Cambridge (CIE) AS Biology Your notes
The Immune System
Contents
Phagocytes
Antigens
Primary Immune Response
Memory Cells & Immunity
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, Phagocytes
Your notes
Phagocytes: Origin & Mode of Action
Phagocytes are white blood cells that are produced continuously in the bone marrow
They are stored in the bone marrow before being distributed around the body in the
blood
They are responsible for removing dead cells and invasive microorganisms
They carry out what is known as a non-specific immune response
There are two main types of phagocyte, each with a specific mode of action. The two
types are:
Neutrophils
Macrophages
Phagocytes carry out phagocytosis
Neutrophils
Neutrophils are short-lived cells that travel throughout the body and often leave the
blood by squeezing through capillary walls to ‘patrol’ the body tissues
During an infection they are released in large numbers from their stores
Neutrophils carry out phagocytosis as follows:
Chemicals released by pathogens, as well as chemicals released by the body cells
under attack, e.g. histamine, attract neutrophils to the site where the pathogens are
located
This response to chemical stimuli is known as chemotaxis
Neutrophils move towards pathogens
Receptor proteins on the surface of neutrophils attach to antigens on the surface of
pathogens
Once attached to a pathogen, the cell surface membrane of a neutrophil extends
out and around the pathogen, engulfing it and trapping the pathogen within a
phagocytic vacuole
This is an example of endocytosis
The neutrophil then secretes digestive enzymes into the vacuole
This occurs when the phagocytic vacuole, also known as the phagosome, fuses
with a lysosome
The fused phagosome and lysosome are referred to as a phagolysosome
These digestive enzymes destroy the pathogen
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The Immune System
Contents
Phagocytes
Antigens
Primary Immune Response
Memory Cells & Immunity
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 1
, Phagocytes
Your notes
Phagocytes: Origin & Mode of Action
Phagocytes are white blood cells that are produced continuously in the bone marrow
They are stored in the bone marrow before being distributed around the body in the
blood
They are responsible for removing dead cells and invasive microorganisms
They carry out what is known as a non-specific immune response
There are two main types of phagocyte, each with a specific mode of action. The two
types are:
Neutrophils
Macrophages
Phagocytes carry out phagocytosis
Neutrophils
Neutrophils are short-lived cells that travel throughout the body and often leave the
blood by squeezing through capillary walls to ‘patrol’ the body tissues
During an infection they are released in large numbers from their stores
Neutrophils carry out phagocytosis as follows:
Chemicals released by pathogens, as well as chemicals released by the body cells
under attack, e.g. histamine, attract neutrophils to the site where the pathogens are
located
This response to chemical stimuli is known as chemotaxis
Neutrophils move towards pathogens
Receptor proteins on the surface of neutrophils attach to antigens on the surface of
pathogens
Once attached to a pathogen, the cell surface membrane of a neutrophil extends
out and around the pathogen, engulfing it and trapping the pathogen within a
phagocytic vacuole
This is an example of endocytosis
The neutrophil then secretes digestive enzymes into the vacuole
This occurs when the phagocytic vacuole, also known as the phagosome, fuses
with a lysosome
The fused phagosome and lysosome are referred to as a phagolysosome
These digestive enzymes destroy the pathogen
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