Prokaryotes and eukaryotes

• Eukaryotes


  Plant and animal cells
• All cells


  • Have a cell membrane surrounding cytoplasm containing ribosomes
• Prokaryotes


  • Smaller
  • Genetic material in a loop not enclosed in a nucleus, may also have rings of DNA called plasmids
  • No mitochondria
• Eukaryotes


  • Larger
  • Chromosomes enclosed in a nucleus with no plasmids
  • Have mitochondria
• Animal and plant cell structures


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional plant cell structures


  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Cell differentiation


  As an organism develops, cells differentiate to form different types of specialised cells with structures and adaptations to perform a certain task
• Specialised cell types


  • Root hair cell
  • Palisade cell
  • Xylem cells
  • Phloem cells
  • Nerve cells (neurones)
  • Sperm cell
  • Muscle cell
• Root hair cell


  • Increase surface area for absorption of water and ions
  • Large, permanent vacuole increasing movement of water from soil to cell
  • Contains many mitochondria to release energy for active transport of mineral ions
• Palisade cell


  • Column shaped cells can be packed tightly together at upper surface of leaf
  • Packed with chloroplasts for photosynthesis
• Xylem cells


  • Transport water and minerals through the plant
  • Cells form long thin hollow tubes with walls strengthened with lignin so water is transported easily
• Phloem cells


  • Cell wall has holes like a sieve to allow sugars to move freely between cells
  • Cytoplasm is removed to allow free movement of sugars through the cell
• Nerve cells (neurones)


  • Elongated cells carry impulses over long distances
  • Dendrites can make connections with many other neurones
  • Myelin sheath insulates one axon from another
• Sperm cell


  • Large nucleus contains genetic information from the male parent
  • Long tails allow sperm to swim to the egg
  • The middle section contains many mitochondria to provide the energy to move the tail
  • The acrosome contains digestive enzymes for breaking down the outer layers of the egg
• Muscle cell


  • Elongated cells that contain proteins that can contract
  • Contain many mitochondria to release energy
  • Stores glycogen to release glucose for respiration
• Light microscope


  Has limited magnification and resolving power, can only be used to see the larger structures such as the nucleus
• Electron microscope


  Has much greater magnification and resolving power and can be used to study the smaller structures such as mitochondria and ribosomes
• Magnification formula


  Magnification = size of image / size of actual object
• Micrometres (μm) and nanometres (nm)


  Very small measurements, 1000 nanometres in a micrometre
• Binary fission


  Bacteria multiply by splitting in two, as often as every 20 minutes if the temperature is suitable and they have enough nutrients
• Culturing microorganisms


  Bacteria can be grown in laboratories in a liquid nutrient broth or as colonies on a solid agar plate
• Cell division


  New cells are needed for growth and to replace old, worn out cells. They must contain the same genetic information as the original cells
• Human cell nuclei


  Contain 46 chromosomes (in 23 pairs), each chromosome carries a large number of genes that code for proteins
• Stem cells

  Undifferentiated cells that can divide many times to give rise to many cells of different types, found in early embryos, plant meristem tissue, and adult bone marrow
• Many embryonic stem cells are from aborted foetuses or spare embryos from fertility treatment, which raises ethical issues
• Using stem cells to treat patients can also transmit viruses