Question

Nucleolus was discovered by
A. Robert Brown
B. Leeuwenhoek
C. Robert Hooke
D. Fontana

Answer 1

Nucleolus is a darkly stained, dense, spherical structure present in the nucleus of the cell. It can be observed during the interphase of cell division.

Complete answer:
-Robert Brown
Robert Brown in 1831 observed the presence of nucleus in the root cells of the orchids. A nucleus id=s called the director of the cell. A cell has a single, spherical and centric nucleus that is formed of four components- nuclear membrane, nucleoplasm, nucleolus and nuclear chromatin.
-Anton Van Leeuwenhoek
Anton Van Leeuwenhoek was a Dutch draper who first observed living cells like bacteria from ponds and tartar of teeth, erythrocytes of a fish, sperms, and protozoans. He is commonly called an animalist.
Robert Hooke
-Robert Hooke was an English botanist who observed thin sections of cork under the compound microscope and noticed honey-comb like compartments. He coined the term cells derived from a Latin word ‘cellula’ which means a hollow space. He explained his observations in a book named, Micrographia.
-Fontana
Felice Fontana in 1774 discovered nucleolus. It is a dense region rich in DNA, RNA, and proteins that are formed from nucleolar organizing regions which are specific regions on chromosomes. It is the largest structure in the nucleus that acts as the site of biogenesis and storage or rRNA. It also plays an important role in the cell’s response to cell and participates in the formation of cell recognition signals.
So, the correct answer is “Option D”.

Note: Cell organelles are the living cytoplasmic sub-cellular structures like endoplasmic reticulum, Golgi complex, ribosomes, mitochondria, lysosomes, plastids, centrioles, etc.