In Order to Test How Sea Urchin Sperm Bind to Eggs

question 29

Multiple Choice

In order to test how sea urchin sperm bind to eggs, scientists isolated the egg receptor protein that binds to the sperm acrosomal protein called bindin. Plastic beads were coated with egg receptor for bindin (ERB1) from eggs of the sea urchin Strongylocentrotus purpuratus, and then the beads mixed with sperm from S. purpuratus or from the related species, S. franciscanus. The researchers counted how many sperm were bound to each bead. The results are shown in the graph below. (Adapted from Kamei and Glabe 2003)
Treatments:
A: S. purpuratus sperm mixed with S. purpuratus ERB1 beads
B: S. purpuratus sperm mixed with beads containing no ERB1 protein
C: S. franciscanus sperm mixed with S. purpuratus ERB1 beads
D: S. franciscanus sperm mixed with beads containing no ERB1 protein
-Based on the data in the graph, which of the following conclusions is supported?

• A) Plastic beads will bind to sperm from both species of sea urchin.
• B) ERB1 prevents S. franciscanus sperm from binding the beads.
• C) Sperm from S. purpuratus bind to beads only if ERB1 is present.
• D) S. franciscanus and S. purpuratus are actually the same species.