This document discusses the history and process of photosynthesis. It describes several key experiments that advanced understanding, including van Helmont's experiment showing plant mass comes from water, Priestley's showing plants release oxygen, and Ingenhousz's showing this only occurs with sunlight. The overall reaction of photosynthesis is described as using sunlight, water and carbon dioxide to produce sugars and oxygen. Chlorophyll is identified as the main light-absorbing pigment located in chloroplasts, with chlorophyll a directly participating in light reactions and chlorophyll b transferring energy.

1. Unit 3: Cells
Chapter 8:
Photosynthesis
8-2: Photosynthesis:
An Overview
Ms. Petrucci
Biology

2. PhotosynthesiPhotosynthesi
ss
8-2 Photosynthesis: An

3. History of PhotosynthesisHistory of Photosynthesis
& Plant Pigments& Plant Pigments

4. PhotosynthesisPhotosynthesis
• Involves the Use Of lightInvolves the Use Of light
Energy to convertEnergy to convert WaterWater
(H(H22 0)0) andand Carbon DioxideCarbon Dioxide
(CO(CO22 )) intointo Oxygen (OOxygen (O22 )) andand
High Energy CarbohydratesHigh Energy Carbohydrates
(sugars, e.g. Glucose) &(sugars, e.g. Glucose) &
StarchesStarches

5. InvestigatingInvestigating
PhotosynthesisPhotosynthesis
• Many Scientists HaveMany Scientists Have
Contributed ToContributed To
UnderstandingUnderstanding
PhotosynthesisPhotosynthesis
• Early ResearchEarly Research Focused OnFocused On
TheThe Overall ProcessOverall Process
• Later ResearchersLater Researchers
Investigated The DetailedInvestigated The Detailed

6. Early Questions onEarly Questions on
PlantsPlants
Several Centuries Ago,Several Centuries Ago,
The Question Was:The Question Was:
Does the increase inDoes the increase in
mass of a plant comemass of a plant come
from the air? The soil?from the air? The soil?
The Water?The Water?

7. Van HelmontVan Helmont ’s’s
Experiment 1643Experiment 1643
• Planted aPlanted a seedseed into Ainto A
pre-measured amount ofpre-measured amount of
soil andsoil and wateredwatered for 5for 5
yearsyears
• Weighed Plant & Soil.Weighed Plant & Soil.
Plant Was 75 kg, SoilPlant Was 75 kg, Soil
The Same.The Same.
• Concluded Mass CameConcluded Mass Came
From WaterFrom Water

8. 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 (O2)
Necessary For burning.

9. IngenhouszIngenhousz ’s Experiment’s Experiment
17791779
Repeated Priestly experiment with & without sunlightRepeated Priestly experiment with & without sunlight

10. Results of IngenhouszResults of Ingenhousz ’s’s
ExperimentExperiment
• Showed That PriestleyShowed That Priestley ’s’s
Results Only Occurred InResults Only Occurred In
The Presence OfThe Presence Of
SunlightSunlight..
• Light Was Necessary ForLight Was Necessary For
Plants To Produce ThePlants To Produce The
“Burning Gas” or“Burning Gas” or oxygenoxygen

11. Julius Robert Mayer 1845Julius Robert Mayer 1845
Proposed ThatProposed That
Plants canPlants can
ConvertConvert LightLight
Energy IntoEnergy Into
ChemicalChemical
EnergyEnergy

12. Samuel Ruben & MartinSamuel Ruben & Martin
KamenKamen
19411941
UsedUsed
Isotopes ToIsotopes To
DetermineDetermine
That TheThat The
OxygenOxygen
Given Off InGiven Off In
PhotosynthePhotosynthe
sissis ComesComes
From WaterFrom Water
KAMENKAMEN
RUBINRUBIN

13. 13
The PhotosynthesisThe 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.

14. 14
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

15. 15
Light andLight and
PigmentsPigments
• Energy From The Sun
Enters Earth’s Biosphere
As Photons
• Photon = Light Energy
Unit
• Light Contains A Mixture
Of Wavelengths
• Different Wavelengths

16. 16
Light & PigmentsLight & Pigments
• Different pigmentsDifferent pigments absorbabsorb
differentdifferent wavelengthswavelengths of lightof light
• Photons of lightPhotons of light ““exciteexcite””
electrons in the plantelectrons in the plant’’s pigmentss pigments
• Excited electrons carry theExcited electrons carry the
absorbed energyabsorbed energy
• Excited electrons move toExcited electrons move to
HIGHERHIGHER energy levelsenergy levels
• LinkLink

17. 17
ChlorophyllChlorophyll
There are 2 main typesThere are 2 main types
of chlorophyllof chlorophyll
molecules:molecules:
Chlorophyll aChlorophyll a
Chlorophyll bChlorophyll b
Magnesium atom at the
center of chlorophyll

18. 18
Chlorophyll a and bChlorophyll a and b

19. 19
Chlorophyll aChlorophyll a
•Found in allFound in all plants, algae, &plants, algae, &
cyanobacteriacyanobacteria
•Makes photosynthesis possibleMakes photosynthesis possible
•ParticipatesParticipates directlydirectly in the Lightin the Light
ReactionsReactions
•CanCan accept energyaccept energy from chlorophyllfrom chlorophyll
bb

20. 20
Chlorophyll bChlorophyll b
• Chlorophyll b is anChlorophyll b is an accessoryaccessory
pigmentpigment
• Chlorophyll b actsChlorophyll b acts indirectlyindirectly inin
photosynthesis by transferringphotosynthesis by transferring
the light it absorbs tothe light it absorbs to
chlorophyllchlorophyll aa
• Like chlorophyll a, it absorbsLike chlorophyll a, it absorbs
red & blue light andred & blue light and REFLECTSREFLECTS
GREENGREEN