2.9 Photosynthesis
The background is an microscope image of leaf
cells. You can clearly see the cells are packed with
chloroplasts. These specialised organelles contain
chlorophyll (and other pigments) which trap light
energy and use it to build glucose molecules.
Essential idea: Photosynthesis uses the energy in sunlight to
produce the chemical energy needed for life.
https://bioweb.uwlax.edu/bio203/s2013/siebold_alic/chloroplast1.jpg
Understandings, Applications and Skills
2.9.U1
2.9.U2
2.9.U3
2.9.U4
2.9.U5
2.9.U6
2.9.A1
2.9.S1
2.9.S2
2.9.S3
Statement
Photosynthesis is the production of carbon
compounds in cells using light energy.
Visible light has a range of wavelengths with violet
the shortest wavelength and red the longest.
Chlorophyll absorbs red and blue light most
effectively and reflects green light more than other
colours.
Guidance
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.
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.
Changes to the Earth’s atmosphere, oceans and
rock deposition due to photosynthesis.
Drawing an absorption spectrum for chlorophyll and
an action spectrum for photosynthesis.
Design of experiments to investigate the effect of Water free of dissolved carbon dioxide for
photosynthesis experiments can be produced
limiting factors on photosynthesis.
by boiling and cooling water.
Paper chromatography can be used to
Separation of photosynthetic pigments by
separate photosynthetic pigments but thin
chromatograph. (Practical 4)
layer chromatography gives better results.
Be sure to re-read chapter 10
• Bring your chapter 10 reading guide to school.
2.9.U1 Photosynthesis is the production of carbon compounds in cells using light energy.
Photosynthesis is a metabolic pathway. Carbon dioxide and along with water is used to
produce carbohydrates. Oxygen is released as a waste gas.
Light energy is transferred to chemical
energy stored in the glucose molecule
Water is split: the hydrogen is used to help
in the production of glucose, but the
oxygen is excreted as a waste gas.
Carbon is ‘fixed’ from carbon dioxide and
used to produce to glucose.
n.b. metabolic pathways are controlled by enzymes
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
2.9.U4 Oxygen is produced in photosynthesis from the photolysis of water.
2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
One use of the energy consumed in photosynthesis
is photolysis (splitting of water molecules)
sunlight
Most of the oxygen is excreted
as a waste product
Glucose can be used by cell
respiration or stored as starch.
electrons
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
n.b. larger molecules tend to
contains more bonds than
smaller ones. Therefore more
ATP is required to build the
bonds and generate larger
molecules. Consequently large
molecules can act as energy
stores.
2.9.U4 Oxygen is produced in photosynthesis from the photolysis of water.
2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
One use of the energy consumed in photosynthesis
is photolysis (splitting of water molecules)
sunlight
Most of the oxygen is excreted
as a waste product
Glucose can be used by cell
respiration or stored as starch.
electrons
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
n.b. larger molecules tend to
contains more bonds than
smaller ones. Therefore more
ATP is required to build the
bonds and generate larger
molecules. Consequently large
molecules can act as energy
stores.
2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
2.9.U2 Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.
2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other
colours.
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
https://app.box.com/s/88edjbrgbff0febtiyfk8x9l0cdnyshr
https://app.box.com/s/88edjbrgbff0fe
btiyfk8x9l0cdnyshr
(Edited by Chris Paine)
http://www.mhhe.com/biosci/genbio/biolink/j_explorations/ch09expl.htm
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
% of the maximum rate of photosynthesis
This shows the rate of photosynthesis for all the
wavelengths of light as a % of the maximum possible rate.
(Edited by Chris Paine)
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
% of the maximum rate of photosynthesis
This shows the absorbance of light by photosynthetic
pigments (here chlorophyll) for all the wavelengths of
light.
(Edited by Chris Paine)
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
http://homepages.abdn.ac.uk/p.marston/pages/flash/sa
mples/photosyn.swf
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
2.9.S3 Separation of photosynthetic pigments by chromatograph. (Practical 4)
What pigments can you find and identify in a leaf?
Gather leaves of different types and colours and use Thin Layer
Chromatography (TLC) to separate the pigments, including
chlorophyll present in a leaf.
Thin layer chromatography for photosynthetic pigments
SAPS have published two (slightly) different protocols:
• http://www.saps.org.uk/secondary/teaching-resources/189-investigation-ofphotosynthetic-pigments-in-green-plants
• http://www.saps.org.uk/secondary/teaching-resources/181-student-sheet-10thin-layer-chromatography-for-photosynthetic-pigments
Simplified Bioknowledgy protocol based on the SaPS outline:
https://app.box.com/s/i8cc161713atmk7ks5zoex1psyrjir89
In the absence of equipment use the virtual lab and self-test quiz:
http://www.phschool.com/science/biology_place/labbench/lab4/pigsep.html
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on
the rate of photosynthesis.
Rate of Photosynthesis
At high levels of light intensity further increases have no effect on the rate of
photosynthesis. Therefore light intensity is not the limiting factor, another
factor (e.g. temperature, CO2 concentration, enzymes or chloroplasts working
at maximum efficiency) is limiting photosynthesis.
When light intensity is increased the rate of
photosynthesis increases therefore it is the
limiting factor at low levels.
Light intensity
Light intensity refers to the amount of light, of a given
wavelength, which is available to the plant.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
Rate of Photosynthesis
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on
the rate of photosynthesis.
Another factor (e.g. temperature, light, enzymes working at
maximum efficiency) is limiting photosynthesis as further
increases in carbon dioxide do not increase the rate of
photosynthesis.
CO2 is a substrate for the
metabolic pathway hence
the relationship is similar to
how enzyme reactions are
limited by substrate
concentration.
When carbon dioxide concentration is increased
the rate of photosynthesis increases therefore it is
the limiting factor at low concentrations.
Carbon dioxide concentration
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
Rate of Photosynthesis
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on
the rate of photosynthesis.
Photosynthesis is a
metabolic pathway hence
the relationship is similar to
how enzyme reactions are
affected by temperature.
As the temperature
approaches the
optimum the enzymes
begin to denature
(active site changes to
become non-functional)
causing the rate of
photosynthesis to
increase more slowly
and eventually peak.
Increases in temperature give
molecules more kinetic energy
causing substrates to collide with
active sites more frequently, this
increases the rate of
photosynthesis
After the optimum
temperature enzymes
denature rapidly
causing a fast
decrease in the rate of
photosynthesis as
temperature increases
further.
Temperature
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Placing the plant in a closed space
with water.
CO2 reacts with the water producing
bicarbonate and hydrogen ions, which
increases the acidity of the solution.
Increased CO2 uptake -> increased pH
-> increased rate of photosynthesis.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Aquatic plants can submerged
in water in a closed space with
a gas syringe attached.
Alternatively gas volume can
be measured by displacing
water in an inverted
measuring cylinder or by
simply counting bubbles.
Oxygen probes can be used
with terrestrial plants kept in
closed environments to
measure increases in oxygen
concentration.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Glucose production can be
(indirectly) measured by a
change in a plant's dry
biomass.
starch levels in a plant (glucose
is stored as starch)
can be identified by staining
with iodine solution, this can
be quantitated using a
colorimeter.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own
investigation what questions need to be asked
and considerations need to be made?
http://sbi4uphotosynthesis.weebly.com/uploads/1/9/2/8/1928
4461/5941741_orig.jpg
http://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own
investigation what questions need to be asked
and considerations need to be made?
The independent variable
• Only one limiting factor should be investigated
at a time
http://sbi4uphotosynthesis.weebly.com/uploads/1/9/2/8/1928
• The range of values should reflect conditions
experienced
4461/5941741_orig.jpg
by the organism
• The range of values should allow the limiting factor to
range from values that restrict photosynthesis to values
that allow photosynthesis to happen at it’s optimum rate.
• The increments should be sufficiently in size that a trend
can be clearly detected
http://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own
investigation what questions need to be asked
and considerations need to be made?
Dependent variable
• An accurate method for measuring the rate
of
http://sbi4uphotosynthesis.weebly.com/uploads/1/9/2/8/1928
photosynthesis needs to be used.
4461/5941741_orig.jpg
• Oxygen production per time unit is recommended.
Leaf discs are a successful and easy way to measure
oxygen generation by leaves
http://www.saps.org.uk/secondary/teaching-resources/284investigating-photosynthesis-with-leaf-discs
http://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own
investigation what questions need to be asked
and considerations need to be made?
The control variables
• These should include the limiting factorshttp://sbi4unot being
photosynthesis.weebly.com/uploads/1/9/2/8/1928
investigated.
4461/5941741_orig.jpg
• Other key control variables should include
any factor that
affects a metabolic pathway controlled by enzymes, e.g. pH.
• Ambient light should be considered as it affects the
wavelength and intensity of light absorbed by the organism.
• The values chosen for the control variables should be close to
their optimum values so that the control variables do not
limit photosynthesis.
(If the control variables limit photosynthesis it may not be possible to
see the impact of the limiting factor being investigated)
http://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
Nature of Science: Experimental design - controlling relevant variables in photosynthesis experiments is essential.
(3.1)
Before designing an carrying out your own
investigation what questions need to be asked
and considerations need to be made?
The control variables - Nature of Science
• Explain why it is essential to control http://sbi4uthe limiting factors
photosynthesis.weebly.com/uploads/1/9/2/8/1928
not being investigated.
4461/5941741_orig.jpg
• Evaluate which of the identified reasons are the most
important.
http://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
2.9.A1 Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.
Primordial Earth had a reducing atmosphere that
contained very low levels of oxygen gas (approx. 2%).
Cyanobacteria (prokaryotes) containing chlorophyll first
performed photosynthesis about 2.5 billion years ago.
Photosynthesis creates oxygen gas as a by-product (by the photolysis of water).
Oxygen levels remained at 2% until about 750 million years ago (mya).
From 750 mya until the now there has been a significant rise to 20%.
Oxygen generation also allowed the formation of an ozone layer (O3).
Ozone shielded the Earth from damaging levels of UV radiation. This, in
turn, lead to the evolution of a wider range of organisms.
Iron compounds in the oceans were oxidized:
• The insoluble iron oxides precipitated onto the seabed.
• Time and further sedmentation has produced rocks with
layers rich in iron ore called the banded iron formations.
Oxygen in the atmosphere
lead to the production of
oxidised compounds (e.g.
CO2) in the oceans.
http://commons.wikimedia.org/wiki/File:Blue_Marble_Eastern_Hemisphere.jpg
Bibliography / Acknowledgments
Jason de Nys