Cell Biology

• Cell


  Basic unit of all forms of life
• Cells


  • Structural differences between types of cells enables them to perform specific functions within the organism
  • Differences in cells are controlled by genes in the nucleus
  • For an organism to grow, cells must divide by mitosis producing two new identical cells
  • If cells are isolated at an early stage of growth before they have become too specialised, they can retain their ability to grow into a range of different types of cells

  
• Stem cell technology


  A new branch of medicine that allows doctors to repair damaged organs by growing new tissue from stem cells
• Eukaryotic cells


  Plant and animal 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, and the genetic material is not enclosed in a nucleus
• Parts of animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional parts of plant cells

  • Chloroplasts
  • Permanent vacuole filled with cell sap
  • Cell wall made of cellulose
• Specialised cells


  • Sperm cells, nerve cells and muscle cells in animals
  • Root hair cells, xylem and phloem cells in plants

  
• Electron microscope


  Has much higher magnification and resolving power than a light microscope, enabling the study of cells in much finer detail
• Magnification


  Size of image / size of real object
• Bacteria


  • Multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature
  • Can be grown in a nutrient broth solution or as colonies on an agar gel plate
  • Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics
• Aseptic technique


  • Petri dishes and culture media must be sterilised before use
  • Inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame
  • The lid of the Petri dish should be secured with adhesive tape and stored upside down
  • Cultures should generally be incubated at 25°C in school laboratories
• Chromosomes


  Made of DNA molecules, each carrying a large number of genes, normally found in pairs in body cells
• Cell cycle


  1. Genetic material is doubled and then divided into two identical cells

  2. Cell needs to grow and increase the number of sub-cellular structures before division

  3. DNA replicates to form two copies of each chromosome

  4. In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides

  5. Cytoplasm and cell membranes divide to form two identical cells

  
• Stem cell


  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


  • Can divide to produce new cells, which can then divide into different cell types
  • Have the potential to be transplanted into patients to treat medical conditions and disease
  • 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
• Therapeutic cloning


  An embryo is produced with the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body and may be used for medical treatment
• Potential risks of stem cell use

  • Transfer of viral infection
  • Ethical or religious objections
• Cloning of plants using 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 in and out of cells by diffusion

  • Oxygen
  • Carbon dioxide
  • Urea
• Factors affecting rate of diffusion

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


  • Have a relatively large surface area to volume ratio, allowing sufficient transport of molecules into and out of the cell to meet the needs of the organism
• Multicellular organisms


  • Surfaces and organ systems are specialised for exchanging materials, to allow sufficient molecules to be transported into and out of cells for the organism's needs
  • Effectiveness of an exchange surface is increased by having a large surface area, a thin membrane to provide a short diffusion path, an efficient blood supply, and being ventilated
• Specialised exchange surfaces


  • Small intestine has a large surface area with villi for nutrient absorption
  • Lungs have alveoli for gas exchange
  • Fish use gills to extract oxygen from water
  • Plants have roots for water and mineral absorption and leaves for gas exchange
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane - the movement of water particles from an area of high water potential to an area of low water potential across a partially permeable membrane
• Active transport


  Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient), requiring energy from respiration
• Active transport in plants and animals

  • Allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil
  • Allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration
• Sports drinks


  • Designed to help replace water, salts (ions/electrolytes) and glucose lost from the body during exercise
  • Isotonic sports drinks contain similar concentrations of salt and sugar (glucose) as the human body and are primarily used for hydration and fluid replacement
  • Hypertonic sports drinks contain concentrations of salt and sugar higher than typical blood levels, providing high salt and sugar levels for absorption from the small intestine during intense physical exercise
  • Hypotonic sports drinks contain concentrations of salt and sugar lower than typical blood levels, creating a concentration gradient that draws water into the bloodstream by osmosis for rapid rehydration