BBC Bitesize can appear a little patronizing at times, but this one is so good so you need to look at it to get this right, for what they say here is excellent for this last exam of the English Language side of things. The one that I looked at earlier today with my students asked...
but this structure also aids in the membranes' flexibility and fluidity. Some phospholipids will induce negative curvature of a membrane, while others induce a positive curvature, depending on their makeup. Proteins also contribute to the membrane curvature...