B 2.3 - CELL SPECIALISATION

• What is fertilization?


  the fusion of a male and female gamete to produce a single cell
• what happens in multicellular organisms after fertilisation

  cell divides repeatedly to generate an embryo of may cells
• what does mitosis ensure


  the cells in an embryo are all genetically identical (they have all genes in the organism's genome and could develop in any way)
• are cells specialised in the early-stage embryo

  cells are unspecialized but as they develop they become specialized
• what do specialized cells allow

  each cell to carry its functions out more efficiently than if it had multiple roles
• why are specialised cells useful

  allows the cell to develop the ideal structure, with enzymes needed to carry out all the chemical reactions associated with its functions
• What is differentiation?

  The process by which a cell changes to become specialised for its job
• What is gene expression?

  the process by which DNA directs protein synthesis
• why does cell differentiation happen

  because a different sequence of genes is expressed in different cell types
• what determines which pathway a cell embryo takes

  position of a cell in the embryo; gradients of signalling chemicals indicate a cell's position in the embryo
• why have stem cells been researched extensively

  role in development and because they have many potential therapeutic or regenerative uses
• how many times can stem cells divide

  repeatedly
• What is a stem cell?

  a cell that can differentiate and become any type of human cell (undifferentiated cell)
• where are stem cells present

  in many human tissues e.g. bone marrow, skin and liver
• What is a stem cell niche?

  The conditions around a stem cell that cause it to form a particular tissue
• what does bone marrow and hair follicles stem cell niche allow

  continuous stem cell proliferation and differentiation (production of replacement blood cells and in hair growth)
• why are stem cell niches of research interest

  if they can be simulated outside the body for a particular stem cell type, it should be possible to generate human tissue in vitro and use it in restorative surgery
• what can stem cells be used for in human consumption

  can be used to produce large quantities of striated muscle fibres for human consumption (meat)
• What does totipotent mean?

  can form any cell in the body (early embryos are composed of totipotent cells)
• why are totipotent embryonic stem cells useful?

  can be useful in the growth of while replacement hearts, kidneys or/and other organs
• What are pluripotent stem cells?

  stem cells with the ability to differentiate to many, but not all tissues types (happens during embryo development)
• What are multipotent stem cells?

  They are more limited but have abilities to differentiate into many different types of cells (stem cells in adult body which have restricted potential)
• what is one way cells are adapted to preform specific functions?

  size of a mature differentiated cell
• what is the evidence for this in humans? - size being a factor contributing to specialisation

  sperm, egg, red blood cells, white blood cells and cerebellar granule cells
• Sperm cells adaptations

  50um long but is narrow thus giving it a small volume to reduce resistance and allowing sperm to swim to the egg more easily
• Egg cells' adaptations

  110um in diameter and spherical, giving it a large volume allowing large quantities of food reserves to be stored in the cytoplasm
• red blood cells adaptions

  6-8 um in diameter but indented in both sides to allow for a large surface area to volume ratio, increasing the volume of oxygen carries, loading and unloading of oxygen and allowing movement in capillaries
• white blood cells adaptions

  B-lymphocytes are 10um in diameter when inactive but enlarge to as much as 30um when activated; extra volume is cytoplasm with rER and golgi apparatus for protein synthesis
• cerebellar granule cells adaptations

  the cell body is only 4.0 um in diameter but have twin axons extended for 3mm (small volume of neurons allow cerebellum to accommodate 50 billion - 75% of brain neurons)
• what occurs in the cytoplasm of the cells

  many chemical reactions take place - metabolism of the cell
• what is the rate of reaction like in cells

  proportional to the volume of the cell
• what must happen for metabolism to continue


  substances used int he reaction must be absorbed by the cell and waste products must be removed
• surface area to volume ratio equation

  surface area (mm2) // volume (mm3)
• Why is SA:V ratio important?

  waste products, size, heat production
• SA:V - waste products

  waste products will accumulate because they are produced more rapidly than can be excretes - size also effects this
• SA:V - size

  if too small substances will enter and leave the cells slower than required, leading to build up of metabolic waste
• SA:V - heat production


  if ratio too small then cells may overheat due to metabolism producing heat faster than it is lost in the cell
• adaptions to increase SA:V ratio - red blood cells

  small shape and size of RBC allow for large SA:V ration allowing O2 to be loaded and unloaded rapidly
• adaptions to increase SA:V ratio - Proximal convoluted tubule cells

  have two membranes which are adapted for the function of reabsorption (basal membrane and apical membrane)
• basal membrane


  Side of cell facing underlying cells and have infoldings in membrane along with proteins to increase SA