BIO 110 Lab Practical 2

At what wavelength do the chloroplasts absorb red light?

700 nm

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.

Calibration of the oxygen detection device requires which of the following?

-Water that has no dissolved oxygen -Water that is saturated with oxygen

Assume that when a chlorophyll molecule absorbs 1 photon the energy content of the chlorophyll increases by 3.2 x 10-19 joules.

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The chlorophylls and carotene you extracted in lab absorb visible light photons. This capture of photons allows the plant to obtain useful energy from its enviroment

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At what wavelength do the chloroplasts absorb blue light?

400 nm

Which range of wavelengths is used to determine the absorption peaks of the pigments tested in the chlorophyll extraction lab?

400 nm to 700 nm

The pigments you extracted in lab absorb visible light photons. This capture of photons is the first step in photosynthesis and allows the plant to extract useful energy from its environment. The energy of a photon may be calculated as follows: E = hν where ν = c/λ "h" is Planck's constant, "c" is the speed of light, and λ is the wavelength of the photon With that information in mind, what is the relationship between photon energy and photon wavelength?

As the wavelength increases the energy decreases

What is the independent/dependent variable of the Photosynthesis I lab?

IV: Wavelength DV: Absorbance

What is the independent/dependent variable of the Photosynthesis II lab?

IV: amount of chloroplasts in mixture DV: rate of water oxidation

If the "no light control" rate was negative, what was happening to oxygen in the dark Chlorella tube?

Chlorella were consuming oxygen.

What is the independent/dependent variable of the Photosynthesis III lab?

IV: light quantity DV: rate that Chlorella produces oxygen

DCMU is as an herbicide; it blocks the transfer of electrons out of 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.

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 should at 10 minutes should be less than at 0 minutes.

The energy of a photon in joules may be calculated as follows

E = 2 x 10-16 /λ where: λ is the wavelength of the photon in nanometers (nm).

Extraction of photosynthetic pigments from spinach requires

Exposing spinach leaves first to boiling water, then to boiling ethanol

What would be the consequences to photosynthesis be if the chlorophyll molecule were transparent to light?

For chlorophyll to be of any use in photosynthesis, it must absorb or capture light energy. The captured energy is used to excite electrons that are utilized to produce ATP and reduce NADPox. The ATP and reduced NADP (along with CO2 and other compounds) are used in the production of sugars.

What is the relationship between PFR and oxygen production rate in Chlorella?

Generally, the higher the PFR, the greater the oxygen production rate.

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.

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.

What would the absorption spectrum of a colorless, transparent substance look like?

It would not absorb light; useless in photosynthesis

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.

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

What method is used in "Oxidation of Water" lab to measure the rate of water oxidation?

Measure the color change of DPIP over time

Does chlorophyll absorb in the green region of the spectrum?

Not much

In order to control for the possibility that DPIP spontaneously loses color, which of the following is done?

Put the aluminum foil cocooned experimental tube in front of the light with the water tank with the light on for 10 minutes.

In order to control for the possibility that DPIP loses color due to heat alone, what is done?

Put the aluminum foil cocooned experimental tube in front of the light without the water tank with the light on for 10 minutes.

How much photosynthesis would a plant carry out if it were illuminated by blue or red light?

Since chlorophylls absorb light in these regions, a plant should carry out photosynthesis (and therefore grow) considerably better under these lights than with green light alone.

What is the role of sodium sulfite in the calibration procedure

Sodium sulfite reacts with oxygen to remove the dissolved oxygen from water.

What happens to oxidized DPIP when it is mixed with illuminated chloroplasts?

The absorbance/wavelength will go from a gradual increase in slope than then abruptly decreases to a slope of 0

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.

In the experiment where the amount of chloroplasts was varied, what do your results show about chloroplast function?

The direct relationship between rate of DPIP reduction and amount of chloroplasts indicates the dependence of water oxidation/dye reduction on active chloroplasts.

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.

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 does the calibration procedure establish?

The relationship between the voltage produced by the apparatus and oxygen concentration.

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.

For what do plants use oxygen?

To oxidize sugars that they had made previously

What was the purpose of adding sodium sulfite and cobalt chloride (a catalyst) to distilled water in the oxygen chamber?

To remove dissolved oxygen from water in the oxygen chamber

In the reaction you have been studying in this laboratory, where are the electrons that reduce the DPIP coming from?

Water

What major property of chlorophyll a, chlorophyll b and carotenoids did we take advantage of in order to separate them from one another?

We exploited the different solubilities of the pigments in petroleum ether for chlorophyll a, ethanol for caroten, and methanol for chlorophyll b.

What does a spectrophotometer measure?

light absorbance as a function of wavelength

How is the concentration of oxygen measured in the oxygen production lab?

With a probe that produces an electrical signal that is proportional the oxygen concentration

How does the calibration process work for photosynthesis III?

You want to get water with no oxygen in it. To do this, you add sodium sulfite and cobalt chloride to get rid of the oxygen. Then you take a reading in the spec 20 of the voltage with the water with no oxygen. Then you take another reading in the spec 20 with the saturated water with 8.3 mg of oxygen. Then you will have your conversion factor.

At what wavelength do the chloroplasts REFLECT green light?

between 400 and 700 nm

Chlorophyll is green; how does this relate to its absorption spectrum?

chlorophyll a and chlorophyll b have absorption peaks in the blue and red regions. This means that chlorophylls transmit green light and, therefore, appear green.

How much photosynthesis would a plant carry out if it were illuminated by green light alone?

not much, because chlorophyll cannot absorb much light energy in the green region.

If the photon has a wavelength (λ) of 400 nm, what is the fraction of the photon's energy captured by the chlorophyll?

photon energy = 2 x 10^-16 /400 = 5 x 10^-19 J fraction captured = 3.2 x 10^-19 J/ 5 x 10^-19 J = 0.64 or 64%

How does the calibration process work for photosynthesis I?

turn the left knob to infinite and then with the blank in the chamber, turn the right knob to 0