Cell biology

• Eukaryotic cells


  Plant and animal cells
• Differences between eukaryotic and prokaryotic cells


  • Prokaryotic cells are much smaller than eukaryotic cells
  • Eukaryotic cells contain membrane bound-organelles and a nucleus containing genetic material, while prokaryotes do not
• Prokaryotic cell wall


  Composed of peptidoglycan
• Genetic information storage in prokaryotic cells

  Found free within the cytoplasm as: Chromosomal DNA (single large loop of circular DNA), Plasmid DNA
• Plasmids


  Small, circular loops of DNA found free in the cytoplasm and separate from the main DNA, carry genes that provide genetic advantages e.g. antibiotic resistance
• Order of magnitude


  A power to the base 10 used to quantify and compare size
• Nanometre (nm)


  1 x 10-9 metres
• Components of both plant and animal cells


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional cell components found in plant cells


  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Function of the nucleus (other than storing genetic information)

  Controls cellular activities
• Structure of the cytoplasm

  Fluid component of the cell, contains organelles, enzymes and dissolved ions and nutrients
• Function of the cytoplasm


  Site of cellular reactions e.g. first stage of respiration, Transport medium
• Function of the cell membrane


  Controls the entry and exit of materials into and out of the cell
• Function of the mitochondria


  Where most of the reactions for aerobic respiration occur
• Function of the ribosomes

  Synthesises proteins
• Function of the plant cell wall


  Provides strength, Prevents the cell bursting when water enters by osmosis
• Contents of the permanent vacuole


  Cell sap (a solution of salts, sugars and organic acids)
• Function of the permanent vacuole


  Supports the cell, maintaining its turgidity
• Function of chloroplasts


  Site of photosynthesis
• Adaptations of muscle cells in animals


  • Arrangement of protein filaments allows them to slide over each other to produce muscle contraction
  • Mitochondria to provide energy for muscle contraction
  • lots of mitochondria to provide energy for muscle contraction
• Adaptations of root hair cells in plants

  • Large surface area to absorb nutrients and water from surrounding soil
  • Thin walls that do not restrict water absorption
• Adaptations of xylem cells in plants

  • No end walls to provide a continuous flow of water and no internal structures to make it easier for water and minerals to flow
  • walls contain lignin to give strength and support to the plant
• Adaptations of phloem cells in plants


  • Sieve plates let dissolved amino acids and sugars be transported up and down the stem
  • Companion cells provide energy needed for active transport of substances along the phloem
• Cell differentiation


  The process by which cells become specialised
• Importance of cell differentiation


  Allows production of different tissues and organs that perform various vital functions in the human body
• Timing of cell differentiation in animal cells


  Early in their life cycle
• Timing of cell differentiation in plant cells


  Throughout their entire life cycle
• Purpose of cell division in mature animals


  Repair and replacement of cells
• Changes a cell goes through as it differentiates


  Becomes specialised through acquisition of different sub-cellular structures to enable a specific function to be performed by the cell
• Magnification


  The number of times bigger an image appears compared to the size of the real object
• Cell division in mature animals


  Repair and replacement of cells
• Cell differentiation


  Cells become specialised through acquisition of different sub-cellular structures to enable a specific function to be performed
• Resolution


  The smallest distance between two objects that can be distinguished
• How a light microscope works


  Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed
• Advantages of light microscopes


  • Inexpensive
  • Easy to use
  • Portable
  • Observe both dead and living specimens
• Disadvantage of light microscopes


  Limited resolution
• How an electron microscope works


  It uses a beam of electrons which are focused using magnets. The electrons hit a fluorescent screen which emits visible light, producing an image
• Types of electron microscope


  • Transmission electron microscope (TEM)
  • Scanning electron microscope (SEM)
• Advantage of electron microscopes


  Greater magnification and resolution
• Electron microscopes have greater magnification and resolution because they use a beam of electrons which has a shorter wavelength than photons of light