Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Pathogens are microorganisms that cause infectious diseases, including bacteria, viruses, fungi, and protozoa.
The body has mechanical barriers to prevent entry: the skin (a physical tough outer layer) and hairs in the nose (which trap dust and pathogens).
Chemical barriers provide protection by killing pathogens: stomach acid (containing ) kills bacteria in food, and mucus (produced by goblet cells) traps pathogens in the airways.
Phagocytes are white blood cells that perform phagocytosis. They engulf pathogens into a food vacuole and digest them using enzymes.
Lymphocytes are white blood cells that produce antibodies. Antibodies have specific shapes that are complementary to the antigens on the surface of a pathogen.
Antigen-antibody binding leads to the destruction of pathogens through agglutination (clumping) or by marking them for phagocytes.
Active immunity is long-term defense against a pathogen by the production of antibodies in the body. This can be gained through natural infection or vaccination.
Vaccination involves introducing weakened or dead pathogens into the body, which stimulates lymphocytes to produce antibodies and, crucially, memory cells.
Passive immunity is short-term defense acquired by receiving ready-made antibodies (e.g., across the placenta or via breast milk). No memory cells are produced.
Memory cells remain in the blood and provide a rapid secondary immune response if the same pathogen () re-enters the body.
📐Formulae
💡Examples
Problem 1:
An image of a lymphocyte measures in diameter. If the actual diameter of the lymphocyte is , calculate the magnification used.
Solution:
Explanation:
First, convert the image size from millimeters to micrometers (). Then divide the image size by the actual size to find the magnification.
Problem 2:
Explain why a child who has had measles is unlikely to catch it again, even if exposed to the virus.
Solution:
The child has developed active immunity. During the first infection, lymphocytes produced memory cells specific to the measles antigens. If exposed again, these memory cells facilitate a much faster and larger production of antibodies (), destroying the virus before symptoms appear.
Explanation:
This demonstrates the secondary immune response, where the concentration of antibodies rises rapidly compared to the primary response.
Problem 3:
Identify the chemical barrier in the stomach and its effect on pathogens.
Solution:
The stomach contains Hydrochloric acid (). The low (high acidity) denatures the enzymes and proteins of most pathogens ingested with food, effectively killing them.
Explanation:
Chemical barriers use substances with specific chemical properties (like ) to neutralize biological threats before they reach the bloodstream.