LAB EXAM 2
If the "no light control" rate was negative, what was happening to oxygen in the dark Chlorella tube?
If the "dark control" was negative, then Chlorella were consuming oxygen.
What is the dependent variable in Photosynthesis #3?
The rate at which Chlorella produces oxygen
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.
What are the results of oxidation of water in photosynthesis?
- production of oxygen gas - production of electrons and protons which later help make ATP and reduce CO2
At what wavelength did the ether layer (chlorophyll a) peak?
425.3
At what wavelength did the ethanol layer (carotene) peak?
438.2
At what wavelengths did the methanol layer (chlorophyll b) peak?
438.2 and 468.5
What did the graph of absorbance as a function of time for 0.0 mL chloroplasts, 0.1 mL chloroplasts, 0.2 mL chloroplasts, and 0.4 mL chloroplasts look like?
As concentration of chloroplasts increased, the starting absorbance of the trials decreased. The 0.0 mL chloroplasts line is horizontal. The change of absorbance over time for 0.1 mL is indicated by a slight slant, and 0.2 mL and 0.4 mL increase in slant (change in absorbance over time).
What is the relationship of initial population size and carrying capacity?
As is suggested in the previous question, initial population size does not affect the carrying capacity.
PHOTOSYNTHESIS #1
CHLOROPHYLL EXTRACTION
What absorbs visible light?
Chlorophyll, a pigment that makes plants green.
Independent variable of Photosynthesis #2?
Chloroplast added (0 mL - 0.4 mL)
What important process is carried out by photosynthetic autotrophs?
Conversion of light energy into ATP (useful biological energy) and conversion of carbon dioxide and water into sugar ("reducing power")
DCMU is an herbicide; it blocks the transfer of electrons out of photosystem II. (The P680 reaction center is located in photosystem II.) How would DCMU affect the production of oxygen in plants?
DCMU should lower the rate of oxygen production when compared to the rate produced by the same PFR and no DCMU. Oxygen production will fall because it is dependent on an electron-deficient P680. If P680 can't pass electrons to the next electron carrier in the thylakoid membrane, it won't become electron-deficient; this means that water oxidation and oxygen production will slow or stop. (The DCMU blockade may not be 100% effective.)
If heat is necessary for the DPIP to change color, what should have happened in the "no light, heat" control?
DPIP should lose its blue color and the absorbance should at 10 minutes be less than at 0 minutes.
What appears to be the relationship between the concentration of pigment and the height of the peaks?
Direct relationship, as concentration increases, peak height increases
What is the relationship between mL chloroplast preparation and change in Abs./min.?
Direct, positive relationship
A chlorophyll molecule absorbs 1 photon, 3.2 e (-19). If the photon has a wavelength of 400 nm, what is the fraction of the photon's energy captured by the chlorophyll?
E = 2 e (-16)/400 Fraction of photon's energy captured by chlorophyll = 3.2 e (-19)/E = 64%
What is the relationship between PFR and oxygen production rate in Chlorella?
Generally, the higher the PFR (photon fluence rate), the greater the oxygen production rate. Photons (essentially packets of light energy) strike photosystem II and cause it to lose an electron that is "caught" by a nearby electron acceptor. The electron-deficient photosystem II then removes electrons from water bringing about the production of oxygen. The higher the PFR, the higher the rate at which photons strike photosystem II and the higher the rate of water oxidation.
Which graph best represents competition? Which graph best represents predation? How can you tell?
Graph A is most likely to be a competition in which species 2 is the loser. This conforms to the data presented in the lab. The oscillations in graph B looks like the predator-prey situation presented in lab.
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.
A fish farmer wishes to raise the population level by simply adding more fish to the pond. Will this work in the long term? Why or why not?
If the fish population is already at carrying capacity, then this won't work for long. The augmented population will simply decline toward the carrying capacity and become steady at the old level. A better strategy would be to increase the carrying capacity and allow the population to expand naturally to this new, higher level.
How is the wavelength of a photon related to its energy?
Inverse relationship (a 450 nm wavelength packs more energy than a 650 nm wavelength)
If DPIP spontaneously loses its blue color, what should have happened in the "no light, no heat" control?
It should lose its blue color and the absorbance at 10 minutes should be less than at 0 minutes.
Compare the birth rate to the death rate during the lag, log, and stationary phases of logistic growth.
Lag: birth rate>death rate, but since the population is small, growth is slow. Log: birth rate>death rate, the population is large, so growth is rapid. Stationary: birth rate = death rate, growth is zero.
Does light alone appear to be needed to drive the DPIP reduction?
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.
Differentiate between linear, unrestricted exponential, and logistic growth.
Linear: - equation - N = ct + N0 - growth rate - dN/dt = c - growth rate is constant and independent of population size Unrestricted exponential: - equation - N = N0e^(rt) - growth rate - dN/dt = rn - growth rate is proportional to population size Logistic: - equation/growth rate - dN/dt = rN((K-N)/K) - growth rate is influenced by the difference between carrying capacity (K) and population size
How does changing the concentration of the pigment affect the absorbance spectrum?
Lower concentration = lower peaks = lower absorbance
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 today?
Maximum absorbance of photosynthetic pigments is in the blue and red regions of the visible spectrum. So, blue or red wavelengths should have been the most effective at driving the DPIP reduction reaction.
Chlorophyll is green; how does this relate to its absorption spectrum? Does chlorophyll absorb in 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?
No, does not absorb in the green region, it reflects (therefore appearing green to us). As a result, green light is of little use alone in photosynthesis. Red and blue light are absorbed by chlorophylls and are thus very useful in providing the energy required for photosynthesis.
Does changing the concentration of the pigment substantially alter the position (wavelength) of the peaks?
No, not significantly
What are the products of water oxidation? What are each used for?
O2 (oxygen gas), protons, and electrons - O2 - vital for cellular respiration and extracting the full potential energy of glucose - protons - vital for the production of ATP, used in Calvin-Benson cycle to make glucose - electrons - vital for the reduction of CO2 to produce energy-rich molecules like glucose
PHOTOSYNTHESIS #2
OXIDATION OF WATER
PHOTOSYNTHESIS #3
OXYGEN PRODUCTION
What would be the consequences to photosynthesis if the chlorophyll molecule were transparent to light? What would the absorption spectrum of a colorless, transparent substance look like?
Photosynthesis cannot occur without the absorption of light by the chlorophyll molecule. The transparent chlorophyll would absorb no light, and thus be useless in photosynthesis. The absorption spectrum of a colorless and transparent substance would be a flat line near zero absorbance across the visible spectrum.
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 substances?
Positions of the peaks are unique for each substance and not dependent on concentration as height is, thus they would be more useful for identifying a substance.
QUANTITATIVE CHANGES IN POPULATIONS
QUANTITATIVE CHANGES IN POPULATIONS
For what do plants use oxygen?
The Chlorella were carrying out aerobic respiration, that is, they were using oxygen to oxidize sugars that they had made previously.
What is the independent variable in Photosynthesis #3?
The amount of light, measured by photon fluence rate (PFR), operationally defined as predetermined distances from a light source
Why was bisulfite added to the "blank" tubes in your experiments with chloroplast function?
The bisulfite reduced the DPIP, so the blank had everything in it that the experimental tube had, except the blue color.
Note the graphical data below. What seems to be the carrying capacity (K) in this case? How can you tell?
The carrying capacity should be the population size where the population levels off. Irrespective of initial size, the population seems to level off at 200. So, 200 is the carrying capacity.
What happens to chlorophyll's electrons when it absorbs light energy?
The electrons are excited and transferred to other electron acceptors, creating an electron-deficit which is filled by electrons removed from water via oxidation.
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.
In the reaction you have been studying in this lab, where are the electrons that reduce the DPIP coming from?
The electrons originate from water.
How might DCMU negatively affect the production of glucose in a plant?
The electrons that ultimately are used to help make sugar (which the plant needs to survive) come from water that photosystem II oxidizes. If photosystem II can't deliver electrons, sugar production will stop, and eventually, the plant will die.
What is a limiting factor?
The limiting factor will affect carrying capacity when the factor is changed.
In the experiment where the amount of chloroplasts was varied, what do your results show about chloroplast function?
The more chloroplasts, the faster the dye reduction, as shown by the data when graphed. The direct relationship between rate of DPIP reduction and amount of chloroplasts indicates the dependence of water oxidation/dye reduction on active chloroplasts.
What is the carrying capacity of an environment?
The number of individuals in a population that an environment can support indefinitely.
Define absorption spectrum
The pattern of absorption by a substance
Dependent variable of Photosynthesis #2?
The rate of water oxidation, measure rate of DPIP reduction and subsequent loss of blue color via spectrophotometer
What does the photon energy absorbed by chlorophyll permit to happen?
The removal of electrons from water (producing oxygen and protons) and the shuttling of the electrons and protons to generate ATP and reduced CO2.
What major property of chlorophyll a, chlorophyll b, and carotenoids did we take advantage of in order to separate them from one another?
The solubilities of the three solvents - ether, ethanol, and methanol
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 a greater loss of blue color in the "light and heat" experiment than the "light" alone experiment.
When photosystem II absorbs light, what happens to water?
Water is oxidized, loses its electrons
Does changing the concentration of the pigment substantially alter the height (absorbance) of the peaks?
Yes, lower concentration = lower peaks
What are the wavelengths of the spectrum of light, in order of highest energy to lowest?
blue 450 blue-green 500 yellow-green 550 orange 600 red 650
The chlorophylls and carotene extracted in Lab 1 absorb visible light ... which allow the plant to obtain useful energy from its environment. What is the equation for the energy of a photon in joules?
photons E = 2 e (-16)/lambda, where lambda = the wavelength of the photon in nanometers (nm)
