Biology

• Prokaryotes


  Organisms without a nucleus
• Eukaryotes


  Organisms with a nucleus
• Plant and Animal Cells have Similarities and Differences
• Bacterial Cells Are Much Smaller
• Cell structures-become an estate agent...
• Microscopy


  Techniques used to study cells
• Light microscopes


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


  • Use electrons instead of light to form an image
  • Have a much higher magnification and resolution than light microscopes
  • Allow us to see smaller structures like ribosomes and plasmids
• 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 down eyepiece and use coarse adjustment to roughly focus

  5. Adjust fine focus for clear image

  6. Swap to higher-powered lens to see more detail
• Draw observations neatly with a pencil
• A light microscope is better than a heavy one
• Cell differentiation


  Process by which a cell changes to become specialised for its job
• Examples of specialised cells

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


  • Long tail and streamlined head to swim to egg
  • Many mitochondria to provide energy
  • Enzymes in head to digest egg cell membrane
• Nerve cells


  • Long to cover more distance
  • Branched connections at ends to connect to other nerve cells
• Muscle cells


  • Long to have space to contract
  • Many mitochondria to generate energy for contraction
• Root hair cells


  • Long "hairs" that stick out into soil to absorb water and minerals
• Phloem and xylem cells


  • Long and joined end to end to form tubes
  • Phloem cells have few subcellular structures to allow flow of substances
  • Xylem cells are hollow in the centre
• Chromosomes


  Coiled up lengths of DNA molecules that contain genetic information
• Body cells normally have two copies of each chromosome
• Cell cycle


  Series of stages that allow cells to divide and produce new cells
• Mitosis


  The stage of the cell cycle when the cell divides
• Multicellular organisms use mitosis to grow or replace damaged cells
• The end of the cell cycle results in two new cells identical to the original cell
• The cell cycle


  Series of stages
• Multicellular organisms


  • Use mitosis to grow or replace cells that have been damaged
• Monomers are the smaller units from which larger molecules are made
• Processes that occur during the cell cycle

  • Growth
  • DNA replication
• Chromatin condenses into chromosomes during cell division
• Each chromosome is made up of two identical sister chromatids
• The diagram shows the 23 chromosome pairs for a human cell
• The cell cycle


  • Makes new cells for growth, development and repair
• In a non-dividing cell, the DNA is spread out in the nucleus
• Cell division


  1. DNA replication

  2. Chromosome formation

  3. Chromosome separation

  4. Nuclear division

  5. Cytoplasmic division
• The daughter cells contain exactly the same DNA as the parent cell
• Mitosis can seem tricky at first, but it's best to go through it step-by-step
• 11 cells were observed undergoing mitosis and 62 cells were not
• Differentiation is the process by which a cell changes to become specialised for its job
• Stem cells


  Undifferentiated cells that can divide to produce more undifferentiated cells and differentiate into different cell types
• Embryonic stem cells can turn into any type of cell