B2 Cell division

  • Created by: msahay
  • Created on: 31-07-17 12:43

B2.1 Cell division

Chromosomes carry genes. Gene= small packet of DNA. Genes control characteristics.

46 chromosomes in human body cell in 23 pairs. One inherited from father, one from mother. Sex cells (gametes) have only 23 chromosomes.

Cell Cycle

Stage 1: Cells grow bigger, mass increased, DNA replicated to form two copies of each chromosome and sub-cellular structures e.g. mitochondria increased.

Stage 2: Mitosis occurs. Chromosomes pulled to each end of cell and nucleus divides.

Stage 3: Cytoplasm and cell membranes divide to form two identical daughter cells.

Important in growth, repair and development of multi-cellular organisms.

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B2.2 Growth and differentiation

Differentiation in animal cells

  • Cell specialisation happens early in life
  • Nerve cells, muscle cells, skin cells
  • Specialised cells have different sub-cellular structures to carry out specific functions
  • Specialised cells able to divide by mitosis to make more of the same cell
  • Adult stem cell replace dead or damaged cells
  • Mature animal = no growth, only repair and replacement of cells

Differentiation in plant cells

  • Plant cells able to differentiate all through life
  • Undifferentiated cells formed in meristems - shoots and roots. Mitosis takes place, cells elongate, then divide.
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B2.3 Stem cells

Embryonic stem cells - undifferentiated (stem) cells from an early embryo that can differentiate to form all specialised cells in the body.

Adult stem cells - undifferentiated (stem) cells that are found in adults that can differentiate and form a limited number of cells.

Embryonic stem cells (from human embryos) and adult stem cells (from adult bone marrow) can be cloned and differentiated into many different types of cell.

Treatment using stem cells = paralysis (nerve cells) and diabetes

Stem cells in plants

Plant meristems contain stem cells. 

Clones can be made quickly and economically

Research, horticulture and agriculture. 

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B2.4 Stem cell dilemmas

Problems with stem cells

  • Stem cells come from aborted and spare embryos. Violation of human rights.
  • Religious believers cannot interfere with human reproduction.
  • Slow, difficult, expensive

Problems with adult stem cells

  • Risk of infection from viruses
  • Cells may be rejected by patient's body.


Using embryonic stem cells from umbilical cord instead of aborted embryos = more ethical

Therapeutic cloning - embryo produced that is genetically identical to patient so can be used in treatment with no rejection from cells.

Stem cells can be used to make special insulin producing cell for diabetics.

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so far I am loving your resources.  A big thank you and

could you pls make a set of revision cards for B3 Organisation and the digestive system or if u have already made it pls send the link to me.

Question:  are u taking the information from the kerboodle digital books? 

If yes is it the combined science: Trilogy book or the student book because they both contain different topics,

THX in advance...


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