Practise predicting water movement across cell membranes, then compare how aquaporins change water uptake in controlled frog-cell experiments.
In the early 1990s, investigations involving egg cells from the African clawed frog (Xenopus laevis) led to the discovery of membrane channel proteins called aquaporins.
In one investigation, scientists injected 10 frog egg cells with a solution containing mRNA encoding for an aquaporin, and another 10 frog egg cells with distilled water (control cells). All the frog egg cells were then incubated in a hypotonic solution. The volume of the frog egg cells was then measured during a period of five minutes.
The graph shows the mean results of the investigation.
State the direction of net movement of water across the plasma membrane of all the frog egg cells between 0 and 3 minutes.
Explain the reasons for the different results obtained for the frog egg cells with aquaporin mRNA and the control frog egg cells.