Defence Against Disease (Edexcel GCSE Combined Science: Biology): Flashcards
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Physical barrier
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Cards in this collection (33)
Physical barrier
A structure that makes it difficult for pathogens to get into the body (e.g. skin, hairs and mucus in the nose).
Chemical barrier
A substance produced by body cells that traps or kills pathogens before they can cause disease (e.g. stomach acid, lysozymes).
How does the skin act as a defence against pathogens?
It covers the body to prevent pathogens entering, and if cut or grazed it heals itself, often by forming a scab.
How do mucus and cilia in the trachea and bronchi defend the lungs?
Pathogens get trapped in mucus, and cilia waft the mucus up to the back of the throat to be removed from the body.
How do hairs and mucus in the nose help defend the body?
They make it difficult for pathogens to get past them, so they are not inhaled into the lungs.
How does stomach acid act as a chemical barrier?
It contains hydrochloric acid, which is strong enough to kill pathogens that are swallowed or consumed in food and water.
What are lysozymes, and where are they found?
Enzymes produced by the eyes and released in tears, which break down and kill bacteria on or around the eye.
How does natural bacterial flora in the gut and vagina protect against infection?
It outcompetes pathogenic bacteria, protecting against infection.
What is the role of sebum on the surface of the skin?
It kills bacterial and fungal pathogens.
Stomach acid contains , which kills pathogens that have been swallowed.
hydrochloric acid
In the airways, waft mucus up to the back of the throat so it can be removed from the body.
Cilia
Phagocytosis
The process by which a phagocyte engulfs and digests a pathogen, releasing digestive enzymes.
Antibody
A Y-shaped protein made by lymphocytes with a shape that is specific (complementary) to an antigen on a pathogen.
Antigen
A molecule found on the surface of a cell that the immune system can recognise.
What are the two main types of white blood cell, and what does each do?
Phagocytes carry out phagocytosis.
Lymphocytes produce antibodies and antitoxins.
Why is phagocytosis described as a non-specific immune response?
Because the response is the same for any pathogen it encounters.
How can a phagocyte be recognised under the microscope?
By its multi-lobed nucleus and granular cytoplasm.
What is agglutination, and why is it useful?
Clumping together of pathogens by antibodies. It stops the pathogens moving easily and signals phagocytes to destroy them.
What is an antitoxin?
A protein produced by lymphocytes that neutralises toxins released by pathogens.
On a second infection by the same pathogen, why is the immune response faster and larger?
Memory cells remain in the blood and can produce larger quantities of the specific antibody in a much shorter time.
Why are antibodies described as specific?
Each antibody has a shape complementary to only one type of antigen, so it will only fit that pathogen.
Antibodies attach to antigens and cause , clumping the pathogens together.
agglutination
engulf and digest pathogens in a non-specific immune response.
Phagocytes
Vaccine
A preparation containing a harmless version of a pathogen, used to induce immunity to an infectious disease.
What does a vaccine contain?
A harmless version of a pathogen, which carries the necessary antigens.
Give three methods scientists use to make the pathogen in a vaccine harmless.
Killing the pathogen.
Making it unable to grow or divide (attenuated).
Using fragments of the pathogen that include the antigens.
By what routes can a vaccine be administered?
Orally, nasally or via an injection.
Describe how a vaccine triggers an immune response.
Lymphocytes recognise the antigens in the vaccine.
The activated lymphocytes produce specific antibodies.
Memory cells and antibodies then remain circulating in the blood.
What remains in the blood after vaccination, giving long-term immunity?
Memory cells and antibodies specific to the antigen.
How does the body respond if it meets the same pathogen again after vaccination?
The response is much faster and much larger, so the pathogen is destroyed before it can cause disease.
Why is a vaccinated person said to be immune to the disease?
Because the rapid, large secondary response means the pathogen is unable to cause disease.
Vaccines are used to induce to infectious diseases by introducing a version of a pathogen.
immunity / harmless
After vaccination, cells remain circulating in the bloodstream, ready for future infection.
Memory
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