Global challenges Study Guide

The human body possesses a sophisticated array of defence mechanisms to protect itself from harmful pathogens, such as bacteria, viruses, fungi, and parasites. These defences can be broadly categorised into specific and non-specific immunity. Non-specific defences, also known as innate immunity, are the body's immediate, general response to any perceived threat and do not distinguish between different types of pathogens, acting as a first line of defence. These mechanisms are always present and ready to act, providing rapid protection. Key examples include physical barriers like the skin and mucous membranes, chemical defences such as stomach acid and lysozyme in tears, and cellular responses like phagocytosis by white blood cells. The skin forms an impermeable outer layer that prevents most pathogens from entering the body. Mucous membranes, lining respiratory and digestive tracts, trap pathogens, which are then expelled. Internally, stomach acid creates an acidic environment that kills many ingested microorganisms. Cilia in the respiratory tract sweep trapped pathogens away. These non-specific systems are crucial for preventing infections from establishing themselves before the specific immune system can mount a targeted response.

Communicable diseases, caused by pathogens like bacteria, viruses, fungi, and protists, can spread rapidly among animal and plant populations, leading to significant economic losses and environmental damage. Effective strategies to reduce or prevent their spread are crucial. In animals, common methods include vaccination, which stimulates the immune system to produce antibodies, offering protection against specific pathogens. Isolation of infected animals prevents contact with healthy ones, breaking the chain of transmission. Maintaining good hygiene, such as regular cleaning of living spaces and equipment, reduces pathogen presence. Culling, the selective slaughter of infected animals, is used in severe outbreaks to control spread, although it is a controversial measure. Limiting animal movement and trade can prevent the introduction of diseases to new areas. For plants, similar principles apply. Removing and destroying infected plants prevents pathogens from spreading to healthy plant tissues or soil. Crop rotation can disrupt the life cycles of soil-borne pathogens. Using disease-resistant varieties of plants, developed through selective breeding or genetic modification, provides inherent protection. Controlling vectors, like insects that transmit diseases, through pesticides or biological controls, is also vital. Good sanitation practices, such as sterilising tools and ensuring clean irrigation water, prevent contamination. Finally, strict quarantine measures and careful inspection of imported plants and animals are essential to prevent the entry of new diseases into a region. Understanding the specific transmission routes of a pathogen is key to implementing the most effective control measures.