AQA 9-1 B2 Cell Division

AQA 9-1 B2 Cell Division

1. B2.1 Cell Division

   • The Cell Cycle
     • Stage 1 : The longest stage in the cell cycle, the cell increases in size, mass and replicates its DNA into 2 chromosomes in preparation for the division.
       • Stage 2 : Mitosis, one set of chromosomes in the cell is pulled to each end of dividing cell and the nucleus divides
         • Stage 3 : Cytoplasm and cell membrane of the cell also divide to form 2 daughter cells
     • Can take several hours or several years
     • Important in growth, repair and development of multicellular organisms

2. B2.2 Growth and Differentiation

   • Differentiation : a cell changes from one cell type (usually a stem cell) to another: Stem cell differentiates into a specialised nerve cell.
     • Animal cells:
       • Cells specialise very early in development and what the stem cells have differentiated into, is permanent.
     • Plant cells:
       • Differentiation in a plant cell can take place at any time in its lifetime, and changes arent permanent, the plant cell can constantly differentiate
         • Occurs in the meristems of a plant, found in the shoot and root tips.
   • in early development of animal cells and plant cells, the cells are unspecialised (stem cells)
   • Specialised cells divide by mitosis
   • Cloning : producing identical offspring
     • Easier to clone plant cells than animal cells due to the early permanent differentiation of stem cells in an embryo whereas in a plant cell, you can easily clone it to the parent cell as the cells are constantly differentiating depending on different factors such as temperature, humidity, pressure

3. B2.3 Stem Cells

   • Function of Stem Cells
     • When a sperm cell fertilises an egg cell, a new singular zygote cell forms, which then divides and appears as a hollow ball of cells. These are embryotic stem cells, the ones which differentiate early in an embryos development
     • Even as an adult, you still have stem cells in different parts of your body (adult stem cells) such as bone marrow, liver, brain and blood.
   • Using Stem Cells
     • Many people are paralyzed in their spine as their nerve cells cannot repair, people with type 1 diabetes need to inject themselves with insulin as specialised cells in their pancreas don't work
       • Of course, these people would benefit if we could repair their damaged bodies
         • We could with stem cells! Scientists could grow completely new organs for transplants, there is much potential for stem cell research.
   • Stem Cells in Plants
     • Stem cells from plants meristems are used to produce new plant clones quickly and economically, usually used for agriculture, research and horticulture.

4. B2.4 Stem Cell Dilemmas

   • Problems With Embryonic Stem Cells
     • Embryonic stem cells usually come from aborted embryos, donated ones or spare embryos. Some feel that this is a violation of human rights as we are taking what is the embryos.
     • Research into stem cells is slow, difficult to control and expensive
     • May cause cancer or pass on infections from donor patient
   • Future of Stem Cells
     • Some scientists found stem cells in the umbilical cord and amniotic fluid which surrounds foetus as it grows, using these stem cells may overcome some ethical concerns
     • Scientists are also finding ways of growing adult stem cells, which is called therapeutic cloning
       • This has huge potential, however is proving difficult for scientists.
       • An embryo is produced with same genes as the patient so the stem cells produced are not rejected and may be used for medical treatment
     • Scientists are attempting to use stem cell research to aid humans in:
       • Spinal cord after injuries
       • Heart damage after heart attack
       • Diabetes
       • Eyesight in the blind
       • Damaged bone and cartilege