permeability of membrane

Question 1

how do water soluble molecule cross the membrane ? e.g glucose
polar molecules and ions

Answer 1

they can not pass through the phospholipid layer

so uses channel / carrier proteins to pass through by faciliated diffusion

Question 2

how do lipid soluble molecule cross the membrane ? e,g vitamin a

Answer 2

they can pass directly through the phospholipid layer by diffusion

Question 3

what does it mean that a cell membrane is selectively permeable?

Answer 3

it is permeable to water soluble molecules and small molecules

but is not permeable to larger molecules

the membrane allows some molecules to pass through but doesnt let others across