Biology MCQs
Topic Notes: Biology
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
1
How is the infection mode of lysogenic viruses characterized?
Answer:
Both B and C
Lysogenic viruses are classified as temperate phages because they can integrate their genome into the host chromosome without immediately causing cell lysis. This state is often described as non-virulent during the lysogenic phase, as the host cell continues to survive and replicate. Therefore, both terms are used to describe this specific viral lifestyle compared to strictly lytic, virulent viruses.
2
In what form can a temperate bacteriophage exist within a host cell during the lysogenic cycle?
Answer:
Prophage
A temperate phage can enter a lysogenic state where its DNA integrates into the host bacterial chromosome. In this integrated state, the viral genome is referred to as a prophage, which is replicated along with the host DNA during cell division.
3
In the lysogenic cycle, what is the term for the process where the integrated phage DNA is excised from the host chromosome to initiate the lytic cycle?
Answer:
Induction
Induction is the specific biological process by which a prophage is excised from the bacterial genome, typically triggered by environmental stressors such as UV radiation or chemical damage, thereby transitioning the virus from the dormant lysogenic state into the active lytic cycle.
4
Which of the following statements regarding the lysogenic cycle of a bacteriophage is factually incorrect?
Answer:
Lysogenic bacteria may get infected by the related phage
In the lysogenic cycle, the viral genome integrates into the host chromosome as a prophage. The host bacterium survives and replicates normally. Under stress, the prophage can undergo induction to enter the lytic cycle. Option D is incorrect because lysogenic bacteria exhibit superinfection immunity, meaning they are resistant to infection by the same or closely related phages.
5
During the lytic cycle of a bacteriophage, what is the fate of the host cell's DNA?
Answer:
Digested into its nucleotides
In the lytic cycle, the bacteriophage injects its genome and produces enzymes that degrade the host cell's DNA into its constituent nucleotides. This process effectively halts host cell functions and provides the raw materials necessary for the synthesis of new viral components.
6
During which phase of the viral life cycle are the protein coats (capsids) of viruses synthesized?
Answer:
Lytic cycle
The lytic cycle is the active phase of viral replication where the virus hijacks the host cell's metabolic machinery to transcribe and translate viral genes. This results in the mass production of viral proteins, including capsid proteins, which are then assembled into new virions before the host cell is lysed.
7
What occurs to the bacteriophage DNA during the lysogenic cycle upon entering the host cell?
Answer:
Joins the bacterial chromosomes
During lysogeny, the viral DNA is inserted into the host genome at a specific site. Once integrated, it becomes a prophage and remains dormant, replicating passively as the host bacterium undergoes binary fission without causing immediate cell lysis.