Question

How do molecules move across the plasma membrane?

Answer 1

The Plasma membrane is a semi permeable membrane which is found in the outer side of cells to separate inner and outer regions of cells. In bacterial and plant cells this cell or plasma membrane attaches the cell wall to its outer side. It is semi permeable in nature so it only allows certain chemicals or enzymes to cross it. It helps in protecting the inner organelles of cells from viruses, bacteria or any other foreign bodies.

Complete answer:
plasma membrane is semi permeable in nature. So it only allows certain molecules to enter the cell. There are two major ways for a molecule to move across the membrane.
-Passive transport
-Active transport

-Passive Transport
We should know that the word passive means to happen without resistance. So as the word suggests it happens down the potential gradient i.e. from higher concentration to lower concentration. Energy (ATP) is not needed in this type of movement as we got to know that diffusion is a spontaneous process.
Types of Passive Transport:
-Simple diffusion: The movement of molecules down the potential gradient without any channel protein is called a simple diffusion.
-Facilitated diffusion: The movement of molecules from higher concentration to lower concentration with the help of channel proteins or carrier proteins.

-Active Transport
As the name suggests Active Transport needs energy to move molecules across the cell membrane. They move molecules against the potential gradient which means from lower concentration to higher concentration. Active transport requires ATP to move the molecule against the potential gradient. Active transport needs specific protein channels which use energy molecule ATP to move the molecules or ions.
Types of Active Transport:
-Primary Active Transport: It directly pumps an ion or molecule against the protein gradient across the membrane. It is also known as Uniport.
-Secondary Active Transport: It uses electrochemical energy instead of ATP. This energy is created by pumping ions across the cell membrane. It is called Cotransport. It can be Antiport or Symport.

Note: The most common example of primary active transport is Sodium Potassium pump which is present in animal cells. Sodium glucose transport on secondary active transport by symport. Osmosis is an example of simple diffusion.