AQA GCSE Biology (8461) — Biological Organisation
Why do news headlines constantly claim different foods either cause or cure cancer? Media reports often confuse a correlation (a link where two variables change together) with a true scientific cause. A non-communicable disease is a disease that is not caused by a pathogen and cannot be spread from person to person.
To prove that a lifestyle factor actually causes a non-communicable disease, scientists must find a causal mechanism. This is a proven biological process explaining exactly how one variable directly leads to another. For example, a graph showing that people who watch more TV have higher obesity rates shows a positive correlation, but the TV itself does not cause obesity.
To provide valid data on risk factors (factors linked to an increased rate of disease), scientific studies must use excellent sampling principles. Samples must be large to minimize the effect of anomalies, random to avoid bias, and unbiased to ensure they represent the whole population accurately.
Understanding how our habits affect our blood vessels explains why many heart attacks are preventable. Coronary Heart Disease (CHD) occurs when layers of fatty material (plaques or atheromas) build up inside the coronary arteries, narrowing the lumen (the central space of the blood vessel).
Smoking and poor diet provide clear causal mechanisms for CHD. Nicotine increases heart rate and blood pressure, causing vasoconstriction, while carbon monoxide binds to haemoglobin to form carboxyhemoglobin, reducing the blood's oxygen-carrying capacity. A high-saturated fat diet increases blood cholesterol, leading to fatty deposits, and high salt intake increases blood pressure, which damages the artery lining (the endothelium).
Narrowed arteries reduce the volume of oxygenated blood reaching the heart muscle. This causes a decrease in aerobic respiration, meaning less energy is available for heart contractions. If oxygen is severely restricted, the heart muscle switches to anaerobic respiration, causing a buildup of , muscle fatigue, and eventually cell death (a heart attack).
When evaluating treatments for cardiovascular disease, you must consider both surgical and medical interventions.
| Treatment | Description | Advantages | Disadvantages |
|---|---|---|---|
| Stent | A metal mesh tube inserted to keep narrowed arteries open. | Restores blood flow immediately; long-lasting effect. | Risk of complications during surgery (e.g., bleeding, infection) and risk of blood clots near the stent. |
| Statin | A drug that lowers LDL ("bad") cholesterol in the blood. | Slows the buildup of fatty deposits without surgery. | Requires long-term daily compliance; can cause side effects like muscle pain or liver damage. |
Your body can produce plenty of insulin but still suffer from dangerously high blood sugar. Obesity is a major risk factor for Type 2 Diabetes, a disorder where the body's cells no longer respond to insulin. This phenomenon is known as insulin resistance.
The pancreas continues to produce insulin, but the liver and muscle cells ignore the signal to take up glucose from the blood. Fat stored around the abdomen is more strongly linked to insulin resistance than fat stored elsewhere. High-carbohydrate diets cause rapid glucose spikes, which lead to insulin overproduction and eventually drive this cellular resistance.
Doctors use mathematical models to assess the risk of developing Type 2 Diabetes based on body measurements.
Body Mass Index (BMI) Formula:
Step 1: Write down what you know.
Step 2: Substitute into the equation.
Step 3: Calculate the final answer.
Another key measurement is the Waist-to-Hip Ratio. The risk of Type 2 Diabetes increases significantly if this ratio is above for men and for women.
A quick drink might feel relaxing, but inside your body, your liver and brain are working overtime to process a toxic substance. Alcohol is a depressant that slows nerve impulse transmission in the brain, increasing reaction times. Long-term use physically damages the brain, causing atrophy (shrinking) and a loss of normal structure.
In the liver, alcohol can cause cirrhosis, a condition where healthy liver tissue is irreversibly replaced by scar tissue. This leads to metabolic failure, meaning the liver can no longer detoxify substances like ammonia, convert glucose into glycogen, or break down lactic acid after exercise.
Liver failure also severely impacts digestion because less bile is produced. Without bile, fats cannot be emulsified, resulting in a smaller surface area for lipase enzymes to work on. Alcohol is also classified as a carcinogen because it increases the risk of developing liver cancer.
Every time a heavy smoker inhales, they pull around 4,000 different chemicals into their lungs. Between 50 and 60 of these are known carcinogens, such as tar. These chemicals cause mutations in DNA, which leads to uncontrolled cell division (mitosis) and the formation of a tumour.
Chemicals in smoke also paralyse the cilia lining the respiratory tract. Because the cilia cannot waft mucus and trapped pathogens upwards, smokers develop a persistent cough and are highly prone to lung infections.
Smoking is the primary cause of emphysema, a disease where the delicate walls of the alveoli break down and fuse together. This drastically reduces the surface area to volume ratio available for gas exchange. For an ideal alveolus, the surface area is approximated by , and any reduction in this area heavily decreases the efficiency of oxygen diffusion into the blood.
Imagine trying to breathe through a thick straw while running—that is similar to how a fetus feels when a pregnant mother smokes. Carbon monoxide from cigarette smoke binds irreversibly to maternal haemoglobin.
Because the maternal red blood cells are carrying carbon monoxide instead of oxygen, less oxygen crosses the placenta to the fetus. The fetus is forced to carry out less aerobic respiration, providing less energy for growth and resulting in a low birth weight, premature birth, or even stillbirth.
Alcohol (ethanol) also severely impacts fetal development. It is a small molecule that acts as a teratogen by diffusing easily across the placenta, and the fetal liver is entirely unable to process it. This causes Fetal Alcohol Syndrome (FAS), which results in brain damage and physical deformities. The AQA specification mandates that there is absolutely no safe level of alcohol consumption during pregnancy.
Students often state that a graph shows one factor directly causing another. Remember that correlation does not prove causation unless a valid biological causal mechanism is explicitly provided.
In 6-mark questions explaining how smoking causes a heart attack, examiners expect a logical, step-by-step chain: carbon monoxide/nicotine → narrowed arteries → less oxygen to the heart → less aerobic respiration → lactic acid buildup/cell death.
For questions regarding Type 2 Diabetes, always use the exact phrasing that the body cells 'no longer respond to insulin'. Do not write that the body 'stops producing insulin', as that describes Type 1 Diabetes.
Always explicitly refer to the 'surface area' or 'surface area to volume ratio' when explaining why emphysema reduces the rate of oxygen entering the blood.
When explaining the effect of smoking on pregnant mothers, ensure you specifically mention 'carbon monoxide' binding to 'haemoglobin' to score the mechanism marks.
Correlation
A relationship or link between two variables where they change together, which does not necessarily prove one causes the other.
Non-communicable disease
A disease that is not caused by a pathogen and cannot be spread from person to person.
Causal mechanism
A proven biological process that explains exactly how one variable or risk factor directly leads to a disease.
Risk factors
Aspects of a person's lifestyle or substances present in their body/environment that have been shown to be linked to an increased rate of a disease.
Coronary Heart Disease (CHD)
A condition where layers of fatty material build up inside the coronary arteries, narrowing them and reducing blood flow to the heart muscle.
Lumen
The central space inside a blood vessel through which blood flows.
Carboxyhemoglobin
The stable complex formed when carbon monoxide binds irreversibly to haemoglobin, reducing the blood's capacity to carry oxygen.
Endothelium
The thin layer of cells that lines the inside of blood vessels.
Aerobic respiration
The process of releasing energy from glucose using oxygen.
Lactic acid
A toxic byproduct of anaerobic respiration that causes muscle fatigue.
Stent
A metal mesh tube surgically inserted into an artery to keep it open and maintain blood flow.
Statin
A drug prescribed to lower blood cholesterol levels, thereby slowing down the rate at which fatty materials build up in the arteries.
Type 2 Diabetes
A non-communicable disorder where the body's cells no longer respond to the insulin produced by the pancreas.
Insulin resistance
A condition where liver and muscle cells ignore the signal from insulin to take up glucose from the blood.
Cirrhosis
A disease of the liver where healthy functioning tissue is irreversibly destroyed and replaced by scar tissue.
Glycogen
A complex carbohydrate used as a storage form of glucose in the liver and muscles.
Carcinogen
A substance or form of radiation capable of causing cancer by mutating DNA.
Emphysema
A lung disease caused by the breakdown and fusing of alveoli walls, which heavily reduces the surface area available for gas exchange.
Surface area to volume ratio
The relationship between the surface area of a structure and its total volume; essential for efficient diffusion in gas exchange.
Placenta
The organ that develops in the uterus during pregnancy, allowing the exchange of nutrients, oxygen, and waste products between the mother and fetus.
Teratogen
A substance, such as alcohol, that can cause physical malformations or defects in a developing embryo or fetus.
Put your knowledge into practice — try past paper questions for Biology
Correlation
A relationship or link between two variables where they change together, which does not necessarily prove one causes the other.
Non-communicable disease
A disease that is not caused by a pathogen and cannot be spread from person to person.
Causal mechanism
A proven biological process that explains exactly how one variable or risk factor directly leads to a disease.
Risk factors
Aspects of a person's lifestyle or substances present in their body/environment that have been shown to be linked to an increased rate of a disease.
Coronary Heart Disease (CHD)
A condition where layers of fatty material build up inside the coronary arteries, narrowing them and reducing blood flow to the heart muscle.
Lumen
The central space inside a blood vessel through which blood flows.
Carboxyhemoglobin
The stable complex formed when carbon monoxide binds irreversibly to haemoglobin, reducing the blood's capacity to carry oxygen.
Endothelium
The thin layer of cells that lines the inside of blood vessels.
Aerobic respiration
The process of releasing energy from glucose using oxygen.
Lactic acid
A toxic byproduct of anaerobic respiration that causes muscle fatigue.
Stent
A metal mesh tube surgically inserted into an artery to keep it open and maintain blood flow.
Statin
A drug prescribed to lower blood cholesterol levels, thereby slowing down the rate at which fatty materials build up in the arteries.
Type 2 Diabetes
A non-communicable disorder where the body's cells no longer respond to the insulin produced by the pancreas.
Insulin resistance
A condition where liver and muscle cells ignore the signal from insulin to take up glucose from the blood.
Cirrhosis
A disease of the liver where healthy functioning tissue is irreversibly destroyed and replaced by scar tissue.
Glycogen
A complex carbohydrate used as a storage form of glucose in the liver and muscles.
Carcinogen
A substance or form of radiation capable of causing cancer by mutating DNA.
Emphysema
A lung disease caused by the breakdown and fusing of alveoli walls, which heavily reduces the surface area available for gas exchange.
Surface area to volume ratio
The relationship between the surface area of a structure and its total volume; essential for efficient diffusion in gas exchange.
Placenta
The organ that develops in the uterus during pregnancy, allowing the exchange of nutrients, oxygen, and waste products between the mother and fetus.
Teratogen
A substance, such as alcohol, that can cause physical malformations or defects in a developing embryo or fetus.
