cell division.

• DNA.

  material inside the nucleus of cells, carries the genetic information of a living being.
• chromosome.

  • structure made of DNA.
  • codes for all characteristics of an organism.
• human body cell.

  contains 46 chromosomes.

  can be arranged into 23 pairs.

  23rd pair is a sex chromosome.

  females are referred to as XX.

  males are referred to as XY.
• mitosis.

  a type of cell division where a diploid cell copies itself and divides into two identical diploid daughter cells.
• interphase.

  the DNA copies itself ready for mitosis.
• prophase.

  DNA condenses, chromosomes become more visible and the nuclear membrane breaks down.
• metaphase.

  chromosomes and their copies line up in the middle of the cell.
• anaphase.

  chromosomes and their copies are pulled to different ends of the cell.
• telophase.

  new membranes form around the chromosomes at each end of the cell.
• cytokinesis.

  the cell membrane pinches in and eventually divides into two daughter cells.
• diploid cell.

  include 23 pairs of chromosomes.
• diagram of mitosis:

  diagram of mitosis:

  
• meristem.

  produce new cells as they divide.
• differentiation.

  when an unspecialised cell becomes a more specialised cell type.
• circulatory system.

  transport substances, defend the body, regulate temperature.
• muscular system.

  bring about movement.
• nervous system.

  carry messages for the body to work.
• respiratory system.

  deliver oxygen for respiration and remove waste.
• reproductive system.

  bring about fertilisation to produce a new offspring.
• skeletal system.

  bring about movement, support and protect internal structures, produce blood cells.
• palisade mesophyll.

  carry out photosynthesis.
• spongy mesophyll.

  carry out photosynthesis.
• guard cells.

  open and close to control the exchange of gases.
• xylem vessels.

  transport water and dissolved minerals from the roots, up the plant.
• stem cells.


  cells that have not undergone differentiation.

  could be used to replace cells that have been damaged or destroyed, for example: type 1 diabetes.
• embryonic stem cell.


  a type of stem cell found in the embryo.

  can differentiate into a wider range of cell types.
• adult stem cell.


  a type of stem cell found in specific locations in adults.

  differentiate into a narrower range of cell types.
• undifferentiated.

  a cell which has not yet become specialised.
• stem cells in plants.

  stem cells in plants.

  
• potential of stem cells:

  treating patients with currently untreatable conditions.

  growing organs for transplants.

  medical research.
• clinical issues of stem cells:

  no guarantees of how successful the procedure will be.

  difficulty in finding suitable stem cell donors.

  contaminated stem cells could be transferred to the patient.
• nerve cells.

  called neurones and are adapted to carry electrical impulses from one place to another.
• three types of neurone:

  sensory.

  motor.

  relay.
• common features of the neurones:

  long fibre ( axon ) which is insulated by a fatty ( myelin sheath ) that carry messages up and down the body.

  tiny branches ( dendrons ) that receive incoming impulses from other neurones.
• synapse.


  when two neurones meet.
• receptors to effectors.

  receptors to effectors.

  
• KEY FACT.


  stimulus - receptor - coordinator - effector - response.
• receptors.


  groups of specialised cells that detect a change in the environment and stimulate electrical impulses in response.
• organs and their stimulus.

  organs and their stimulus.

  
• effectors.


  produce a specific response to a detected stimulus.