Biology – Bacteria & Viruses (Solved Test)
SECTION 1: MULTIPLE CHOICE QUESTIONS
(Each carries 1 mark)
-
Which of the following component is not found in all kinds of bacteria?
✅ (c) Nucleoid
(Note: Some bacteria may lack a true nucleoid-like structure in dormant stages, but ribosomes & cell membrane are always present.) -
The bacterial chromosome is typically:
✅ (c) Circular, double-stranded DNA -
In bacterial cells, respiration occurs at:
✅ (b) Cell membrane -
Which group of bacteria is known as a good source of antibiotics?
✅ (d) Actinomycetes -
What is the primary function of flagella in bacterial cells?
✅ (c) Motility -
Which type of motility in bacteria is mediated by pili?
✅ (c) Twitching motility -
Which of the following bacterial structures is responsible for detecting and responding to chemicals?
✅ (b) Flagella (via chemotaxis) -
Which one of the following are not nitrifying bacteria?
✅ (c) Azotobacter (it fixes nitrogen, not nitrifies it) -
The enzyme responsible for converting HIV RNA into DNA is:
✅ (b) Reverse transcriptase -
The HIV capsid contains:
✅ (b) Single-stranded RNA and reverse transcriptase
SECTION 2: SHORT QUESTIONS (Solved)
1. Structural components of a bacterial cell wall and their arrangement:
- Major component: Peptidoglycan (murein)
- Arrangement: Long glycan chains cross-linked with short peptide chains.
- In Gram-positive: Thick peptidoglycan layer.
- In Gram-negative: Thin peptidoglycan + outer membrane (lipopolysaccharides, lipoproteins).
2. Composition of the peptidoglycan layer in bacterial cell walls:
- Composed of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) units.
- These alternate to form glycan chains, cross-linked with tetrapeptide side chains.
3. What are mesosomes? Functions?
- Mesosomes: Infoldings of the plasma membrane.
- Functions: DNA replication, cell division, respiratory processes.
4. How can plasmids be used in genetic engineering?
- Plasmids: Extra-chromosomal, circular DNA.
- Used as vectors to transfer foreign genes into bacteria for cloning or protein synthesis (e.g., insulin production).
5. Define sporulation.
- Formation of endospores by bacteria in unfavorable conditions for survival.
6. Function of the bacterial capsule:
- Protects bacteria from phagocytosis and desiccation.
- Helps in adhesion to surfaces.
7. Role of pili in bacterial cells. How do they differ from flagella?
- Pili: Help in attachment, conjugation (DNA transfer), twitching motility.
- Difference: Pili are shorter, thinner, non-motile (except twitching), while flagella are longer, whip-like, and used for swimming motility.
8. What are plasmids, and how do they help bacteria resist unfavourable conditions?
- Plasmids carry resistance genes (R-plasmids).
- Provide resistance to antibiotics, toxins, and metals.
9. Role of endospores in bacterial survival:
- Endospores allow survival in extreme heat, drought, chemicals, radiation.
- Very resistant dormant structures.
10. Significance of lipopolysaccharides and lipoproteins in Gram-negative bacteria:
- LPS (Lipopolysaccharides): Provide structural integrity, act as endotoxins.
- Lipoproteins: Anchor outer membrane to peptidoglycan.
11. How do spirochetes achieve motility?
- Motility via axial filaments (endoflagella), located inside periplasmic space.
12. Differentiate between twitching and gliding movements in bacterial motility:
- Twitching: Short, jerky movements mediated by pili.
- Gliding: Smooth surface motility without flagella, mediated by slime secretion.
13. How do bacteria without flagella achieve motility?
- Through pili (twitching motility) or slime secretion (gliding motility).
14. Difference between swimming motility and swarming motility:
- Swimming: Individual cells move in liquid using flagella.
- Swarming: Coordinated movement of bacterial colonies across solid surfaces using flagella.
 Chapter 2 Solved Exercise){kind=link}
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