B1 - Cell Biology

• Prokaryotes


  Simpler, single-celled organisms
• 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 chloroplasts or mitochondria
  • Have a single circular strand of DNA in the cytoplasm
  • May contain plasmids
• Microscopy


  Techniques that allow us to see things we can't see with the naked eye
• Light microscopes


  • Use light and lenses to form an image and magnify it
  • Allow us to see individual cells and large subcellular structures
• Electron microscopes


  • Use electrons instead of light to form an image
  • Have much higher magnification and resolution than light microscopes
  • Allow us to see smaller structures like mitochondria, chloroplasts, ribosomes, and plasmids
• Magnification


  The ratio of the image size to the real size of an object
• Using a light microscope

  1. Clip slide onto stage

  2. Select lowest-powered objective lens

  3. Use coarse adjustment to move stage up

  4. Look through eyepiece and use coarse adjustment to roughly focus

  5. Use fine adjustment to get clear image

  6. Swap to higher-powered lens to see greater magnification
• Standard form


  A way to write very big or small numbers with a decimal and a power of 10
• Preparing a slide to view onion cells

  1. Add drop of water to slide

  2. Use tweezers to peel off epidermal tissue from onion

  3. Place tissue in water

  4. Add drop of iodine stain

  5. Carefully lower cover slip over specimen
• Stains are used to highlight objects in a cell by adding colour to them
• Drawing microscope observations


  • Use a pencil and take up at least half the space
  • Don't include colouring or shading
  • Draw subcellular structures in proportion
  • Include title and magnification
• Differentiation


  The process by which a cell changes to become specialised for its job
• Most differentiation occurs as an organism develops, and in mature animals the ability to differentiate is then lost
• Plant cells often don't lose the ability to differentiate
• Examples of specialised cells

  • Sperm cells
  • Nerve cells
  • Muscle cells
  • Root hair cells
  • Phloem and xylem cells
• Chromosomes


  • Coiled up lengths of DNA molecules
  • Each chromosome carries many genes
  • Body cells normally have two copies of each chromosome, one from each parent
• Cell cycle


  The series of stages that body cells go through to divide and produce new cells
• Phloem cells


  • Hollow in the centre
  • Very few subcellular structures, so stuff can flow through them
• Phloem


  A tissue in plants that transports food
• Xylem


  A tissue in plants that transports water
• Chromosomes contain genetic information
• Chromosomes


  • Coiled up lengths of DNA molecules
  • Each chromosome carries a large number of genes that control the development of different characteristics
• Body cells normally have two copies of each chromosome, one from the organism's 'mother', and one from its 'father'
• The diagram shows the 23 pairs of chromosomes from a human cell
• The cell cycle


  1. Growth & DNA replication

  2. Mitosis
• Mitosis


  • The stage of the cell cycle when the cell divides
  • Multicellular organisms use mitosis to grow or replace cells that have been damaged
  • Results in two new cells identical to the original cell, with the same number of chromosomes
• Growth & DNA replication

  1. DNA is all spread out in long strings

  2. Cell grows and increases subcellular structures

  3. DNA is duplicated and forms X-shaped chromosomes
• Mitosis


  1. Chromosomes line up at the centre of the cell

  2. Cell fibres pull the chromosomes apart, with the two arms going to opposite ends

  3. Membranes form around each set of chromosomes to become the nuclei of the two new cells

  4. Cytoplasm and cell membrane divide to produce two new daughter cells
• Stem cells


  Undifferentiated cells that can divide to produce more undifferentiated cells and differentiate into different types of cell
• Stem cells are found in early human embryos and have the potential to turn into any kind of cell
• Adults also have stem cells, but they're only found in certain places like bone marrow and can't turn into any cell type
• Stem cells from embryos and bone marrow can be grown in a lab to produce clones and made to differentiate into specialised cells