Global challenges Revision Notes

Defining Health and Disease

Health is defined by the World Health Organization as a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity. This means being healthy involves feeling good mentally and having strong social connections, in addition to being free from illness. Disease, however, refers to any condition that impairs the normal functioning of the body or mind. This can range from infections to chronic conditions.

The Continuum of Health

Health and disease are not distinct, separate states but rather exist on a continuum. One person might be perfectly healthy, while another is acutely ill. However, many individuals fall somewhere in between, experiencing varying degrees of health and wellness. For example, a person might have a chronic condition like asthma but manage it well, leading a relatively healthy life. Conversely, someone without a diagnosed disease might still lack optimal health due to poor diet or high stress levels.

Factors Influencing Health and Disease

Several factors interact to influence an individual's health status. These include genetic predispositions, which are inherited characteristics that can increase or decrease susceptibility to certain diseases. Lifestyle choices, such as diet, exercise, smoking, and alcohol consumption, play a significant role. Environmental factors like exposure to pollutants, access to clean water, and sanitation also profoundly impact health. Lastly, socioeconomic factors, including income, education level, and access to quality healthcare, are critical determinants of well-being and disease prevalence.

Interconnectedness of Factors

The relationship between these factors is often interconnected. For example, poor nutrition (lifestyle) can weaken the immune system, making an individual more susceptible to infectious diseases (environmental factor). A genetic predisposition to diabetes might be triggered or worsened by an unhealthy diet and lack of exercise. Understanding these complex interactions is essential for effective disease prevention and health promotion strategies.

What is Genetic Engineering?

Genetic engineering involves transferring genes from one organism to another to introduce new characteristics or produce desired products. It's a method of altering the genetic makeup of an organism by inserting DNA from a different source. This allows for the precise modification of living systems, with applications ranging from medicine, such as insulin production, to agriculture, like developing pest-resistant crops. The entire process relies on the ability to manipulate DNA at a molecular level.

Step 1: Gene Isolation

The first critical step is to identify and isolate the gene of interest from the donor organism's DNA. This is achieved using special enzymes called restriction enzymes. These enzymes recognise specific DNA sequences and cut the DNA at these points. This creates DNA fragments, one of which contains the desired gene. The specific restriction enzyme chosen will cut both the donor DNA and the vector DNA in a way that allows them to be joined together later, ensuring compatibility.

Step 2: Gene Insertion into a Vector

Once isolated, the gene needs a 'carrier' to transport it into the recipient organism. This carrier is called a vector. Plasmids, which are small, circular DNA molecules found in bacteria, are commonly used vectors. The isolated gene is inserted into the opened plasmid using the same restriction enzyme that initially cut the gene. This creates 'sticky ends' on both the gene and the plasmid, allowing them to join together. DNA ligase, another enzyme, then seals the gene into the plasmid, forming a recombinant plasmid.

Step 3: Transfer into the Recipient Organism and Expression

The recombinant plasmid, containing the foreign gene, is then introduced into a suitable recipient organism, most commonly bacteria. This process is called transformation. The bacterial cells are treated to make their cell membranes permeable, allowing them to take up the plasmid. Once inside, the bacteria multiply, and as they reproduce, they copy the recombinant plasmid, including the new gene. The recipient organism can then 'express' the gene, meaning it will start producing the protein or characteristic encoded by the new gene. For example, bacteria with the human insulin gene will produce human insulin.

What are Non-Communicable Diseases (NCDs)?

Non-communicable diseases (NCDs) are conditions that cannot be transmitted directly or indirectly from one person to another. They are also known as chronic diseases because they tend to be of long duration and generally progress slowly. Examples include heart disease, cancer, diabetes, and chronic respiratory diseases. Unlike infectious diseases caused by pathogens, NCDs are rooted in an individual's physiology and are influenced by a complex interplay of internal and external factors.

Multifactorial Nature of NCDs

Many non-communicable human diseases do not arise from a single cause but are the result of an interaction of several contributing factors. This means that a combination of different elements increases an individual's risk. It is rarely just one factor in isolation; instead, multiple factors often work together, amplifying the overall risk of developing the disease. Understanding this complex web of influences is key to both prevention and treatment strategies.

Key Contributing Factors

The main types of factors contributing to NCDs are:

1. Genetic Factors: Inherited predispositions from parents can increase an individual's susceptibility to certain diseases, such as some cancers, type 2 diabetes, or cardiovascular conditions. However, genes usually only increase risk, they do not guarantee disease development.
2. Lifestyle Factors: These are an individual's choices and behaviours, including diet (e.g., high sugar, high fat), physical activity levels (sedentary lifestyle), smoking, and alcohol consumption. Unhealthy lifestyle choices are major modifiable risk factors.
3. Environmental Factors: External influences from the living and working environment can also contribute. Examples include exposure to air pollution, certain chemicals, UV radiation, and even socioeconomic conditions that impact access to healthcare, nutritious food, or safe exercise spaces.

Interaction of Factors

It is the interaction between these different types of factors that often leads to the development of NCDs. For instance, a person might have a genetic predisposition to high blood pressure (genetic factor), but this risk is significantly increased if they also consume a high-salt diet (lifestyle factor) and live in a stressful, polluted environment (environmental factor). Similarly, while smoking (lifestyle factor) is a strong risk factor for lung cancer, an individual's genetic make-up may influence how susceptible their cells are to the carcinogens in smoke.

What is Selective Breeding?

Selective breeding, also known as artificial selection, is a process used by humans to develop new organisms with desired characteristics. Individuals with desirable traits are chosen from a mixed population and bred together. This process is repeated over many generations. The aim is to enhance particular features that are beneficial to humans, often relating to food production efficiency or product quality. This method relies on the natural genetic variation present within a species, selecting for specific alleles that confer advantageous traits.

Impact on Food Plants

For food plants, selective breeding has led to significant improvements. Key impacts include increased crop yield, meaning more food can be produced from the same land area. Plants have been bred for enhanced resistance to common pests and diseases, reducing crop loss and the need for chemical treatments. Desirable characteristics also include tolerance to adverse environmental conditions, such as drought, frost, or saline soils, allowing cultivation in more challenging regions. Furthermore, selective breeding has improved the nutritional content, flavour, and shelf-life of many fruits, vegetables, and grains, directly benefiting consumers.

Impact on Domesticated Animals

In domesticated animals, selective breeding has resulted in animals with traits specifically suited for human needs. For instance, dairy cows are bred to produce larger quantities of milk, and beef cattle are selected for rapid growth and higher meat yield. Chickens are bred to lay more eggs or to grow quickly for meat production. Other improvements include increased fertility rates, better disease resistance, and enhanced temperament for easier handling. These targeted breeding programmes have significantly increased the efficiency and productivity of animal agriculture, contributing to a more reliable food supply.

Advantages and Disadvantages

The main advantage of selective breeding is the rapid improvement in desired characteristics, leading to increased food production, better quality, and greater efficiency in agriculture. This helps to feed a growing human population. However, a significant disadvantage is the reduction in genetic diversity. By repeatedly selecting for specific traits, many other genes are lost from the population. This lack of genetic variation can make selectively bred populations more susceptible to new diseases, pests, or sudden environmental changes, as they may lack the genetic resilience to adapt or resist new threats. Inbreeding can also lead to increased incidence of genetic disorders.