Topic 1 - Cells

• Light Microscopes:

  • Cheap to make
  • Can see the outline of cells
• Electron Microscopes:

  • Can see finer details including organelles
  • Greater resolving power and higher resolution
• Magnification = image size/ actual size
• mm --> µm / 1000

  µm --> mm x 1000
• Cell membrane: A semi-permeable barrier that surrounds the cell and controls what enters and leaves the cell
• Nucleus: Contains DNA and controls the cell
• Mitochondria: Site of aerobic respiration, where most of the energy for cellular respiration is produced
• Cytoplasm: Where chemical reactions take place
• Ribosomes: Site of protein synthesis in the cell.
• Cell Wall: Only in plant cells. Made of cellulose and keeps the structure of the cell so it doesn't burst- strong
• Chloroplast: Site of photosynthesis and contains chlorophyll
• Permanent Vacuole: Storage area of dissolved ions/minerals and water
• Plasmid: Only in prokaryotic cells. Loop of DNA
• Prokaryotic cells = Don't have a nucleus
• Eukaryotic cells = Have a nucleus
• Bacteria reproduce by binary fission, which is the division of a bacterial cell into two identical daughter cells. They divide every 10 minutes.
• Making cultures with aseptic technique:

  1. Lift the lid of the Petri dish towards a flame to sterilise it
  2. Put a drop of culture on the agar or spread it evenly
  3. Put drops/discs of antibiotics on culture if needed
  4. Place a few strips of tape around the lid to secure it but leave a gap for aerobic respiration and incubate it at 25 degrees
  5. Measure size of cultures/areas with no bacteria on it with pi r^2
• All human cells (diploids) have 23 pairs of chromosomes
• Haploid cells (gametes) have only 23 chromosomes
• Mitosis:

  1. The nucleus dissolves and genetic material is duplicated
  2. The two sets of chromosomes move to opposite sides
  3. Mitochondria, ribosomes and other organelles are duplicated
  4. The cell divides, producing two genetically identical diploid cells (new nuclei are formed)
• Stem cells can be specialised to perform specific functions
• Stem cells are found in animal embryos and plant meristems
• Some stem cells are made in your bone marrow but they can only be specialised into blood cells
• Embryo clones can be made of a person to harvest stem cells from. They can be used to treat conditions without them being rejected by the patient's body
• Cloning can also be used to preserve species or produce crops with desired traits.
• Diffusion is the movement of particles from an area of high concentration to an area of low concentration (down the concentration gradient)
• The diffusion rate can be increased by:

  • Increasing concentration
  • Increasing temperature
  • Increasing surface area
• Osmosis is the diffusion of water across a semi-permeable membrane from an area of high concentration to an area of low concentration.
• Active transport is the movement of particles through a membrane via carrier proteins from an area of low concentration to an area of high concentration. This requires energy so is slower than passive transport
• Osmosis Practical:

  1. Weigh and place identical cylinders of a potato in varying sugar concentration
  2. After a set time, remove excess water from the cylinders' surface and reweigh
  3. Calculate change in mass = (final mass-initial mass / initial mass) x 100
  4. Plot % change in mass against concentration and using the line of best fit, the concentration at 0% change in mass is the same as inside the potato