Stem Cells in Animals & Plants (OCR A Level Biology)

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Stem cells in the bone marrow

  • Examples of distinct types of differentiated cell that arise from a common stem cell within bone marrow include:
    • erythrocytes
    • neutrophils
  • Stem cells in bone marrow are multipotent adult stem cells

Erythrocytes

  • Erythrocytes are red blood cells, specialised to aid oxygen transport around the body
  • Red blood cells lack a nucleus so they cannot perform mitosis to give rise to new cells; this means that new erythrocytes develop from bone marrow stem cells in order to maintain the red blood cell count in the blood
  • The process by which erythrocytes arise from stem cells includes changes such as:
    • loss of the nucleus
    • a shape change to form a biconcave disc
    • increased production of haemoglobin protein
    • an increase in membrane flexibility

Erythropoiesis 1, downloadable AS & A Level Biology revision notesErythropoiesis 2, downloadable AS & A Level Biology revision notes

Stem cells in bone marrow differentiate to give rise to erythrocytes

Neutrophils

  • The same stem cells that form erythrocytes also give rise to neutrophils, a type of white blood cell that is specialised to destroy pathogens by phagocytosis
  • Changes that occur as stem cells differentiate into neutrophils include:
    • indentations form in the nucleus, giving it a lobed structure
    • production of hydrolytic enzymes increases
    • lysosomes that contain hydrolytic enzymes accumulate
    • membrane flexibility increases

Meristems

  • Plant stem cells are found in regions where growth is taking place; these tissues are known as meristems
  • Examples of distinct types of differentiated cell that arise from a common stem cell within plant meristems include:
    • xylem
    • phloem
  • The specialised cells that make up xylem and phloem are located in a meristem known as cambium
  • Cambium cells are found between regions of xylem and phloem tissue in plant stems and roots

Cambium meristem, downloadable AS & A Level Biology revision notes

The cells that make up xylem and phloem tissue arise from the same type of stem cell within a meristem known as cambium

Xylem and phloem

  • Xylem cells are specialised to allow the transport of water and minerals; changes that occur when cambium cells differentiate into xylem cells include:
    • the deposition of lignin in cell walls
    • loss of cytoplasm
    • loss of end walls
  • Phloem tissue is specialised to allow the transport of assimilates; changes that allow cambium cells to differentiate into phloem sieve tubes include:
    • a reduction in cytoplasm volume
    • loss of some organelles
    • end walls develop into sieve plates

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Alistair

Author: Alistair

Expertise: Biology & Environmental Systems and Societies

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.