Describe how the human body responds to a pathogen that has entered the bloodstream. Include in your answer the roles of lymphocytes and phagocytes.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When a pathogen such as the influenza virus enters the bloodstream, the immune system is activated to destroy it.
Model answer (5 marks)
White blood cells recognise the pathogen via receptors that bind to antigens on its surface.
Lymphocytes then release antibodies that are complementary to those antigens.
The antibodies bind to the pathogen, neutralising it or causing agglutination.
Phagocytes engulf the pathogen and digest it with enzymes in a process called phagocytosis.
Memory cells are formed, so that on a second exposure the antibody response is faster.
Lymphocytes then release antibodies that are complementary to those antigens.
The antibodies bind to the pathogen, neutralising it or causing agglutination.
Phagocytes engulf the pathogen and digest it with enzymes in a process called phagocytosis.
Memory cells are formed, so that on a second exposure the antibody response is faster.
Examiner tips
- Use the exact terms: receptors, antigens, lymphocytes, antibodies, phagocytes, phagocytosis, memory cells.
- Show the sequence: detection → antibody release → neutralisation/agglutination → phagocytosis → memory formation.
- Keep each point short and to the point to fit the 5 marks.
Common mistakes
- Mixing up lymphocytes with phagocytes or vice versa.
- Failing to mention memory cells or the speed of the secondary response.
Mark scheme (5 marks)
- White blood cells detect the pathogen using receptors on their cell surface to identify antigens on the pathogen
- Lymphocytes release antibodies that are complementary/specific to the antigen on the pathogen
- Antibodies bind to the antigens on the pathogen to neutralise it / cause agglutination (clumping together of pathogens)
- Phagocytes engulf (ingest) and digest the pathogen using enzymes in a process called phagocytosis
- Memory cells are produced so that if the same pathogen enters the body again, antibodies are produced more quickly
Key terms in this question
pathogen · lymphocyte · phagocyte
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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