Paper 1 Biology

• Cells


  Can be seen with a normal light microscope, but subcellular structures are not visible. Electron microscopes have better resolving power and resolution to see finer details.
• Cell size


  Can be calculated by knowing the magnification of the microscope: Magnification = Image size / Object size
• Cell types


  • Eukaryotic cells (have a nucleus)
  • Prokaryotic cells (no nucleus, DNA in a ring called a plasmid)
• Eukaryotic and prokaryotic cells


  • Contain similar organelles or subcellular structures
• Cell membrane


  • Keeps everything inside the cell, semi-permeable to allow certain substances to pass through
• Plant cells and most bacteria

  • Have an extra cell wall made of cellulose, providing a rigid structure
• Cytoplasm


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


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


  • Where proteins are assembled or synthesized
• Plant cells


  • Contain chloroplasts with chlorophyll, where photosynthesis takes place
  • Contain a permanent vacuole to store sap
• Bacterial multiplication


  1. Binary fission, number doubles every 10 minutes

  2. Can be demonstrated through a practical using agar in a Petri dish and aseptic technique
• Eukaryotic cell nuclei


  • Contain DNA stored in several chromosomes, humans have 23 pairs (diploid cells)
  • Gametes have half the number of chromosomes (haploid cells)
• Cell division


  Mitosis: Genetic material is duplicated, nucleus breaks down, one set of chromosomes pulled to opposite sides, new nuclei form, resulting in two identical cells
• Cell specialization


  • Cells specialize depending on their function, e.g. nerve, muscle, root hair, xylem, phloem, stem cells
• Stem cells


  Unspecialized cells that can differentiate into various cell types, found in embryos and bone marrow
• 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, from an area of high water concentration to an area of low water concentration
• Factors affecting diffusion and osmosis


  Increased difference in concentrations, increased temperature, increased surface area
• Practical on osmosis


  Cut equal size cylinders from a vegetable, weigh, place in varying sugar solutions, reweigh after a day, calculate percentage change in mass, plot against sugar concentration to find no change point
• Active transport


  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, digestive
• Enzymes


  Biological catalysts that speed up chemical reactions, specific to certain substrates due to the lock and key principle
• Factors affecting enzyme activity


  • Increased temperature increases rate until optimum, then denaturation occurs
  • Optimum pH, too high or too low can also denature
• Practical on enzyme activity


  Mix amylase and starch at different temperatures or pH, time how long for starch to be broken down, plot against temperature/pH to find optimum
• Food tests


  Iodine for starch, Benedict's solution for sugars, Biuret's reagent for proteins, ethanol for lipids
• Breathing vs respiration


  Breathing provides oxygen for respiration to occur in cells
• Respiratory system

  • Air moves down trachea, bronchi, bronchioles to alveoli for gas exchange
  • Oxygen binds to hemoglobin in red blood cells and is transported to cells
  • Carbon dioxide and water are expelled
• Circulatory system


  • Double circulatory system, deoxygenated blood enters right side of heart, pumped to lungs, oxygenated blood returns to left side and is pumped to body
  • Arteries carry oxygenated blood, veins carry deoxygenated blood
  • Capillaries allow fast diffusion
• Heart


  • Muscle that needs its own blood supply via coronary arteries
  • Faulty valves can cause backflow, treated with artificial valves
  • Blocked arteries can cause heart attacks, treated with stents
• Cardiovascular disease


  Example of a non-communicable disease, caused by factors within the body, unlike communicable diseases
• Coronary artery

  Delivers blood to the heart muscle to supply oxygen