Global challenges Study Guide

Biodiversity refers to the variety of living organisms in an area, including the diversity of species, genetic diversity within species, and the diversity of ecosystems. Maintaining both local (e.g., a specific forest or pond) and global (e.g., the entire planet) biodiversity is crucial for several reasons. Ecologically, diverse ecosystems are more stable and resilient, meaning they can better withstand environmental changes like disease outbreaks or climate shifts. For instance, if one species is particularly affected by a new pathogen, a diverse ecosystem often has other species that can fill its ecological role, preventing a complete ecosystem collapse. From a human perspective, biodiversity provides essential 'ecosystem services'. These include the provision of food, clean water, medicines (many drugs are derived from plant compounds), and raw materials. Biodiversity also supports pollination of crops, natural pest control, and nutrient cycling in soils, all vital for agriculture and human well-being. Furthermore, many people value biodiversity for its aesthetic and recreational benefits, such as wildlife watching or nature tourism, which can also boost local economies.

However, maintaining biodiversity presents significant challenges. Habitat destruction, primarily due to human activities like deforestation for agriculture, urbanisation, and infrastructure development, is a major threat. Pollution, including air, water, and soil contamination, can directly harm organisms and disrupt entire food webs. Over-exploitation of resources, such as overfishing or excessive logging, depletes species populations faster than they can recover. The introduction of non-native (invasive) species can outcompete native species for resources, predate on them, or introduce diseases, leading to declines in native populations. Climate change, driven by human emissions of greenhouse gases, alters habitats, changes weather patterns, and can push species beyond their ability to adapt, leading to extinctions. Addressing these challenges requires complex solutions, including establishing protected areas, implementing sustainable resource management, controlling pollution, and international cooperation to tackle global issues like climate change and the spread of invasive species.

White blood cells and platelets are essential components of the blood, each with specific adaptations that enable them to perform crucial defence functions in the body. White blood cells, also known as leukocytes, are part of the immune system and are primarily responsible for fighting infections and removing foreign invaders. There are several types of white blood cells, but they generally share key adaptations. Many white blood cells are phagocytes, meaning they can engulf and digest pathogens. This ability is facilitated by their flexible, irregular shape, which allows them to squeeze through capillary walls (a process called diapedesis) to reach sites of infection in tissues. They also have a lobed nucleus, which further aids in their flexibility. Phagocytes contain numerous lysosomes, organelles filled with digestive enzymes that break down engulfed bacteria and cellular debris. Other types of white blood cells, such as lymphocytes, produce antibodies to target specific pathogens, or memory cells for long-term immunity. Platelets, on the other hand, are not whole cells but small fragments of cytoplasm derived from megakaryocytes. Their main role is in haemostasis, the process of stopping bleeding after injury. Platelets are adapted for this function by their small, irregular shape, which allows them to quickly aggregate at the site of a wound. They contain granules that release chemicals when activated, such as serotonin, which causes vasoconstriction (narrowing of blood vessels) to reduce blood flow, and various clotting factors. These factors initiate a cascade of reactions that convert fibrinogen into insoluble fibrin, forming a mesh-like clot that traps red blood cells and seals the wound, preventing further blood loss and blocking entry for pathogens. Without the specific adaptations of both white blood cells and platelets, the body would be highly vulnerable to infections and uncontrolled bleeding.