Question

Short / Long answer type questions.
Write short notes on
(a) Facilitated transport, (b) Cell surface receptors, (c) Endocytosis, (d) Fluid mosaic model

Answer 1

1. Facilitated transport - The diffusion of hydrophilic substances along the concentration gradient through the cell membrane by the use of a carrier or channel proteins present on the cell membrane and without the expenditure of energy. It is a kind of passive transport.
2. Cell surface receptors - They are transmembrane receptors that are embedded in the membrane and helps in receiving signals from the molecules outside the cell membrane such as hormones. It also binds to specific molecules which cannot travel through a membrane and helps in the transportation of such molecules.
3. Endocytosis - The process of engulfing or taking in of materials by living cells through the invagination of the plasma membrane to form a vacuole. This is one of the ways of taking minerals and food.
4. Fluid mosaic model - It is the model of the cell membrane given by Singer and Nicolson. This model describes that the cell membrane is made up of two parallel layers of lipid molecules in between which protein molecules are embedded in the mosaic form which maintains the fluidity of the membrane and are also used by the cell for the transportation of substances and to receive chemical or electrical signals. This the most widely accepted model for the structure of cell membrane.