Class 7 Science Chapter 2 Question Answers - Microorganisms : Friend or Foe

Q1: What are microorganisms? Give four examples.
Ans: Small organisms that cannot be seen through the naked eyes and can only be seen under a microscope are called microorganisms or microbes; e.g., Amoeba, Paramecium, Volvox, Spirogyra, etc.

Q2: Classify bacteria on the basis of their shapes.
Ans: On the basis of their shapes, bacteria are classified into four categories:

• Rod-shaped bacteria (bacilli)
• Spherical-shaped bacteria (cocci)
• Curved-shaped bacteria (vibrios)
• Spiral-shaped bacteria (spirilla)

Q3: Define communicable diseases. Give some examples.
Ans: Communicable diseases are microbial diseases that can spread from an infected person to a healthy person through air, water, or other physical contacts; e.g., cholera, chicken pox, tuberculosis, common cold, etc.

Q4: What do you mean by food spoilage?
Ans: The process in which food is deteriorated to such an extent that it does not remain fit for human consumption is known as food spoilage.

Q5: What role does sugar play in the preservation of food?
Ans: The role of sugar in food preservation is significant. By adding sugar to the food item, we reduce its moisture content and hence, it stops the growth of microorganisms.

Q6: How are carriers harmful to us?
Ans: Carriers take with them many harmful microorganisms or pathogens. They play a significant role in transferring these pathogens to a healthy person, by sitting on the food items, or directly transferring the pathogens inside the body of a person. Hence, they are harmful to us.

Q7: What is vaccination?
Ans: The process of putting a vaccine inside the body of a person to produce immunity against some disease is called vaccination.

Q8: What do you mean by immunity?
Ans: Immunity is the ability of a body to develop resistance against diseases.

Q9: Give two examples of each of the following types of microorganisms:
(a) Algae
(b) Fungi
(c) Protozoa
Ans:
(a) Algae – Spirogyra, Chlamydomonas
(b) Fungi – Aspergillus, yeast
(c) Protozoa – Paramecium, Amoeba

Q10: What are antibodies?
Ans: Whenever any harmful disease-causing microorganism enters the human body, the body produces substances to fight with the entered microbe. These substances are called antibodies.

Q11: What is the role of bacteria in increasing the soil fertility?
Ans: Some bacteria, which are present in the root nodules of leguminous plants or free-living, fix the atmospheric nitrogen in the soil which is ultimately used up by the plants. Hence, they increase the fertility of the soil. For example, Rhizobium, Azotobacter, Azospirillum, etc.

Q12: Define Ohmic heating.
Ans: Ohmic heating is the process in which electric current of high voltage is passed through the food items to kill the microbes that cause the spoilage of food.

Q13: What is sterilisation?
Ans: The process of killing all the microorganisms above the temperature of 100°C is known as sterilisation. It is one of the widely used methods to preserve food and is often used for various food items.

Q14: What is pasteurisation?
Ans: Pasteurisation can be defined as the partial sterilisation of foods at a temperature that destroys harmful microorganisms without major changes in the chemical property of the food.

Q15: Differentiate between viruses and other microorganisms.
Ans: 
Viruses

• They show the characteristics of living organ­isms or reproduce only by entering the host or­ganisms.
• They are non-cellular microbes.

Other microbes

• They do not need to enter any host organ­ism to reproduce or show any characteristics of life.
• They are cellular microbes.

Q16: Mention any three ways through which pathogens are transmitted.
Ans: Three ways because of which pathogens are transmitted are as follows:

• When a person sneezes or coughs, tiny droplets containing a number of disease-causing microorganisms come out of the mouth, and are released in the air. They are transmitted to a healthy person while breathing.
• By making direct contacts with an infected person, pathogens are transferred to a healthy person.
• Carriers of pathogens also help in their transmission. For instance, when a fly sits on animal excreta or garbage, harmful disease-causing microbes stick to its legs. And when this fly sits on the food items, pathogens get transferred to them. This contaminated food items cause serious diseases when it is eaten by a healthy person.

Q17: Explain how malaria is transmitted to humans.
Ans: A protozoan called Plasmodium is responsible for malaria. It lives in the liver and blood of the person who has been infected by this disease. A female Anopheles mosquito when sucks blood from the infected person, Plasmodium along with blood, is taken into its stomach. The Plasmodium, here, multiplies itself and reaches the salivary gland of the mosquito. Now, when this mosquito bites a healthy person, it injects Plasmodium along with saliva to him. The healthy person then gets an attack of malaria. In this way, malaria is transmitted to humans.

Q18: Explain various types of bacteria.
Ans: Bacteria are classified on the basis of their shapes into the following categories:

• Rod-shaped bacteria (bacilli):
  These are aerobic rod-shaped, spore-producing bacteria. They are often occurring in chain-like formations, and they are found primarily in soil; e.g., Lactobacillus.
• Spherical-shaped bacteria (cocci):
  They are spherical or nearly spherical bacteria; e.g., Streptococcus.
• Curved-shaped bacteria (vibrios):
  They are curved-shaped bacteria; e.g., Vibrio.
• Spiral-shaped bacteria (spirilla):
  They are flagellated, aerobic bacteria, having a spirally twisted rod-like form; e.g., Treponema.

Q19: Explain canning.
Ans: Canning is a process used for food preservation. Heat, at a certain temperature and for a limited period of time, is used to kill the harmful microorganisms as well as enzymes. This method also involves the removal of oxygen gas, and to avoid post-process contamination by airtight sealing of food items.

Q20: Explain why antibiotics do not work against flu or any infection caused by viruses.
Ans: Viruses cannot be killed by using antibiotics as their cell pathways are different from that of bacteria. It means taking antibiotics to get rid of flu or any other viral infection is useless, because it does not re-duce the strength of the virus, nor does it reduce the duration of the infection. But, however, antibiotic will work if we get attacks of viral infection and bacterial disease at the same time. Even then, it will cure bacterial disease only but not the viral infection.