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8th Science Guide Lesson 16 Micro Organisms

8th Science Guide Lesson 16 Micro Organisms

8th Std Science Guide Lesson 16  Microorganisms | English Guide

8th Science Guide Unit 16 Micro Organisms book back answers. 8th Standard Science Guide English Medium Book Back Answers. 8th Science Samacheer kalvi guide Tamil Medium and English Medium Book Back and additional questions and answers. 8th Text Book download pdf. 8th std All Subject Guide

8th Science Guide Lesson 16 Micro Organisms

I. Choose the best answer

1. Micro organisms are measured in ______.

  1. cm
  2. mm
  3. micron

Ans : micron

2. _______ shows both living and nonliving characteristics

  1. Protozoa
  2. virus
  3. bacteria
  4. Fungi

Ans : virus

3. ______ is a prokaryotic micro organisms.

  1. Virus
  2. algae
  3. fungi
  4. bacteria

Ans : bacteria

4. The Based on shape, the bacteria are classified into _______ types.

  1. 2
  2. 3
  3. 4
  4. 5

Ans : 4

5. The plant body of algae is called as ______.

  1. stem
  2. thallus
  3. leaf
  4. root

Ans : thallus

II. Fill in the blanks.

  1. _______ is prepared from a mould called Penicillium. Ans : Penicillin
  2. _______ are the infectious protein particles. Ans : Prion
  3. The infact virus particle found outside the host cell is _______. Ans : Virion
  4. Micro organism can be seen with the help of a _______. Ans : microscope
  5. Bacteria, which have a flagellum at one end is classified as _______. Ans : monotrichous

III. True or False

  1. Diseases causing micro organisms are called pathogens.Ans : True
  2. Female anopheles mosquito is a carrier of dengue virus.Ans : False

Cu. St : Female anopheles mosquito is a carrier of Plasmodium.

  1. Chicken pox is a communicable disease.Ans : True
  2. Citrus canker is transmitted by insects.Ans : False

Cu. St : Citrus canker is transmitted by air/water.

  1. Yeast is used in the large scale production of alcohol.Ans : True

IV. Match the following:

  1. Nitrogen fixing bacteria – Vaccine
  2. Tuberculosis – Prion
  3. Kuru – Lactobacillus acidophilus
  4. Probiotics – Bacteria
  5. Edward Jenner – Rhizobium

Ans : 1 – c, 2 – d, 3 – e, 4 – a, 5 – b

V. Assertion & Reason.

1. Direction : In each of the following questions, a statement of Assertion is given and a corresponding statement of Reason is given just below it. Of the four statements, given below, mark one as the correct answer.

  1. If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  2. If both Assertion and Reason are true and Reason is not the correct explanation of Assertion.
  3. If Assertion is true but Reason is false.
  4. If both Assertion and Reason are false.

1. Assertion : Malaria is caused by Protozoa.

Reason : The disease is transmitted by mosquito.

Ans : If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

2. Assertion : Algae are heterotrophic.

Reason : They don’t have chlorophyll.

Ans : If both Assertion and Reason are false.

VI. Answer very briefly:

1. Write the name of any nitrogen fixing bacteria.

  • Rhizobium
  • Cyanobacteria
  • Nostoc

2. Name the bacteria used in the production of vinegar.

  • Acetobacter aceti.

3. Write the names of any three protozoans.

  • Amoeba
  • Plasmodium
  • Paramecium

4. Who discovered penicillin?

  • Alexander Flemming.

5. Which diseases can be prevented by vaccination?

  • Small pox
  • polio
  • measles
  • mumps
  • rubella
  • tuberculosis

VII. Answer briefly:

1. Write the four types of bacteria, based on their shape.

Bacteria are described according to the shape of their cells.

They are:

  • Bacilli – Rod shaped bacteria.
  • Spirilla – Spiral shaped bacteria.
  • Cocci – Spherical or ball shaped bacteria.
  • Vibrio – Comma shaped bacteria.

2. What are antibiotics?

  • Antibiotic is a substance produced by living organisms which is toxic for other organisms.

Example: Penicillin.

3. What are pathogens?

  • A few microorganisms are harmful to human, animals and plants. They cause diseases and hence they are called as Pathogens.

4. How diseases causing micro organisms enter into human beings?

  • Pathogens enter into the body through cuts and wounds in the skin, mouth or nose and cause diseases.

5. Why micro organisms are essential for agriculture?

Natural fertilizer:

Microorganisms are called as decomposers becuse they act upon degradable wastes

Nitrogen fixation:

Rhizobium bacteria living in the root nodule of leguminous plants enrich the soil by fixing the atmospheric nitrogen as nitrates which are essential for the growth of plants.

Biocontrol agents:

Microbes are used to and protect crops from pests.

VIII. Answer in detail:

1. Write a short note on bacteria and its structure.

  • Bacteria are single – celled prokaryotes (cells without nuclei).
  • Bacteria are grouped under the kingdom Monera. The study of Bacteria is called Bacteriology.
  • Bacteria are of two types based on respiration
  1. Aerobic bacteria (requires oxygen).
  2. Anaerobjc bacteria (Does not requires oxygen).
  • A bacterium has an outer covering known as the cell wall. Nuclear material is represented by a nucleoid without nuclear membrane.
  • An extra chromosomal DNA called plasmid is present in the cytoplasm.
  • Protein synthesis is carried out by 70S ribosomes. Other cell organelles (mitochondria, Golgi body endoplasmic reticulum etc.,) are absent. Flagella aids in locomotion.
  • Bacteria are described according to the shape of their cells. They are:
  1. Bacilli – Rod shape bacteria
  2. Spirilla – Spiral shaped bacteria
  3. Cocci – Spherical or ball shaped bacteria
  4. Vibrio – Comma shaped bacteria
  • Bacteria are also classified according to number and arrangement of
  • flagella as follows:
  1. Monotrichous – Single flagella at one end. Example: Vibrio cholera
  2. Lophotrichous – Tuft of flagella at one end. Example: Pseudomonas.
  3. Amphitrichous – Tuft of flagella at both ends. Example:Rhodospirillum rubrum.
  4. Peritrichous – Flagella all around. Example: E.coli.
  5. Atrichous – Without any flagella. Example: Corynebacterium diptherae.

2. How micro organisms are useful in the field of medicine?


It is a substance produced by living organisms which is toxic to other organisms. The antibiotic penicillin got from the fungus Penicillium chrysogenum is used to treat diseases like tetanus, diphtheria. Streptomycin got from streptomyces bacteria is used to cure bacterial infections like plague.


They are prepared from dead or weakened microbes. When a vaccine is injected into the body of a patient, it produces antibodies to fight the germs. These antibodies protect the body from infections in future. Example: MMR vaccine for measles.

3.Write a short note an common human diseases caused by micro organisms

Human Diseases

Micro Organisms

Mode of transmission


Preventive measures / Treatment


Mycobacterium tuberculosis (Bacteria)

Through air and sputum of infected person

Persistent cough, blood mucus, loss of weight, breathlessness

BCG Vaccine


Vibrio cholera (Bacteria)

By flies and by contaminated food and water

Watery diarrhoea, vomiting, rapid dehydration.

Anticholera vaccine, maintaining personal hygiene.

Common cold

Influenza (virus)

Through air 

Running nose, sneezing

Isolation of patient


Rhabdo viridae (virus)

Animal bite

Fever, hallucination,
paralysis inability to swallow

Anti-rabies vaccine.

Amoebic dysentery

Entamoeba histolytica (Protozoa)

Food water and flies

Severe diarrhea and blood in stool

Proper sanitation to be followed and metronidazole antibiotic to be administered


Plasmodium (Protozoa)

Female Anopheles mosquito

Nausea, vomiting High fever

Antimalarial drugs like quinine, chloroquine to be taken and also usage of mosquito repellents and nets

4. How can we improve the beneficial bacterial count in human beings?

We can improve the beneficial bacterial count in human beings by adopting the following methods:

  • Intake of fibre rich foods.
  • Intake of seasonal fruits and vegetables.
  • Intake of plenty of fermented foods with live microbes. Eat more of prebiotic foods.
  • Intake of whole grains.
  • Prefer plant based diet.
  • Avoid artificial sweeteners.

5. Write a short note on Probiotics.

Probiotics are live food supplements used in yoghurt and other fermented milk products.

Example: Lactobacillus acidophilus and Bifidobacterium bifidum.

These bacteria improve the microbial spectrum in the gut and thus contribute to the following effects:

  • Decrease the risk of colon cancer
  • Decrease cholesterol absorption
  • Prevent diarrheal diseases by increasing the immunity power.

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