IB Biology HL - Cell Biology

• Cell Theory


  All living organisms are made up of one or more cells, cells are the basic functional unit in living organisms, new cells are produced from pre-existing cells
• Cell Theory


  • Cells are surrounded by a membrane, contain genetic material, have chemical reactions occurring within the cell that are catalysed by enzymes
• Atypical examples that question the integrity of the cell theory
• Atypical examples


  • Striated muscle fibres, aseptate fungal hyphae, giant alga (Acetabularia)

  
• Functions of Life


  Metabolism, reproduction, homeostasis, growth, response, excretion, nutrition
• Surface Area to Volume Ratio

  As organisms increase in size, their SA:V ratio decreases, limiting the rate of exchange of substances and metabolic reactions
• Limitations to cell size
• Organisation of Multicellular Organisms

  Cells form tissues, tissues form organs, organs form organ systems, which work together to carry out life functions
• Cell Differentiation


  Specialisation of eukaryotic cells for specific functions, with structural adaptations to carry out those functions
• Specialisation


  Cells are specialised for specific functions. This can also be referred to as the division of labour
• Specialised eukaryotic cells


  • Have specific adaptations to help them carry out their functions
  • The structure of a cell is adapted to help it carry out its function
• Structural adaptations


  • The shape of the cell
  • The organelles the cell contains (or doesn't contain)
• Cells adapted for protein production

  • Contain many ribosomes (the organelle responsible for protein production)
• Erythrocytes


  • The biconcave shape increases the surface area available for oxygen absorption
• Every nucleus within the cells of a multicellular organism contains the same genes, that is, all cells of an organism have the identical genome
• Gene expression


  During differentiation certain genes are expressed ('switched' on)
• Controlling gene expression is the key to development as the cells differentiate due to the different genes being expressed
• Once certain genes are expressed the specialisation of the cell is usually fixed so the cell cannot adapt to a new function
• Stem cell


  A cell that can divide (by mitosis) an unlimited number of times
• Potency


  The ability of stem cells to differentiate into more specialised cell types
• Types of potency


  • Totipotency
  • Pluripotency
  • Multipotency
  • Unipotency
• Totipotent stem cells


  Can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta)
• Pluripotent stem cells


  Are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells (the cells that make up the placenta)
• Multipotent stem cells


  Are adult stem cells that can differentiate into closely related cell types
• Unipotent stem cells


  Are adult cells that can only differentiate into their own lineage
• Most cells in animal bodies are unipotent
• Currently, there are very few therapeutic uses of stem cells, although scientists around the world are actively involved in researching potential therapies
• Use of embryonic stem cells

  Due to their ability to differentiate into multiple cell types, stem cells have huge potential in the therapeutic treatment of disease
• For many countries, such as the USA and some countries within the EU, the use of embryonic stem cells is banned, even for research
• In other countries, such as the UK, the use of embryonic stem cells is allowed for research but is very tightly regulated
• Embryonic stem cells


  Can be totipotent if taken in the first 3-4 days after fertilisation or pluripotent if taken on day 5
• The embryos used for research are often the waste (fertilised) embryos from in vitro fertilisation treatment
• This means these embryos have the potential to develop into human beings, which is why many people have ethical objections to using them in research or medicine
• Stargardt's disease


  The most common inherited form of juvenile macular degeneration that mainly affects children and adolescents
• Treatment for Stargardt's disease


  Injection of retina cells derived from embryonic stem cells into patients' eyes
• Adult stem cells


  Small numbers of stem cells that remain to produce new cells for the essential processes of growth, cell replacement and tissue repair
• Multipotent adult stem cells

  Can only differentiate into a limited range of cell types
• Multipotent adult stem cells

  • Hematopoietic stem cells in bone marrow can only differentiate into blood cells
• Stem cell therapy


  Introduction of adult stem cells into damaged tissue to treat diseases and injuries
• Leukaemia


  A group of cancers that develop in the bone marrow, caused by mutations in genes resulting in the over-production of abnormal white blood cells