Exercise Chapter 6: Prokaryotes Class 11

MCQs with answers from Chapter 6 : Prokaryotes (Federal Board, 11th Class):

MCQs – Prokaryotes

1. Cyanobacteria

A) are poisoned by oxygen
B) are not widely distributed
✔️ C) have chlorophyll
D) have chloroplast

2. Cyanobacteria, unlike other types of bacteria that photosynthesize, do

A) not give off oxygen
✔️ B) give off oxygen
C) not have chlorophyll
D) not have a cell wall

3. Pili are made up of pilin, which is

A) carbohydrates
B) lipids
✔️ C) protein
D) triglycerides

4. Most pathogenic bacteria cause disease by

A) directly destroying individual cells of the host
B) depriving the host of their nutrients
✔️ C) producing toxins
D) depriving the host of oxygen

5. Chemosynthetic bacteria

A) are autotrophic
B) use the sun rays
C) oxidize inorganic compounds to acquire energy
✔️ D) both A and C are correct

6. A bacterium with flagella all around is

A) monotrichous
B) lophotrichous
C) amphitrichous
✔️ D) peritrichous

7. Conjugation is facilitated by

A) capsule
✔️ B) pili
C) flagella
D) both pili and flagella

8. Bacterial membrane differs from eukaryotic membrane in

A) lacking proteins
B) lacking lipids
C) lacking polysaccharide
✔️ D) lacking cholesterol

9. Bacterial membrane also contains enzymes for

✔️ A) respiration
B) photosynthesis
C) protein synthesis
D) secretion

10. Facultative anaerobes

A) require a constant supply of oxygen
B) are killed in an oxygenated environment
✔️ C) do not always need oxygen
D) are photosynthetic

11. Ancient cyanobacteria found in fossil stromatolites were very important in the history of life because they

A) were probably the first living things to exist on Earth
✔️ B) produced oxygen in the atmosphere
C) are the oldest known archaea
D) extracted heat from the atmosphere, cooling Earth

12. The bacteria that cause tetanus can be killed only by prolonged heating at temperatures considerably above boiling. This suggests that tetanus bacteria

A) are endotoxin
B) are autotrophic
✔️ C) produce endospore
D) have peptidoglycan

SECTION II: SHORT QUESTIONS WITH ANSWERS

1. Write the pigment composition of cyanobacteria.

Cyanobacteria contain:

Chlorophyll a → Primary pigment for photosynthesis.
Phycocyanin (blue pigment) & phycoerythrin (red pigment) → Accessory pigments for absorbing light.
Carotenoids → Protect against oxidative damage.

2. Differences between bacteria and archaea?

Feature	Bacteria	Archaea
Cell Wall	Contains peptidoglycan	Lacks peptidoglycan, has pseudopeptidoglycan or protein-based walls
Membrane Lipids	Ester-linked phospholipids	Ether-linked phospholipids
RNA Polymerase	Simple (one type)	Complex (more similar to eukaryotes)
Habitat	Ubiquitous (soil, water, human body)	Extreme environments (hot springs, salt lakes)

3. Morphological forms of bacteria?

Cocci → Spherical (Staphylococcus).
Bacilli → Rod-shaped (Escherichia coli).
Spirilla → Spiral (Helicobacter pylori).
Vibrio → Comma-shaped (Vibrio cholerae).
Filamentous → Thread-like (Streptomyces).

4. Functions of the following bacterial structures:

Structure	Function
Ribosomes	Protein synthesis.
Cell Membrane	Regulates transport, houses metabolic enzymes.
Nucleoid	Contains bacterial DNA.
Plasmid	Carries extra genes (e.g., antibiotic resistance).
Mesosomes	Involved in respiration & DNA replication.
Slime Capsule	Prevents desiccation, aids in evasion of immune response.
Flagella	Provides motility.
Cell Wall	Maintains shape, prevents osmotic lysis.
Pili (Fimbriae)	Aid in attachment & conjugation (gene transfer).

5. Similarities & differences in photosynthesis of cyanobacteria & plants?

Feature	Cyanobacteria	Plants
Pigment	Chlorophyll a	Chlorophyll a & b
Organelle	No chloroplasts (thylakoid membranes in cytoplasm)	Chloroplasts
Oxygen Release	Yes	Yes
Carbon Source	CO₂ (autotrophic)	CO₂ (autotrophic)

6. Draw and label the structure of flagellum.

(Diagram required: Include basal body, hook, and filament.)

7. Why are chemosynthetic bacteria autotrophic?

Use inorganic compounds (e.g., sulfur, iron, nitrogen) for energy.
Example: Nitrosomonas (oxidizes ammonia to nitrite).

8. Chemical methods to control microbes?

Disinfectants → Alcohol, chlorine, formaldehyde.
Antiseptics → Iodine, hydrogen peroxide.
Antibiotics → Penicillin, tetracycline.

9. Physical methods to control microbes?

Heat → Autoclaving, pasteurization.
Filtration → Removes microbes from liquids/air.
Radiation → UV & gamma rays for sterilization.

10. Two plant diseases caused by bacteria?

Xanthomonas → Causes citrus canker.
Agrobacterium tumefaciens → Causes crown gall disease.

11. Five bacterial diseases in humans?

Tuberculosis (Mycobacterium tuberculosis).
Cholera (Vibrio cholerae).
Pneumonia (Streptococcus pneumoniae).
Typhoid (Salmonella typhi).
Tetanus (Clostridium tetani).

12. Define normal flora.

Microorganisms naturally residing in the human body (e.g., gut bacteria), often beneficial.

13. Chemical composition of bacterial cell wall?

Composed of peptidoglycan (murein), made of N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM).

14. Differences between the following:

Feature 1	Feature 2	Difference
Lysosome	Mesosome	Lysosomes digest material, mesosomes aid in respiration.
Peptidoglycan	Muramic Acid	Peptidoglycan is a polymer, muramic acid is a component.
Gram-positive	Gram-negative	Gram-positive has thicker peptidoglycan, Gram-negative has outer membrane.
Lytic Bacteria	Lysogenic Bacteria	Lytic → Immediate replication, Lysogenic → Latent phase before activation.
Pathogenic	Non-pathogenic	Pathogenic cause disease, non-pathogenic are harmless/beneficial.
Autotrophy	Heterotrophy	Autotrophs make their own food, heterotrophs depend on others.
Photosynthetic	Chemosynthetic	Photosynthetic use light, chemosynthetic use chemical energy.
Mutation	Mutant	Mutation is DNA change, mutant is an organism carrying it.
Chromosome	Bacteriophage	Chromosome contains DNA, bacteriophage is a virus infecting bacteria.
Bacteria	Mitochondria	Bacteria are free-living, mitochondria are organelles.
Prokaryotes	Eukaryotes	Prokaryotes lack nucleus, eukaryotes have nucleus.
Cyanobacteria	Other Bacteria	Cyanobacteria are photosynthetic, others may not be.

15. What are plasmids?

Small, circular, extra-chromosomal DNA carrying genes for antibiotic resistance, virulence, & metabolism.

16. How do bacteria survive under unfavorable conditions?

Endospore Formation → Highly resistant dormant structures (e.g., Bacillus & Clostridium).

17. Five ways bacteria benefit humans?

Nitrogen Fixation (Rhizobium in plant roots).
Gut Microbiota → Aid digestion, synthesize vitamins (B, K).
Antibiotic Production (Streptomyces → Produces streptomycin).
Biodegradation → Decompose organic matter.
Industrial Uses → Yogurt & cheese production (Lactobacillus).

18. Why are cyanobacteria considered the most prominent photosynthetic bacteria?

First oxygen-producing organisms → Played a major role in Earth’s oxygenation.

19. Benefits of bacterial flora to humans?

Digest food & synthesize vitamins.
Prevent growth of harmful pathogens.
Enhance immune system.
Degrade toxic substances.
Maintain gut microbiome balance.

SECTION III: EXTENSIVE QUESTIONS WITH ANSWERS

1. Taxonomic and Phylogenetic Position of Prokaryotes

Prokaryotes belong to two domains based on molecular and genetic analysis:

Domain Bacteria → Includes true bacteria with peptidoglycan cell walls (E. coli, Streptococcus).
Domain Archaea → Includes extremophiles, lacking peptidoglycan (Methanogens, Halophiles).

Phylogenetic Position:

Earliest life forms (~3.5 billion years ago).
Evolved before eukaryotes, serving as precursors to mitochondria & chloroplasts (Endosymbiotic Theory).
Diverged into different lineages based on rRNA sequencing.

2. Occurrence of Bacteria in Widest Range of Habitats

Bacteria thrive in extreme and moderate environments due to:

Diverse Metabolism: Chemotrophs, phototrophs, heterotrophs.
Survival Strategies: Endospore formation, biofilm production.
Environmental Adaptations: Thermophiles in hot springs, psychrophiles in ice, halophiles in salt lakes.

Examples:

Deinococcus radiodurans → Resistant to radiation.
Pseudomonas → Lives in soil, water, human body.

3. Differences Between Conjugation, Transformation, and Transduction

Process	Mechanism	Accomplishment
Conjugation	Transfer of genetic material via sex pilus (plasmid exchange).	Spreads antibiotic resistance genes.
Transformation	Uptake of naked DNA from environment.	Incorporates new traits into genome.
Transduction	Bacteriophage (virus) transfers DNA between bacteria.	Enables genetic variation & evolution.

4. Shape, Size, and Structure of Bacteria

Shape:

Cocci → Round (Streptococcus).
Bacilli → Rod-shaped (E. coli).
Spirilla → Spiral (Helicobacter).
Vibrio → Comma-shaped (Vibrio cholerae).

Size:

Ranges from 0.1 - 5.0 µm in diameter.

Structure:

Cell Wall → Provides shape & protection (peptidoglycan in bacteria).
Cell Membrane → Selectively permeable, metabolic functions.
Cytoplasm → Contains ribosomes, nucleoid, plasmids.
Flagella & Pili → Motility & attachment.

5. Economic Importance of Bacteria

Beneficial Roles:

Nitrogen Fixation → Rhizobium in leguminous plants.
Fermentation → Lactobacillus for yogurt, cheese.
Medicine → Antibiotic production (Streptomyces).
Bioremediation → Oil spill cleanup (Pseudomonas).

Harmful Effects:

Pathogenic Bacteria → Cause diseases (Tuberculosis, Cholera).
Food Spoilage → Clostridium botulinum produces toxins.

6. Detailed Account of Archaea

Archaea differ from bacteria in:

Cell Wall Composition → No peptidoglycan (uses pseudopeptidoglycan).
Membrane Lipids → Ether-linked instead of ester-linked.
Extreme Environments:
- Methanogens → Produce methane (found in swamps).
- Halophiles → Thrive in high salt (Halobacterium).
- Thermophiles → Survive high temperatures (Sulfolobus).

7. Use of Bacteria in Research & Technology

Genetic Engineering → E. coli used for recombinant DNA technology.
CRISPR Technology → Derived from bacterial defense system for gene editing.
Industrial Applications → Enzyme production (amylase, protease).
Pharmaceuticals → Insulin production via genetically modified bacteria.

8. Nutritional Diversity of Bacteria

Type	Energy Source	Example
Photoautotrophs	Light	Cyanobacteria
Chemoautotrophs	Inorganic chemicals	Nitrosomonas (oxidizes ammonia)
Photoheterotrophs	Light + Organic compounds	Rhodobacter
Chemoheterotrophs	Organic compounds	E. coli

This diversity allows bacteria to survive in extreme and variable environments.

9. What If Bacteria Had Not Evolved?

No oxygen production (no cyanobacteria → no oxygenation event).
No decomposition → Nutrient cycling disruption.
No gut microbiota → Poor digestion, vitamin deficiencies.
No biotechnology → No antibiotics, vaccines, genetic engineering.

Bacteria are essential for ecosystem balance, nutrient recycling, and human health.

10. Importance of Prokaryotes for the Biosphere & Human Society

For the Biosphere:

Primary Producers → Cyanobacteria perform photosynthesis.
Nitrogen Fixation → Rhizobium provides plants with usable nitrogen.
Decomposers → Recycle organic material.

For Human Society:

Medicine → Streptomyces produces antibiotics.
Food Industry → Lactobacillus used in yogurt, cheese.
Bioremediation → Oil spills & waste degradation (Pseudomonas).

Bacteria are fundamental to both natural ecosystems and human technological advancements.

Exercise | Chapter 6 : Prokaryotes | Class 11 Biology Notes (FBISE, Best for Exams)