Question

The non-membranous structure is
(a) Centrioles
(b) Ribosome
(c) Nucleolus
(d) All of the above

Answer 1

Hint: The cell organelles having no membrane are called non-membranous or naked cell organelles. Membraneless cell organelles lie mixed within the nucleoplasm or cytoplasm due to the lack of their membrane.

Complete answer:
The centrioles, ribosomes, and nucleolus are the microscopic cell organelles that lack a typical bilayer of the membrane and hence are called as non-membranous cell organelles. Some features of these cell organelles have been mentioned below -

> Centrioles - These are found in all animal cells except mature mammalian RBCs. The centrioles are a microtubular structure and are formed of microtubules arranged in a (9+0) manner where all the nine microtubules are peripheral in position. Centrioles form asters during cell division in the animal cell and they also form basal bodies. The Centrosome is formed of two darkly stained granules called centrioles, which are collectively called diplosomes. Tubulin is the main protein found in the centrioles.

> Ribosomes - Claude was the first to isolate the ribosomes in 1983A.D. Ribosomes were first reported in the root cells of broad beans. They are the smallest known electron microscopic cells organelle. Ribosomes are the site of protein synthesis and based on the sedimentation coefficient, these are of two types- 70s ribosomes and 80s ribosomes.

> Nucleolus - The nucleolus is also known as ‘little nucleus’. It was first observed by Fontana in the skin cell of an eel. The nucleolus is absent is muscle fibers, RBC, yeast, sperm, and prokaryotes.

So, the correct answer is, ‘All of the above.’

Note: A cell organelle is a special structure or subunit found within the cell, which is responsible for carrying out specific functions within the cell. The plasma membrane is a semipermeable membrane, which means it only allows selective substances to pass through it.