Global challenges Revision Notes

Human Infection: Influenza

Influenza, or the flu, is a respiratory illness caused by viruses. It is highly contagious and spreads through airborne droplets from coughing or sneezing. Common symptoms include fever, cough, sore throat, and muscle aches. The virus changes often, requiring new vaccines annually. Prevention involves vaccination, hand washing, and avoiding sick people. Treatment focuses on rest, fluids, and sometimes antiviral medicines.

Plant Disease: Tobacco Mosaic Virus (TMV)

Tobacco Mosaic Virus (TMV) affects many plants, including tobacco and tomatoes. It causes a distinct mosaic pattern on leaves (light and dark green areas), leads to stunted growth, and reduces crop yield. TMV spreads through contact, contaminated tools, or human handling. It is a very stable virus that can persist in dead plant material. There is no cure; prevention involves good hygiene, removing infected plants, and planting resistant varieties.

Sexually Transmitted Infections (STIs) and HIV/AIDS

Sexually Transmitted Infections (STIs) are transmitted through sexual contact. HIV (Human Immunodeficiency Virus) is an STI that weakens the immune system. If untreated, HIV progresses to AIDS (Acquired Immunodeficiency Syndrome), the most severe stage. HIV spreads via specific body fluids, typically through unprotected sex, shared needles, or mother-to-child transmission. Initial symptoms can be flu-like. AIDS is defined by severe opportunistic infections due to a compromised immune system. Prevention includes safe sex practices (condoms), avoiding shared needles, and antiretroviral therapy (ART).

Reducing Disease Spread in Animals

To reduce the spread of communicable diseases in animals, several key methods are employed. Isolation of infected animals prevents direct contact with healthy ones, stopping transmission via airborne particles or physical interaction. Good hygiene practices, such as routine cleaning and disinfection of animal housing, equipment, and handlers' hands, remove pathogens from the environment. Vaccination programmes are crucial; they introduce weakened or inactive forms of pathogens to stimulate an animal's immune system, building resistance to future infections. Controlling vectors, like insects or rodents, that carry and transmit pathogens from one animal to another, is also an effective strategy to break the chain of infection.

Reducing Disease Spread in Plants

Preventing communicable diseases in plants involves similar principles. Removing and destroying infected plant material, like leaves or whole plants, eliminates sources of inoculum and prevents further spread. Crop rotation is a cultural practice where different crops are grown in succession on the same land, which can disrupt pathogen life cycles and reduce the build-up of soil-borne diseases. Using disease-resistant crop varieties, developed through selective breeding or genetic modification, makes plants naturally less susceptible to specific pathogens. Controlling pests, such as aphids or other insects that act as vectors for plant viruses or bacteria, is vital to prevent transmission between plants. Applications of fungicides can protect plants from fungal infections.

Common Principles of Disease Control

Many strategies to prevent disease spread rely on common biological principles. Breaking the chain of infection is central; this involves preventing the pathogen from moving from an infected host to a new susceptible host. This can be achieved by reducing the pathogen load in the environment (hygiene, destruction of infected material), protecting susceptible hosts (vaccination, resistant varieties), or interrupting transmission pathways (isolation, vector control, pest control). Early detection and rapid response are critical for effective disease management to contain outbreaks before they become widespread. Understanding the specific mode of transmission for each disease guides the most appropriate control measures.

White Blood Cell Adaptations for Immune Defence

White blood cells (leukocytes) are key to the immune system, primarily tasked with defending the body against pathogens. A major adaptation is their irregular and flexible shape, which includes a lobed nucleus. This plasticity allows them to change shape easily, enabling a process called diapedesis where they can squeeze through the narrow walls of capillaries. This is crucial for them to move from the bloodstream into infected tissues. Once at the site of infection, many white blood cells, specifically phagocytes, engulf and digest foreign particles, bacteria, and dead cells through a process called phagocytosis. They are rich in lysosomes, which are vesicles containing potent digestive enzymes to break down these engulfed materials. Other white blood cells, such as lymphocytes, are adapted to produce specific antibodies that target and neutralise pathogens, or to remember past infections.

Platelet Adaptations for Blood Clotting

Platelets are not complete cells but small, anucleated fragments of cytoplasm derived from bone marrow cells called megakaryocytes. Their primary role is in preventing blood loss through blood clotting, also known as haemostasis. A key adaptation is their small, discoid, and irregular shape, which allows them to quickly respond to injuries. When a blood vessel is damaged, platelets are activated by exposure to collagen in the vessel wall. Upon activation, they become sticky and aggregate rapidly at the injury site, forming a temporary plug. They also release various chemical signals and clotting factors from their granules. These factors initiate a complex cascade that results in the conversion of soluble fibrinogen into insoluble fibrin protein threads. Fibrin forms a mesh-like network that traps red blood cells and more platelets, creating a stable blood clot that seals the wound, stops bleeding, and prevents pathogen entry.

Benefits of Biodiversity

Biodiversity, the variety of life on Earth, provides numerous benefits. Ecologically, it ensures stable and resilient ecosystems, meaning they are better able to recover from disturbances like disease or extreme weather events. If one species struggles, others can often compensate, preventing ecosystem collapse. Economically, biodiversity offers valuable 'ecosystem services' such as food, fresh water, medicines, and raw materials. It also supports agricultural processes like crop pollination and natural pest control. Furthermore, biodiversity provides aesthetic pleasure and opportunities for recreation, such as wildlife tourism, which can generate income for local communities.

Challenges to Maintaining Biodiversity: Habitat Destruction and Pollution

One of the most significant challenges to maintaining biodiversity is habitat destruction. This occurs primarily due to human activities like converting natural land for agriculture, building towns and cities, and constructing infrastructure (e.g., roads). When habitats are destroyed, species lose their homes and food sources, often leading to population declines or extinction. Pollution, arising from industrial waste, agricultural runoff, and vehicle emissions, also poses a major threat. Water pollution harms aquatic life, air pollution can damage plant growth and animal health, and soil pollution can make land uninhabitable for many species, disrupting entire ecosystems.

Challenges to Maintaining Biodiversity: Over-exploitation and Invasive Species

Over-exploitation refers to the unsustainable harvesting of natural resources, such as overfishing or excessive logging. When species are removed from an ecosystem faster than they can reproduce and replenish their numbers, their populations decline, sometimes to the point of extinction. Another significant challenge is the introduction of non-native, or invasive, species. These species, when introduced to a new environment, often have no natural predators and can outcompete native species for resources, prey on them directly, or introduce novel diseases. This can severely disrupt local ecosystems and lead to a reduction in native biodiversity.

Challenges to Maintaining Biodiversity: Climate Change

Climate change is a global threat to biodiversity, driven by human activities that release greenhouse gases. Rising global temperatures lead to altered weather patterns, more frequent extreme weather events, and changes in rainfall distribution. These shifts can drastically alter habitats, making them unsuitable for species that are not adapted to the new conditions. For example, polar ice melting threatens species like polar bears, while ocean acidification impacts marine organisms. Many species struggle to adapt or migrate quickly enough to these changes, increasing their risk of extinction and reducing global biodiversity.