Test: Cell Oragnelles (May 19) - NEET MCQ

A plant cell has rigid wall on the outside. It has plastids and a centrally located large vacuole. All of these are absent in an animal cell.

Ribosomes may-occur singly as monosomes or in rosettes and helical groups called polyribosome. The different ribosomes are connected with a 10-20A thick strand of mRNA. They are formed during periods of active protein synthesis when a number of copies of the same polypeotide are required.

Cell wall is the outer rigid protective and supportive covering of plant cells,fungi and some protists. Cell membrane is covering of protoplasm which occurs inside the cell wall. 

According to Robertson's concept of unit membrane, the cell membrane is trilaminar. It has a thickness of about 75Å with a central lipid layer of 35Å thick and two peripheral protein layers of 20Å each.

Plasmodesmata are cytoplasmic bridges between adjacent plant cells which develop in minute pores of their walls. They form a protoplasmic continuum called symplast.
It provides channels for controlled passage of small sized particles between adjacent cells as well as transfer of some specific signals.

The SER provides surface for the synthesis of  including phospholipids, cholesterol, steroid hormones and hormones, adrenal corticoid hormones), ascorbic acid are visual pigments.

ER functions as cytoskeleton or skeletal framework by providing mechanical support to colloidal cytoplastic matrix. It conducts information from cell to cell. RER helps in protein synthesis. SER takes part in detoxification of tox chemicals in liver.

The lysosomes may be called "suicide bags’ of the cell in view of their autolytic role, or "disposal units’ of the cell because they digest the incoming food materials and remove the foreign bodies, toxic molecules, and debris, or "recyling centres" as they break down worn out cells cell organelles to component molecules for building organelles and cells.

A covering membrane is absent around ribosomes, centrioles and nucleolus.

In many cells proteins released from the endoplasmic reticulum are combined with carbohydrate to produce complexes like glycoproteins. This occurs in both Golgi complex and rough endoplasmic reticulum as they contain enzymes called glycosyl-transferases.