Mass Transport in Animals

AQA A-Level Biology Exam Prep

Key Topics Covered

• Hemoglobin
• Oxygen Dissociation Curve
• Heart Structure
• Circulatory System
• Heart Disease

Hemoglobin

• Protein with Quaternary Structure
  • 4 Polypeptide chains: 2 alpha & 2 beta
  • Contains a prosthetic group with an iron ion (Fe2+)
  • Can carry 4 O2 molecules (8 O atoms)
  • Iron ion (Fe2+) associates with oxygen
  • Hemoglobin types:
    • High affinity: Associates more readily, dissociates less readily
    • Low affinity: Dissociates more readily
• Oxyhemoglobin: Hemoglobin bound to oxygen

Hemoglobin Saturation & Dissociation

• High PO2: High concentration of oxygen (lungs)
• High PCO2: High concentration of carbon dioxide (tissues)
• Oxygen Dissociation Curve
  • Sigmoid shape: Less steep at start & end, steep in middle
  • Conformational changes: Easier binding of subsequent O2 after the first
• Bohr Effect: Curve shifts based on CO2 levels and pH
  • Shift to the Right: Lower affinity for O2 (high CO2, low pH)
  • Shift to the Left: Higher affinity for O2

Adaptations in Different Organisms

• High altitude (e.g., llamas): Higher affinity hemoglobin
• Low oxygen environments (e.g., lugworms): Higher affinity hemoglobin
• High metabolic rate (e.g., shrews): Lower affinity hemoglobin

Circulatory System

• Components: Heart, arteries, veins, capillaries
• Function: Increased rate of exchange for substances like O2, CO2, glucose, and urea
• Blood Flow
  • Oxygenated blood from lungs to heart via pulmonary vein
  • To body via aorta
  • Deoxygenated blood to lungs via pulmonary artery
  • Heart pump mechanics explained

Heart Structure

• External structure & key vessels
  • Aorta: Left ventricle
  • Vena cava: Right atrium
  • Pulmonary artery: Right ventricle
  • Pulmonary veins: Left atrium
• Internal chambers: Left/right atrium & ventricles
• Valves
  • Atrioventricular: Bicuspid (left) & tricuspid (right)
  • Semilunar: Base of pulmonary artery & aorta

Tissue Fluid Formation

• Tissue fluid consists of plasma with nutrients: oxygen, glucose, CO2, urea
• Formation: High hydrostatic pressure at arterial end forces fluid out
• Reentry: Protein presence at venule end creates osmotic gradient; water reenters via osmosis
• Lymph System: Collects excess fluid, returns to circulation

The Cardiac Cycle

• Steps
  1. Atrial Systole: Atria contract, filling ventricles
  2. Ventricular Systole: Ventricles contract, atria relax
  3. Relaxation Period: Both atria and ventricles relax
• Valve Function: Based on pressure changes in atria and ventricles

Cardiovascular Disease

• Atheroma: Fatty deposits in artery walls, increasing BP
• Aneurysm: Balloon-like swelling of arteries
• Thrombosis: Blood clots
  • Risks: Smoking, poor diet (high LDLs), high BP
  • Myocardial Infarction (Heart attack): When coronary arteries are blocked
• Non-Preventable Risks: Family history, age, gender (males more at risk)

Exam Practice Questions

1. Adaptations of Capillaries
   • Permeable walls: Flattened endothelial cells; single cell thick
   • Fenestrations: Allow large molecules
   • Narrow lumen: Slows blood flow, provides large surface area
2. Formation of Tissue Fluid
   • High hydrostatic pressure at arterial end
   • Soluble molecules pass out, proteins stay in
   • Lower water potential at venule end, reentry by osmosis
   • Lymph system returns excess fluid to circulation

Note: Answers provided for exam questions with mark points.

Final Thoughts: Understand key terms and processes, especially around hemoglobin affinity, cardiac cycle, and cardiovascular disease. Review diagrams and practice sketching the oxygen dissociation curve.