Global challenges Revision Notes

Negative Human Impacts on Biodiversity

Human activities often lead to a reduction in biodiversity. Deforestation, the clearing of forests, destroys habitats for countless species, reducing their populations and, in some cases, causing extinction. Pollution from industry, agriculture, and domestic waste contaminates air, water, and soil, directly harming organisms and disrupting ecosystems. For example, plastic pollution can entangle marine life, and pesticides can poison insects and their predators. Overexploitation of resources, such as overfishing or excessive logging, depletes populations faster than they can reproduce, leading to species decline and ecosystem imbalance. Climate change, largely caused by human emissions, shifts weather patterns and habitats, making areas uninhabitable for some species.

Positive Human Actions for Biodiversity

Humans also take actions to protect and restore biodiversity. Conservation involves setting aside protected areas like national parks and wildlife reserves to safeguard critical habitats and species. Reforestation programmes plant new trees to replace those lost, restoring forest ecosystems. Sustainable practices in agriculture and fishing aim to use resources responsibly, preventing overexploitation and reducing environmental damage. For instance, selective fishing gear can reduce bycatch. Recycling and reducing waste help to decrease pollution and conserve natural resources, indirectly benefiting biodiversity by minimising habitat destruction and contamination.

Understanding Biodiversity

Biodiversity refers to the variety of life on Earth. This includes the diversity within species (genetic diversity), between species (species diversity), and of ecosystems (ecosystem diversity). A high level of biodiversity indicates a healthy and resilient ecosystem, as more varied species can adapt to changes and provide a wider range of ecosystem services, such as pollination, water purification, and nutrient cycling. A loss of biodiversity can make ecosystems more fragile and less able to cope with environmental challenges, potentially impacting human well-being.

Consequences of Biodiversity Loss

The loss of biodiversity has significant consequences. It can lead to the collapse of food webs, as the disappearance of one species can affect many others that depend on it. Ecosystem services, such as clean air and water, pest control, and soil fertility, can be diminished, directly impacting human society. Loss of genetic diversity within a species makes it less resilient to diseases or environmental changes. Fewer species also mean a reduced potential for new medicines and resources. Overall, a decline in biodiversity can destabilise global ecosystems and reduce their capacity to support life, including human life.

Non-Specific Defences against Pathogens

The human body has several non-specific defence mechanisms that provide immediate, general protection against pathogens. The skin acts as a physical barrier, preventing most microorganisms from entering the body. The respiratory tract lining produces mucus, which traps pathogens, and cilia then sweep this mucus upwards to be swallowed. In the stomach, hydrochloric acid creates a highly acidic environment that kills most ingested pathogens. Tears and saliva contain enzymes that can break down bacterial cell walls. Phagocytes, a type of white blood cell, carry out phagocytosis, a process where they engulf and digest foreign particles, including pathogens, without specifically identifying them.

Specific Immune Response: Lymphocytes and Antibodies

If pathogens breach the non-specific defences, the specific immune system is activated. This involves lymphocytes, which are specialised white blood cells. B-lymphocytes (B-cells) are responsible for producing antibodies. Antibodies are proteins that are highly specific to particular antigens (unique molecules found on the surface of pathogens). Antibodies work by binding to pathogens, clumping them together to make them easier for phagocytes to engulf, or neutralising toxins produced by pathogens. T-lymphocytes (T-cells) also play a crucial role, with some types directly killing infected cells and others coordinating the overall immune response. This specific response is slower to develop but is highly effective.

Immunological Memory and Vaccination

A vital characteristic of the specific immune system is its ability to develop immunological memory. After a pathogen has been encountered and dealt with by the immune system, certain B-cells and T-cells differentiate into memory cells. These memory cells persist for a long time, sometimes for life. If the same pathogen is encountered again, these memory cells can quickly recognise it and mount a much faster, stronger, and more effective immune response. This prevents the individual from getting ill. Vaccination works by introducing a weakened, inactivated, or partial version of a pathogen (antigen) into the body, stimulating the immune system to produce memory cells without causing the disease, thereby providing artificial immunity against future infections.

Genetic Modification (GM) for Food Production

Genetic modification (GM) involves altering the genetic material (DNA) of an organism to introduce new, desirable traits. In agriculture, this means creating crops that are more resistant to pests, tolerate herbicides, or have increased nutritional value (e.g., Golden Rice with added vitamin A). GM crops can also exhibit higher yields, allowing more food to be grown on less land. For livestock, GM can lead to faster growth rates or resistance to specific diseases, increasing productivity. This technology helps address food scarcity and nutritional deficiencies in a growing global population by enhancing the efficiency and resilience of food sources.

Hydroponics and Aeroponics

Hydroponics is a method of growing plants using mineral nutrient solutions in water, without soil. Aeroponics takes this a step further by growing plants in an air or mist environment without the use of soil or an aggregate medium. Both techniques offer significant advantages: they use less water than traditional farming, allow for precise control over nutrient delivery, enable year-round cultivation regardless of climate, and can be implemented in urban environments or areas with poor soil. This means higher yields per square meter and reduced need for large agricultural land, contributing to sustainable food production for a larger population.

Tissue Culture and Micropropagation

Tissue culture is a biotechnological technique used to grow cells, tissues, or organs in an artificial environment separate from the parent organism. In agriculture, a specific application called micropropagation involves growing entire plants from small tissue samples in a sterile, nutrient-rich medium. This allows for the rapid and asexual multiplication of desirable plant varieties, ensuring that all new plants are genetically identical to the parent. It is particularly useful for propagating plants that are difficult to grow from seeds, producing disease-free plants, and preserving endangered species, thereby contributing to the efficient and consistent supply of food resources.

Benefits and Challenges of Biotechnology in Food

Biotechnology offers significant benefits such as increased food yield, improved nutritional content, reduced pesticide use, and the ability to grow food in challenging environments. These solutions are crucial for feeding a growing human population. However, challenges include public concern about the safety of GM foods, potential environmental impacts such as the development of 'superweeds' or harm to non-target organisms, ethical considerations, and the cost of implementing these technologies, which can limit access for developing countries. Balancing these benefits against risks and ensuring equitable access is key to responsible biotechnological development.

Physical Barriers

The human body has several physical barriers that act as the first line of defence against pathogens. The most prominent is the skin, which forms a tough, impenetrable outer layer that prevents most microorganisms from entering the body. Intact skin acts as a major physical obstacle. Mucous membranes, found lining the respiratory, digestive, and urogenital tracts, also serve as physical barriers. These membranes produce mucus, a sticky substance that traps pathogens before they can reach cells and cause infection. Cilia, tiny hair-like structures in the respiratory tract, sweep mucus containing trapped pathogens towards the throat to be swallowed or expelled.

Chemical Barriers

In addition to physical barriers, the body uses chemical defences to destroy or neutralise pathogens. The stomach produces hydrochloric acid, a strong acid that creates a highly acidic environment (low pH) capable of killing most bacteria and other pathogens ingested with food and water. Tears and saliva contain enzymes, such as lysozyme, which can break down the cell walls of certain bacteria. Earwax also contains antimicrobial properties that help protect the ear canal from infection. These chemical substances contribute significantly to the non-specific defence by actively destroying pathogens at various entry points.

Cellular Defences: Phagocytes

Even if pathogens manage to breach the physical and chemical barriers, the body has internal non-specific cellular defences. Phagocytes are a type of white blood cell that plays a crucial role in ingesting and digesting pathogens. When pathogens enter the body, phagocytes are attracted to the site of infection. They engulf the pathogens through a process called phagocytosis, internalising them within a vacuole. Once inside the phagocyte, enzymes break down and destroy the pathogens. This process is a vital part of the inflammatory response and helps to clear infections before they can become severe.

The Importance of Non-Specific Defences

Non-specific defence systems are crucial because they provide immediate protection against a wide range of pathogens without needing prior exposure. They are always active and ready to respond, preventing most infections before they can even begin. These defences are not tailored to specific pathogens but treat all potential invaders in a similar manner. This rapid, general response is essential for maintaining health and acts as a vital buffer, allowing the more complex and pathogen-specific adaptive immune system time to activate its response when a novel or severe infection occurs.