Cell Biology

• Order of magnitude


  A power to the base 10 used to quantify and compare size
• Difference in order of magnitude between a human hair (length = 100 µm) and the HIV virus (length = 100 nm)

  100 µm = 10-4 m, 100 nm = 10-7 m, -4-(-7) = -4 + 7 = 3
• Additional cell components found in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Adaptations of sperm cells in animals

  • Haploid nucleus contains genetic information
  • Tail enables movement
  • Mitochondria provide energy for tail movement
  • Acrosome contains enzymes that digest the egg cell membrane
• Adaptations of nerve cells in animals

  • Long axon allows electrical impulses to be transmitted all over the body from the central nervous system
  • Dendrites from the cell body connect to and receive impulses from other nerve cells, muscles and glands
  • Myelin sheath insulates the axon and speeds up the transmission of impulses along the nerve cell
• Chromosomes


  DNA molecules combined with proteins that contain genes which provide the instructions for protein synthesis
• 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
  • Merged cells in skeletal muscle allow muscle fibre contraction in unison
• Gene


  A section of DNA which codes for a protein
• 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
• The nucleus of human body cells contains 46 chromosomes
• Adaptations of xylem cells in plants

  • No upper or lower margins between cells to provide a continuous route for water to flow
  • Thick, woody side walls strengthen their structure and prevent collapse
• The nucleus of gametes contains 23 chromosomes
• 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
• Arrangement of chromosomes in body cell nucleus

  Arranged in pairs - 46 chromosomes form 23 pairs
• Timing of cell differentiation in animals

  Early in their life cycle
• Timing of cell differentiation in plants


  Throughout their entire life cycle
• Diffusion


  The net movement of particles from an area of higher concentration to an area of lower concentration
• Purpose of cell division in mature animals


  Repair and replacement of cells
• Factors affecting rate of diffusion

  • Concentration gradient - larger gradient, faster diffusion
  • Temperature - higher temperature, faster diffusion
  • Surface area - larger surface area, faster diffusion
• Substances transported by diffusion

  • Lungs: oxygen, carbon dioxide
  • Kidney: urea
• Changes during cell differentiation


  Becomes specialised through acquisition of different sub-cellular structures to enable a specific function to be performed by the cell
• Adaptations of single-celled organisms for diffusion

  • Large surface area to volume ratio - maximises the rate of diffusion of molecules to meet the organism's needs
• Stem cell


  An unspecialised cell which is capable of differentiating into other cell types and of self-renewal
• Magnification


  The number of times bigger an image appears compared to the size of the real object
• Calculating surface area to volume ratio

  1. Surface Area = Number of Sides x (Side Length x Side Width)

  2. Volume = Length x Width x Depth

  3. Ratio = Surface Area:Volume
• Function of embryonic stem cells

  • Can replicate themselves and differentiate into many other types of cells
  • May be able to treat conditions such as paralysis and diabetes by dividing to replace damaged cells
• Function of adult stem cells in bone marrow

  • Can differentiate into several cell types to replace dead or damaged tissues, eg. form different types of blood cell
• Factors increasing effectiveness of gas exchange surface

  • Large surface area
  • Thin membrane (short diffusion path)
  • Efficient blood supply (animals)
  • Ventilation (animals)
• Osmosis


  The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Cell division in mature animals

  Repair and replacement of cells
• Function of stem cells in plant meristems


  • Retain the ability to differentiate into any type of plant cell throughout their lifespan - they can differentiate into any cell which is required by the plant
• Isotonic solution


  The concentrations of the external and internal (inside cell) solutions are the same
• Hypertonic solution


  The concentration of the external solution is higher than that of the internal solution (inside cell)
• Cell differentiation


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


  A cloning method where an embryo is produced with the same genetic makeup as the patient, so the stem cells will not be rejected by the patient's immune system and can be used to treat certain medical conditions
• Hypotonic solution


  The concentration of the external solution is lower than that of internal solution (inside cell)
• Advantages of cloning plants using meristem stem cells

  • Can prevent rare plants from becoming extinct
  • Can produce large numbers of plants with a favourable characteristic
  • Can produce identical plants for research
• Animal cell in very hypotonic solution


  Water moves into the cell, causing it to burst