Use the following information to answer the question.
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.

Question

Use the following information to answer the question.
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.

Quizplus · Accepted Answer

The graph shows that S. purpuratus sperm bind to ERB1-coated beads, but not to control beads without ERB1. Additionally, S. franciscanus sperm do not bind to ERB1-coated beads nor to control beads. Therefore, the presence of ERB1 is necessary for S. purpuratus sperm to bind to the plastic beads, supporting the conclusion that sperm from S. purpuratus bind to beads only if ERB1 is present. Option A is incorrect because the graph indicates that sperm from both species do not bind to control beads without ERB1. Option B is incorrect because the graph shows that S. franciscanus sperm do not bind to ERB1-coated beads regardless of the presence of control beads. Option D is obviously incorrect as no information in the graph suggests that the two species are the same.

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