Cells

• Cells


  Building blocks of every organism on the planet
• Organisms


  • Can be Prokaryotes or Eukaryotes
• Facts about cells


  • All living things are made of cells
  • Cells can be either prokaryotic or eukaryotic
  • Eukaryotic cells are complex and include all animal and plant cells
  • Prokaryotic cells are smaller and simpler, e.g. bacteria
• Eukaryotes


  Organisms made up of eukaryotic cells
• Prokaryote


  A prokaryotic cell, a single-celled organism
• Subcellular structures in most animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional subcellular structures in plant cells

  • Rigid cell wall
  • Permanent vacuole
  • Chloroplasts
• Bacterial cells


  • Smaller than eukaryotic cells
  • Don't have a 'true' nucleus, instead have a single circular strand of DNA floating in the cytoplasm
  • May contain small rings of DNA called plasmids
  • Don't have chloroplasts or mitochondria
• Bacterial cells don't have a cell membrane
• You could get asked to estimate the area of a subcellular structure in your exam, and should treat it as a regular shape
• Cell differentiation


  The process by which a cell changes to become specialised for its job
• Most differentiation occurs as an organism develops
• In most animal cells, the ability to differentiate is then lost at an early stage, after they become specialised
• Lots of plant cells don't ever lose the ability to differentiate
• Undifferentiated cells


  Stem cells
• Sperm cells


  • Specialised for reproduction
  • Have a long tail and streamlined head to help swim to the egg
  • Have lots of mitochondria to provide energy
  • Carry enzymes in the head to digest through the egg cell membrane
• Nerve cells


  • Specialised for rapid signalling
  • Long to cover more distance
  • Have branched connections at the ends to connect to other nerve cells and form a network
• Muscle cells

  • Specialised for contraction
  • Long to have space to contract
  • Contain lots of mitochondria to generate energy for contraction
• Root hair cells

  • Specialised for absorbing water and minerals
  • Grow into long "hairs" that stick out into the soil to increase surface area
• Phloem and xylem cells


  • Specialised for transporting substances
  • Form phloem and xylem tubes to transport food and water around plants
  • Phloem cells have very few subcellular structures so substances can flow through
  • Xylem cells are hollow in the centre
• Stem Cells


  Undifferentiated cells that can divide to produce more undifferentiated cells and differentiate into different types of cells
• Embryonic Stem Cells

  • Can turn into any type of cell
  • Found in early human embryos
• Adult Stem Cells


  • Found in certain places like bone marrow
  • Can only turn into certain cell types, not any cell type
• Differentiation


  Process by which a cell changes to become specialised for its job
• Stem cells from embryos and bone marrow

  Can be grown in a lab to produce clones and made to differentiate into specialised cells
• Medicine already uses adult stem cells to cure disease
• Embryonic stem cells could be used to replace faulty cells in sick people
• Therapeutic cloning


  Making an embryo with the same genetic information as the patient so the stem cells produced wouldn't be rejected
• There are risks involved in using stem cells in medicine, like stem cells grown in the lab becoming contaminated with a virus
• Arguments against stem cell research

  • Human embryos shouldn't be used for experiments as each is a potential human life
  • Curing existing patients is more important than the rights of embryos
  • Embryos used are usually unwanted ones from fertility clinics that would be destroyed anyway
  • Scientists should concentrate on finding other sources of stem cells
• Stem cell research is allowed in the UK as long as it follows strict guidelines
• Plant Stem Cells


  • Found in the meristems (parts of the plant where growth occurs)
  • Throughout the plant's life, can differentiate into any type of plant cell
• Plant stem cells can be used to produce clones of whole plants quickly and cheaply
• Plant stem cells can be used to grow crops of identical plants with desired features like disease resistance