Cell Membranes & Transport (College Board AP® Biology)

Water potential (Ψ) is described by the following formulas.

Ψ = Ψ_p + Ψ_s

Ψ = −iCRT

Discuss the variables in both formulas and how they affect water potential.  

In an experiment, rats averaging 300 g of body mass were tested several times over a three-month period. For each individual rat, urine was collected over a three-hour period after ingestion of 10 mL of liquid (water, 1% ethyl alcohol solution, or 5% ethyl alcohol solution). The volume of urine was then measured, and the results were averaged for all individuals within each experimental group. The data are shown in the table below. 

THREE-HOUR URINE OUTPUT FOLLOWING FLUID INGESTION

Pose ONE scientific question that the researchers were most likely investigating with the experiment

State a hypothesis that could be tested to address the question you posed in part (a). 

Using the data in the table, describe the effect of ethyl alcohol on urine production. 

A student studying two different aquatic, plant-eating, unicellular protist species (species A and B) designed an experiment to investigate the ecological relationship between the two species (Table 1).

TABLE 1. EXPERIMENTAL TREATMENT GROUPS

In treatment group I, the student placed 10 individuals of species A into a container with liquid growth medium and 10 individuals of species B into a separate container with an equal amount of the same liquid growth medium. In treatment group II, the student placed 5 individuals of each species into a single container with the liquid growth medium. The student then maintained the containers under the same environmental conditions and recorded the number of individuals in each population at various time points. The results are shown in Table 2.

TABLE 2. NUMBER OF INDIVIDUALS IN EACH PROTIST POPULATION IN BOTH TREATMENT GROUPS

Many protists contain an organelle called a contractile vacuole that pumps water out of the cell. The student repeated the experiment using a growth medium with a lower solute concentration. Predict how the activity of the contractile vacuole will change under the new experimental conditions. Justify your prediction.

The petal color of the Mexican morning glory (Ipomoea tricolor) changes from red to blue, and the petal cells swell during flower opening. The pigment heavenly blue anthocyanin is found in the vacuole of petal cells. Petal color is determined by the pH of the vacuole. A model of a morning glory petal cell before and after flower opening is shown in Table 1.

Identify the cellular component in the model that is responsible for the increase in the pH of the vacuole during flower opening AND describe the component’s role in changing the pH of the vacuole.

 A researcher claims that the activation of the K⁺/H⁺ transport protein causes the vacuole to swell with water.

Provide reasoning to support the researcher’s claim.