Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A pathogen is a disease-causing organism, such as bacteria, viruses, fungi, or protozoa.
Transmissible diseases are those where pathogens can be passed from one host to another, either through direct contact (blood, body fluids) or indirect contact (contaminated surfaces, food, air).
The body has three main lines of defense: Mechanical barriers (skin, nose hairs), Chemical barriers (mucus, stomach acid containing ), and Cellular barriers (phagocytosis and antibody production by white blood cells).
Antibodies are -shaped proteins produced by lymphocytes that bind to specific antigens on the surface of pathogens, marking them for destruction or causing them to clump together (agglutination).
Active immunity is long-term defense against a pathogen by the production of antibodies in the body; this can occur naturally via infection or artificially via vaccination.
Vaccination involves the injection of weakened, dead, or harmless forms of a pathogen. This stimulates lymphocytes to produce antibodies and, crucially, memory cells that remain in the blood.
Passive immunity is a short-term defense acquired by receiving antibodies from another individual (e.g., across the placenta or via breast milk). No memory cells are produced in passive immunity.
The secondary immune response is much faster and produces a higher concentration of antibodies compared to the primary response because of the presence of memory cells.
📐Formulae
💡Examples
Problem 1:
Contrast the antibody concentration in the blood during the primary response (first exposure to pathogen ) versus the secondary response (second exposure to pathogen ).
Solution:
In the primary response, there is a lag phase, and antibody concentration rises slowly to a low peak. In the secondary response, the concentration rises almost immediately, reaches a significantly higher peak, and stays elevated for longer.
Explanation:
This occurs because memory cells created during the first exposure recognize the and rapidly divide into plasma cells to secrete large amounts of specific antibodies.
Problem 2:
A baby is born with antibodies against measles despite never being vaccinated. Explain this phenomenon.
Solution:
This is an example of natural passive immunity. Antibodies () passed from the mother's blood to the fetus via the placenta or through colostrum/breast milk after birth.
Explanation:
Passive immunity provides immediate but temporary protection as the baby's own lymphocytes have not been stimulated to produce memory cells.