C1.3 - PHOTOSYNTHESIS Flashcards
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
- Light energy from the sun is absorbed by chlorophyll/photosynthetic pigments
- 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
- Light energy is converted into chemical energy (starches) through photosynthesis in plants/autotrophs/producers
- Chemical energy is stored in the chemical bonds of carbon compounds/organic compounds/sugars/food
- Light energy from the sun supplies the chemical energy needed for life in most ecosystem
Outline the conversion of carbon dioxide to glucose in photosynthesis
- Conversion of carbon dioxide to glucose in photosynthesis using hydrogen obtained by splitting water
PHOTOLYSIS: the splitting of water using light energy
H2O -> 2 H+ and 2e- + O2
- Water is split into hydrogen, electrons, and oxygen
- 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 - Oxygen is released as a by-product of photolysis/photosynthesis in plants, algae and cyanobacteria
- Electrons replace the electrons lost on PSII (photosystem II)
Describe the history/significance of oxygen being produced as a by-product
- Oxygen is produced as a by-product of photosynthesis in plants, algae, and cyanobacteria
- 3 Billion years ago: that earth’s atmosphere had NO OXYGEN, carbon dioxide, methane, ammonia, hydrogen, or water vapour
- 2.5 billion years ago: cyanobacteria evolved, underwent photosynthesis -> produces oxygen
- Oxygen concentration remained low in the atmosphere UNTIL all of the oxygen was absorbed by iron in branded iron formations
- 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
- Chromatography: process used to separate photosynthetic pigments
- Pigments are concentrated in a spot above the solvent
- 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
- Pigmetns will be separated based in their solubility in the solvent
- 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 chromotogram
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).
- Measure the distance travelled by pigment
- Measure distance travelled by solvent front
- Calculate Rf value
- Compare Rf value to known value
- Identify by colour and analyse with a spectrometer
Describe the absorption of specific wavelengths
- Photosynthetic pigments absorb specific wavelengths of light
- Chlorophyll absorbs red & blue wavelengths efficiently and reflects green
- 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
- Primary pigment is chlorophyll
- 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:
- Little photosynthesis occurs
- As light intensity increases, the rate of photosynthesis increases
- At moderate light intensity, there is a linear increase in the rate of photosynthesis
- At light compensation point, photosynthesis = respiration rate and CO2 uptake = O2 release
- Light is the LIMITING FACTOR
AT HIGH LIGHT INTENSITY:
- As light intensity increases, a max rate of photosynthesis is reached (plateau) - LIGHT SATURATION POINT
- Any further increase will not result in a further increase in rate
- Chloroplasts work at maximum efficiency
- 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
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
Outline the impact of carbon dioxide on the rate of photosynthesis
AS CARBON DIOXIDE CONCENTRATION INCREASES:
- Little photosynthesis occurs
- At moderate concentrations, there is a linear increase in rate
- At higher carbon dioxide concentrations, there is a low increase in the rate
- At higher carbon dioxide concentrations, there is no further increase in the rate (plateaus)
- Some other factor is the limiting rate of photosynthesis (temp/light)
Recall the role of limiting factors on the rate of photosynthesis
- Limting factors are light, carbon dioxide, and temp that are furthest away from their optimum
- As you increase limiting factor, the rate of photosynthesis increases
- 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
- 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
- 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
- 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 absorbace/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:
1. Enclosed greenhouses trap CO2 in the atmosphere
2. Allows for control/measure environmental variables (nutrients, sunlight, light intensity, wavelengths, temp)
3. Collect large amounts of continuous data, but lack natural variations/abiotic conditions
4. Plants need to be small enough to be enclosed
5. 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
- 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)
- Energy is passed to a reaction centre & electrons are photoactivated
- Photolysis of water splits water into hydrogen, oxygen, and electrons
- Electrons from photolysis replace electrons lost in PS II, with oxygen as a waste product
- 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 - Electrons from PS II are passed to PS I
- Light energy is absorbed by PS I and electrons are photoactivated - 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
- Non-cyclic photophosphorylation produced ATP and NADPH in light dependent reactions
Define and explain the location & type of photosystems
DEFINITON: 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 cynobacteria
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
- Structured array of pigments allows for light energy to be absorbed, energy & electrons to be transferred to the reaction centre in CONTROLLED WAY
- Accessory pigments allow for wider RANGE of wavelengths to be absorbed
- Hundreds of pigment molecules allow for MORE energy to be absorbed and photo activation to occur
- 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
- Carotenoids prevent photo-oxidative DAMAGE to chlorophyll from occurring
Describe the production of ATP production by chemiosmosis in thylakoid in photosystem I and II
- In non-cyclic photophosphorylation, ATP is produced by photosystem II
- Chemiosmosis couples electron movement to proton gradient formation and the synthesis and ATP
- Electrons are photoactivated in PS II and are passed through a series of electron carriers in the thylakoid membrane
- Movement of electrons releases energy and pumps hydrogen from stroma to thylakoid lumen, forming a proton gradient
- Protons diffuse through ATP synthase and the movement of protons from the thylakoid lumen to the stroma generates ATP by photophosphorylation/ ADP + Pi -> ATP
- In cyclic 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
- Photolysis is the splitting of water in PS II using light energy – only occurs in PS II and is non-cyclic photophosphorylation
- Photolysis splits water into hydrogen, oxygen and electrons
- Electrons: replace the electrons lost in PS II
- Hydrogen: used to form proton gradient and reduce NADP to form NADPH
- 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
- Light energy is absorbed by chlorophyll or photosystem I, where 2 electrons are photoactivated
- Electrons from PS II are passed to PS I and replace the electrons that were photoactivated
- 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
MADP:
NADP+ + 2e- + 2 H+ -> MADPH
Recall the light-dependent reactions that occur along the thylakoid membrane
- photolysis of water
- synthesis of ATP by chemiosmosis
- reduction of NADP
Outline cyclic photophosphorylation
- Only involves photosystem I and occurs in bacteria
- 2 electrons return back to PSI
- ATP is produced
Outline the name, products, and location of light independent reactions
- Called the calvin cycle
- produces carbohydrates
- Occurs in the stroma
Recall the significance of rubisco
- Rubisco is the most abundant enzyme on earth
- High concentrations of Rubisco are needed in the stroma of chloroplasts
- Works relatively slowly and ineffectively
Describe light independent reactions!
- CARBON FIXATION BY RUBISCO
- RuBP (ribulose bisphosphate) is a 5-C compound
- rubisco (enzyme) adds CO2 to RuBP
- Forms 6-C compound -> breaks down to form 2 molecules of glycerate 3-phosphate (the first identifiable product) - 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 - 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)
- 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
- Light dependent reactions produce ATP & NADPH
- Light independent reactions require the products of the light dependent reactions (ATP and NADPH)
- ATP provides the energy to convert glycerate 3-phosphate to triose phosphate
- NADPH provides the hydrogen/reducing power to convert glycerate 3-phosphate to triose phosphate
