Identify and describe What Are Pathogens?, Nonspecific vs Specific Defences and The Nose as a Physical Barrier in the context of human defence systems.
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GCSE Biology Revision
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GCSE Biology revision
Human defence systems
Communicable diseases
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Explain the relationships between What Are Pathogens?, Nonspecific vs Specific Defences and The Nose as a Physical Barrier and how they contribute to human defence systems.
Apply and analyse knowledge of What Are Pathogens?, Nonspecific vs Specific Defences and The Nose as a Physical Barrier to interpret unfamiliar information about human defence systems.
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What Are Pathogens?
- Pathogens are microorganisms that cause disease, including bacteria and viruses.
- Bacteria reproduce inside the body and produce toxins (poisons) that damage cells and tissues.
- Viruses reproduce inside host cells, using the cell's own chemicals, which damages and destroys those cells.
Nonspecific vs Specific Defences
- The body uses two broad types of defence: nonspecific methods (physical barriers) and specific methods (the immune system).
- Nonspecific defences act as the first line of defence, preventing pathogens from entering the body regardless of the type of pathogen.
- If pathogens get past the physical barriers, the immune system — the specific defence — kicks in.
The Nose as a Physical Barrier
- The inside of the nose is lined with hairs and mucus that trap pathogens, dust, and other particles.
- Trapped microbes are moved to the back of the throat where they are swallowed and passed to the stomach.
The Stomach as a Physical Barrier
- The stomach produces hydrochloric acid with a pH of approximately 2, which kills most pathogens that are swallowed.
- Any microbes entering through food or being swallowed from the nose can be destroyed by this strong acid.
The Skin as a Physical Barrier
- The skin is a single organ covering the entire body and acts as a physical barrier against pathogens.
- Pathogens such as bacteria and viruses cannot penetrate the skin unless it has been cut or damaged.
The Trachea and Bronchi as Physical Barriers
- The trachea (windpipe) and bronchi are lined with microscopic hair-like structures called cilia and a layer of mucus.
- The mucus traps dust, germs, and microbes, preventing them from reaching the lungs and entering the bloodstream.
- The cilia beat to push trapped particles back up and out of the body.
Phagocytosis
- Phagocytosis is the process by which white blood cells engulf or ingest pathogens.
- Once engulfed, the microbe is digested and broken down, destroying it completely.
- This is the first method by which the immune system responds to pathogens that have entered the body.
Antibodies and Antigens
- White blood cells produce antibodies, which are specific proteins that target particular pathogens.
- Pathogens carry surface proteins called antigens, which are unique to each type of microorganism.
- Antibodies have a shape that fits a specific antigen — they are complementary in shape, not identical.
- Antibodies can bind to antigens on pathogens, clumping them together so they can be destroyed by the immune system.
- Because the body must produce the correct antibody for each new pathogen, it can take time to fight off a new infection.
Antitoxins
- Some pathogens produce toxins that damage cells and tissues, making you feel ill.
- White blood cells produce antitoxins, which are specific to particular toxins and neutralise them, making them harmless.
- By neutralising toxins, antitoxins prevent damage to body cells and tissues and reduce the symptoms of disease.