differentiation and specialisation + chromosomes and mitosis

• Differentiation is when a cell..

  changes to specialise for a job
• undifferentiated cells are called..

  stem cells
• In mature animals differentiation is mainly in blood or skin cells as repair and replacement.
• Why is differentiation needed?

  For growth, repair and replacement
• Name examples of specialised cells.

  Sperm cells

  Nerve cells

  Muscle cells

  Root hair cells

  Phloem and xylem cells
• How are sperm cells specialised for function?

  long tail for swimming

  streamlined head

  lots of mitochondria

  carries enzymes in head to digest egg cell membrane
• What do sperm cells take part in?

  reproduction
• How are nerve cells specialised for function?

  long

  carry electrical signals

  branched connections to form networks
• How are root hair cells specialised for function?

  long hairs

  large surface area for fast absorption
• How are phloem + xylem cells specialised for function?

  xylem = hollow

  phloem = very little sub-cellular structures
• How are muscle cells specialised for function?

  contract quick

  long

  lots of mitochondria for energy
• chromosomes contain..

  genetic information
• The nucleus contains genetic material in the form of chromosomes
• Chromosomes are coiled up lengths of DNA molecules
• Body cells normally have two copies of each chromosome, one from each parent.
• There are 23 pairs of chromosomes in a human cell
• The cell cycle makes new cells for growth, development and repair
• Mitosis is used to grow or replace cells that have been damaged
• The stage of the cell cycle where the cell divides is called mitosis
• The end of the cell cycle results in two new cells identical to the original cell
• In a cell that is not dividing, DNA is all spread out in long strings
• Describe mitosis

  cell increases subcellular structures

  cell duplicates DNA

  chromosomes line up at centre

  cell fibres pull DNA to each cell pole

  membranes form around each DNA set forming nuclei

  cytoplasm and cell membrane divide
• prokaryotic cells replicate by binary fission
• In binary fission the cell splits in two
• Describe binary fission

  The circular DNA and plasmids replicate

  the cell gets bigger and DNA moves to opposite poles

  cytoplasm begins to divide forming new cell walls

  cytoplasm divides and two daughter cells are produced

  (each daughter cell has one DNA copy but varying plasmids)
• What conditions do bacteria need for quick division?

  warmth

  lots of nutrients
• Use mean division time to find the number of bacteria in a population
• The mean division time is the average amount of time it takes for one bacterial cell to divide into two.
• number of bacteria cell divisions = total time / mean division time
• Give the definition of differentiation.

  When a cell changes to become specialised for it's job.
• In most animal cells, the ability to differentiate is lost at an early stage, after they become specialised.
• Undifferentiated cells are called..

  Stem cells