Topic 1: Key concepts

• Diffusion


  The passive movement of particles from an area of high concentration to low concentration. This happens along a concentration gradient
• Osmosis


  A passive movement of water molecules through a semi-permeable membrane. Water moves from an area of low solute concentration to high solute concentration
• Active Transport


  An active movement where an input of energy is required. Particles move from low concentration to high concentration
• Nucleus


  The control centre of the cell that hold all genetic material
• Cytoplasm 


  Where chemical reactions take place
• Cell membrane 


  Controls what enters and leaves the cell
• Mitochondria 


  Where energy is produced from chemical reactions
• Ribosomes 


  Where protein synthesis takes place
• Cell wall


  A protective layer that helps to support the cell
• Vacuole


  Contains cell sap, it keeps the cell firm
• Chloroplasts


  Contains chlorophyll, which is found in plants and algae that carry out photosynthesis
• Prokaryotic 


  Organisms, such as bacteria, that do not have a nucleus or organelles
• Eukaryotic 


  Cells that have a nucleus and sub cellular organelles
• Plasmid


  Extra genes of DNA
• Resolution


  Shortest distance between two points that can still be distinguished
• Magnification


  How much larger the image is than the object
• magnification = image size / object size
• What is the role of fibre?


  Helps food to move through our intestines
• What are proteins broken down into?

  Amino acids
• What are carbohydrates broken down into?

  Sugars
• What are lipids broken down into?

  Fatty acids and glycerol
• Positives of light microscopes

  • Easy to use
  • Relatively cheap
• Negatives of light microscopes

  • Rely on light
  • Resolution is limited to 0.2µm
  • Not good enough to study sub cellular structures
• Negatives of electron microscopes

  • Very expensive
  • Hard to use
• Positives of electron microscopes

  • Use electrons instead of light
  • Maximum resolution is 0.1nm
  • Can use them to study sub cellular structures
• Flagellum


  Propels the cell so it can move
• Catalyst


  A substance that inceases the speed of a chemical reaction without being changed or used up in the process
• Carbohydrases break down carbohydrates into simple sugars
• Proteases break down proteins into amino acids
• Lipases break down lipids into glycerol and fatty acids
• Microscopy Practical


  1. Collect a sample of the cell you wish to observe
  2. Remove the inner skin of a layer of onion using forceps
  3. Plave the slice onto a clean glass slide. Use forceps to keep the cell on the glass slide
  4. Using a pipettes, add one or two drops of dilute iodine solution on top of cell
  5. Hold the coverslip by its side and lay one edge onto slide near the specimen
  6. Lower the coverslip so that liquid spreads out
• To test for sugars, add Benedic’s reagent to the food and boil in a water bath and positive test will turn from blue to brick red
• To test for protein/amino acids, add Biuret’s reagent to the food and positive test will go from blue to purple
• Test for Starch


  1. Add a drop of iodine in each well in a spotting tile
  2. Using a water bath, warm amylase and starch and buffer solution
  3. In intervals, take drops of the solution and add into the wells
  4. The starch will break down completely when the solution remains brown
  5. The time for this to occur is recorded at 100/time
  6. Repeat experiment at diffrent pH values while controlling other factors like temperature
• To test for starch, add iodine and will turn blue-black if present