Infection with the protozoan parasite Cryptosporidium parvum causes cryptosporidiosis, characterized by watery diarrhoea. C. parvum produces a surface glycoprotein, GP900, which enables the parasite to bind to the epithelial cells lining the small intestine (ileum). This binding leads to the destruction of microvilli on these epithelial cells.
Explain why the loss of microvilli reduces the absorption of the products of digestion and why this leads to a large volume of water in the faeces.
Not all infants infected with C. parvum develop severe watery diarrhoea. Scientists measured the concentration of anti-GP900 antibodies in three groups of hospitalised infants:
The table below shows the mean anti-GP900 antibody concentrations (in arbitrary units, AU) at different stages of the hospital stay:
| Group | Day 0 (Admission) | Day 4 | Day 8 | Recovery |
|---|---|---|---|---|
| Group 1 (Infected, mild/no symptoms) | 2.10 | 3.40 | 4.10 | 3.90 |
| Group 2 (Infected, with severe diarrhoea) | 0.80 | 0.60 | 0.75 | 0.90 |
| Group 3 (Uninfected controls) | 0.50 | 0.55 | 0.50 | 0.52 |
Scientists suggest that monoclonal anti-GP900 antibodies could be administered to some infants as a form of passive immunity.
Use the table to suggest how this passive immunity would work and which infants should be offered this antibody treatment.
To be used as a passive immunity treatment, the monoclonal antibody must be injected. If it were administered by mouth (orally), it would be digested.
Describe how the antibody would be digested in the human gut.
12 exam-style questions on AQA A Level Biology Digestion and absorption, covering Digestion and absorption. Each one has a worked solution and a mark scheme showing where the marks go.