Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
I. Choose the Best Answer (MCQs)
Q1. Micro organisms are measured in ______
- (a) cm (b) mm (c) micron (d) meter
Q2. Shows both living and non-living characteristics ______
- (a) Protozoa (b) Virus (c) Bacteria (d) Fungi
Q3. ______ is a prokaryotic micro organism.
- (a) Virus (b) Algae (c) Fungi (d) Bacteria
Q4. Based on shape, bacteria are classified into ______ types.
- (a) 2 (b) 3 (c) 4 (d) 5
Q5. The plant body of algae is called ______
- (a) Stem (b) Thallus (c) Leaf (d) Root
Additional MCQs
Q6. ______ is absent in bacteria.
- (a) DNA (b) RNA (c) Mitochondria (d) Cell wall
Q7. ______ is not a shape seen in bacteria.
- (a) Spiral (b) Rod shaped (c) Spherical (d) Tadpole
Q8. E.coli is an example of ______ bacteria.
- (a) Peritrichous (b) Atrichous (c) Lophotrichous (d) Monotrichous
Q9. ______ is not a fungus.
- (a) Agaricus (b) Nostoc (c) Penicillium (d) Albugo
Q10. 'Grass of water' refers to ______
- (a) Fungi (b) Bacteria (c) Algae (d) Bryophytes
Q11. ______ is a biocontrol agent.
- (a) Mycorrhizae (b) Rhizobium (c) Trichoderma (d) Agaricus
II. Fill in the Blanks
1. Penicillin is prepared from a mould called Penicillium. 2. Prions are the infectious protein particles. 3. The infective virus particle found outside the host cell is Virion. 4. Micro organisms can be seen with the help of a Microscope. 5. Bacteria which have a flagellum at one end is classified as Monotrichous. 6. One word virus means Poison in Latin. 7. Bacteria are considered to be the first living organisms on earth. 8. The nuclear material of bacteria is called Nucleoid. 9. The extra chromosomal DNA in bacteria is called Plasmid. 10. Yeast is a unicellular fungus. 11. The study of fungi is called Mycology. 12. Yeast has an enzyme called Zymase. 13. The mode of respiration in yeast is Anaerobic.
III. True or False
IV. Match the Following
Match 1:
| Column A | Column B | Answer |
|---|---|---|
| 1. Nitrogen fixing bacteria | (a) Vaccine | 1 — (e) Rhizobium |
| 2. Tuberculosis | (b) Prion | 2 — (d) Bacteria |
| 3. Kuru | (c) Lactobacillus acidophilus | 3 — (b) Prion |
| 4. Probiotics | (d) Bacteria | 4 — (c) Lactobacillus acidophilus |
| 5. Edward Jenner | (e) Rhizobium | 5 — (a) Vaccine |
Match 2:
| Column A | Column B | Answer |
|---|---|---|
| i. Probiotic | (a) Kuru | i — (c) Curd |
| ii. Preservation | (b) Methanogen | ii — (d) Sugar |
| iii. Prion | (c) Curd | iii — (a) Kuru |
| iv. Biogas | (d) Sugar | iv — (b) Methanogen |
Match 3:
| Column A | Column B | Answer |
|---|---|---|
| i. Amoeba | (a) Autotrophs | i — (d) Sporulation |
| ii. Algae | (b) Gills | ii — (a) Autotrophs |
| iii. Agaricus | (c) Biocontrol | iii — (b) Gills |
| iv. Bt cotton | (d) Sporulation | iv — (c) Biocontrol |
V. Assertion and Reason
VI. Very Short Answers
Q1. Write the name of any nitrogen-fixing bacteria. Answer: Rhizobium (free-living example: Nostoc).
Q2. Name the bacteria used in the production of vinegar. Answer: Acetobacter aceti.
Q3. Write the names of any three protozoans. Answer: Amoeba, Plasmodium, Paramecium.
Q4. Who discovered penicillin? Answer: Alexander Fleming (1928).
Q5. Which diseases can be prevented by vaccination? Answer: Smallpox, polio, measles, mumps, rubella, tuberculosis.
Q6. What is a plasmid? Answer: The extra chromosomal DNA present in bacterial cells, separate from the nucleoid, is called a plasmid.
Q7. Why is the nuclear content of a bacterial cell called nucleoid? Answer: Since the nuclear material in bacteria lacks a nuclear membrane, it is referred to as a nucleoid rather than a true nucleus.
Q8. What are chemosynthetic bacteria? Answer: Bacteria that synthesize food using chemicals like ammonia or hydrogen sulphide instead of sunlight, thriving in harsh environments.
Q9. Why does yeast help in fermentation? Answer: Yeast respires anaerobically and contains the enzyme zymase, which converts sugars into alcohol and carbon dioxide.
Q10. Name the pigments found in algae. Answer: Chlorophylls (green), fucoxanthin (brown), xanthophylls (yellow), phycoerythrin (red), phycocyanin (blue).
Q11. What is biocontrol? Answer: The use of microbes to protect crops from pests and pathogens. Example: Trichoderma fungus safeguards plant roots.
Q12. What is pasteurization? Answer: A preservation method where milk is heated to 70 degree C to destroy bacteria, then rapidly cooled to 10 degree C to inhibit residual bacterial growth, and stored in sterilized containers.
VII. Short Answers
Q1. Write the four types of bacteria based on shape. Answer: 1. Bacilli — Rod-shaped 2. Spirilla — Spiral-shaped 3. Cocci — Spherical/ball-shaped 4. Vibrio — Comma-shaped
Q2. What are antibiotics? Answer: An antibiotic is a substance produced by living organisms that is toxic to other organisms. Example: Penicillin, derived from the fungus Penicillium, treats diseases like tetanus and diphtheria.
Q3. What are pathogens? Answer: Disease-causing organisms are termed pathogens. Example: Mycobacterium tuberculosis causes TB in humans.
Q4. How do disease-causing micro organisms enter human beings? Answer: Pathogens enter through: 1. Cuts and wounds in skin, mouth, or nose 2. Air — when infected persons sneeze, droplets with microbes spread (e.g., TB, Flu) 3. Contaminated food and water (e.g., Cholera) 4. Blood transfusion from infected to healthy person (e.g., AIDS)
Q5. Why are micro organisms essential for agriculture? Answer:
- Natural fertilizer: Decomposer microbes break down dead organic matter, releasing nutrients and enriching soil as compost.
- Nitrogen fixation: Certain bacteria convert atmospheric nitrogen into usable nitrate salts. Examples: Rhizobium in legume root nodules; free-living Nostoc.
- Biocontrol agents: Microbes naturally protect crops from pests, e.g., Baculoviruses attack harmful insects.
Q6. Mention two living characteristics of viruses. Answer: 1. They respond to heat, chemicals, and radiation. 2. They reproduce inside host cells, producing copies of themselves.
Q7. Mention two non-living characteristics of viruses. Answer: 1. They remain inactive when freely present in the environment. 2. They can be crystallized and stored for long periods, similar to non-living things.
Q8. How are protozoans classified? Answer: 1. Ciliates — possess cilia for locomotion (e.g., Paramecium) 2. Flagellates — possess flagella for locomotion (e.g., Euglena) 3. Pseudopods — use pseudopodia for movement (e.g., Amoeba) 4. Sporozoans — parasitic forms (e.g., Plasmodium)
VIII. Detailed Answers
Q1. Write a short note on bacteria and its structure. Answer: Bacteria are single-celled prokaryotes grouped under Kingdom Monera. The study of bacteria is called Bacteriology.
Structure: A bacterial cell has an outer cell wall. The nuclear material forms a nucleoid without a nuclear membrane. An extra chromosomal DNA called plasmid exists in the cytoplasm. Protein synthesis occurs via 70S ribosomes. Membrane-bound organelles like mitochondria, Golgi body, and ER are absent. Flagella help in locomotion.
Shape-based classification: Bacilli (rod), Spirilla (spiral), Cocci (spherical), Vibrio (comma)
Flagella-based classification:
- Monotrichous — single flagellum at one end (e.g., Vibrio cholera)
- Lophotrichous — tuft of flagella at one end (e.g., Pseudomonas)
- Amphitrichous — tuft at both ends (e.g., Rhodospirillum rubrum)
- Peritrichous — flagella all around (e.g., E. coli)
- Atrichous — no flagella (e.g., Corynebacterium diphtheriae)
Q2. How are micro organisms useful in the field of medicine? Answer: 1. Antibiotics: Substances produced by living organisms that are toxic to others. Penicillin from Penicillium chrysogenum treats tetanus and diphtheria. Streptomycin from Streptomyces bacteria cures bacterial infections like plague. 2. Vaccines: Prepared from dead or weakened microbes. When injected, they stimulate the body to produce antibodies that provide future protection. Example: MMR vaccine for measles.
Q3. How can we improve the beneficial bacterial count in human beings? Answer: 1. Consume fibre-rich foods 2. Eat seasonal fruits and vegetables 3. Consume fermented foods with live microbes and prebiotic foods 4. Include whole grains in the diet 5. Prefer plant-based diets 6. Avoid artificial sweeteners
Q4. Write a short note on Probiotics. Answer: Probiotics are live food supplements found in yoghurt and other fermented milk products. Examples include Lactobacillus acidophilus and Bifidobacterium bifidum. These bacteria enhance the microbial spectrum in the gut, providing these benefits: 1. Reduce the risk of colon cancer 2. Decrease cholesterol absorption 3. Prevent diarrheal diseases by boosting immunity
Q5. How are microbes useful in industry? Answer: 1. Sewage Treatment: Aerobic microbes consume organic matter in primary effluent. Anaerobic Methanobacterium is used in anaerobic sewage treatment. 2. Biogas Production: Anaerobic bacteria (methanogens) break down waste to produce methane (biogas) along with CO2 and hydrogen. 3. Alcohol and Wine Production: Yeast ferments sugars in grapes for wine, and sugars in rice/barley for beer. 4. Retting: Bacteria loosen stem fibres of flax plants in water, enabling linen thread production. 5. Tanning: Bacteria soften animal skins for leather production.
Q6. Describe the structure of Chlamydomonas. Answer: Chlamydomonas is a simple, unicellular, motile freshwater alga, oval/spherical/pyriform in shape.
- Surrounded by a thin, firm cellulose cell wall.
- Cytoplasm lies between the cell membrane and chloroplast.
- A large dark nucleus lies inside the cavity of the cup-shaped chloroplast.
- The anterior end bears two flagella for locomotion.
- Two contractile vacuoles are found at the base of each flagellum.
- A tiny red eyespot is present on the anterior side of the chloroplast.
Common Mistakes
- Treating all microbes as harmful: Many microbes are beneficial — Lactobacillus (curd), Rhizobium (nitrogen fixation), Penicillium (antibiotic).
- Confusing virus with bacteria: Viruses are acellular and need a host to reproduce; bacteria are cellular prokaryotes that can reproduce independently.
- Saying Anopheles mosquito carries dengue: Anopheles carries malaria; Aedes carries dengue.
- Confusing nucleoid with nucleus: Bacteria have a nucleoid (no nuclear membrane), not a true nucleus.
- Calling phycoerythrin a blue pigment: Phycoerythrin is red; phycocyanin is blue.
- Mixing up probiotics and preservation: Probiotics are beneficial live bacteria, not a preservation method.
Exam Checklist
- [ ] Can you classify bacteria by shape and by flagella type?
- [ ] Can you explain why viruses are on the border of living and non-living?
- [ ] Can you list at least 4 useful roles of microorganisms in agriculture?
- [ ] Can you describe how pathogens enter the human body?
- [ ] Can you explain antibiotics and vaccines with examples?
- [ ] Can you define pasteurization and probiotics?
- [ ] Can you describe the structure of a bacterial cell?
- [ ] Can you classify protozoans and give examples?
- [ ] Can you explain nitrogen fixation and biocontrol?
- [ ] Can you differentiate between prions and viruses?