Chapter 45, Problem 1TYK

Summary Introduction

Introduction:

Immune system is the defense system of an organism which consists of various biological processes and structures that provide protection against various pathogens. The immune system must be able to identify variety of pathogenic microbes and to differentiate them from the host’s cells.

Answer to Problem 1TYK

Correct answer:

The three lines of defenses i.e. physical barrier, innate immune system and adaptive immune system, work independently of each other in defending against a particular pathogen.

Explanation of Solution

Justification for the correct answer:

Option (a) states that ‘the three lines of defense work independently of each other in defending against a particular pathogen’. This is a true statement as each organism, which is exposed to the disease causing viruses and organisms, consists of three lines of defense against these threats. First line is physical barriers like skin, second line is innate immune system and third line of defense includes adaptive immune system. Notably, these three host defense lines take cumulative actions to defend the host against pathogenic microbes. Hence, option (a) is correct.

Justification for the incorrect answers:

Option (b) states that ‘physical barriers are part of the immune system. This statement is not true as physical barriers are not a part of immune system. The mammalian immune system of an organism is made up of innate and adaptive immunity. So, it is an incorrect option.

Option (c) states that ‘the adaptive immune system reacts faster to pathogens than the innate immune system. This is false as the innate immune responses are the first one to act when the host’s body is attacked by pathogenic microbes, whereas adaptive immunity takes several days to become protective. So, it is an incorrect option.

Option (d) states that ‘once the adaptive immune system is activated in response to a specific pathogen, the innate immune system stops functioning against that specific pathogen’. This is an incorrect statement because the innate and adaptive immunity take cumulative action against pathogens. So, it is an incorrect option.

Option (e) states that ‘white blood cells are the key participants in adaptive immunity but not in innate immunity’. This is an incorrect statement as the white blood cells are part of both innate and adaptive immune response. So, it is an incorrect option.

Hence, options (b), (c), (d) and (e) are incorrect.

Conclusion

Thus, it can be concluded that host defense system prevents the invasion of pathogens by the three lines of defenses i.e. physical barrier, innate immune system and adaptive immune system.