The Lab Procedures: read the following descriptions and write a problem that you can answer using one of these measuring devices. Develop a hypothesis based on your literature search.

The investigation: involved growing Thalassiosira weissflogii diatom cultures under three different CO2 concentrations.  100 ppm, 370 ppm, and 750 ppm carbon dioxide were bubbled through three individual bottles for a period of seven days.  The growth chambers were replicated by five different researchers over the same time period.  The pure culture of diatoms received equal quantities of nutrients, vitamins, and trace metals required for growth.  Earth's atmosphere currently contains about 370 ppm carbon dioxide.  This concentration was used as the control.

The changes in each bottle were monitored quantitatively throughout the seven day growth period using the following laboratory tools:

carbon dioxide growth chambers
a) cell counts- each researcher repeated his/her measurements four times on each data collection day. The cells were individually counted as they passed through a beam of light in the cell counter. cell counter
b) chlorophyll fluorescence- the amount of fluorescence represents the amount of chlorophyll A in the culture bottle on a specific day. fluorometer
c) pH of the solution- involved measuring the three cultures pH at intervals during growth.  Carbon dioxide reacts with water and forms carbonic acid having a low pH.  When carbonic acid is converted into carbon dioxide, the pH rises. An enzyme called carbonic anhydrase (CA) is involved in this conversion.  Diatoms can use only carbon dioxide in photosynthesis, not carbonic acid. pH meter
d) CA assay-quantitatively measured carbonic anhydrase activity on day four of the growth cycle by monitoring the rate of pH increase (from 6.2 to 6.7) as the enzyme converted bicarbonate HCO3- into CO2 and H20.  The faster the change in pH, the greater the amount of carbonic anhydrase. (CA)  This enzyme makes dissolved carbon dioxide available for photosynthesis.  The rate of pH increase was converted to amount of CA in the cell culture and reported in the data. pH rate sensor
e) the amount of nitrate, silicate and phosphate still available for the cultures were measured on day 0, 4, and day 7. These nutrients are needed for cell growth.  Nitrates can be re-released when a cell dies. Each of these nutrients were measured by comparing to a stand curve using a spectrophotometer.

 

 spectrophotometer
After writing your problem and hypothesis, go to the page of student data and select the values you need to test your hypothesis.

student data

student instructions

student record sheet