Biology

• Cells


  The building blocks of life
• Mitosis


  1. Cytoplasm and cell membrane divide

  2. Membranes form around each set of chromosomes, becoming the nuclei of the two new cells

  3. Cell has now produced two new daughter cells
• Daughter cells after mitosis


  • Contain exactly the same DNA as the parent cell
  • Their DNA is identical to the parent cell
• The first stage of mitosis

  1. Chromosomes line up at the centre of the cell

  2. Cell fibres pull the chromosomes apart

  3. The two arms of the chromosome go to opposite ends of the cell
• DNA replication


  • In a cell that's not dividing, the DNA is all spread out in long strings
  • Before it divides, the cell has to grow and increase the amount of subcellular structures like mitochondria
  • The cell duplicates its DNA - so there's one copy for each new cell
  • The DNA is copied and forms X-shaped chromosomes, with each 'arm' an exact duplicate of the other
• Mitosis


  Used to grow and develop or replace cells that have been damaged
• Resolution


  • The ability to distinguish between 2 points
  • Higher resolution gives a clearer image
• Eukaryotic cell


  A cell which has a nucleus
• Prokaryotic cell


  A cell with no nucleus
• Structures in a bacteria cell

  • Cell wall
  • Cell membrane
  • Ribosomes
  • Cytoplasm
  • No nucleus
  • Single strand of DNA (nucleoid)
  • Plasmids
  • Flagella
• Structures in an animal cell

  • Cell membrane
  • Nucleus
  • Ribosomes
  • Mitochondria
  • Cytoplasm
• Five kingdoms of life

  • Fungi
  • Animals
  • Plants
  • Bacteria
  • Protists
  • Archaea
• Structures in a plant cell

  • cell wall
  • cell membrane
  • cytoplasm
  • chloroplasts
  • ribosomes
  • mitochondria
  • permanent vacuole
  • nucleus
• Equation for Calculating image size

  image size = Size: magnification x real size
• Light microscopes


  • Use light and lenses to form an image of a specimen and magnify it
  • Allow us to see individual cells and large subcellular structures
• Chloroplast


  Contains chlorophyll so photosynthesis can take place
• Electron microscopes


  • Use electrons instead of light to form an image
  • Have a higher magnification than light microscopes
  • Have 4+ higher resolution
• Stains such as iodine


  Used to highlight objects in a cell by adding colour to them
• Parts of a light microscope

  • Eyepiece lens
  • Stage
  • Light
  • Fine adjustment knob
  • Coarse adjustment knob
  • High and low power objective lenses
• How to prepare a microscope slide

  1. Add a drop to the middle of a clean slide

  2. Cut up an onion and peel off a 1 cell thick layer with tweezers

  3. Place the onion layer into the water on the microscope slide

  4. Add a drop of iodine to serve as a stain

  5. Place a cover slip on top, trying to avoid air bubbles
• Undifferentiated cells


  Stem cells
• How to use a microscope to look at a microscope slide

  1. Clip the slide prepared on to the stage

  2. Start with the lowest powered objective lens (closest magnification)

  3. Use the coarse adjustment knob to move the stage up, just below the objective lens

  4. Roughly adjust until the image is in focus

  5. Adjust the focus with the fine adjustment knob to produce a clear image

  6. Increase the magnification if needed and refocus
• Specialised cells


  • Reproduction: Sperm cells - long tail and streamlined head to help it swim to the egg, a lot of mitochondria to provide energy, enzymes in the head to digest the egg cell membrane
  • Rapid signalling: Nerve cells - long to cover more distance, branched connections at their ends to connect to other nerve cells and form a network
• What do phloem and xylem cells do

  1. Form phloem and xylem tubes

  2. Transport substances such as food and water around plants
• Phloem and xylem cells

  • Cells are long and joined end to end to form the tubes
  • Xylem cells are hollow in the centre
  • Phloem cells have very few subcellular structures so stuff can flow through them
• Magnification


  image size / real size
• Cell cycle


  Where body cells in multicellular organisms divide to produce new cells
• Chromosomes


  Coiled up lengths of DNA molecules that carry a large number of genes
• The human body has 23 pairs of chromosomes (46 altogether)
• Genes


  Control the development of different characteristics e.g. hair colour
• Nucleus


  Contains the genetic material in the form of chromosomes
• Stem cells


  One risk: Stem cells grown in the lab may become contaminated with a virus which could be passed on to the patient and make them sicker
• Therapeutic cloning


  Where an embryo could be made to have the same genetic information as the patient, making it less likely to be rejected by the patient's body if used to replace faulty cells
• Where stem cells can be found

  • Early human embryos
  • Adult bone marrow
• Differentiation


  The process by which a cell changes to become specialised for its job
• Muscle cells


  • They are long (so they have space to contract)
  • They contain a lot of mitochondria to generate energy needed for the contraction
• Root hair cells


  • They are on the surface of plant roots, which grow into long "hairs" that stick out into the soil
  • This gives the plant a big surface area for absorbing water + mineral ions from the soil