Biology 332 Laboratory:

Grazing rate in Paramecium

Data for 2001 and selected other years

2001 Data: Total bacteria counted and number of small squares they occupied (e.g 110 bact /7 squares).

Note: I recommend that you ignore the first point in your calculations; start with 10 minutes.

2000 Data: Bacteria counts per small square

1999 Data:  Mean  bacteria  per small square

Note: These 1999 data are not as bad as they looked.

Analysis of data:

1. Data work-up. Convert bacteria counts to an estimate of the number of bacteria per ml. Do the same with the paramecium counts. Plot the bacteria counts as a function of time.
2. Estimate the rate at which bacteria are eaten at each point. There are several approaches that could be used. The best would be to make a general model for the relationship between rate of feeding and prey density for a filter feeder, and to then examine the fit of the expected function to the data. Alternatively you can try to estimate the feeding rate at each data point. This is substantially less accurate and the nature of the inaccuracies need to be discussed. Key idea: If filter feeders are non selective, and if their rate of feeding is not limited by internal processes (assume here that it is not, unless your data indicate otherwise) the rate of feeding should be proportional to prey density. What are the units of the feeding rate? Would you expect the feeding rate to change with time? if so, how? and why?
3. Calculate the clearance rates corresponding to the feeding rate. Key idea: You calculated the number of bacteria per ml at each point, think about ml/ bacterium. As I explained in your initial laboratory handout, please express the clearance rate as vol/ time, express volume both as ml. and as fractions of the paramecium cell volume. A better approach is to calculate clearance rate from the parameters of the regression line. 

Osmoregulation in Paramecium

Osmoregulation data. I suggest that you plot both sets of data and compare the values obtained. In your analysis use the 1989 data.

Calculate the rate of water expulsion for each experimental sample. Plot rate of water expulsion against external sucrose concentration. How can you estimate the iso-osmotic concentration of sucrose from the graph? What is the iso-osmotic concentration of sucrose. Assuming that sucrose is an ideal solute, calculate the osmotic pressure of the cytoplasm. Calculate the rate of water flow across the plasma membrane. What assumptions do you need to make? Discuss your estimate of membrane permeability with regard to the sample values supplied in your initial handout. How does the membrane permeability of paramecium compare with that for vertebrate cells? What do you make of the difference.