Question 1

What is the difference between active and passive immunity?

Accepted Answer

Active immunity occurs when the body produces its own antibodies after exposure to an antigen, either through infection or vaccination. It is long-lasting due to memory cells. Passive immunity involves receiving antibodies from another source, such as from a mother via breast milk or through an injection of antibodies. It provides immediate but short-term protection because no memory cells are formed.

Question 2

How do vaccines work to prevent disease?

Accepted Answer

Vaccines contain a harmless form of a pathogen (e.g., dead, weakened, or just its antigens). When injected, they stimulate the immune system to produce plasma cells that secrete antibodies and memory cells specific to that pathogen. If the real pathogen later infects the body, the memory cells quickly trigger a rapid, strong immune response, preventing illness. This is an example of active artificial immunity.

Question 3

Why can't antibiotics cure the common cold?

Accepted Answer

The common cold is caused by viruses (e.g., rhinoviruses), not bacteria. Antibiotics target bacterial structures like cell walls or ribosomes, which viruses do not have. Viruses replicate inside host cells using the host's machinery, so antibiotics are ineffective. Antiviral drugs may help, but they are often specific and not widely used for colds.

Question 4

What is the role of helper T cells in the immune response?

Accepted Answer

Helper T cells (CD4+ T cells) are crucial for coordinating the immune response. They are activated when they encounter an antigen presented by an antigen-presenting cell (e.g., a macrophage). Once activated, they release cytokines that stimulate B cells to divide and produce antibodies, and they also activate cytotoxic T cells to kill infected cells. Without helper T cells, the immune response is severely impaired, as seen in HIV/AIDS.

Question 5

How does HIV cause AIDS?

Accepted Answer

HIV (human immunodeficiency virus) infects and destroys helper T cells (CD4+ T cells). Over time, the number of helper T cells declines, weakening the immune system. When the helper T cell count falls below a critical level, the body becomes vulnerable to opportunistic infections and cancers, leading to AIDS (acquired immunodeficiency syndrome). HIV is transmitted via bodily fluids and can be managed with antiretroviral therapy.

Question 6

What is herd immunity and why is it important?

Accepted Answer

Herd immunity occurs when a high percentage of a population is immune to a disease (through vaccination or prior infection), reducing the spread of the pathogen. This protects individuals who cannot be vaccinated (e.g., due to medical conditions or age) because the pathogen has fewer hosts to infect. For highly contagious diseases like measles, vaccination rates of 90-95% are needed to maintain herd immunity.

Communicable diseases, disease prevention and the immune system

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

Before You Start

Likely Command Words

Ready to test yourself?

Related Topics in OCR A-Level Biology

Analysis

Biodiversity

Biological membranes

Biological molecules

How to Revise Communicable diseases, disease prevention and the immune system — OCR A-Level Biology

Examiner Tips for Communicable diseases, disease prevention and the immune system

Common Mistakes in Communicable diseases, disease prevention and the immune system

Key Marking Points