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What was the goal of photosynthesis lab 1?
use a spectrophotometer to construct an absorption spectrum of pigments and determine how pigment concentration affects the spectra
what pigments were tested in photosynthesis lab 1?
carotene, chlorophyll a and chlorophyll b (all extracted from spinach)
what is photosynthesis?
the conversion of light energy into useful biological energy (ATP) and "reducing power" that drives the conversion of carbon dioxide and water into sugar
what is chlorophyll and its function?
chlorophyll is a pigment that makes plants green, it absorbs visible light photons
what are photons?
"packets" of light energy
the energy associated with a photon is ___ related to its wavelength
inversely (ex: a 450 nm wavelength photon packs more energy than a 650 nm wavelength photon)
the photon energy absorbed by chlorophyll permits the
removal of electrons from water and the shuttling of the electrons and protons (in ways that drive ATP generation and CO2 reduction)
the spectrophometer operates in the wavelength range of
400 to 700 nm
what are the major components of a spectrophotometer?
light source, monochromator (splits light into component wavelengths, perceived by us as colors), cuvette (passes light through solvent and pigment), detector (converts light signal from light that is not absorbed by mixture into an electrical signal that can be sent to a computer)
chlorophylls are separated from
carotenoids
what chemicals were used in photosynthesis lab 1?
95% ethanol, petroleum ether, 92% methanol
what were the 3 layers formed during photosynthesis lab 1?
1) carotene/ethanol
2) chlorophyll b/methanol
3) chlorophyll a/petroleum ether
Does changing the concentration of the pigment substantially alter the position (wavelength) of the peaks?
No, changing the concentration of the pigment changed the absorption but not the wavelength value of the peaks.
Does changing the concentration of the pigment substantially alter the height (absorbance) of the peaks?
Yes, changing the concentration of the pigment significantly alters the height (absorbance) of the peaks.
What appears to be the relationship between the concentration of pigment and the height of the peaks?
The concentration of pigment and the height of the peaks (absorbance) have a linear/direct relationship.
The absorbance spectra showed that the different pigments have peaks of absorbance that differ in position and height. Of the two (position or height), which would be more useful in identifying a substance? Explain.
Positions of the peaks would be more useful for identifying a substance because they are unique for each substance.
What would be the consequences to photosynthesis be if the chlorophyll molecule were transparent to light?
If the chlorophyll molecule were transparent to light, it would not absorb any light, transmitting everything.
What would the absorption spectrum of a colorless, transparent substance look like?
The absorption spectrum of a colorless, transparent substance would have absorbance values at zero for all visible wavelengths.
Chlorophyll is green; how does this relate to its absorption spectrum?
In relation to its absorption spectrum, chlorophyll is green meaning it shows strong absorption in blue and red spectrums.
Does chlorophyll absorb in the green region of the spectrum?
Chlorophyll does not absorb green light (the green region of the spectrum)
How much photosynthesis would a plant carry out if it were illuminated by green light alone? By blue light? By red light?
A plant would not be able to carry out photosynthesis if it were illuminated by a green light alone. The plant would be able to carry out photosynthesis in blue or red light.
What major property of chlorophyll a, chlorophyll b and carotenoids did we take advantage of in order to separate them from one another?
The different solubilities of the pigments in the 3 solutions (ethanol, methanol, and ether).
The energy of a photon in joules may be calculated as follows
E = 2E-16 /λ
What was the purpose of photosynthesis lab 3?
to study the effect of light quantity on the rate of oxygen production by Chlorella (an algae)
What is Chlorella?
an aquatic photosynthetic unicellular organism
Chlorella is a member of ___ ___
phylum Chlorophyta (a division of green algae)
What help Photosystem II remove electrons from water after absorbing light energy
manganese atoms and proteins
What does the oxidation of water yield?
electrons, protons, and oxygen gas (2 H₂O → 4e⁻ + 4H⁺ + O₂)
Why are the electrons (e-) produced by water oxidation important?
they are energized by light and eventually used to reduce CO₂ to produce energy-rich molecules, like glucose
Why are the protons (H+) produced by water oxidation important?
they play an important part in the production of ATP by chloroplasts (ATP is used in the Calvin-Benson cycle to help make glucose)
Why is the oxygen (O2) produced by water oxidation important?
while it has no direct role in photosynthesis, it is vital in cellular respiration. oxygen allows many organisms to fully extract the potential energy of glucose
What was the independent variable in photosynthesis lab 3?
light quantity
What was the dependent variable in photosynthesis lab 3?
the rate at which Chlorella produces oxygen
How is light quantity measured?
a quantum sensor that measures photon fluence rate (PFR)
What are the units of PFR?
µmoles of photons/m²/s
One micromole of photons is equal to _____ photons
6.023e17
How was the rate at which Chlorella produced oxygen measured?
A device that generates tiny flashes of light that are detected by a photodiode (oxygen sensor)
The rate at which the flashes are produced by the device is ___ to dissolved oxygen concentration
proportional
What were the various marks for the probe stand?
0 (no light), 22, 45, 90, 180
What was the duration of the no light run?
400 seconds (measurements at 100 and 400)
What was the duration of the light runs (22, 45, 90, 180)?
250 seconds (measurements at 50 and 250)
During photosynthesis lab 3, we measured the oxygen concentrations (mg/L) at the start and end of the experiment. How did we use these values to calculate the rate of change in oxygen amount (mg/sec)?
1) Calculate A, the change in dissolved oxygen concentration (mg/L), by subtracting the start concentration value from the end concentration value
2) Calculate B, the change in amount of oxygen in 8 mL of water (mg), by multiplying A by 0.008 L
3) Calculate C, the rate of change in oxygen amount (mg/sec), by dividing B by the time duration of the experiment
What is the relationship between PFR and oxygen production rate in Chlorella?
Direct (as PFR increases, oxygen production rate increases)
If the "no light control" rate was negative, what was happening to oxygen in the dark Chlorella tube?
the oxygen in the dark Chlorella tube was being consumed
What do plants use oxygen for?
plants use oxygen for cellular respiration, the process of breaking down sugar to make energy
What does the herbicide DCMU block and prevent?
DCMU blocks the transfer of electrons out of photosystem II, preventing a plant from using water to generate oxygen during photosynthesis
How would DCMU affect the production of oxygen in plants?
DCMU would lower the rate of oxygen production by inhibiting the electron transport chain in Photosystem II (blocking the process where water is split to release oxygen as a byproduct of photosynthesis)
How might DCMU negatively affect the production of glucose in a plant?
DCMU might negatively addect the product of glucose by inhibiting the electron transport chain within Photosystem II (blocking the conversion of light energy into chemical energy needed to produce glucose during photosynthesis) This means the plant cannot generate the necessary ATP and NADPH to fix carbon dioxide into sugar molecules, ultimately limiting glucose synthesis.
What was the goal of photosynthesis lab 2?
to measure the rate at which water is oxidized during photosynthesis when we vary the amount of chloroplasts participating in the reaction
what is produced as a result of chloroplasts' ability to oxidize water?
oxygen gas, electrons, and protons
Graphic of photosystem I & II
what's the independent variable in photosynthesis lab 2?
amount of chloroplasts added to the reaction mixture (0, 0.1, 0.2, or 0.4 mL of chloroplast suspension)
what's the dependent variable in photosynthesis lab 2?
rate of water oxidation
To make an indirect measure of rate of water oxidation, what was the water oxidation reaction coupled with?
the reduction of DPIP
What happens to DPIP when it is reduced and how to this correlate to rate of water oxidation?
DPIP loses its blue color and the loss of color is easy to measure with a spectrophotometer and it serves as an accurate reflection of the rate of water oxidation
In photosynthesis lab 2, what were the constant components in all the samples/control/blanks tested?
Buffer, KCl, DPIP (1 mL for all)
In photosynthesis lab 2, what were the varying components in all the samples/control/blanks tested?
Distilled water, bisulfate, and chloroplasts
As mL of chloroplast increased, what happened to the rate/slope, representing absorbance vs time, of the experiments?
it increased
What data was collected in photosynthesis lab 2?
Absorbance (at 600 nm) vs time (at 0, 2, 4, 6, 8, and 10 minutes)
To control for the possibility that the DPIP spontaneously loses color, what experiment was done?
No light, no heat (foil wrapped tube was used in front of water tank with the light on)
To control for the possibility that the DPIP loses color simply due to heat, what experiment was done?
No light, heat (foil wrapped tube was used in front of light without water tank)
To control for the possibility that the DPIP loses color due to the combined effect of heat and light, what experiment was done?
Light and heat (unwrapped tube was used in front of light without the water tank)
Why do you suppose a buffer was used for the isolation and function assessment of chloroplasts?
A buffer was used to control the pH. This is necessary to maintain a constant external environment for the chloroplasts, which helps them survive the experimental procedures. Also, many biological reactions are sensitive to pH; the buffer held the pH steady to eliminate changes in pH as an experimental variable.
Why was bisulfite added to the "blank" tubes in your experiments with chloroplast function?
The bisulfate reduced DPIP, so the blank had everything in it that the experimental tube had, except the blue color.
In the experiment where the amount of chloroplasts was varied, what do your results show about chloroplast function?
The more chloroplasts, the faster the reduction. The direct relationship between rate of DPIP reduction and amount of chloroplasts indicates the dependence of water oxidation/dye reduction on active chloroplasts.
If DPIP spontaneously loses its blue color, what should have happened in the "No light, no heat" control?
It should lose blue color and the absorbance at 10 minutes should be less than at 0 minutes.
If heat is necessary for the DPIP to change color, what should have happened in the "No light, heat" control?
DPIP should lose blue color and the absorbance at 10 minutes should be less than at 0 minutes.
If light and heat are required for DPIP to lose its color, how should the change in absorbance be different between the "light and heat" control and the "light, no heat" condition?
There should be greater loss of blue color in the light and heat experiment than the light alone experiment.
Does light alone appear to be needed to drive the DPIP reduction? How can you tell?
Light alone appears to account for the great majority of the color change of DPIP because light alone causes the greatest loss of blue color.
In the reaction you have been studying in this laboratory, where are the electrons that reduce the DPIP coming from?
you have been studying in this laboratory, where are the electrons that reduce the DPIP coming from?
The electrons come from the split of water.
Where do these electrons normally end up when the full process of photosynthesis is occurring? How important is this for the overall process of photosynthesis?
The electrons are normally given to CO2, thereby reducing it. Reduction of CO2 to sugar is the essence of photosynthesis.
If we had been able to provide illumination of different wavelengths for the chloroplast preparation that all had equivalent energy levels, what wavelength(s) do you think would have been most effective for driving the reduction of DPIP in the reaction you studied?
Maximum absorbance of photosynthetic pigments is in the blue and red regions of the visible spectrum. Thus, blue or red wavelengths should have been the most effective at driving the DPIP reduction reaction.
What wavelengths do you think would have been least effective for driving the reduction of DPIP? Why?
Green wavelengths would have been least effective because they are least well absorbed.
What are the three patterns of population increase?
linear, unrestricted exponential, and logistic
Given the proper conditions, populations of living things...
increase numerically
What's an example of linear growth?
a corn seed
In linear growth, a fixed number of cells ____ in each generation
reproduce
What's the equation for population size (N) in the linear growth model?
N = ct + Ni (c = rate of increase, t = time, Ni = initial population size)
Mathematically, the slope in linear growth represents...
growth rate, dN/dt = c
The rate of increase (slope) is constant in which growth model?
linear
In unrestricted exponential growth, a fixed proportion of cells ____
reproduce
What's the equation for population size (N) in the unrestricted exponential growth model?
N = Ni * e^rt (e = euler's number 2.718, r = intrinsic rate of increase, t = time in generations, Ni = initial population size)
In unrestricted exponential growth, the rate of increase (slope) are ____ ____
constantly changing
In unrestricted exponential growth, growth rate is ___ to the population size
proportional
Mathematically, the slope in unrestricted exponential growth represents...
growth rate, dN/dt = rN
What are the phases of logistic growth?
lag phase, log phase, and stationary phase
What happens during the lag phase?
number of births is greater than the number of deaths, but the growth is slow because of the small number of individuals in the population
What happens during the log phase?
the number of individuals increases as the birth rate still exceeds the death rate and the population enters a period of rapid growth
What happens during the stationary phase
the population size doesn't change because the birth and death rates are equal
A population may remain at the stationary phase for a long period of time IF...
the environment can meet the demands for food and space on a continuing basis
What is the carrying capacity (K)?
the number of individuals in a population that an environment can support indefinitely
What factors may limit population growth?
resource and space limitations, competition, or predation
Mathematically, the slope in logistic growth represents...
growth rate, dN/dt = (rN(K-N)) / K
In logistic growth, the rate of increase is influenced by how large __ is in comparison to __
N, K
If the condition is N<<K, what is dN/dt for logistic growth?
lag phase (slow growth)
If the condition is N is approaching K, what is dN/dt for logistic growth?
log phase (rapid growth), close to 0
If the condition is N=K, what is dN/dt for logistic growth?
stationary phase, 0
If the condition is N>K, what is dN/dt for logistic growth?
negative, decrasing
Identify the type of growth based on the description: "Growth rate is constant and independent of population size"
linear
Identify the type of growth based on the description: "Growth rate is cproportional to population size"
unrestricted exponential
Note 
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