AQA Biology GCSE Topic 2: Organisation

Principles of Organisation (2.1)

• All living things are made up of cells.
• Tissues:
  • Definition: A group of specialized cells with similar structure and function.
  • Can comprise multiple cell types (e.g., muscular tissue, epithelial tissue).
• Organs:
  • Formed from multiple tissues working together for specific functions.
  • Example: The stomach contains muscular and epithelial tissues.
• Organ Systems:
  • Groups of organs that work together to perform a specific function.
  • Example: The digestive system includes the stomach, liver, and small intestine.

The Human Digestive System (2.2.1)

• The digestive system is a collection of organs that breaks down food into absorbable nutrients.
• Key Organs:
  1. Glands (salivary glands, pancreas): Produce digestive juices with enzymes.
  2. Stomach: Produces hydrochloric acid for optimal enzyme function and bacteria kill.
  3. Small Intestine: Site for absorption of soluble molecules into the blood.
  4. Liver: Produces bile to assist in lipid digestion; bile is stored in the gall bladder.
  5. Large Intestine: Absorbs water from undigested food, forming faeces for elimination.

Enzymes: Biological Catalysts

• Enzymes are proteins that speed up reactions without being consumed.
• Can break down large molecules and link smaller ones.
• Active Site:
  • Each enzyme has a uniquely shaped active site where the substrate binds.
• Lock and Key Hypothesis:
  1. Substrate shape complements active site, forming an enzyme-substrate complex.
  2. Products are released after the reaction.

Factors Affecting Enzyme Activity

• Optimum Temperature: Generally around 37°C (body temperature).
  • Higher temperatures increase reaction rates until denaturation occurs (enzyme structure is altered).
  • High temperatures break bonds in the enzyme, changing its shape.
• Optimum pH: Most enzymes work best at pH 7, except some in acidic conditions (e.g., stomach).
  • Extreme pH levels can also denature enzymes.

Types of Enzymes and Their Functions

• Carbohydrases: Break down carbohydrates into simple sugars.
  • Example: Amylase (found in salivary glands, pancreas, small intestine).
• Proteases: Convert proteins into amino acids.
  • Example: Pepsin (produced in the stomach).
• Lipases: Transform lipids into fatty acids and glycerol.
  • Produced in pancreas and small intestine.

Tests for Biological Molecules

• Benedict’s Test: Tests for reducing sugars (turns brick red).
• Iodine Test: Tests for starch (turns blue-black).
• Biuret Test: Tests for proteins (turns purple).
• Emulsion Test: Tests for lipids (cloudy layer with ethanol).

Role of Bile in Digestion

• Produced in liver, stored in gall bladder.
• Functions:
  1. Neutralizes stomach acid for optimal enzyme function in the small intestine.
  2. Emulsifies fats to increase surface area for lipase action.

Investigating Enzyme Activity

• Experiment to see the effect of pH on enzyme activity using amylase and starch.
  • Use iodine to detect starch breakdown.
  • Measure time taken for starch to disappear at different pH levels.

The Heart and Blood Vessels (2.2.2)

• Circulatory System: Transports oxygen and nutrients, removes waste products.
• Heart Structure:
  • Has muscular walls (strong heartbeat).
  • Four chambers separate oxygenated and deoxygenated blood.
  • Valves prevent backflow.

Blood Flow in the Heart

1. Blood enters right atrium via vena cava and left atrium via pulmonary vein.
2. Atria contract, pushing blood into ventricles.
3. Right ventricle pumps blood to lungs; left ventricle pumps blood to body.

Pacemaker and Electric Control

• Natural pacemaker regulates heart rate (~70 beats/min).
• Artificial pacemaker used for irregular heartbeats.

Blood Vessel Types

• Arteries: Carry blood away from the heart; thick muscular walls to handle high pressure.
• Veins: Carry blood towards the heart; wider lumen, contain valves to maintain direction.
• Capillaries: Provide a short diffusion pathway with one-cell-thick walls for exchange of substances.