Studied by 9 people
Recall the equation for photosynthesis
6CO2 + 6H2O --> C6H12O6 + 6O2
carbon dioxide + water -> glucose + oxygen (with light & chlorophyll)
Outline the transformation of light energy to chemical energy
1. Light energy from the sun is absorbed by chlorophyll/photosynthetic pigments
2. Chlorophyll:
absorbs red & blue wavelengths, reflects green wavelengths (plants r green lol!)
is the primary pigment used in photosynthesis
is located in the thylakoid membranes of chloroplast
3. Light energy is converted into chemical energy (starches) through photosynthesis in plants/autotrophs/producers
4. Chemical energy is stored in the chemical bonds of carbon compounds/organic compounds/sugars/food
5. Light energy from the sun supplies the chemical energy needed for life in most ecosystems
Outline the conversion of carbon dioxide to glucose in photosynthesis
1. PHOTOLYSIS: the splitting of water using light energy
H2O -> 2 H+ and 2e- + O2
2. Water is split into hydrogen, electrons, and oxygen
3. Hydrogen from photolysis is:
used to convert carbon dioxide to glucose in photosynthesis
used to power fixation of carbon into organic molecules
pumped across the thylakoid membrane
4. Oxygen is released as a by-product of photolysis/photosynthesis in plants, algae and cyanobacteria
5. Electrons replace the electrons lost on PSII (photosystem II)
Describe the history/significance of oxygen being produced as a by-product
1. Oxygen is produced as a by-product of photosynthesis in plants, algae, and cyanobacteria
2. 3 Billion years ago: that earth's atmosphere had NO OXYGEN, carbon dioxide, methane, ammonia, hydrogen, or water vapour
3. 2.5 billion years ago: cyanobacteria evolved, underwent photosynthesis -> produces oxygen
4. Oxygen concentration remained low in the atmosphere UNTIL all of the oxygen was absorbed by iron in branded iron formations
5. Multicellular organisms, algae, and plants thus then increased the amount of oxygen in the atmosphere in later stages
Outline the separation and identification of photosynthetic pigments by chromatography
1. Chromatography: process used to separate photosynthetic pigments
2. Pigments are concentrated in a spot above the solvent
3. Solvent mixture (ethanol/acetone) moves up the paper chromatography paper by capillary action -> pigments are carried up the paper in the solvent (based on their solubility)
4. Pigments will be separated based in their solubility in the solvent
5. Each pigment is represented by the specific Rf value that can be used to identify different pigments -- can be compared to a table of reference values
Recall how to interpret the chromatogram
The Rf value of a compound is equal to the distance travelled by the compound divided by the distance travelled by the solvent front (both measured from the origin)
1. Measure the distance travelled by pigment
2. Measure distance travelled by solvent front
3. Calculate Rf value
4. Compare Rf value to known value
5. Identify by colour and analyse with a spectrometer
Describe the absorption of specific wavelengths
1. Photosynthetic pigments absorb specific wavelengths of light
2. Chlorophyll absorbs red & blue wavelengths efficiently and reflects green
3. Chlorophyll absorbs light energy and electrons are photoactivated
Compare and contrast the absorption and action spectra
ABSORPTION SPECTRUM:
1. Shows the amount of light absorbed at different wavelengths by photosynthetic pigments
2. Primary pigment is chlorophyll
3. Accessory pigments are carotenoids
ACTION SPECTRUM : Shows rates of photosynthesis at different wavelengths of light
Outline the impact of light intensity on the rate of photosynthesis
AT LOW LIGHT INTENSITY:
1. Little photosynthesis occurs
2. As light intensity increases, the rate of photosynthesis increases
3. At moderate light intensity, there is a linear increase in the rate of photosynthesis
4. At light compensation point, photosynthesis = respiration rate and CO2 uptake = O2 release
5. Light is the limiting factor
AT HIGH LIGHT INTENSITY:
1. As light intensity increases, a max rate of photosynthesis is reached (plateau) - light saturation point
2. Any further increase will not result in a further increase in rate
3. Chloroplasts work at maximum efficiency
4. At this point, some other factor (temp, concentration of CO2) is the limiting factor
Outline the impact of temperature on the rate of photosynthesis
AS TEMPERATURE INCREASES:
1. Kinetic energy increases
2. Frequency that substrate collide with active sites increases
3. Rate of photosynthesis increases
4.Temperature is limting
OPTIMUM TEMPERATURE:
1. As temp approaches optimum, enzymes begin to denature
2. Rate of photosynthesis increases more slowly and eventually peak
3. Rate of photosynthesis increases up to an optimal temperature
ABOVE OPTIMAL:
1. Enzyme denature rapidly
2. Fast decrease in rate of photosynthesis and temperatures increases further
3.Another factor is limiting
Outline the impact of carbon dioxide on the rate of photosynthesis
AS CARBON DIOXIDE CONCENTRATION INCREASES:
1. Little photosynthesis occurs
2. At moderate concentrations, there is a linear increase in rate — carbon dioxide is limiting
3. At higher carbon dioxide concentrations, there is a low increase in the rate
4. At higher carbon dioxide concentrations, there is no further increase in the rate (plateaus)
5. Some other factor is the limiting rate of photosynthesis (temp/light)
Recall the role of limiting factors on the rate of photosynthesis
1. Limiting factors are light, carbon dioxide, and temp that are furthest away from their optimum
2. As you increase limiting factor, the rate of photosynthesis increases
3. Increasing other factors doesn't increase the rate of photosynthesis
Describe how to measure the rate of photosynthesis
Rate = change (measured) divided by time (controlled)
Measure rate of the uptake of CARBON DIOXIDE over time!
CO2 gas sensor to collect concentration of CO2 gas OVER TIME
pH meter/pH indicator to measure change/rise in pH of water surrounding an aquatic plant per unit time
Measure rate of the release of OXYGEN GAS over time!
oxygen gas sensor to collect concentration of oxygen gas OVER TIME
dissolved oxygen gas sensor to collect concentration of gas emitted from aquatic plant per unit time
water displacement to collect volume of oxygen emitted from an aquatic plant per unit time
count the number of bubbles emitted from an aquatic plant per unit time - (indirect)
time how long it takes for a leaf disk to rise
Measure increase in BIOMASS over time!
measure the increase in dry mass of plant before/after a period of time — glucose will be stored as starch
can be observed with colorimeter to measure absorbance /transmittance of light
Outline the significance of carbon dioxide enrichment experiments
Carbon dioxide can be enriched in greenhouses and FACE (free-air carbon enrichment experiments)
GREENHOUSES:
Enclosed greenhouses trap CO2 in the atmosphere
Allows for control/measure environmental variables (nutrients, sunlight, light intensity, wavelengths, temp)
Collect large amounts of continuous data, but lack natural variations/abiotic conditions
Plants need to be small enough to be enclosed
Large increase of 30% in crop yield
FACE - Free-air Carbon Enrichment Experiments
Carbon dioxide is pumped into the atmosphere through a piping system
Simulates natural variation/response in the environment
Higher cost
Meta-study identified a small increase (5-7%) in crop yield produced through photosynthesis
Compare light dependent and light independent reactions
LIGHT DEPENDENT:
1. Occurs in the thylakoid (membrane)
2. Removes ATP and NADH
LIGHT INDEPENDENT:
1. Occur in the stroma
2. Produces carbohydrate, glucose and ATP
Outline light dependent reactions
Non-cyclic photophosphorylation produces ATP and NADPH in light dependent reactions
1. Light is absorbed by photosystems (array of pigment molecules and Light Harvesting Complexes or LHC's, I/II) or chlorophyll — embedded in thylakoid membranes (algae, eukaryotic producers, bacteria)
2. Energy is passed to a reaction centre & electrons are photoactivated
3. Photolysis of water splits water into hydrogen, oxygen, and electrons
4. Electrons from photolysis replace electrons lost in PS II, with oxygen as a waste product
5. ATP is produced by chemiosmosis in the thylakoid membranes :
electrons are passed along electron carrier molecules (in thylakoid) and creates energy
energy is used to pump protons from stroma to thylakoid lumen
proton gradient is formed
protons diffuse through ATP synthase - forms ATP by photophosphorylation
ADP + PI -> ATP
6. Electrons from PS II are passed to PS I - Light energy is absorbed by PS I and electrons are photoactivated
7. Two electrons are passed to NADP + (In PS I), which is reduced as it accepts two electrons, two hydrogen atoms form NADPH + H+, or reduced NADP
Define and explain the location & type of photosystems
DEFINITION: Photosystems are molecular arrays of chlorophyll and accessory pigments with a special chlorophyll reaction centre
LOCATION: Thylakoid membranes in chloroplasts of photosynthetic eukaryotes and in membranes of cyanobacteria
TYPE:
There are photosystems I and II
absorbs light energy
energy is passed along until it reaches a reaction centre (a special chlorophyll) where electrons are photoactivated
Outline the advantages of photosystems
1. Structured array of pigments allows for light energy to be absorbed, energy & electrons to be transferred to the reaction centre in controlled way
2. Accessory pigments allow for wider range of wavelengths to be absorbed
3. Hundreds of pigment molecules allow for more energy to be absorbed and photoactivation to occur
4. LHC's are enzymes which catalyse the formation of ATP and the reduction of NADP to NADPH, and electron carrier molecules allow for the efficient transfer of energy
5. Carotenoids prevent photo-oxidative damange to chlorophyll from occurring
Describe the production of ATP production by chemiosmosis in thylakoid in photosystem I and II
NON-CYLIC PHOTOPHOSPHORYLATION:
1. In non-cyclic photophosphorylation, ATP is produced by photosystem II
2. Chemiosmosis couples electron movement to proton gradient formation and the synthesis and ATP
3. Electrons are photoactivated in PS II and are passed through a series of electron carriers in the thylakoid membrane
4. Movement of electrons releases energy and pumps hydrogen from stroma to thylakoid lumen, forming a proton gradient
5. Protons diffuse through ATP synthase and the movement of protons from the thylakoid lumen to the stroma generates ATP by photophosphorylation/ ADP + Pi → ATP
CYLIC PHOTOPHOSPHORYLATION
ATP is produced by photosystem I:
only invovles photosystem I
only produces ATP
electrons excited in PS I returns to PS I
only in bacteria
Describe the generation of oxygen by the photolysis of water in photosystem II
1. Photolysis is the splitting of water in PS II using light energy -- only occurs in PS II and is non-cyclic photophosphorylation
2. Photolysis splits water into hydrogen, oxygen and electrons
3. Electrons: replace the electrons lost in PS II
4. Hydrogen: used to form proton gradient and reduce NADP to form NADPH
5. Oxygen: released as a by-product
EQUATION:
H2O -> 2H+ + 2e- + 1/2 O2 H+ + NADP -> reduced NADP
2e- -> goes to photosystem II
Outline the reduction of NADP by photosystem I
1. Light energy is absorbed by chlorophyll or photosystem I, where 2 electrons are photoactivated
2. Electrons from PS II are passed to PS I and replace the electrons that were photoactivated
3. Electrons are passed to NADP+ which is reduced to form NADPH or reduced NADP as it accepts hydrogen (from water in photolysis) and two electrons
NADP+ + 2e- + 2 H+ -> NADPH
Recall the light-dependent reactions that occur along the thylakoid membrane
1. photolysis of water
2. synthesis of ATP by chemiosmosis
3. reduction of NADP
Outline cyclic photophosphorylation
1. Only involves photosystem I and occurs in bacteria
2. 2 electrons return back to PSI
3. ATP is produced
Outline the name, products, and location of light independent reactions
1. Called the calvin cycle
2. produces carbohydrates
3. Occurs in the stroma
Recall the significance of rubisco
1. Rubisco is the most abundant enzyme on earth
2. High concentrations of Rubisco are needed in the stroma of chloroplasts
3. Works relatively slowly and ineffectively
Describe light independent reactions!
1. CARBON FIXATION BY RUBISCO
RuBP is a 5-C compound
ubisco (enzyme) adds CO2 to RuBP
Forms 6-C compound → breaks down to form 2 molecules of glycerate 3-phosphate (the first identifiable product)
2. PHOSPHORYLATION & REDUCTION
Glycerate 3-phosphae is phosphorylated by ATP (provides the energy)
Glycerate 3-phosphate is reduced by NADPH → forms triose phosphate/glyceraldhyde 3-phosphate
NADPH provides the hydrogen & is the reducing power & electrons
3. REGENERATION OF RUBP
RUBP is regenerated from triosse phosphate using the energy provided by ATP
5 molecules of PGA are equal to 3 molecules of RUBP
most of the triose phosphate is regenerated (5/6)
4. FORMATION OF GLUCOSE
2 triose phosphates are shuttled out → produces glucose
All carbon in compounds in photosynthesising organisms is from the calvin cycle
Glucose is the substrate through which other carbon compounds are formed by metabolic pathways
Outline the interdependence of the light-dependent and light-independent reactions
1. Light dependent reactions produce ATP & NADPH
2. Light independent reactions require the products of the light dependent reactions (ATP and NADPH)
3. ATP provides the energy to convert glycerate 3-phosphate to triose phosphate
4. NADPH provides the hydrogen/reducing power to convert glycerate 3-phosphate to triose phosphate
Note 
Flashcard (116)