Ans.
Different barriers present in the body prevent entry of disease causing agents or pathogens from entering into body and provide protection against them. These barriers include various physical, chemical, and biological barriers.
Physical barrier include skin and coughing and sneezing. Skin provides first line of defense by preventing entry of pathogens, and coughing and sneezing that expels harmful agents out of the body.
Chemical barriers include lysozyme, acids, and oil secretion. Lysozyme is an enzyme that kills bacteria by targeting their cell wall, while oil and acid prevent microbial growth by providing non-favorable environment for them.
Biological barriers include phagocytes and Langerhans cells. Phagocytes are immune cells that engulf and destroy pathogens and Langerhans cells are antigen-presenting cells that help in elimination of pathogens.
<span>The correct answer is b. Option a is incorrect because these models can demonstrate scientific theories, but they don't prove scientific theories (you would need experiments for that). Option c is incorrect because the models aren't always representing something abstract (i.e. DNA is very real, just very small). Option d is incorrect because they don't precisely mimic something in nature, but instead help us visualize something in nature that is difficult to see or comprehend.</span>
Answer:
D.
Explanation:
Viruses are oftentimes short lasted and disappear quickly.
