, algae, & plants, algae, & cyanobacteriacyanobacteria•Makes photosynthesis possibleMakes photosynthesis possible•Participates Participates directlydirectly in the Light in the Light ReactionsReactions•Can Can accept energyaccept energy from chlorophyll from chlorophyll bb

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Chlorophyll bChlorophyll b

• Chlorophyll b is an Chlorophyll b is an accessory accessory pigmentpigment

• Chlorophyll b acts Chlorophyll b acts indirectlyindirectly in in photosynthesis by transferring photosynthesis by transferring the light it absorbs to the light it absorbs to chlorophyll chlorophyll aa

• Like chlorophyll a, it absorbs Like chlorophyll a, it absorbs red & blue light and red & blue light and REFLECTS REFLECTS GREENGREEN