3.1.1 Disease may be caused by infectious pathogens or may reflect the effects of lifestyle.

Pathogens

• Pathogens include bacteria, viruses and fungi.
• Disease can result from pathogenic microorganisms penetrating any of an organism’s interfaces with the environment. These interfaces include the digestive and gas-exchange systems.
• Pathogens cause disease by damaging the cells of the host and by producing toxins.

Lifestyle

• Lifestyle can affect human health.
• Specific risk factors are associated with cancer and coronary heart disease.
• Changes in lifestyle may also be associated with a reduced risk of contracting these conditions.
• Analyse and interpret data associated with specific risk factors and the incidence of disease
• Recognise correlations and causal relationships.

A disease is an illness or disorder of the body or mind that leads to poor health 😷. As a GCE AQA Biology student, you’ll be expected to look closely into the causes of disease. We’ll be looking at:

1. Pathogens

2. Lifestyle effects

1. Pathogens 🦠

• A pathogen is any micro-organism capable of causing disease. 
  • They include organisms like bacteria and fungi and their non-living counterparts, viruses. 
• In order for pathogens to cause disease in an organism, they need to first enter the organism. This can be done by penetrating the organism’s surfaces that are exposed to the surrounding environment. For example, this may be: 
  • Pathogens in uncooked food entering via the lining of the alimentary canal in the digestive system of humans 
  • Airborne pathogens that are inhaled and touch the inner surface of the nasal passages, bronchi, or lungs in humans’ respiratory system 
• Once the pathogens have entered the organism, the organism is known as the host, as they are ‘hosting’ or carrying the pathogen around. 
• Next, once the pathogens have entered the body, they need to find a way to hurt the organism to cause the specific symptoms of their disease. There are many ways pathogens can do so: 
  • Pathogens may choose to damage the cells of the host. For example, the HIV virus damages the T lymphocyte cells of the human immune system, eventually leading to an inability of the immune system to function. 
  • Pathogens can also make toxins that hurt the host. For example, the cholera bacterium secretes a toxin that causes body cells to release ions into the intestinal lumen, leading to diarrhoea.
     

2. In GCE AQA Biology, you will also examine how lifestyle affects the risk of disease:

• Many diseases are affected or accelerated by the lifestyle choices that individuals make. Lifestyle choices include, but are not limited to: 
  • Diet 
  • Exercise 
  • Stress 
  • Smoking 
  • Drinking 
• Two diseases that are strongly associated with lifestyle choices are some cancers and coronary heart disease. 
  • Cancers: 
    • Lung cancer is strongly correlated with smoking, as there are many carcinogens (cancer-causing chemicals) in the tar of cigarette smoke.  
  • Coronary heart disease (CHD) is the gradual blockage of the coronary arteries that supply oxygenated blood to the heart. 
    • Consuming foods high in saturated fats or trans fats is strongly correlated with an increased incidence of CHD. 
    • This is because saturated/trans fat increase the level of low-density lipoproteins in the blood, causing the coronary arteries to harden and narrow. 
    • The increased deposition of fatty substances in the arterial walls further narrows the lumen, increasing the risk of blockage. 
• If patients can make changes to their lifestyle that reduces such high-risk activity, they can lower the risk of contracting such conditions. 
  • For example, patients at high risk for CHD may be advised to stop smoking and exercise regularly. 🏃

We know about the relationship between specific diseases and poor lifestyle choices because scientists have been interpreting data that suggests such correlations for decades. In the GCE AQA Biology exam paper, you may be asked to examine a chart or table of data and analyse the nature of any such relationship. 

• For example, below is a famous graph that was used to demonstrate the correlation between lung cancer and smoking

• Both graphs show a similar sigmoidal shape: the sudden increase in cigarette consumption from 1000 to 4000 cigarettes/person/year is matched by the sudden increase in lung cancer deaths from 20 to 150 per 100,000 people. 
• There is a 20 year lag time between the two graphs, suggesting that the negative effects of smoking are gradual and take time to accumulate before leading to severe lung cancer 
• When analysing data, identify a pattern or interesting feature, then use specific data points as evidence, to support your answer.

However, it is important to distinguish between causation and correlation. 

• Causation: when one factor is known to lead to another by “cause and effect” 
• Correlation: when one factor is associated with another. A simple correlation between two variables is not enough to claim causation.

Wanna Boost Up Your GCE AQA Biology? Check out our study tips here!

References

1. Toole, G., & Toole, S. (2015). Aqa biology A level. Oxford: Oxford University Press.

2. Smoking & Disease. N.d. Retrieved from https://en.wikibooks.org/wiki/A-level_Biology/Human_Health_and_Disease/smoking_and_disease

3. Correlation & Causation. N.d. Retrieved from https://medium.com/stylumia/correlation-is-not-as-fashionable-as-causation-a57e753a4835

4. What is a Pathogen? 2019. Retrieved from https://www.healthline.com/health/what-is-a-pathogen