Question

Short / Long answer type questions.
Explain, how the plasma membrane is selectively permeable, and tell how that is related to the movement of materials across the membrane.

Answer 1

A plasma membrane is selectively permeable for ions and molecules and allows the transport of certain molecules only through active or passive transport. Movement can be in two ways -

1. Active transport - when some of the substances are too large they are filtered by membranes, there are certain channels embedded in membranes which attach to these molecules and help in their movement. They require energy for transport.
2. Passive transport - Here molecules are allowed to be transported through diffusion ( movement of a substance from higher to lower concentration), osmosis ( movement of water molecules against the concentration gradient), filtration ( capillaries are thin so they act as filters to avoid transport of any unwanted substance).