CIE IGCSE BIOLOGY!

• All life consists of cells
• Calculating cell size


  1. Measure image size

  2. Divide by magnification
• Cell types


  • Eukaryotic cells (have a nucleus, e.g. plant and animal cells)
  • Prokaryotic cells (no nucleus, DNA in a ring called a plasmid)
• Subcellular structures


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


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


  Diffusion of water across a semi-permeable membrane
• Osmosis practical


  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
• Digestion


  1. Food physically broken down in mouth

  2. Chemically digested in stomach and small intestine using enzymes and bile
• Tooth structure


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


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


  • Increases with temperature (up to optimum), then decreases as enzyme denatures
  • Affected by pH (optimum pH)
• Food tests


  Iodine (starch), Benedict's solution (sugars), Biuret's reagent (proteins), ethanol (lipids)
• Nutrients needed in a balanced diet

  • Carbohydrates (energy)
  • Fats/lipids (energy)
  • Proteins (growth and repair)
  • Vitamins (health)
  • Minerals (health)
  • Fibre (digestion)
• Breathing and gas exchange

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

  2. Oxygen diffuses into blood, carbon dioxide diffuses out
• Circulatory system


  1. Deoxygenated blood enters right side of heart

  2. Pumped to lungs to be oxygenated

  3. Oxygenated blood enters left side of heart

  4. Pumped to body
• Blood vessels


  • Arteries (thick walls, high pressure)
  • Veins (thin walls, low pressure, valves)
• Coronary arteries supply heart muscle with oxygen, blockage can cause heart attack
• Stents


  Tubes inserted into blood vessels to keep them open
• Statins


  Drugs that reduce cholesterol and fatty deposits
• Faulty heart valves can cause backflow, replaced with artificial ones
• Factors affecting transpiration rate

  • Increased temperature
  • Decreased humidity
  • Increased air movement
• Lack of nitrate ions stunts plant growth, chlorosis is yellowing of leaves due to magnesium deficiency
• Leaf structure


  • Cuticle (waterproof)
  • Upper epidermis (transparent)
  • Palisade mesophyll (photosynthesis)
  • Spongy mesophyll (gas exchange)
  • Vascular bundles
  • Lower epidermis (stomata)
• Types of disease


  • Non-communicable (internal causes, e.g. heart disease, cancer)
  • Communicable (caused by pathogens, e.g. viral, bacterial, fungal, protist infections)
• Carcinogen


  Anything that increases cancer risk, e.g. ionizing radiation
• Benign vs malignant cancers

  Benign don't spread, malignant do spread through the body
• Viruses


  Protein casings with genetic code that infect cells and hijack them to make more copies
• Bacteria


  Release toxins that damage body cells
• Fungi


  Cause infections like athlete's foot
• Protists


  Single-celled parasites, e.g. malaria parasite
• Mosquitoes are the vector for malaria protist
• Virus


  Genetic code that it injects into a cell which causes the cell to produce more copies of the virus, then the cell explodes and the virus goes on to infect more cells
• Measles


  A virus that causes a rash, can be deadly, spread by droplets from sneezes or coughs
• HIV


  An STD/STI that compromises the immune system, also called AIDS, can be spread by sharing needles
• Bacteria


  Release toxins that damage body cells, e.g. salmonella, gonorrhea
• Fungi


  Do something similar to bacteria, e.g. athlete's foot
• Protozoa


  Cause diseases like malaria by burrowing into red blood cells, spread by mosquitoes (vectors)
• Plant pathogens


  Particularly susceptible to fungal infections like rose black spot, also affected by viruses like tobacco mosaic virus