Question

Define
(1) Cell wall
(2) Cell membrane
(3) Unit membrane model
(4) Fluid mosaic model
(5) Selective permiable membrane​​

Answer 1

1. Cell wall: A cell wall is a rigid, semi-permeable protective layer in some cell types. This outer covering is positioned next to the cell membrane (plasma membrane) in most plant cells, fungi, bacteria, algae, and some archaea. Animal cells however, do not have a cell wall. The cell wall has many important functions in a cell including protection, structure, and support.
2. Cell membrane: The cell membrane (plasma membrane) is a thin semi-permeable membrane that surrounds the cytoplasm of a cell. Its function is to protect the integrity of the interior of the cell by allowing certain substances into the cell while keeping other substances out.
3. Unit membrane model: a model for the cell membrane in which the membrane consists of a central lipid layer sandwiched between two layers of protein.
4. Fluid Mosaic model: A model that describes the structure of cell membranes. In this model, a flexible layer made of lipid molecules is interspersed with large protein molecules that act as channels through which other molecules enter and leave the cell.
5. Selective permeable membrane: A membrane that is selectively permeable, i.e. being permeable to only certain molecules and not to all molecules.

Answer 2

A cell wall is a fairly rigid layer surrounding a cell located outside of the plasma membrane that provides additional support and protection. They are found in bacteria, archaea, fungi, plants, and algae. Animals and most other protists have cell membranes without surrounding cell walls.

The cell membrane, also called the plasma membrane, is found in all cells and separates the interior of the cell from the outside environment. The cell membrane consists of a lipid bilayer that is semipermeable. The cell membrane regulates the transport of materials entering and exiting the cell.

The unit membrane concept that says that all membranes have an underlying bilayer composed of phospholipids was originally proposed by Danielli and Davson in 1935. This concept extends to a wide variety of membranes from different organisms, each of which has a specific function.

The fluid mosaic model describes the cell membrane as a tapestry of several types of molecules (phospholipids, cholesterols, and proteins) that are constantly moving. This movement helps the cell membrane maintain its role as a barrier between the inside and outside of the cell environments.

Selective permeability is a property of cellular membranes that only allows certain molecules to enter or exit the cell.