chapter 7 photosynthesis: using light to make food laura coronado bio 10 chap 7
TRANSCRIPT
Chapter 7Chapter 7
Photosynthesis: Using Light to Make Food
Laura Coronado Bio 10 Chap 7
Biology and Society: Green Energy
– Wood has historically been the main fuel used to:• Cook• Warm homes• Provide light at night
– Industrialized societies replaced wood with fossil fuels.
– To limit the damaging effects of fossil fuels, researchers are investigating the use of biomass (living material) as efficient and renewable energy sources.
Laura Coronado Bio 10 Chap 7
Figure 7.0Laura Coronado Bio 10 Chap 7
Biology and Society: Green Energy
– Fast-growing trees, such as willows:• Can be cut every three years• Do not need to be replanted• Are a renewable energy source• Produce fewer sulfur compounds• Reduce erosion• Provide habitat for wildlife
Laura Coronado Bio 10 Chap 7
THE BASICS OF PHOTOSYNTHESIS
– Photosynthesis:• Is used by plants, some protists, and some bacteria• Transforms light energy into chemical energy • Uses carbon dioxide and water as starting materials
– The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules.
– Organisms that use photosynthesis are:• Photosynthetic autotrophs• The producers for most ecosystems
Laura Coronado Bio 10 Chap 7
Plants(mostly on land)
Photosynthetic Protists(aquatic)
PHOTOSYNTHETIC AUTOTROPHS
Photosynthetic Bacteria(aquatic)
Micrograph of cyanobacteriaKelp, a large algaForest plants
LM
Figure 7.1Laura Coronado Bio 10 Chap 7
Chloroplasts: Sites of Photosynthesis
– Chloroplasts are:• The site of photosynthesis • Found mostly in the interior cells of leaves
– Inside chloroplasts are membranous sacs called thylakoids, which are suspended in a thick fluid, called stroma.
– Thylakoids are concentrated in stacks called grana.– The green color of chloroplasts is from chlorophyll,
a light-absorbing pigment. – Stomata are tiny pores in leaves where carbon
dioxide enters and oxygen exits.Laura Coronado Bio 10 Chap 7
Leaf cross section
Stomata
Vein
CO2 O2
Interior cellLM
StromaGranum Thylakoid
ChloroplastOutermembrane
Innermembrane
TEM
Figure 7.2-2Laura Coronado Bio 10 Chap 7
Carbon dioxide
6 O26 CO2 6 H2O C6H12O6
Water GlucosePhoto-synthesis Oxygen gas
Light energy
Figure 7.UN1Laura Coronado Bio 10 Chap 7
Photosynthesis– Sunlight provides the energy– Electrons are boosted “uphill” and added to carbon
dioxide– Sugar is produced– During photosynthesis, water is split into:• Hydrogen • Oxygen
– Hydrogen is transferred along with electrons and added to carbon dioxide to produce sugar.
– Oxygen escapes through stomata into the atmosphere.
Laura Coronado Bio 10 Chap 7
A Photosynthesis Road Map
– Photosynthesis occurs in two stages:• The light reactions convert solar energy to chemical
energy • The Calvin cycle uses the products of the light reactions
to make sugar from carbon dioxide
Laura Coronado Bio 10 Chap 7
Light
H2O
O2
Chloroplast
Lightreactions
NADPH
ATP
Calvincycle
CO2
NADP+
ADPP
Sugar(C6H12O6)
Figure 7.3-2Laura Coronado Bio 10 Chap 7
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY
– Chloroplasts:• Are chemical factories powered by the sun • Convert solar energy into chemical energy
Laura Coronado Bio 10 Chap 7
The Nature of Sunlight
– Sunlight is a type of energy called radiation, or electromagnetic energy.
– The full range of radiation is called the electromagnetic spectrum.
Laura Coronado Bio 10 Chap 7
Visible light
Wavelength (nm)
Radiowaves
380 400 500 600 750700
Wavelength = 580 nm
Micro-waves
Gammarays
InfraredUVX-rays
10–5 nm 10–3 nm 103 nm1 nm 106 nm 1 m 103 m
Increasing wavelength
Figure 7.4Laura Coronado Bio 10 Chap 7
The Process of Science: What Colors of Light Drive Photosynthesis?
– Observation: In 1883, German biologist Theodor Engelmann saw that certain bacteria tend to cluster in areas with higher oxygen concentrations.
– Question: Could this information determine which wavelengths of light work best for photosynthesis?
– Hypothesis: Oxygen-seeking bacteria will congregate near regions of algae performing the most photosynthesis.
Laura Coronado Bio 10 Chap 7
The Process of Science: What Colors of Light Drive Photosynthesis?– Experiment: Engelmann:• Laid a string of freshwater algal cells in a drop of water on
a microscope slide• Added oxygen-sensitive bacteria to the drop• Used a prism to create a spectrum of light shining on the
slide– Results: Bacteria:• Mostly congregated around algae exposed to red-orange
and blue-violet light • Rarely moved to areas of green light
– Conclusion: Chloroplasts absorb light mainly in the blue-violet and red-orange part of the spectrum.
Laura Coronado Bio 10 Chap 7
Bacterium
Wavelength of light (nm)400 500 600 700
Light
Num
ber o
f bac
teria
Algal cells
Prism
Microscope slide
Figure 7.5Laura Coronado Bio 10 Chap 7
Light
Chloroplast
Reflectedlight
Absorbedlight Transmitted
light
Figure 7.6Laura Coronado Bio 10 Chap 7
Chloroplast Pigments
– Chloroplasts contain several pigments:• Chlorophyll a:– Absorbs mostly blue-violet and red light – Participates directly in the light reactions
• Chlorophyll b:– Absorbs mostly blue and orange light – Participates indirectly in the light reactions
Laura Coronado Bio 10 Chap 7
Carotenoids• Absorb mainly blue-green light• Participate indirectly in the light reactions• Absorb and dissipate excessive light energy
that might damage chlorophyll• The spectacular colors of fall foliage are due
partly to the yellow-orange light reflected from carotenoids.
Laura Coronado Bio 10 Chap 7
Figure 7.7Laura Coronado Bio 10 Chap 7
How Photosystems Harvest Light Energy
– Light behaves as photons, discrete packets of energy.–A photosystem is a group of chlorophyll and
other molecules that function as a light-gathering antenna.–Chlorophyll molecules absorb photons.• Electrons in the pigment gain energy.• As the electrons fall back to their ground state,
energy is released as heat or light.Laura Coronado Bio 10 Chap 7
Light
(b) Fluorescenceof a glow stick
Photon
Heat
Light (fluorescence)
Ground stateChlorophyllmolecule
Excited statee–
(a) Absorptionof a photon
Figure 7.8Laura Coronado Bio 10 Chap 7
Chloroplast
Thylakoidmembrane
Pigment molecules
Antenna pigmentmolecules
PrimaryelectronacceptorReaction-centerchlorophyll a
Photon
Electrontransfer
Reactioncenter
PhotosystemTransfer of energy
Figure 7.9-3Laura Coronado Bio 10 Chap 7
How the Light Reactions Generate ATP and NADPH
– Two types of photosystems cooperate in the light reactions:• The water-splitting photosystem• The NADPH-producing photosystem
– The light reactions are located in the thylakoid membrane.
Laura Coronado Bio 10 Chap 7
Primaryelectronacceptor
Water-splittingphotosystem
Light
H2O
2 H
Reaction-centerchlorophyll
2e –
2e–
O2++
Electron transport chain
Energyto make
ATP
Primaryelectronacceptor
2e–
Light
NADPH-producingphotosystem
Reaction-centerchlorophyll
2e –
NADPH
NADP
1
2
Figure 7.10-3Laura Coronado Bio 10 Chap 7
– An electron transport chain:• Connects the two photosystems • Releases energy that the chloroplast uses to make ATP
Laura Coronado Bio 10 Chap 7
Light
H2O
Thylakoidmembrane
2e –
O2
ATP
NADP
Light
Stroma
Inside thylakoid
Photosystem PhotosystemElectron transport chain
NADPH
ADP P
ATPsynthase
To Calvin cycle
Electron flow
H
1
2
HH
H
H H
H
Figure 7.11aLaura Coronado Bio 10 Chap 7
Water-splittingphotosystem
e–
Phot
on
ATP
NADPH
e–
e–
e–
e–
e–
Phot
on
e–
NADPH-producingphotosystem
Figure 7.12Laura Coronado Bio 10 Chap 7
THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE
– The Calvin cycle:• Functions like a sugar factory within the stroma of a
chloroplast• Regenerates the starting material with each turn
Laura Coronado Bio 10 Chap 7
ATP
NADPH
Calvincycle
ADP P
NADP
P
P
P
P P
P
ADP P
ATP
G3P sugar
Three-carbon molecule
G3P sugar
G3P sugar
RuBP sugar
CO2 (from air)
Glucose (and other organic compounds)
Figure 7.13-4Laura Coronado Bio 10 Chap 7
Evolution Connection:Solar-Driven Evolution
–C3 plants:• Use CO2 directly from the air
• Are very common and widely distributed– C4 plants:
• Close their stomata to save water during hot and dry weather • Can still carry out photosynthesis
– CAM plants:• Are adapted to very dry climates • Open their stomata only at night to conserve water
Laura Coronado Bio 10 Chap 7
Sugar
C4 Pathway(example: sugarcane)
C4 plant CAM plantSugar
Calvincycle
Calvincycle
Day
Celltype 1
Four-carboncompound
Night
Four-carboncompound
Celltype 2
CAM Pathway(example: pineapple)
ALTERNATIVE PHOTOSYNTHETIC PATHWAYS
CO2 CO2
CO2 CO2
Figure 7.14Laura Coronado Bio 10 Chap 7
Carbon dioxide
6 O26 CO2 6 H2O C6H12O6
Water GlucosePhoto-synthesis Oxygen gas
Light energy
Figure 7.UN1Laura Coronado Bio 10 Chap 7
Light reactions
CO2
O2
H2O
(C6H12O6)
NADPH
Light
Sugar
ATP
ADPP
NADP
Calvin cycle
Figure 7.UN2Laura Coronado Bio 10 Chap 7
Light reactions
CO2
O2
H2O
(C6H12O6)
NADPH
Light
Sugar
ATP
ADPP
NADP
Calvin cycle
Figure 7.UN3Laura Coronado Bio 10 Chap 7
Light H2O
O2
Chloroplast
Lightreactions
NADPH
ATP
Calvincycle
CO2
NADP+
ADPP
Sugar
(C6H12O6)
Stack ofthylakoids Stroma
Figure 7.UN5Laura Coronado Bio 10 Chap 7
acceptor
Water-splittingphotosystem
Photon
H2O
2 H
Chlorophyll
2e –
O2++
Electron transport chain
ATP
NADPH-producingphotosystem
Chlorophyll
NADPH
NADP+
e –
2e –
2e –
2e –
e –
acceptorADP
Photon
21
Figure 7.UN6Laura Coronado Bio 10 Chap 7
NADPH
Calvincycle
ADP P
NADP
P
ATP
G3P
CO2
Glucose andother compounds
Figure 7.UN7Laura Coronado Bio 10 Chap 7