Stem cells in animals and plants

• Stem cells


  Undifferentiated/Limited ability to differentiate/partially specialised cells
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
  • Meristems
• Embryonic stem cells


  • Found in the inner cell layer of the embryo
  • Can produce all the different types of specialised cells found in the body
• Adult stem cells


  • Found in bone marrow, skin, liver, brain, etc.
  • Limited ability to differentiate
  • Can produce cells of the blood, skin layers, and other tissues
• Meristems


  • Found at the tips of roots and shoots
  • Undifferentiated cells that can divide to produce a whole new plant
• Multipotent


  Can only differentiate into a limited range of cell types
• Stem cells found in bone marrow are multipotent adult stem cells
• Bone marrow stem cells can differentiate into erythrocytes, monocytes, neutrophils and lymphocytes
• Erythrocytes


  Red blood cells, main function is transport of oxygen and carbon dioxide
• Erythrocytes lack a nucleus, so cannot divide
• Erythropoiesis


  Formation of new erythrocytes from bone marrow stem cells
• Changes during erythropoiesis


  • Cell becomes biconcave shape for greater surface area
  • Haemoglobin builds up in cytoplasm
  • Nucleus and organelles ejected to create more room for haemoglobin
  • Elastic membrane allows squeezing through capillaries
• The same stem cells that form erythrocytes also form neutrophils
• Changes during neutrophil differentiation

  • Nucleus becomes lobed
  • Granules (lysosomes) accumulate
• Neutrophils


  First white blood cells to arrive at an infection site, destroy pathogens by phagocytosis and digestion
• Neutrophil adaptations


  • Flexible shape and nuclear membrane to squeeze between capillary walls
  • Many lysosomes containing digestive enzymes
• Xylem


  Plant transport system for water and minerals
• Phloem


  Plant transport system for food (sugars)
• Cambium


  Undifferentiated tissue between xylem and phloem that contains stem cells
• Differentiation of cambium cells

  1. Inner cells become xylem, outer cells become phloem

  2. Xylem cells lose cytoplasm and deposit lignin

  3. Phloem cells lose some cytoplasm and organelles, develop sieve plates
• Hormones stimulate the differentiation of cambium cells into xylem or phloem