C1.3  Photosynthesis

Theme:  Interaction and Interdependence

Interaction occurs when energy is transferred as light and/or molecules collide.

• Specific wavelengths of light interact with chlorophyll and accessory pigments. 
• Photolysis is a critical interaction where light energy is used to split water molecules. 
• The arrangement of photosystems and the electron transport chain (ETC) in the thylakoid membrane ensures that electrons can be passed efficiently between carriers.

Interdependence is demonstrated by the light-dependent and light-independent reactions relying on each other.  Additionally, the entire biosphere relies on photosynthesis as a mechanism for bringing energy into the system.

• The Calvin Cycle depends on the light-dependent reactions for a supply of ATP and reduced NADP. Conversely, the light-dependent reactions require the ADP, Pi, and NADP+ regenerated by the Calvin Cycle to continue.
• The rate of photosynthesis is interdependent on external limiting factors such as light intensity, CO2 concentration, and temperature. 
• The "Great Oxidation Event" shows how the waste product photosynthesis fundamentally changed the atmosphere, making aerobic life (and our existence) possible.
• Modern ecosystems remain interdependent on photosynthesis for the carbon fixation that forms the base of almost all food chains.

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How is energy from sunlight absorbed and used in photosynthesis?
• How do abiotic factors interact with photosynthesis?

​
​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What are the consequences of photosynthesis for ecosystems?
• What are the functions of pigments in living organisms?

Key Terms to Know: * higher level only

Absorption Spectra
Accessory Pigment*
Action Spectra
Adenosine Triphosphate (ATP)*
Algae
Amino Acid*
ATP Synthase*
Calvin Cycle*
Carbon Compound
Carbon Dioxide (CO2)
Carbon Fixation*
Chemical Energy
Chemiosmosis*
Chlorophyll*
Chloroplast*
Chromatography
CO2 Enrichment
Control Variable
Carbohydrate*
Cyanobacteria
Cyclic Photophosphorylation*
Dependent Variable
Ecosystem

Electron
Enzyme*
Eukaryote*
Free-Air CO2 Enrichment (Face)
Glucose
Glycerate 3-Phosphate (GP)*
Greenhouse
Hydrogen
Hydrogen Ion*
Hypothesis
Independent Variable
Light Energy
Light Intensity
Light-Dependent Reactions*
Light-Independent Reactions*
Limiting Factor
Metabolic Pathway*
Mineral Nutrients*
NADP+*
NADPH*
Non-Cyclic Photophosphorylation*
Oxygen (O2)
Paper Chromatography

Photolysis*
Photosynthesis
Photosystem*
Photosystem I*
Photosystem II*
Pigment
Plant
Proton*
Proton Gradient*
Pump*
Reaction Centre*
Reduced NADP*
Reduction*
Rf Value
Ribulose Bisphosphate (RuBP)*
Rubisco*
Stroma*
Temperature
Thin-Layer Chromatography
Thylakoid*
Triose Phosphate (TP)*
Water
Wavelength

C1.3.1— Transformation of light energy to chemical energy when carbon compounds are produced in photosynthesis.

• Outline how light energy is converted to chemical energy in carbon compounds.
• Draw a flowchart to illustrate the energy conversions performed by living organisms.
• List three reasons why living organisms need energy for cell activities.
• State that sunlight is the principal energy source in most ecosystems. ​

C1.3.2— Conversion of carbon dioxide to glucose in photosynthesis using hydrogen obtained by splitting water.

• State the chemical equation for photosynthesis.
• Outline the source of the atoms used to form glucose (C6H12O6) during photosynthesis.
• Define photolysis.

C1.3.3— Oxygen as a by-product of photosynthesis in plants, algae and cyanobacteria.

• State the source of the oxygen produced as a by-product in photosynthesis.

C1.3.4— Separation and identification of photosynthetic pigments by chromatography.

• Outline the process of separating pigments using chromatography.
• Identify pigments that result from chromatography by color and calculated Rf value.  ​

C1.3.5— Absorption of specific wavelengths of light by photosynthetic pigments.

• State the range of wavelengths that fall within the visible spectrum.
• Outline the function of pigments.
• State the primary and accessory pigments found in chloroplasts. 
• Explain why most plants look green. 
• Sketch the chlorophyll pigment absorption spectrum, including both wavelengths and colors of light on the X-axis.​

C1.3.6- Similarities and differences of absorption and action spectra.

• Compare and contrast the action spectrum and absorption spectrum.
• Explain the shape of the curve of the photosynthesis action spectrum.
• Outline a technique for calculating the rate of photosynthesis by measuring either oxygen production or carbon dioxide consumption.

C1.3.7- Techniques for varying concentrations of carbon dioxide, light intensity or temperature experimentally to investigate the effects of limiting factors on the rate of photosynthesis. 

• Define “limiting factor.”
• Explain how the following factors limit the rate of photosynthesis: temperature, light intensity, CO2 concentration.
• Identify manipulated (independent), responding (dependent) and controlled variables in experiments testing limiting factors on the rate of photosynthesis. 
• Outline techniques for measuring the rate of photosynthesis while manipulating either temperature, light intensity, or CO2 concentration.

C1.3.8- Carbon dioxide enrichment experiments as a means of predicting future rates of photosynthesis and plant growth.

• State the source of atmospheric carbon dioxide beyond the historical average of about 300 ppm.
• Compare enclosed greenhouse and free-air carbon dioxide enrichment (FACE) experiments.
• List the questions that are addressed in carbon dioxide enrichment experiments.

AHL ​​​​C1.3.9- Photosystems as arrays of pigment molecules that can generate and emit excited electrons.

• Describe the arrangement of pigments into photosystems in membranes. 
• Outline the advantage of pigments being arranged in photosystems as opposed to being dispersed.
• State the function of the reaction center pigment in a photosystem. 
• Compare the peak absorbance of the reaction center chlorophyll molecules of photosystem I and photosystem II.

AHL ​​​​C1.3.10- Advantages of the structured array of different types of pigment molecules in a photosystem.

• Outline advantages of pigment molecules being arranged within a photosystem.

AHL ​​​C1.3.11- Generation of oxygen by the photolysis of water in photosystem II.

• Describe the role of photosystem II in photolysis.
• Outline the movement of electrons generated by photolysis of water at photosystem II. 
• State that photolysis of water at photosystem II contributes to the proton gradient in the thylakoid lumen.
• Outline the role of photosynthesis of the “Great Oxygenation Event” on early Earth.
• Outline the evidence for the “Great Oxygenation Event” provided by banded iron formations.

AHL ​​​C1.3.12-  ATP production by chemiosmosis in thylakoids.

• Sketch a cross section of the thylakoid membrane, inclusive of photosystem II, ATP synthase, an electron transport chain (with Pq) and photosystem II. 
• Define chemiosmosis and photophosphorylation. 
• State that electrons generated by photosystem II pass from plastoquinone (Pq) through a chain of electron carrier molecules.
• State that the energy released by the movement of electrons is used to pump protons across the thylakoid membrane, from the stroma into the thylakoid lumen.
• State that the result of the electron transport chain is a proton gradient, with a high concentration of protons in the thylakoid lumen.
• Outline the generation of ATP by chemiosmosis as protons move down their concentration gradient through ATP synthase.
• Compare the flow of electrons in cyclic vs noncyclic photophosphorylation.

AHL ​​​C1.3.13-  Reduction of NADP by photosystem I.

• State that photoactivation of the reaction center chlorophyll in photosystem I excites electrons which pass through a different electron transport chain.
• Outline the flow and function of electrons from photosystem I in cyclic photophosphorylation. 
• Outline the flow and function of electrons from photosystem I in non-cyclic photophosphorylation. 
• State that in noncyclic photophosphorylation, the electrons of photosystem I are used to reduce NADP+ to form NADPH.
• State the function of the enzyme NADP reductase.
• State that the light dependent reactions convert light energy into chemical energy in the form of ATP and reduced NADP (=NADPH).

AHL ​​​C1.3.14- Thylakoids as systems for performing the light-dependent reactions of photosynthesis.  

• Describe the structure of the thylakoid grana and stroma lamellae.
• Outline how the thylakoid functions as a system of interacting parts.
• State the location of the light-dependent reactions of photosynthesis, including photoactivation, photolysis, electron transport chain, chemiosmosis, and reduction of NADP.

AHL ​​​C1.3.15- Carbon fixation by Rubisco.

• Define carbon fixation and carboxylation.
• State that carbon fixation occurs in the chloroplast stroma.
• State that the 5-carbon molecule ribulose bisphosphate (RuBP) is carboxylated by CO2, forming two 3-carbon molecules called glycerate-3-phosphate (GP).
• State that the enzyme that catalyzes the carboxylation of RuBP is called ribulose bisphosphate carboxylase (rubisco).
• State that the enzyme rubisco is the most abundant enzyme on Earth.
• State the effectiveness of rubisco at low concentrations of CO2.​
• State the source of the carbon and oxygen atoms that become part of the carbohydrate molecule (ie C6H12O6) produced in photosynthesis.
  

AHL ​​​C1.3.16- Synthesis of triose phosphate using reduced NADP and ATP.

• State the source of the hydrogen atoms that become part of the carbohydrate molecule (ie C6H12O6) produced in photosynthesis. 
• State that ATP (from the light dependent reaction) provides the energy for NADPH (also from the light dependent reaction) to reduce glycerate-3-phosphate (GP), forming a three-carbon carbohydrate, triose phosphate (TP). 
• State that synthesis of triose phosphate (TP) occurs in the chloroplast stroma.​

AHL ​​​C1.3.17- Regeneration of RuBP in the Calvin cycle using ATP.

• Outline the formation of a hexose monosaccharide (ie glucose) from the triose phosphate produced in the light independent reactions.
• Outline the reason that ribulose bisphosphate (RuBP) must be regenerated in the Calvin cycle. 
• State that in the Calvin Cycle, five molecules of 3-carbon triose phosphate (TP) are used to regenerate  the three molecules of the 5-carbon ribulose bisphosphate (RuBP).
• State that six turns of the Calvin Cycle are needed to produce one molecule of a hexose monosaccharide (ie glucose).
• State that ATP is used to regenerate RuBP from triose phosphate. ​

AHL ​​​C1.3.18- Synthesis of carbohydrates, amino acids and other carbon compounds using the products of the Calvin cycle and mineral nutrients.

• State that carbon fixation during the light independent reactions is the basis for carbon entering a food web.
• Outline the formation of glucose, sucrose, starch and cellulose from the triose phosphate (TP) formed during photosynthesis.
• State that enzymes in plant cells can create fatty acids, glycerol, amino acids and nucleotides using metabolic pathways that can be traced back to the light independent reactions of photosynthesis. ​

AHL ​​​C1.3.19- Interdependence of the light-dependent and light-independent reactions.

• List the major steps of the light dependent and light independent reactions of photosynthesis. 
• Discuss the interdependent relationship between the light dependent and light independent reactions of photosynthesis. 
• State the rate limiting step of photosynthesis in low and high light intensity conditions. ​