Question

Assertion- plasma membrane is trilaminar.
Reason- one optically light layer is lipids and on both the sides of it two optically dense layers of protein are present.
a) Both assertion and reason are correct and reason is correct explanation for assertion
b) Both assertion and reason are correct but reason is not the correct explanation for assertion.
c)Assertion is correct but reason is incorrect.
d)Both assertion and reason are incorrect.

Answer 1

Hint: Plasma membrane is also called as the cell membrane. It is found in all cells. They consist of the phospholipid’s molecules. They consist of the head and tail which are arranged in a pattern that they form the bilayer.

Complete step by step answer: In 1935, Hugh Davson and James Danielli proposed a model for the plasma membrane of the cell. They described the plasma membrane as trilaminar and lipoproteins in nature. They said that phospholipid bilayer is two layers of globular proteins. The phospholipids have a tail and a head end which come together to form a chain. The tail end is the long chain of hydrogen and carbon atoms and it is hydrophobic in nature making it the nonpolar end. The head is the polar end and consists of oxygen, nitrogen and phosphorous atoms. They make hydrophilic ends or the water loving end. If there are a small number of phospholipids present then they form a micelle. If the volume of the phospholipid increases then membrane is formed. This cell membrane formed is known as the trilaminar cell membrane. In this structure the hydrophobic tails of phospholipids are sandwiched between two layers of hydrophilic heads.it is called bilayer as it is made up of two layers of phospholipid. To escape the watery environment the tail of the first layer faces the tail of the second layer and both the layers have their heads towards the watery environment.

So, the answer is ‘both assertion and reason are correct and reason is the correct explanation for the assertion’.

Note: Plasma membranes provide mechanical strength to the cell. They help in the transportation of the materials, ions and molecules from inside the cell to the outside. It helps in the osmoregulation of the cell. Diffusion also takes place through it.