BIO LAB - Photosynthesis and Cell respiration Experiment questions

How many cells do you typically see per coenobium?

The most common coenobia consists of 4 cells

Do the S. Obliquous vary in color? What does the intensity of the color tell you about the algae?

Chlorophylls are green. The greener the algae the more chlorophyll it contains. The more chlorophyll it contains, the more efficient its light capture for photosynthesis.

As algae photosynthesize, how will the pH of the CO2 indicator change? How will the pH change if the cells begin to respire?

Under bright light, the rate of photosynthesis will exceed that of cellular respiration, and the pH of CO2 indicator will increase, turning the CO2 purple. In the absence of light, cellular respiration will dominate, and the pH of the CO2 indicator will decrease turning it yellow.

Imagine that the algae are experiencing the light conditions that would result in the graph from page 10. Predict what color changes will happen in the CO2 indicator between compensations points 1 and 2, and explain why. What about after the compensation point 2?

Between the points 1 and 2, light is sufficient so that the rate of photosynthesis exceeds that of cellular respiration. This means that more CO2 is being consumed than produced, which causes the solution to become more basic. This will change the indicator from yellow to purple. After point 2, light is low enough that the rate of cellular respiration exceeds that of photosynthesis, this means more CO2 is being produced than consumed, which cause the solution to become more acidic. This will change the indicator from purple to yellow.

The algae beads provide a convenient system because they are uniform in size and contain roughly the same number of alga cells per bead. Why are these advantages for the experiments you will perform?

We will be measuring rates of photosynthesis and cellular respiration and these rates will depend on the number of organelles, or cells, that we use. The algae beads are easy to see, manipulate, and count. A consistent number of beads queal a consistent number of alga cells.

Under the light, which processes will be taking place: photosynthesis, cellular respiration, or both?

Both will be taking place simultaneously, but under bright light, photosynthesis will be the dominant process.

Why are you measuring the absorbance of the solution at 550nm?

Since the spectrophotometer measures, the amount of light absorbed by a sample and the samples will be yellow or purple, due to CO2 indicator, then the best wavelength of light to shine on the samples is the green spectrum. 550nm corresponds with green wavelengths of light and will be absorbed.

Are your slopes positive or negative for light and dark conditions? What does this mean about the change in CO2?

In the light the slope should be positive, meaning CO2 down, in the dark the slope should be negative, meaning CO2 up.

Under which condition did the CO2 indicator turn more alkaline? Why?

The CO2 indicator will turn more alkaline under light conditions b/c the algae beads photosynthesize faster than they respire, resulting in a decrease of CO2, which increases the pH of the CO2 indicator.

Under which condition did the solution start to change color more quickly?

The rate of color change will be faster in the light than in the dark.

How does cellular respiration impact the observed rate of photosynthesis? Is your calculated rate of photosynthesis accurate?

No, cellular respiration decreases the observed rate of photosynthesis by producing CO2. This makes the observed rate of photosynthesis lower than the actual rate.

Current pH in oceans is ~8.1, which is lower/more acidic, than the 8.2 at which its been for the past 300 million years. This is probably due to an increase in CO2 in our atmosphere dissolving into the ocean water. A change from pH 8.2 to 8.1 may sound small, but remember pH is on a log scale. This may allow better growth for organisms that prefer higher pH environments and make seminal harder for organisms that prefer higher pH environments. This may lead to a cascading effect on the ecosystem depending on how these organisms interact with the ecosystem.