Zoology MCQs for NEET — Practice Questions with Answers

(c) Phase contrast microscope was developed by Zernicke (1935, Nobel Prize 1953) to observe living cells and the events occurring in them (e.g., Spindle formation, movement of chromosomes, endocytosis, exocytosis). It is similar to optical microscope except that it has an annular diaphragm in the condenser and a transparent phase plate at the back focal plane of objective. the microscope converts differences in refractive indices into differences in brightness.

(a) Both mitochondria and chloroplast are semi-autonomous organelles as they possess their own DNA, RNA and 70S ribosomes to have sufficient functional independence from cellular machinery. Chloroplasts DNA is bigger than mitochondrial DNA. However, genetic information contained in these DNAs is limited. DNA is naked (without histone proteins) in both.

(c) Nucleus contains nucleoli and chromatin network. Chromatin contains DNA and some basic proteins called histones, some nonhistone proteins and also RNA.

(b) The tunnel proteins or transmembrane proteins run throughout the lipid bilayer and
individually or in group form channels for the passage of water and water soluble substances.
The channels however, possess selective properties for passage of different ions and other polar substances.

(a)

If a biochemical analysis of mitochondria has to be done, the best procedure would be subject the cell to cell fractionation (centrifuge) and obtain mitochondria.

The band region of polytene chromosome is not feulgen negative area, therefore, this statement is incorrect.

Ribosomes are smallest known electron microscopic ribonucleoprotein particles attached either to endoplasmic reticulum, floating free in cytoplasm and also found is mitochondria and chloroplast. These structures is an organelle with in an organelle. These are site of protein synthesis.

Fluid mosaic model of plasma membrane was given by Singer and Nicholson in year 1972. The biological membrane are considered to be a quasified structure in which the lipids and integral proteins are arranged in a mosaic manner. Gorter and Grantal measured the lipid content of haemolyzed eythrocytes and concluded that cell membrane are chiefly formed of phospholipids arranged to form a bimolecular lipid sheet.

(b) Less than 0.1% of plasma membrane is perforated by pores which allows the ions to pass through.