Which of the following acts as a physical barrier that prevents the entry of pathogens into the human body?

The chemotherapeutic substance derived from a living organism that has an inhibitory effect on a parasitic organism is known as:

Consider the following statements:
$I.$ People should get vaccinated to avoid infection.
$II.$ Vaccination is available against polio,cholera,typhoid,tuberculosis,and many other diseases.
$III.$ Eradication of vectors is necessary for diseases like malaria and filariasis.
$IV.$ Dengue and chikungunya are both spread by $Culex$ mosquitoes.
Which of the statements given above are correct?

Which scientist discovered the vaccines for anthrax,chicken cholera,and rabies?

Which of the following cells do not act as phagocytes?

What is the mechanism of action of antibiotics?