Which type of transport takes place when a protein allows an ion to enter a cell without using energy ?

Why has two different alleles for the same trait?

Which to produce involved from a symbiotic relationship of organisms which resulted in eukaryotic organisms contain chloroplast

Select the correct answer. which statement applies only to the axial skeleton, not the appendicular skeleton? a. it contains a pivot joint. b. it has muscles attached that work in pairs. c. it contains red bone marrow. d. it possesses fossa for bone articulation. e. it protects the heart and lungs.