Biology IGCSE CIE Revision

• All life consists of cells
• Light microscope


  Can see cells and maybe the nucleus, but not subcellular structures
• Electron microscope


  Can see finer details and subcellular structures, has better resolving power and higher resolution
• Calculating cell size


  1. Measure image size

  2. Divide by magnification
• Cell types


  • Eukaryotic cells
  • Prokaryotic cells
• Eukaryotic cells


  • Have a nucleus where DNA is found
  • Examples: plant and animal cells
• Prokaryotic cells


  • Don't have a nucleus, DNA is in a ring called a plasmid
• Subcellular structures


  • Cell membrane
  • Cell wall (plant cells and bacteria)
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts (plant cells)
• Cell membrane


  Keeps everything inside the cell, semi-permeable
• Cell wall


  Provides rigid structure (plant cells and bacteria)
• Cytoplasm


  Liquid that makes up the cell, where most chemical reactions take place
• Mitochondria


  Where respiration takes place, releasing energy for the cell
• Ribosomes


  Where proteins are assembled or synthesized
• Chloroplasts


  Contain chlorophyll, where photosynthesis takes place (plant cells)
• Diffusion


  Movement of molecules or particles from an area of high concentration to an area of low concentration, down the concentration gradient, passive process
• Osmosis


  Diffusion of water across a semi-permeable membrane
• Factors that increase rate of diffusion and osmosis


  • Increase difference in concentrations
  • Increase temperature
  • Increase surface area
• Practical on osmosis


  1. Cut equal size cylinders from potato

  2. Weigh and place in test tubes with varying sugar solution concentrations

  3. After a day, remove, dab excess water, and reweigh

  4. Calculate percentage change in mass

  5. Plot percentages against sugar concentration

  6. Where graph crosses x-axis is the concentration with no change in mass (same as inside potato)
• Active transport


  Movement of substances through a membrane against a concentration gradient, using energy
• When cells are organised together, they form tissues, which form organs, which work together in organ systems
• Organ systems


  • Circulatory system
  • Digestive system
• Digestion in the digestive system


  1. Food physically broken down in mouth

  2. Chemically digested in stomach with acid

  3. Bile and enzymes in small intestine break down food further
• Tooth structure


  4 main types of teeth: incisors, canines, premolars, molars
• Enzymes


  • Biological catalysts that break down larger molecules into smaller ones
  • Specific to the substrate, work on a lock and key principle
• Factors affecting enzyme activity


  • Increased temperature increases rate until active site is denatured
  • Optimum pH, too high or too low can also denature enzyme
• Practical on enzyme activity


  1. Mix amylase with starch at different temperatures or pH

  2. Every 10 seconds, test for presence of starch with iodine

  3. Plot time taken for starch to be broken down against temperature or pH

  4. Optimum is between the two lowest points
• Food tests


  • Iodine turns black with starch
  • Benedict's solution turns orange with sugars
  • Biuret's reagent turns purple with proteins
  • Ethanol goes cloudy with lipids
• Nutrients in a balanced diet


  • Carbohydrates (for energy)
  • Fats/lipids (for energy)
  • Proteins (for growth and repair)
  • Vitamins (for health)
  • Minerals (for health)
  • Fibre (for digestion)
  • Water (for all cells)
• Breathing provides oxygen for respiration, but breathing and respiration are not the same thing
• Breathing/gas exchange


  1. Air moves down trachea, bronchi, bronchioles to alveoli

  2. Oxygen diffuses into blood, carbon dioxide diffuses out
• The heart is at the centre of the circulatory system, a double circulatory system
• Blood flow through the heart

  1. Deoxygenated blood enters right atrium

  2. Passes through right ventricle to lungs

  3. Oxygenated blood returns to left atrium

  4. Passes through left ventricle to body
• Blood vessels


  • Arteries carry oxygenated blood away from heart, have thick walls
  • Veins carry deoxygenated blood to heart, have thin walls and valves
• Coronary arteries supply the heart muscle with oxygen and nutrients
• Coronary heart disease


  Blockage of coronary arteries, can cause heart attacks
• Stents


  Tubes inserted into blood vessels to keep them open
• Statins


  Drugs that reduce cholesterol and fatty deposits
• Faulty heart valves


  Can be replaced with artificial ones
• Blood also carries white blood cells and platelets
• Plant organs


  • Leaves (photosynthesis, transpiration)
  • Roots (water and mineral absorption)
  • Stems (transport)