Biology (Paper 1)

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotes


  Cells that lack a nucleus and membrane-bound organelles
• Components of animal and plant cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• Orders of magnitude


  A way to understand how much bigger or smaller one object is compared to another
• Prefixes to show multiples of units

  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• Structures in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional structures in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures in bacterial cells

  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA
  • Plasmids
• Cell specialization


  The process where cells gain new sub-cellular structures to be suited to their role
• Specialized animal cells


  • Sperm cells
  • Nerve cells
  • Muscle cells
• Specialized plant cells


  • Root hair cells
  • Xylem cells
  • Phloem cells
• Cell differentiation


  The process where stem cells switch on/off genes to produce specialized cells
• In animals, most cells differentiate early and lose ability to differentiate later
• In plants, many cell types retain ability to differentiate throughout life
• Light microscope


  Has two lenses (objective and eyepiece), magnifies up to x2000, resolving power of 200nm
• Electron microscope


  Uses electrons instead of light, magnifies up to x2,000,000, resolving power of 10nm (SEM) and 0.2nm (TEM)
• Magnification of light microscope = magnification of eyepiece x magnification of objective
• Size of object = size of image / magnification
• Culture medium


  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• Ways to grow microorganisms in the lab

  • In nutrient broth solution
  • On agar plates
• Culturing microorganisms


  • Microorganisms are very small, so scientists need to grow many of them in the lab using nutrients
• Culture medium


  Contains carbohydrates for energy, minerals, proteins and vitamins
• Growing microorganisms in nutrient broth

  Make a suspension of bacteria, mix with sterile nutrient broth, stopper with cotton wool, shake regularly to provide oxygen
• Growing microorganisms on agar gel plate


  1. Pour hot sterilised agar jelly into a sterilised Petri dish, let it cool and set

  2. Dip inoculating loops in microorganism solution and spread over agar

  3. Tape lid on and incubate for a few days
• Petri dishes and culture media must be sterilised before use, often by autoclave or UV light
• Inoculating loops must be sterilised by passing through a flame
• Petri dish lid should be sealed but not completely to allow oxygen
• Petri dish should be stored upside down to prevent condensation
• Culture should be incubated at 25 degrees to prevent growth of harmful bacteria
• Testing antibiotic effectiveness


  1. Soak paper discs in different antibiotics and place on agar plate with bacteria

  2. Leave plate at 25 degrees for 2 days

  3. Measure zone of inhibition around discs to see antibiotic effectiveness
• Inhibition zone


  The clear area left when bacteria die around an antibiotic disc
• Need to calculate cross-sectional areas using πr^2 formula
• Chromosomes


  Contain coils of DNA, with each chromosome carrying many genes
• There are 23 pairs of chromosomes in each body cell, and 23 chromosomes in each sex cell
• Cell cycle and mitosis

  1. Interphase: cell grows, organelles increase, DNA replicates

  2. Mitosis: chromosomes line up at equator, cell fibres pull them to each side

  3. Cytokinesis: two identical daughter cells form
• Importance of mitosis


  • Growth and development, replacing damaged cells, asexual reproduction
• Stem cells


  Undifferentiated cells that can divide to produce more similar cells, some of which will differentiate
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
  • Meristems in plants
• Therapeutic cloning


  Producing an embryo with the same genes as the patient, to obtain embryonic stem cells that could be grown into needed cells/tissues