The Immune System (Cambridge (CIE) AS Biology): Flashcards
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Define phagocytosis.
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Define phagocytosis.
Phagocytosis is the process by which a phagocyte engulfs and digests a pathogen or foreign particle.
What are the two main types of phagocyte?
Neutrophils and macrophages.
Describe the mode of action of a phagocyte.
The phagocyte is attracted to the pathogen and recognises its antigens as non-self.
It engulfs the pathogen by endocytosis, enclosing it in a vesicle called a phagosome.
Lysosomes fuse with the phagosome and release hydrolytic enzymes.
The enzymes digest the pathogen.
How do neutrophils and macrophages differ?
Neutrophils are short-lived and act quickly, travelling to sites of infection.
Macrophages are larger and longer-lived, and after engulfing a pathogen they display its antigens to help activate lymphocytes.
Define phagosome.
A phagosome is the vesicle formed around a pathogen after it has been engulfed by a phagocyte.
After a pathogen is engulfed, lysosomes fuse with the phagosome and release to digest it.
After a pathogen is engulfed, lysosomes fuse with the phagosome and release hydrolytic enzymes to digest it.
Where are phagocytes produced?
Phagocytes are white blood cells made in the bone marrow.
Define antigen.
An antigen is a molecule (usually a protein or glycoprotein) on the surface of a cell that the immune system recognises and that can stimulate an immune response.
What is the difference between self and non-self antigens?
Self antigens are the body's own antigens and do not stimulate an immune response.
Non-self antigens are foreign (e.g. on pathogens) and trigger an immune response.
Antigens found on an organism's own cells are called antigens.
Antigens found on an organism's own cells are called self antigens.
Give examples of things that carry non-self antigens.
Pathogens such as bacteria and viruses, and cells or tissue from another organism (e.g. a transplant).
True or False?
Self antigens stimulate an immune response.
False.
Self antigens are recognised as belonging to the body, so they do not trigger an immune response; only non-self antigens do.
Define primary immune response.
The immune response that occurs on the body's first exposure to a particular antigen.
What is the role of macrophages in the immune response?
They engulf pathogens and display the pathogen's antigens on their surface, becoming antigen-presenting cells that activate lymphocytes.
What is the role of T-helper cells?
They recognise antigens on antigen-presenting cells and release cytokines that stimulate B-lymphocytes and other cells to carry out the immune response.
What is the role of T-killer cells?
They attach to and destroy body cells that are infected with a pathogen, such as virus-infected cells.
What is the role of B-lymphocytes in the immune response?
When activated, they divide to form plasma cells, which secrete large numbers of antibodies specific to the antigen.
Define plasma cell.
A plasma cell is a cell derived from a B-lymphocyte that secretes antibodies.
Outline the sequence of events in a primary immune response.
A macrophage engulfs the pathogen and displays its antigens (antigen-presenting cell).
T-helper cells recognise the antigens and release cytokines.
This activates specific B-lymphocytes, which divide into plasma cells.
Plasma cells secrete antibodies, and some cells become memory cells.
Activated B-lymphocytes divide to form plasma cells, which secrete .
Activated B-lymphocytes divide to form plasma cells, which secrete antibodies.
Define memory cell.
Memory cells are long-lived lymphocytes produced after an immune response that remain in the body and respond rapidly if the same antigen is met again.
What is the secondary immune response?
The faster and stronger immune response that occurs on the second (and later) exposure to the same antigen.
Why is the secondary immune response faster than the primary response?
Memory cells specific to the antigen are already present, so they divide rapidly into plasma cells and produce antibodies much more quickly.
How do memory cells provide long-term immunity?
They persist in the body for years, so if the same pathogen returns it is destroyed before it can cause symptoms.
The response on a second exposure to an antigen is faster and stronger and is called the immune response.
The response on a second exposure to an antigen is faster and stronger and is called the secondary immune response.
Compare antibody production in the primary and secondary responses.
Primary: antibodies produced slowly and in smaller amounts.
Secondary: antibodies produced rapidly and in larger amounts.
True or False?
Memory cells secrete antibodies.
False.
Memory cells do not secrete antibodies; they divide rapidly into plasma cells, which secrete the antibodies.
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