Biology IGCSE Edexcel

• 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
• Cell organelles


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


  Cells specialize to fulfill different functions, e.g. nerve, muscle, root hair, xylem, phloem cells
• Stem cells


  Unspecialized cells that can differentiate into different cell types, found in embryos and meristems of plants
• Cloning plants can be used to prevent species from becoming extinct or produce crops with specific characteristics
• Diffusion


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


  The diffusion of water across a semi-permeable membrane
• Osmosis practical


  1. Cut equal size cylinders from a 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 and find the x-intercept, which is the concentration with no change in mass (same as inside the potato)
• Active transport


  The movement of substances through a membrane against a concentration gradient, using energy
• Tissues


  Groups of similar cells connected and working together
• Organs


  Groups of tissues working together to perform a specific function
• Organ systems


  Groups of organs working together, e.g. circulatory system, digestive system
• Enzymes


  Biological catalysts that speed up chemical reactions without being consumed or permanently altered
• Enzymes


  • They are specific, working on a lock-and-key principle with their substrates
  • Their activity increases with temperature up to an optimum, then decreases as they denature
• Enzyme activity practical


  1. Mix amylase with starch at different temperatures or pH

  2. Every 10 seconds, remove a sample and test with iodine

  3. Time when all starch is broken down

  4. Plot time against temperature or pH and find the optimum
• Nutrients in a balanced diet


  • Carbohydrates
  • Fats/lipids
  • Proteins
  • Vitamins
  • Minerals
  • Fiber
  • Water
• Respiration


  The process that releases energy from food, different from breathing which supplies oxygen for respiration
• Respiratory system


  The system responsible for gas exchange, with air moving through the trachea, bronchi, bronchioles and alveoli
• Circulatory system


  The transport system of the body, with blood entering the heart twice in a double circulatory system
• Blood vessels


  • Arteries carry oxygenated blood away from the heart, have thicker walls
  • Veins carry deoxygenated blood towards the heart, have thinner walls and valves
• Coronary artery


  Supplies the heart muscle with oxygen and nutrients
• Stents


  Tubes inserted into blood vessels to keep them open
• Plant organs


  • Leaves - site of photosynthesis and transpiration
  • Roots - where water and minerals enter
  • Xylem - transport water upwards
  • Phloem - transport food and sap
• Non-communicable diseases


  Diseases caused by factors within the body, e.g. cardiovascular disease, cancer, diabetes
• Communicable diseases


  Diseases caused by pathogens that enter the body, e.g. viral, bacterial, fungal, protist infections
• Carcinogens


  Agents that increase the risk of cancer, e.g. ionizing radiation
• Benign cancers don't spread through the body and are relatively easy to treat, while malignant cancers spread and are much worse
• Viruses can't reproduce by themselves, they inject their genetic code into cells to make the cells produce more copies of the virus
• Bacteria release toxins that damage body cells, e.g. salmonella, gonorrhea
• Fungi and protists also cause diseases in various ways, e.g. athlete's foot, malaria
• Plants are susceptible to fungal infections like rose black spot
• The virus goes on to infect more cells, creepy isn't it
• Measles


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


  An STD or STI (sexually transmitted disease or infection) that compromises the immune system, also called AIDS for short, can be spread by sharing needles