Global challenges Study Guide

Monoclonal antibodies (MAbs) are identical antibodies produced from a single clone of B lymphocytes. This means they are specific to one particular antigen. Their unique specificity makes them incredibly valuable tools in medicine and research. One key application is in diagnosis. For instance, they are used in pregnancy tests to detect human chorionic gonadotropin (hCG) in urine. The antibody in the test strip binds specifically to hCG, triggering a colour change to indicate pregnancy. Diagnosis extends to identifying specific pathogens (like bacteria or viruses) or cancer markers in blood samples. In cancer treatment, MAbs are designed to target cancer cells specifically. They can be manufactured to bind to antigens found only on cancer cells, leaving healthy cells unharmed. Once bound, they can mark cancer cells for destruction by the immune system, block signals that promote cancer cell growth, or deliver toxic drugs or radioactive substances directly to the cancer cells, minimising harm to surrounding healthy tissues. MAbs are also used to measure drug levels in the blood, detect hormones, or identify blood groups for transfusions. Immunotherapy using MAbs represents a significant advance, offering targeted approaches to various diseases. The development of MAbs involves fusing antibody-producing B lymphocytes with myeloma (cancer) cells to create hybridoma cells. These hybridoma cells can then be cultured to produce large quantities of identical antibodies.

Plants, like animals, are susceptible to diseases caused by pathogens such as bacteria, fungi, and viruses. To counteract these threats, plants have evolved a range of physical defence mechanisms. These physical barriers are the plant's first line of defence, aiming to prevent pathogens from entering the plant tissues or to limit their spread once an infection has started. A key outer defence is the waxy cuticle, a waterproof layer covering leaves and stems, which acts as a protective shield against the entry of pathogens and also reduces water loss. Cell walls, made primarily of cellulose, provide structural rigidity to most plant cells and act as a robust barrier that pathogens must overcome to gain access to the cytoplasm. Stomata, while essential for gas exchange, can also be entry points for pathogens. However, plants can alter the size of stomatal openings or even close them in response to pathogen detection, thereby limiting entry. Bark, found on older stems and trees, is a tough, impenetrable outer layer that offers significant protection against pathogen entry and insect damage. Additionally, plants can employ specific structural changes, such as producing tough lignin-rich layers around infected areas to wall off pathogens, or shedding infected leaves or fruits to remove the source of infection from the plant body.