In the following passage, each numbered space can be filled with a biological term.
In the cell-mediated immune response, foreign (1) ___________ are displayed on the surface of host cells, turning them into (2) ___________-presenting cells. Receptors on specific T-lymphocytes bind to these, triggering rapid division by mitosis, a process known as clonal (3) ___________. These T-cells differentiate into helper T-cells, which release (4) ___________ to stimulate B-cells, or cytotoxic T-cells, which destroy infected host cells. The production of a person's own antibodies and memory cells results in (5) ___________ immunity. Conversely, the direct transfer of pre-formed antibodies, such as across the placenta, provides immediate but temporary (6) ___________ immunity.
Write the correct biological term beside each number from 1 to 6 that matches the space in the passage.
Developing an effective vaccine against the Human Immunodeficiency Virus (HIV) has proven extremely challenging. Suggest one reason why.
Table 1 shows the action of two antimicrobial agents.
Table 1
| Antimicrobial agent | Action of antimicrobial |
|---|---|
| Tetracycline | Binds to bacterial 70S ribosomes, preventing translation of mRNA. |
| Penicillin | Inhibits the transpeptidase enzyme, preventing the cross-linking of peptidoglycan in bacterial cell walls. |
Using the information in Table 1, explain why each antimicrobial agent is not effective against the Human Immunodeficiency Virus (HIV).
