Biology

• Principles of organisation:

  • Cell: smallest structural and functional unit of an organism, e.g. muscle cell
  • Tissue: group of cells with a similar structure and function, e.g. muscle tissue
  • Organ: aggregation of tissues performing specific functions, e.g. stomach
  • Organ system: group of organs performing specific functions, e.g. digestive system
• Levels of organisation in organisms:

  • Cell
  • Tissue
  • Organ
  • Organ system
• Common misconceptions:

  • The nucleus of a cell is not an organ, it is a sub-cellular structure
  • Food does not pass through the liver and pancreas in the digestive system, they are 'accessory organs'
• Human digestive system:

  • Digestion is breaking down large, insoluble molecules in food into smaller, soluble molecules that can be absorbed into the blood
  • Enzymes are protein molecules that act as biological catalysts
  • Enzymes work through the 'lock and key theory' where the substrate fits into the enzyme's active site
  • Each enzyme can only catalyse a specific reaction due to its specific active site shape
• Enzymes in digestion:

  • Lipase breaks down lipids into fatty acids and glycerol
  • Carbohydrase (e.g. amylase) breaks down carbohydrates into simple sugars
  • Protease breaks down proteins into amino acids
• Products of digestion:

  • Fatty acids and glycerol are used to build new lipids
  • Simple sugars (e.g. glucose) are used to build new carbohydrates and for respiration
  • Amino acids are used to build new proteins
• Bile in digestion:

  • Produced in the liver, stored in the gall bladder, and released into the small intestine
  • Functions: neutralises hydrochloric acid, emulsifies lipids to increase surface area for lipase to work on
• Enzyme denaturation:

  • Active site changes shape due to high temperature or extreme pH
  • Substrate no longer binds, and the reaction cannot be catalysed
• Factors affecting enzyme activity:

  • Temperature: as temperature increases, the rate of reaction increases up to an optimum, then decreases as enzymes denature
  • pH: enzyme activity is at a maximum at an optimum pH, deviations from this pH lead to decreased enzyme activity
• Safety precautions in practical activities:

  • Wear goggles to protect eyes
  • Clean up spills immediately as some reagents are irritant, corrosive, or poisonous
• Investigating enzyme activity:

  • Independent variable: pH of buffer solution
  • Dependent variable: time for no starch to be detected
  • Control variables: volume & concentration of amylase and starch solution, temperature
• Example application questions:

  • How could a more accurate value for the optimum pH be obtained?
  • How could a more accurate time be obtained?
  • How could the investigation be extended to determine the effect of a different factor on amylase activity?
• The heart and blood vessels:

  • Function of the human heart: pump blood around the body in a double circulatory system
  • Double circulatory system: blood passes through the heart twice for every circuit around the body
• Journey of blood through the heart:

  • Deoxygenated blood enters right atrium via vena cava
  • Blood flows into right ventricle, then to the lungs via pulmonary artery
  • Oxygenated blood returns to the heart, entering left atrium via pulmonary vein
  • Blood flows into left ventricle, then to the rest of the body via aorta
• Functions of blood vessels entering and leaving the heart:

  • Vena cava: returns deoxygenated blood to the heart
• Functions of blood vessels entering and leaving the heart:

  • Vena cava returns deoxygenated blood to the heart from the body
  • Pulmonary artery transports deoxygenated blood away from the heart to the lungs
  • Pulmonary vein returns oxygenated blood to the heart from the lungs
  • Aorta transports oxygenated blood away from the heart to the body
• Natural resting heart rate controlled by a group of cells in the right atrium acting as a pacemaker by sending regular electrical impulses

  • Irregularities in heart rate treated with artificial pacemakers, which are electrical devices that send out regular electrical impulses
• Structure of arteries related to their function:

  • Carry blood away from the heart at high pressure
  • Thick muscle tissue to withstand high pressure
  • Thick elastic tissue to stretch & recoil, maintaining high pressure
  • Narrow lumen to maintain high pressure
• Structure of veins related to their function:

  • Carry blood back to the heart at low pressure
  • Valves prevent backflow of blood
  • Large lumen for less resistance to blood flow
• Structure of capillaries related to their function:

  • Enable diffusion of substances between blood and cells
  • One cell thick/thin walls for short diffusion distance
  • Narrow lumen for slow blood movement, allowing more time for diffusion
• Blood is a tissue because it is a group of cells with a similar structure and function

  • Components of blood and their functions:
  • Plasma transports dissolved substances
  • Red blood cells transport oxygen
  • White blood cells part of the immune system, destroy pathogens
  • Platelets help clot blood at wounds
• Red blood cells adapted to their function:

  • Contain haemoglobin that binds to oxygen
  • Biconcave discs for a large surface area for rapid diffusion of oxygen
  • No nucleus for more space for haemoglobin
• White blood cells adapted to their function:

  • Can produce antibodies and engulf pathogens through phagocytosis
• Cause of coronary heart disease (CHD):

  • Fatty material builds up inside coronary arteries, narrowing them and reducing blood flow
  • Lack of oxygen/glucose for heart muscle
• How CHD can cause a heart attack:

  • Restricted blood flow through coronary arteries leads to insufficient oxygen reaching the heart muscle
  • Resulting in less aerobic respiration/energy released
• Treatment of coronary heart disease:

  • Stent inserted into coronary artery to keep it open
  • Statins reduce blood cholesterol to slow down fatty material deposition in arteries
• Consequences of faulty heart valves:

  • Valve issues restrict blood flow, leading to less oxygen reaching body cells
  • Less aerobic respiration, less energy released, more anaerobic respiration, causing tiredness/muscle fatigue/increased breathing rate
• Treatment of faulty heart valves:

  • Biological valve replacement from animals or human donors
  • Mechanical valve replacement, longer-lasting
• Treatment of heart failure:

  • Transplant of a donor heart or donor heart and lungs
  • Artificial heart occasionally used to keep patients alive while waiting for a transplant or to allow the heart to rest as an aid to recovery
• Factors that can cause ill health:

  • Communicable diseases caused by pathogens
  • Non-communicable diseases not caused by pathogens
  • Poor diet, stress, and life situations
• Types of disease interaction:

  • Defects of the immune system lead to a higher likelihood of suffering from infectious disease
  • Viruses living in cells can trigger cancers
  • Immune reactions caused by pathogens can trigger allergies
  • Severe physical ill health can lead to depression and other mental illness
• Risk factors:

  • Aspects of a person's lifestyle or substances in the body/environment linked to an increased rate of disease
• Main risk factor for Type 2 diabetes:

  • Obesity
• Effects of diet, smoking, and exercise on cardiovascular disease:

  • High saturated fat in diet increases cholesterol and fatty material build-up in arteries
  • Smoking damages artery lining and raises blood pressure
  • Lack of exercise raises blood pressure
• Effect of alcohol on the liver and brain function:

  • Breakdown of alcohol by liver cells produces toxic substances leading to cirrhosis and liver failure
  • Neurones in the brain are damaged, increasing the risk of liver cancer
• Effects of smoking on lung disease and lung cancer:

  • Damages alveoli, reducing gas exchange
  • Inflames bronchi, damages cilia, higher risk of lung infections
  • Carcinogens in smoke increase the risk of lung cancer
• Effects of smoking and alcohol on unborn babies:

  • Smoke contains carbon monoxide, reducing oxygen to the fetus, increasing the risk of premature birth/stillbirth/reduced birth mass
  • Alcohol increases the risk of miscarriage/premature birth/fetal alcohol syndrome
• Carcinogens as risk factors in cancer:

  • Carcinogens can cause DNA mutations leading to uncontrolled cell division
• Difference between correlation and causation of risk factors in disease:

  • Correlation shows a link between factors and disease incidence, while causation results in the disease incidence as the risk factor increases
• Correlation:

  • Link between a factor and the incidence of a disease
  • As one changes, the other does