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Essential idea: Photosynthesis uses the energy in sunlight to produce the chemical energy needed for life.
By Chris Paine
https://bioknowledgy.weebly.com/
2.9 PhotosynthesisThe 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.
https://bioweb.uwlax.edu/bio203/s2013/siebold_alic/chloroplast1.jpg
Understandings, Applications and Skills
Statement Guidance
2.9.U1 Photosynthesis is the production of carbon
compounds in cells using light energy.
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.
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.
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.
2.9.U6 Temperature, light intensity and carbon dioxide
concentration are possible limiting factors on the
rate of photosynthesis.
2.9.A1 Changes to the Earth’s atmosphere, oceans and
rock deposition due to photosynthesis.
2.9.S1 Drawing an absorption spectrum for chlorophyll and
an action spectrum for photosynthesis.
2.9.S2 Design of experiments to investigate the effect of
limiting factors on photosynthesis.
Water free of dissolved carbon dioxide for
photosynthesis experiments can be produced
by boiling and cooling water.
2.9.S3 Separation of photosynthetic pigments by
chromatograph. (Practical 4)
Paper chromatography can be used to
separate photosynthetic pigments but thin
layer chromatography gives better results.
2.9.U1 Photosynthesis is the production of carbon compounds in cells using light energy.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
Photosynthesis is a metabolic pathway. Carbon dioxide and along with water is used to produce carbohydrates. Oxygen is released as a waste gas.
Carbon is ‘fixed’ from carbon dioxide and used to produce to glucose.
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.
n.b. metabolic pathways are controlled by enzymes
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.
sunlight
electrons
One use of the energy consumed in photosynthesis
is photolysis (splitting of water molecules)
Most of the oxygen is excreted as a waste product
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
Glucose can be used by cell respiration or stored as starch.
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.
sunlight
electrons
One use of the energy consumed in photosynthesis
is photolysis (splitting of water molecules)
Most of the oxygen is excreted as a waste product
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
Glucose can be used by cell respiration or stored as starch.
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.
(Edited by Chris Paine)
https://app.box.com/s/88edjbrgbff0febtiyfk8x9l0cdnyshr
https://app.box.com/s/88edjbrgbff0febtiyfk8x9l0cdnyshr
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.
This shows the rate of photosynthesis for all the wavelengths of light as a % of the maximum possible rate.
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(Edited by Chris Paine)
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.%
of
the
max
imu
m r
ate
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ph
oto
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is
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/samples/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)
In the absence of equipment use the virtual lab and self-test quiz:http://www.phschool.com/science/biology_place/labbench/lab4/pigsep.html
Simplified Bioknowledgy protocol based on the SaPS outline: https://app.box.com/s/i8cc161713atmk7ks5zoex1psyrjir89
Thin layer chromatography for photosynthetic pigments
SAPS have published two (slightly) different protocols:• http://www.saps.org.uk/secondary/teaching-resources/189-investigation-of-
photosynthetic-pigments-in-green-plants• http://www.saps.org.uk/secondary/teaching-resources/181-student-sheet-10-
thin-layer-chromatography-for-photosynthetic-pigments
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.
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on
the rate of photosynthesis.R
ate
of
Ph
oto
syn
thes
is
Light intensity
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
When light intensity is increased the rate of photosynthesis increases therefore it is the limiting factor at low levels.
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.
Light intensity refers to the amount of light, of a given wavelength, which is available to the plant.
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on
the rate of photosynthesis.
When carbon dioxide concentration is increasedthe rate of photosynthesis increases therefore it is the limiting factor at low concentrations.
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Carbon dioxide concentration
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.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
CO2 is a substrate for the metabolic pathway hence the relationship is similar to how enzyme reactions are limited by substrate concentration.
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on
the rate of photosynthesis.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-photosynthesis/
Photosynthesis is a metabolic pathway hence the relationship is similar to how enzyme reactions are affected by temperature.
After the optimum temperature enzymes denature rapidly causing a fast decrease in the rate of photosynthesis as temperature increases further.
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
Temperature
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2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-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.
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-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.
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
http://i-biology.net/ahl/08-cell-respiration-photosynthesis/8-2-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.
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://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
http://sbi4u-photosynthesis.weebly.com/uploads/1/9/2/8/19284461/5941741_orig.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?
http://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
http://sbi4u-photosynthesis.weebly.com/uploads/1/9/2/8/19284461/5941741_orig.jpg
The independent variable• Only one limiting factor should be investigated at a time• The range of values should reflect conditions experienced
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
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://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
http://sbi4u-photosynthesis.weebly.com/uploads/1/9/2/8/19284461/5941741_orig.jpg
Dependent variable• An accurate method for measuring the rate of
photosynthesis needs to be used.• Oxygen production per time unit is recommended.
Leaf discs are a successful and easy way to measure oxygen generation by leaveshttp://www.saps.org.uk/secondary/teaching-resources/284-investigating-photosynthesis-with-leaf-discs
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://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
http://sbi4u-photosynthesis.weebly.com/uploads/1/9/2/8/19284461/5941741_orig.jpg
The control variables• These should include the limiting factors not being
investigated.• 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)
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?
http://i.ytimg.com/vi/n-YeCeSQS3w/maxresdefault.jpg
http://sbi4u-photosynthesis.weebly.com/uploads/1/9/2/8/19284461/5941741_orig.jpg
The control variables - Nature of Science• Explain why it is essential to control the limiting factors
not being investigated.• Evaluate which of the identified reasons are the most
important.
2.9.A1 Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.
http://commons.wikimedia.org/wiki/File:Blue_Marble_Eastern_Hemisphere.jpg
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.
