The cell membrane of a red blood cell will allow water , carbon dioxide, oxygen and glucose to pass through. because other substances are blocked from entering, this membrane is called

Chemical in the birds foot produces the red coloring.

Explanation:

Hypothesis refers to a statement about particular observation. A hypothesis is tested for its validity through experimentation. The hypothesis about the causes of presence of red feathers in scarlet ibis can by represented by statement "Chemical in the birds foot produces the red coloring". This testable statement tells about possible cause of presence of red feathers in scarlet ibis.