Ch 10: Photosynthesis
2016
Chapter 10: Photosynthesis
From Topic 2.9
Essential idea: Photosynthesis uses the energy in sunlight to produce
the chemical energy needed for life.
Nature of science: Experimental design—controlling relevant variables
in photosynthesis experiments is essential (3.1).
Understandings:
• Photosynthesis is the production of carbon compounds in cells using
light energy.
• Chlorophyll absorbs red and blue light most effectively and reflects
green light more than other colours.
• Oxygen is produced in photosynthesis from the photolysis of water.
• Energy is needed to produce carbohydrates and other carbon
compounds from carbon dioxide.
• Temperature, light intensity and carbon dioxide concentration are
possible limiting factors on the rate of photosynthesis.
Applications and skills:
• Application: Changes to the Earth’s atmosphere, oceans and rock
deposition due to photosynthesis.
• Skill: Drawing an absorption spectrum for chlorophyll and an action
spectrum for photosynthesis.
• Skill: Separation of photosynthetic pigments by chromatograph
(Practical 4).
• Skill: Design of experiments to investigate the effect of limiting
factors on photosynthesis.
Guidance:
• Water free of dissolved carbon dioxide for photosynthesis
experiments can be produced by boiling and cooling water.
• Students should know that visible light has wavelengths between
400 and 700 nanometres, but they are not expected to recall the
wavelengths of specific colours of light.
• Paper chromatography can be used to separate photosynthetic
pigments but thin layer chromatography gives better results.
From Topic 8.3
Essential idea: Light energy is converted into chemical energy.
Nature of science: Developments in scientific research follow
improvements in apparatus—sources of 14C and autoradiography
enabled Calvin to elucidate the pathways of carbon fixation (1.8).
Understandings:
•The structure of the chloroplast is adapted to its function in
photosynthesis.
• Light-dependent reactions take place in the intermembrane space of
the thylakoids.
• Reduced NADP and ATP are produced in the light-dependent
reactions.
• Absorption of light by photosystems generates excited electrons.
• Photolysis of water generates electrons for use in the lightdependent reactions.
• Transfer of excited electrons occurs between carriers in thylakoid
membranes.
• Excited electrons from Photosystem II are used to contribute to
generate a proton gradient.
• ATP synthase in thylakoids generates ATP using the proton gradient.
• Excited electrons from Photosystem I are used to reduce NADP.
Light-independent reactions take place in the stroma.
• In the light-independent reactions a carboxylase catalyses the
carboxylation of ribulose bisphosphate.
• Glycerate 3-phosphate is reduced to triose phosphate using reduced
NADP and ATP.
• Triose phosphate is used to regenerate RuBP and produce
carbohydrates.
• Ribulose bisphosphate is reformed using ATP.
Chapter 10: Photosynthesis
From Topic 8.3
Applications and skills:
• Application: Calvin’s experiment to elucidate the carboxylation of RuBP.
•Skill: Annotation of a diagram to indicate the adaptations of a chloroplast to its function.
Aim 6: Hill/s method demonstrating electron transfer in chloroplasts by observing DCPIP reduction, immobilization of a culture of an alga such as
Scenedesmus in alginate beads and measurement of the rate of photosynthesis by monitoring their effect on hydrogencarbonate indicator are all
possible experiments.
Utilization:
• The Global Artificial Photosynthesis (GAP) project aims to create an artificial “leaf” within the next decade. An electronic version of the leaf
that creates oxygen and hydrogen from water and sunlight has already been invented and will be developed for use in the next decade.
From Topic 9.1
Understandings:
• Transpiration is the inevitable consequence of gas exchange in the leaf.
Applications and skills:
• Application: Adaptations of plants in deserts and in saline soils for water conservation.
Ecology Review
• Plants, algae and other autotrophs are the producers in the
ecosystem.
• Autotrophs synthesize organic molecules from inorganic
raw materials.
• Heterotrophs acquire organic molecules from
compounds made by other organisms. (consumers,
decomposers)
Review of Plant Cell Structure
Site of Photosynthesis
• Site of photosynthesis is in
the chloroplast.
• Chloroplasts are found
mainly in the mesophyll of
the leaf, in the palisade
layer.
•
•
•
•
Structure and Function of Chloroplast
Folded Thylakoid membranes
Separate Areas (compartments)
Lumen for Proton Accumulation
Fluid Stroma
Guard Cells
• Stomata: little openings in
the leaf controlled by guard
cells
- let’s in CO2 but also
let’s out water
• How do guard cells work?
http://www.phschool.com/science/biology_place/labbench/lab9/stomamov.html
Chlorophyll
• Chlorophyll: a green pigment in the chloroplast that absorbs
light
• Two types of chlorophyll:
- Chlorophyll a: best absorbs light at violet-blue and red
- Chlorophyll b: best absorbs light at blue and orange
Overview of Photosynthesis
• Transforms solar energy into chemical
energy.
• CO2 and H2O into Glucose
• CO2 is carbon source and light is energy
source.
Two Stages of Photosynthesis
• Light Dependent Reactions
(Light Reactions)
• Products
• Oxygen
• NADPH
• ATP
• Light Independent
Reactions (Dark Reactions
or Calvin Cycle)
• Products:
• Glucose
http://www.mhhe.com/biosci/bio_animations/02_MH_Photosynthesis_Web/index.ht
ml
Light Reactions (Non-Cyclic e- Flow)
• Light Reactions: the “photo” part of photosynthesis; requires
light to make it happen
- Similar to how the ETC of Cellular Respiration works
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120072/bio13.swf::Photosynthetic%20Electron%20Transport%20and%20ATP%20Synthesis
http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html
Light Reactions (Non-Cyclic e- Flow)
• Light Reactions: use solar energy to produce ATP and NADPH
for the light-independent reactions (aka Calvin Cycle)
- ATP is used for chemical energy
- NADPH is used for reducing power
Light Reactions (Cyclic e- Flow)
• Produces only ATP; no NADPH is produced
• Occurs when [ATP] is gets low for Calvin Cycle to continue
• Involves only Fd, Pc, and PS 1 in cyclic pattern
http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter39/cyclic_and_noncyclic_photophosphorylation.html
Light Independent Reactions (Calvin Cycle)
• Light-Independent
Reactions: uses ATP
and NADPH to convert
CO2 to sugar
• There are 3 parts:
1) Carbon Fixation
2) Reduction
3) Regeneration of
CO2 acceptor
(RuBP)
Summary of Photosynthesis
• Light Reactions
• Products
• NADPH
• ATP
• Oxygen
• Dark Reaction
• Products
• Glucose
Action Spectrum of Photosynthesis
• Which
wavelength of
light best drives
photosynthesis?
400
500
600
700
Intro to Other Types of Carbon Fixation
Angiosperms: Flowering Plants
• Two basic division:
1) Monocots: “one leaf”
2) Dicots: “two leaves”
Alternatives to Carbon Fixation
•
•
•
C3: basic photosynthesis that forms a 3-Carbond
compound as its 1st product; includes both dicots and
monocots such as rice, wheat & soybean
C4: forms a 4-Carbon compound as its 1st product; include
agriculturally important monocots…sugar cane and corn
CAM: include many succulents, cacti, and pineapple
C4 Structure
• C4: two distinct types of photosynthetic cells:
1) Mesophyll cells: CO2 incorporation occurs here
2) Bundle-sheath cells: Calvin cycle occurs here
• Specifically useful for hot regions with a lot of sunlight
C3 vs C4 Structure
CAM Structure
• CAM: open their stomata at night and closes them during
the day to prevent water loss
• Useful in arid environments and found in succulent plants
• Carbon fixation occurs in the same cell but occurs at
different times
Carbon Fixation Comparisons
• Compare the three
types of carbon
fixation. What do
they have in
common? What
differences do they
have?
Limiting Factors
• Light Intensity: increases up to a certain point
• Temperature: has an optimal temp; too cold or hot is
no good.
• Concentration of CO2: increases to a certain point
Why?