Cell Biology

• Eukaryotic cells


  • Have a cell membrane, cytoplasm and genetic material enclosed in a nucleus
• Prokaryotic cells (bacterial cells)


  • Are much smaller in comparison
  • Have cytoplasm and a cell membrane surrounded by a cell wall
  • Genetic material is not enclosed in a nucleus, it is a single DNA loop and may have one or more small rings of DNA called plasmids
• Cell differentiation


  1. As an organism develops, cells differentiate to form different types of cells

  2. Most types of animal cell differentiate at an early stage

  3. Many types of plant cells retain the ability to differentiate throughout life
• Cell division in mature animals


  Is mainly restricted to repair and replacement
• Cell specialisation


  As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function
• Electron microscope


  • Has much higher magnification and resolving power than a light microscope
  • Can be used to study cells in much finer detail
  • Has enabled biologists to see and understand many more sub-cellular structures
• Magnification

  Size of image/size of real object
• Bacterial cell division


  1. Multiply by simple cell division (binary fission)

  2. Can occur as often as once every 20 minutes if they have enough nutrients and a suitable temperature
• Bacterial growth


  • In a nutrient broth solution
  • As colonies on an agar gel plate
• Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics
• Cell cycle


  1. Cells divide in a series of stages

  2. Includes mitosis
• During the cell cycle the genetic material is doubled and then divided into two identical cells
• Cell preparation for division


  1. Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria

  2. The DNA replicates to form two copies of each chromosome
• Mitosis


  1. One set of chromosomes is pulled to each end of the cell

  2. The nucleus divides

  3. The cytoplasm and cell membranes divide to form two identical cells
• Cell division by mitosis


  Is important in the growth and development of multicellular organisms
• Stem cell


  An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation
• Stem cells


  • Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells
  • Stem cells from adult bone marrow can form many types of cells including blood cells
• Meristem tissue in plants


  Can differentiate into any type of plant cell, throughout the life of the plant
• Treatment with stem cells


  May be able to help conditions such as diabetes and paralysis
• Therapeutic cloning


  • An embryo is produced with the same genes as the patient
  • Stem cells from the embryo are not rejected by the patient's body so they may be used for medical treatment
• The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections
• Uses of plant stem cells


  • Rare species can be cloned to protect from extinction
  • Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers
• Diffusion


  The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Substances transported by diffusion


  • Oxygen and carbon dioxide in gas exchange
  • Waste product urea from cells into the blood plasma for excretion in the kidney
• Factors affecting rate of diffusion


  • Difference in concentrations (concentration gradient)
  • Temperature
  • Surface area of the membrane
• Single-celled organism


  • Has a relatively large surface area to volume ratio
  • Allows sufficient transport of molecules into and out of the cell to meet the needs of the organism
• Exchanging materials in multicellular organisms


  • Surfaces and organ systems are specialised
  • To allow sufficient molecules to be transported into and out of cells for the organism's needs
  • Effectiveness increased by: having a large surface area, a membrane that is thin to provide a short diffusion path, (in animals) having an efficient blood supply, (in animals, for gaseous exchange) being ventilated
• Active transport


  • Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient)
  • Requires energy from respiration
• Active transport


  • Allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil
  • Plants require ions for healthy growth