biological concepts

• plant cell


  cell membrane - controls what enters and leaves the cell

  nucleus - contains genes and controls the activities of the cell

  mitochondria - where respiration occurs, releasing energy for cell processes

  ribosomes - where proteins are made

  cytoplasm - jelly-like substance where many reactions take place
• microscopes


  magnification = eyepiece lens x objective lens

  resolution - the smallest distance between two points that can still be seen as two points
• specialised cells


  They have a specific function and have adapted to do their functions.

  digestion - cells have adapted to have microvilli to increase surface area

  reproduction - gametes, egg and sperm cells

  plants - root hair cells and xylem cells
• Osmosis


  Cell membranes are semi-permeable and trap large soluble molecules inside the cell, but water molecules can diffuse through it.

  If there are more water molecules in a certain volume on one side of the membrane than the other, there will be an overall movement of water molecules to the side where there are fewer water molecules.

  The overall movement of solvent molecules will stop when the concentration of solutes is the same on both sides of a membrane.
• Active transport


  Cells may need to transport molecules against a concentration gradient or transport molecules too big to diffuse through the cell membrane, this is active transport.

  This process is carried out by transport proteins in cell membranes.

  The transport proteins capture certain molecules and carry them across the membrane.

  This is an active process and requires energy.
• Bacteria cell


  Slime coat - for protection (not all bacteria have this)

  Flexible cell wall - for protection and support

  Chromosomal DNA - contains most of the bacterial gene

  Cytoplasm - where the cell's activities occur

  Plasmid - contains additional genes

  Flagellum - for moving
• Food tests

  Starch

  • Iodine - turns blue/black if starch is present

  Reducing sugars

  • Benedict's - gradually turns from blue to cloudy orange or brick red if reducing sugars are present

  Proteins

  • Biuret - turns a mauve or purple colour

  Lipids

  • Emulsion - turns from clear to milky if lipids are present
• Enzyme action


  Enzymes are folded into complex 3D shapes that allow smaller molecules to fit into them. The place where these molecules fit is called the active site.

  In the lock and key hypothesis, the shape of the active site matches the shape of its substrate molecules. This makes the enzymes highly specific. Each type of enzyme can usually catalyse only one type of reaction (some can catalyse a few types of reactions).
• Using microscopes (core practical)

  Aim - to produce a labelled plant diagram

  Apparatus - light microscope, unlined paper, pencil, rubber, ruler

  Method:

  1. Focus the microscope on a single cell
  2. Carefully draw the details of the parts that are important to your study. Other parts can just be drawn as an outline.
• Food tests (core practical) Pt.1

  Aim - to investigate the use of chemical reagents to identify substances in food.

  Apparatus - test tubes, water bath, iodine solution, Benedict's solution, 0.1$moldm^{-3}$ potassium hydroxide solution, 0.01$moldm^{-3}$ copper sulphate solution, ethanol, water, food
• Food tests (core practical) Pt.2

  Method:

  Starch - place a few drops of iodine solution solid food, or mix with a solution of the food.

  Reducing sugars - add an equal volume of Benedict's solution to a food solution and mix. Heat the mixture in a $95^{\circ}$C water bath for a few minutes.

  Proteins(Buiret) - add an equal volume of 0.1$moldm^{-3}$ potassium hydroxide solution to the food solution and mix.

  Fats - add an equal volume of ethanol to the food solution, and shake thoroughly. Add water to the mixture.
• pH and enzymes (core practical)

  Aim - to investigate the effect of pH on amylase activity

  Method:

  1. Add amylase to buffered starch solution in a test tube.
  2. Place the test tube in a water bath for a constant temperature.
  3. Take samples of the mixture at regular intervals and mix them with a drop of iodine in a dimple tile.
  4. Repeat the test until the iodine solution stops changing colour when the starch/amylase mixture is added. Record the time taken for this to happen.
  5. Repeat the procedure at different pH values.

  Conclusion - the results show that the optimum pH is 6 for this enzyme.
• Osmosis in potatoes (core practical) Pt.1

  Aim - to investigate osmosis in potatoes

  Apparatus - pieces of potatoes about 3x1x1cm, boiling tubes, accurate balance, paper towels, forceps, solutions of different solute concentrations, maker pen
• Osmosis in potatoes (core practical) Pt.2

  Method:

  1. Mark the value of one solute concentration one one tube and repeat using a different tube for each concentration. Fill each 2/3 full of the appropriate solution.
  2. Blot a piece of potato dry on paper towel, and then measure and record its mass. Use the forceps to place it into one of the tubes. Repeat for all the tubes.
  3. After 20 minutes, use the forceps to remove each piece of potato, blot it dry and measure its mass again. Record all final masses.

  Conclusion - when the solution concentration is very dilute, water enters the potato