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Common Misconceptions
3 min read

Cell : The Unit Of Life

- Clear the fog of misconceptions and get a clarity of concepts.
1
Prokaryotic cells: No Nucleus, No DNA? In a cell, where is DNA found? In nucleus, right? But if this is true, what about prokaryotic cells? They do not have a defined nucleus, so they don't have DNA too? No, this is not true. They have DNA but it is not covered by any membrane; it lies as a coiled structure in the cytoplasm of the prokaryotic cell.
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In prokaryotes the genetic material is
A
Linear DNA with histones
B
Circular DNA with histones
C
Linear DNA without histones
D
Circular DNA without histones
Identify the correct statement.
A
Tissue is a group of dissimilar cells.
B
An organ consists of similar cells.
C
Vacuoles are not found in plant cells.
D
Prokaryotes do not have well defined nucleus.
Prokaryotic cells are characterised by
A
Absence of nuclear envelope
B
Presence of nuclear envelope
C
Presence of distinct chromosome
D
Absence of chromatin material
The best way to identify a cell as either prokaryotic or eukaryotic is to determine whether
A
whether the nucleus is true nucleus or not true nucleus
B
it has a nucleus
C
it has a plasma membrane
D
it has cytosol
2
Gram +ve and Gram -ve Bacteria: Same or Different? Are all bacteria same? No, certainly not. There are different types of bacteria. Gram +ve and Gram -ve bacteria can be distinguished on the basis of the cell wall. Cell wall is made up of peptidoglycan. For Gram-positive bacteria the outer membrane is absent and the cell wall is 20-30 nm thick. However, for Gram-negative bacteria there is an outer membrane and the cell wall is not as thick, just 8-12 nm thick. This difference in the cell wall of both the types of bacteria is observed by a special staining technique developed by Christian Gram in 1884. The technique today is called Gram staining. The procedure involves using a dye called crystal violet and safranin. The bacteria are stained bluish-purple. They are then treated with an iodine solution and then decolorized with alcohol. Gram-positive bacteria retain the blue color of the stain, whereas the Gram-negative bacteria lose the color of the stain and appear red.
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Teichoic acid is found in:
A
Gram (+ve) bacteria
B
Gram (-ve) bacteria
C
Cyanobacteria
D
Mycoplasma
Assertion
Gram-negative bacteria do not retain the stain, when washed with alcohol.
Reason
The outer face of the outer membrane of Gram-negative bacteria contains lipopolysaccharides, a part of which is integrated into the membrane lipids.
A
Both Assertion and Reason are correct and Reason is the 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.
3
Difference between Centrosomes and Centrioles A centrosome comprises two structures made up of microtubules. These are known as centrioles. The main function of centrioles is to form the spindle fibres during cell division. These fibres pull the chromatids apart. Go through the illustration and understand the differences between centrosome and centrioles. Then solve the questions based on the given concept to eliminate any confusion.
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Function of centriole is:
A
Formation of spindle fibres.
B
Formation of nucleolus.
C
Initiation of cell division.
D
Formation of cell plate.
Centrioles are:
A
Microbodies
B
Microtubules
C
Protein bodies
D
Glycogen bodies
Centrosome is found in:
A
Nucleus
B
Nucleolus
C
Cytoplasm
D
Chromosomes