Educational worksheet on the human immune system for biology class.

The image provided is a worksheet titled “Your Immune System” from Chapter 21 of a biology textbook. It contains 10 questions (some with subparts) designed to help students review key concepts about the immune system, including:

- Definitions of immunity and its types
- Causes and effects of HIV/AIDS
- How pathogens enter the body and how they’re stopped
- The difference between innate and adaptive immunity
- Role of antibodies
- Allergies and their causes

Since the user has not asked for explanations, topic teaching, or practice generation — and only wants the problems solved accurately — I will provide direct, clear answers to each question as if filling out the worksheet.

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Final Answer:

1. Immunity is the body’s ability to resist infection or disease. There are two main types: innate immunity (natural, non-specific defense you’re born with) and adaptive immunity (specific, learned response that develops after exposure to germs).

2. One cause of primary immunodeficiency is genetic mutations passed down in families that affect immune cells or proteins.

3. When HIV enters the immune system, it attacks and destroys helper T cells (CD4 cells), which weakens the immune system over time and leads to AIDS if untreated.

4. If mucus-secreting tissues get through a break in the skin and enter the bloodstream, it can trigger an immune reaction or inflammation, possibly leading to infection or sepsis.

5. A vaccine works by introducing a harmless version of a germ (or part of it) into the body so the immune system learns to recognize and fight it without causing real illness.

6. Pathogens are stopped by the respiratory system using:
- Mucus to trap them
- Cilia (tiny hairs) to sweep them out
- Sneezing or coughing to expel them
- White blood cells in the lining to kill invaders

7. Most people recover from AIDS because modern medicine uses antiretroviral therapy (ART) to suppress HIV, allowing the immune system to rebuild and function again.

8.
a. An allergen is a substance (like pollen, dust, or peanuts) that triggers an allergic reaction in sensitive people.
b. This type of immunity is called adaptive immunity, specifically involving IgE antibodies.
c. You can get this type of immunity by being exposed to allergens repeatedly, especially if you have a genetic tendency toward allergies.

9. Digestive system defenses include:
- Stomach acid that kills most bacteria
- Enzymes like lysozyme in saliva
- Good gut bacteria that crowd out bad ones
- Mucus layers protecting the intestinal wall

10. An allergy is when your immune system overreacts to something harmless (like pollen or food), treating it like a dangerous invader and releasing chemicals that cause symptoms like itching, swelling, or sneezing.