Specialised cells and that

• Stem Cell


  • unspecialised cells
  • can differentiate into different types of cells -> differentiation
  • animals - placing damaged cells
  • plants - new shoots and roots, xylem, phloem
  • they can divide themselves
• Bone marrow:


  • bones - living organs that contain nerves and blood vessels
  • marrow in their centres - adult stem cells divide and differentiate into erythrocytes and neutrophils that need replacing
• Meristem:


  • meristems - growth takes place in plants
  • where stem cells are found in plants
  • in the root and stem
  • stem cells of the vascular cambium divide and differentiate into xylem vessels and phloem sieve tubes
• Embryos:


  • taken from the morula (16 cell) stage
  • before a blastocyst is formed as differentiation occurs after the this stage
  • embryonic stem cells
• Differentiation of cells

  1. Totipotent - can differentiate into any type of cell, a person and the cells for during pregnancy (e.g. zygote)
  2. Pluripotent - can differentiate into any type of cell for the body, could make a person (e.g. embryonic stem cells)
  3. Multipotent - (e.g. adult/blood stem cells)
  4. Unipotent - have one specific job (e.g. erythrocytes)
• Differentiation of cells

  • more specialised a cell, the greater the restriction in their potential
  • differentiation occurs after the blastocyst stage, after the morula (16 cell stage)
• Stem cells - treating disease

  • replacement of damaged tissues
  • Alzheimer's - nerve cells in brain die, severe memory loss
  • Parkinson's - loss of nerve cells in brain that release dopamine that controls movement, causing tremors
  • Developmental biology - how organisms grow and develop, developmental disorders and cancer
• For stem cell research:

  • can develop treatment - would be unethical to not develop
  • 'spare' embryos from IVF would have been destroyed anyway
  • organs for transplants are in short supply
  • good for research to happen under supervision, to receive scrutiny and regulation
• Against stem cell research:

  • religious/cultural objections due to rights of an embryo
  • may cause infection or immune response if transferred
  • may have unforeseen consequences in recipients (e.g. uncontrollable growth)
  • women may be put under pressure to provide eggs
• Specialised cell - PALISADE MESOPHYLL CELLS


  • in leaves
  • many chloroplasts for photosynthesis
  • thin walls, easy for CO2 to diffuse
• Specialised cell - ROOT HAIR CELLS

  • absorb water and mineral ions from the soil
  • large surface area for absorption
  • thin, permeable cell wall
  • extra mitochondria for active transport
  • no chloroplasts as underground
• Specialised cell - GUARD CELLS


  • found in pairs, with a gap between them (stoma)
  • form tiny pores used for gas exchange
  • when LIGHT, guard cells take up water, becoming turgid, thin outer walls and thick inner walls, open up stomata, allow gas exchange
  • TURGID - OPEN
  • FLACCID - CLOSED
• Specialised cell - NEUTROPHILS


  • defend from disease
  • flexible shape allows them to engulf foreign particles/pathogens
  • lysosomes contain digestive enzymes to break down pathogens
• Specialised cell - ERYTHROCYTES


  • carry oxygen
  • biconcave disc - large SA for gas exchange
  • no nucleus - more room for haemoglobin to carry oxygen
• Specialised cell - EPITHELIAL CELLS


  • cover organ surfaces
  • interlink membranes
  • ciliated epithelia (airways) - cilia that beat to move mucus and particles away
  • squamous epithelia (lungs) are very thin to allow efficient diffusion
• Specialised cell - SPERM CELLS

  • flagellum to swim to the egg
  • mitochondria to provide energy to swim
  • acrosome - digestive enzymes to penetrate egg's surface
• TISSUE


  Group of cells (+ any extracellular materials secreted by them) are specialised to work together to carry out a particular function
• Cartilage - tissue


  • connective tissue in joints
  • shapes and supports the nose and wind pipe
• Muscle tissues

  • bundles of elongated cells
  • smooth (stomach wall)
  • cardiac (heart)
  • skeletal (to move)
• Ciliated epithelium - tissue


  • layer of cells covered in cilia
  • surfaces which need movement (trachea - waft mucus along)
• Epithelial cells - cover the surface of the body and lines internal cavities

  • squamos
  • columnar
  • ciliated
  • cuboidal
• Epithelial - SQUAMOS

  • thin and flat
  • fluid flows over easily, low resistance
  • thin, good for diffusion
  • e.g. skin, lining blood vessels, lungs
• Epithelial - COLUMNAR

  • tall and thin
  • can secrete mucus
  • e.g. lines stomach and intestines
• Epithelial - CILIATED

  • line air passages
  • beat rhythmically to move mucus
  • can be damaged by smoking and pollution
• Epithelial - CUBOIDAL

  • look like cubes who would have guessed
  • line glands and ducts