Body defence mechanisms ：練習問題

Tears contain an enzyme that can break down the cell walls of certain bacteria, providing a crucial first line of defence. Which enzyme is responsible for this antimicrobial action?

Which of the following immune responses is responsible for conferring long-term immunity against a pathogen, and how does it achieve this?

A patient is born with a genetic mutation that prevents the formation of Helper T cells, but they still have functional B cells and Cytotoxic T cells. Which of the following would be the most likely consequence for their specific immune system?

The skin acts as a physical barrier against pathogens. Which of the following features contributes to the effectiveness of skin as a defence mechanism?

Which of the following statements best explains why the secondary immune response results in a much higher concentration of antibodies in a shorter period compared to the primary immune response?

A graph displays the antibody concentration in a person's blood over several weeks. After the first injection of an antigen at day 0, the response is slow. After a second injection of the same antigen at day 28, the antibody level rises much more steeply. Explain the role of memory cells in causing this difference.

Distinguish between the roles of memory B cells and plasma cells in the specific immune response.

Explain why a total failure in antigen presentation by phagocytes would prevent the development of active immunity, even if the body's non-specific ability to engulf and digest pathogens remains functional. (6 marks)

When a person sustains a minor cut on the finger, the body immediately initiates non-specific defence mechanisms to prevent infection and excessive blood loss.

(a) Explain the importance of blood clotting as a non-specific defence mechanism in this scenario. (2 marks)

(b) The area around the cut may soon become red, swollen, and painful. Identify this biological response and explain how the resulting increased blood flow to the site helps in defending the body. (2 marks)

A child receives a vaccine against a specific viral disease. Two months later, the child is exposed to the actual virus but does not develop any symptoms of the disease.

(a) State the type of immunity the child acquired from the vaccine. (1 mark)

(b) Describe the sequence of events that occur in the child's immune system upon initial vaccination to provide protection. (3 marks)

(c) Explain why the child did not develop symptoms when exposed to the actual virus later, referring to the secondary immune response. (2 marks)