Phagocytosis
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of cell recognition and the role of white blood cells in the immune system (from GCSE). You can test your knowledge on these below.
What is a pathogen?
A microorganism that causes disease, such as bacteria, viruses, or fungi.
What are antigens and why are they important in the immune response?
Antigens are molecules (usually proteins) found on the surface of pathogens. They trigger an immune response.
What type of white blood cell is involved in phagocytosis?
Phagocytes, including macrophages and neutrophils.
Topic Explainer Videos
Check out this @LauraDoesBiology video that explains phagocytosis or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Phagocytosis Explained
What is Phagocytosis?
- Phagocytosis is the process by which phagocytes (a type of white blood cell) engulf and digest pathogens.
- It is part of the non-specific immune response, meaning it happens regardless of the pathogen type or the foreign antigen.
Stages of Phagocytosis
Recognition and Attraction
- The phagocyte detects the pathogen via foreign antigens on its surface.
- Chemicals released by the pathogen or damaged cells attract the phagocyte (this is called chemotaxis).
Engulfing the Pathogen
- The phagocyte extends its membrane around the pathogen, enclosing the pathogen in a phagosome (a vesicle containing the pathogen).
Digestion and Breakdown
- Lysosomes within the phagocyte fuse with the phagosome.
- Lysosomes contain digestive enzymes (lysozymes) that digest the pathogen.
Antigen Presentation (Only in Antigen-Presenting Cells - APCs)
- After digestion, some phagocytes (e.g., macrophages) present the pathogen's antigens on their surface.
- This activates other immune responses, such as T-helper cells in the specific immune response.
Key Terms
- Phagocyte: A type of white blood cell that engulfs and digests pathogens.
- Antigen: A molecule (usually protein) on the surface of a pathogen that triggers an immune response.
- Lysosome: An organelle in the phagocyte containing digestive enzymes that digest pathogens.
- Phagosome: A vesicle formed when a phagocyte engulfs a pathogen.
- Chemotaxis: The movement of a phagocyte towards a pathogen due to chemical signals.
- Antigen: Presenting Cell (APC) – A phagocyte that displays pathogen antigens on its surface to activate other immune cells.
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Exam Tip
When describing phagocytosis in an exam, make sure to use key biological terminology such as phagosome, lysosome, antigen presentation and digestion.
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Describe the process of phagocytosis and explain how it helps in the immune response. (6 marks)
- Pathogens release chemicals that attract phagocytes (chemotaxis).
- The phagocyte engulfs the pathogen by surrounding it with its cell membrane, forming a phagosome.
- Lysosomes within the phagocyte fuse with the phagosome and release digestive enzymes.
- The enzymes digest the pathogen.
- Some phagocytes become antigen-presenting cells (APCs) by displaying the pathogen’s antigens on their surface.
- This activates other immune cells, such as T-helper cells, which trigger the specific immune response.
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!