Bacteriorhodopsin
(a) act as a membrane transport protein
(b) act as a membrane channel protein
(c) act as a membrane protein receptor
(d) act as a membrane gated channel protein

(a) Act as a membrane transport protein

Explanation:

Bacteriorhodopsin is a membrane protein that serves as a proton pump. It is mainly present in archaebacteria such as Halobacterium halobium. Bacteriorhodopsin is a light drive proton pump which means that it uses the energy from solar radiation to serve as a proton pump.

It has seven hydrophobic alpha-helices that span the lipid bilayer and the light-absorbing retinal pigment is buried in the membrane. The function of Bacteriorhodopsin is to generate the proton gradient for ATP synthesis by releasing protons at the outer surface of the membrane.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.