All cells are surrounded by a semipermeable membrane, which regulates the passage of materials in and out of the cell. the principle structure of this membrane is
a. two layers of protein with a single layer of lipids in between.
b. a thick wall of cellulose with a thin lipid coating on the inside.
c. two layers of lipids with proteins associated with the lipids.
d. two layers of lipids with a polysaccharide layer in between.

Me brainliest 1. what does a red shift mean? blue shift? 2. describe the big bang theory. according to this theory, how old is the universe? 3. scientists believe the universe is expanding. what is the evidence that supports this? 4. describe a nebula.5. describe the 3 types of galaxies. what is a barred spiral galaxy? 6. what is a light year? how far is alpha centauri from earth? 7. describe the universal law of gravitation. be sure to include gravitational force between two objects.8. describe the planets’ orbits around the sun.9. what is the asteroid belt? where is it located? 10. describe rotation and revolution of earth. what determines an earth day and year? 11. how do galaxies exist? 12. compare and contrast the inner and outer planets.13. what causes the seasons?