Capturing Solar Energy: Capturing Solar Energy: Photosynthesis Photosynthesis Chapter 7 Chapter 7 Photosynthesis • The process of converting light energy into chemical energy. • Nourish most living organisms directly or indirectly. • Plants are autotrophs, self feeders, producers of organic molecules from CO 2 . Earth’s Timeline Humans have only existed for 1 second of Earth’s 24 hour clock. Phototrophic bacteria (and photosynthesis) evolved close to the beginning of life. Pre-Biotic Earth The very early atmosphere of the earth contained mostly CO 2 , about 80%. The concentration of CO 2 gradually dropped to about 20% by 3,500 Ma (million years ago). The evolution of the first bacteria occurred about 3,500 Ma. age of earth oldest rocks oldest stromatolites earliest bacteria first green algae (Eukaryotic) earliest photosynthetic bacteria earliest biogenic carbon Carbon Dioxide Hydrogen Oxygen Nitrogen stromatolites abundant oldest "red beds" red beds abundant oldest chemical evidence of complex cells banded iron formations (with reduced iron)
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Capturing Solar Energy:Capturing Solar Energy:PhotosynthesisPhotosynthesis
Chapter 7Chapter 7
Photosynthesis• The process of converting light energy into
chemical energy.
• Nourish most living organisms directly orindirectly.
• Plants are autotrophs, self feeders, producers of organic molecules from CO2.
Earth’sTimelineHumans haveonly existed for1 second ofEarth’s 24 hourclock.
Phototrophicbacteria (andphotosynthesis)evolved closeto the beginningof life.
Pre-Biotic Earth The very earlyatmosphere of theearth containedmostly CO2,about 80%.
The concentrationof CO2 graduallydropped to about20% by 3,500 Ma(million years ago).
The evolution ofthe first bacteriaoccurred about3,500 Ma.
age of earth oldest rocks
oldest stromatolites
earliest bacteria first green algae(Eukaryotic)
earliest photosynthetic bacteria
earliest biogenic carbon
Carbon Dioxide
HydrogenOxygen
Nitrogen
stromatolites abundant
oldest "red beds"
red beds abundant
oldest chemical evidence ofcomplex cells
banded iron formations(with reduced iron)
age of earth oldest rocks
oldest stromatolites
earliest bacteria first green algae(Eukaryotic)
oldest chemical evidence ofcomplex cells
earliest photosynthetic bacteria
earliest biogenic carbon
Carbon Dioxide
HydrogenOxygen
Nitrogen
stromatolites abundant
oldest "red beds"
red beds abundantbanded iron formations(with reduced iron)
Oxygen generated after life began.
No Oxygen present in the early atmosphere.
Earliest Evidence ofMicrobial Life
• Graphite bands found 3.8 billion years ago.– Graphite is a material that can be produced when
organic carbon, found in all living organisms, isaltered by heat and pressure over time.
(i.e. evidence ofBiogenic Carbon)
age of earth oldest rocks
oldest stromatolites
earliest bacteria first green algae(Eukaryotic)
oldest chemical evidence ofcomplex cells
earliest photosynthetic bacteria
earliest biogenic carbon
Carbon Dioxide
HydrogenOxygen
Nitrogen
stromatolites abundant
oldest "red beds"
red beds abundantbanded iron formations(with reduced iron)
red beds abundantbanded iron formations(with reduced iron)
Banded Iron Formationsindicate the presence of anoxidizing environment:Oxygen is present locally!
Earliest Evidence ofMicrobial Life
• The Cambrian Explosion, 543 million years ago– Nearly all the major animal groups we are familiar
with first appeared in this period.
Earliest Evidence of Life
Earliest Evidence of Photosynthesis
Evidence for HighConcentrations ofOxygen in theAtmosphere
Photosynthesis6CO2 + 6H2O + light C6H12O6 + 6O2
PhotosyntheticOrganisms
Photosynthetic Adaptations
• Leaves– Designed to Capture Sunlight
• Thin (only a few cells thick)
• Large surface area (to expose all cells to thesun)
– Designed to Prevent Water Loss and allowGas Exchange
• Mesophyll Cells
• Chloroplasts
Leaf Adaptations
1. Capturing Sunlight2. Prevention of Water Loss
•Cuticle–Waxy waterproofcovering that reducesevaporation
•Upper & LowerEpidermis
Leaf Adaptations
1. Capturing Sunlight2. Prevention of Water Loss3. Gas Exchange
•Stoma-Pores, open & close
•Guard Cells- Move to open & closethe ‘stoma’
Leaf Adaptations
Stoma open when humidity is high.Guard cells absorb water and swell.Open stoma let CO2 in and O2 out.
Stoma deflate and closewhen humidity is low toprevent loss of water.
Vascular Bundle and Sheath
• Veins of plants.• Supply water and minerals to mesophyll cells.• Carry sugar from mesophyll cells to other parts
of the plant.
Mesophyll Cells
Palisade Mesophyll(carry-out photosynthesis)
Spongy Mesophyll(allow for gas exchange)
• “Middle of the Leaf”• Major site of photosynthesis in the leaf.• A single cell contains 40-200 chloroplasts.
Chloroplasts• Organelles where photosynthesis takes place.• Contain dish-shaped, interconnected membranous
sacs called thylakoid disks where the light-dependent photosynthetic reactions take place.
• Light-independent photosynthetic reactions takeplace in the stroma.
Chloroplasts
Light Dependent Reaction
Light Independent Reaction
The cuticle is a waxylayer that preventswater loss.
The upper andlower epidermis arethicker cells thatprotect the interiorleaf structure andprevent water andgas exchange withthe atmosphere.The stoma are pores in the lower
epidermis that allow gas exchange.They are regulated by guard cellswhich open and close according tolocal humidity and gas needs.
Chloroplasts are theeukaryotic organelleswhere photosynthesistakes place within theplant cell.
The Vascular Bundle transports water tothe leaves and sugars away from theleaves to other parts of the plant.Bundle Sheath cells protect the vascularbundle and regulate water and sugarmovement from the vascular bundle.
Mesophyll cells makeup most of the interiorof the leaf.Palisades mesophyllcells (top) carryoutmost of thephotosynthesis.Spongy mesophyllcells (bottom) storegasses and water forpalisades cells.
The Thylakoid disksare packed full ofchlorophyll (or otherphotosyntheticpigment).The location of thelight dependentreaction ofphotosynthesis.
The Stroma makes up theremaining interior space.The location of the lightindependent reaction ofphotosynthesis.
Reactions of Photosynthesis
• Light-Dependent Reaction– Takes place within the thylakoid membrane.
– Generates energy-carrier molecules(ATP, NADPH)
• Light-Independent Reaction– Takes place in the stroma.
6CO2 + 6H2O + light C6H12O6 + 6O2
COCO22 + H + H++ + ATP C + ATP C66HH1212OO66 + ADP + ADP
HH22O + O + lightlight + ADP O + ADP O22 + H + H++ + ATP + ATP
LightCaptured by
Pigments
•The visible spectra of energy isquite narrow.
•Light is composed of individualpackets of energy, photons.
•The shorter the wavelength, themore energetic the light.
LightCaptured by
Pigments• Photosynthetic
pigments absorbs lightenergy in the veryhigh and lowwavelengths.
• Light that is notabsorbed is reflectedand gives the objectits color.
Not all light is the samecolor or wavelength.
Chlorophyll a absorbs inthe violet and redwavelengths.
Chlorophyll b absorbs inthe blue and orangewavelengths.
Carotenoids absorb in theviolet to green wavelengths.
Most photosynthesis utilizesthe violet, blue, and redwavelengths of light.
PhotosyntheticPigments
• Chlorophyll absorbs violet, blue,and red light.– Two types of chlorophyll:
• Chlorophyll A, absorbs violet and red.• Chlorophyll B, absorbs blue and orange.
• Additional accessory pigments,carotenoids, absorb blue andgreen light while reflecting redand yellow.
• Chlorophyll breaks down in thecold before carotenoids, givingleaves red and yellow hues inautumn.