Given below are two statements: Statement I: The release of sperms into the seminiferous tubules is called spermiation.
Statement II: Spermiogenesis is the process of formation of sperms from spermatogonia.
In the light of the above statements, choose the
most appropriate answer from the options given
below:
In an E.coli strain i gene gets mutated and its
product can not bind the inducer molecule. If
growth medium is provided with lactose, what will
be the outcome?
AI-generated explanation. Check against your textbook.
Explanation:
The lac operon is normally induced by allolactose binding to the lac repressor (product of lacI). When the inducer binds, the repressor releases the operator, allowing transcription of lacZ, lacY, and lacA. If lacI is mutated so the repressor cannot bind the inducer, the repressor remains active and binds the operator even in the presence of lactose, blocking RNA polymerase. Therefore, z, y, a genes will not be transcribed or translated.
🧠 Did You Know?
In NCERT terms, the lac operon is an example of negative gene regulation where the repressor inhibits transcription unless inactivated by an inducer.
💡 NCERT Memory Line:
In the lac operon, transcription occurs only when inactivator (repressor) is inactivated by inducer; a nonfunctional inducer-binding repressor keeps the operon switched off.
If the length of a DNA molecule is 1.1 metres, what
will be the approximate number of base pairs?
AI-generated explanation. Check against your textbook.
Explanation:
In DNA, each base pair spans about 0.34 nanometres (3.4 × 10^−10 m). For a DNA length of 1.1 m, the number of base pairs ≈ 1.1 / (3.4 × 10^−10) ≈ 3.2 × 10^9 bp, i.e., about 3.3 × 10^9 bp. Therefore, the correct choice is 3.3 × 10^9 bp (option 2).
🧠 Did You Know?
One human diploid cell contains about 6.6 × 10^9 bp in total DNA, arranged into 23 pairs per chromosome set, reflecting the long-tedious length of DNA packaged in the nucleus.
💡 NCERT Memory Line:
DNA length is about 0.34 nm per base pair, so bp count ≈ length / 0.34 nm.
Given below are two statements: Statement I: Autoimmune disorder is a condition where body defense mechanism recognizes its own cells as foreign bodies. Statement II: Rheumatoid arthritis is a condition where body does not attack self cells.
In the light of the above statements, choose the
most appropriate answer from the options given
below:
Which of the following statements with respect to
Endoplasmic Reticulum is incorrect?
AI-generated explanation. Check against your textbook.
Explanation:
The incorrect statement is option 2. In NCERT, Endoplasmic Reticulum (ER) is present in eukaryotic cells. Prokaryotes do not have ER at all; they lack membrane-bound organelles like ER. The RER has ribosomes on its outer surface and is involved in protein synthesis for secretion and membranes, while the SER lacks ribosomes and is the site for lipid synthesis and detoxification. Thus, options 1, 3, and 4 are true, and option 2 is false.
🧠 Did You Know?
RER with attached ribosomes synthesizes secretory and membrane proteins; SER handles lipid metabolism and detoxification processes.
💡 NCERT Memory Line:
ER is a network of sacs and tubules, consisting of RER (with ribosomes) and SER (without ribosomes).