Structure and Function of living things

• Levels of organisation


  • Organelles
  • Cells
  • Tissues
  • Organs
  • Organ systems
• Nucleus


  Contains the genetic material, which codes for a particular protein. Enclosed in a nuclear membrane.
• Cytoplasm


  Liquid substance in which chemical reactions occur. Contains enzymes (biological catalysts, i.e. proteins that speed up the rate of reaction). Organelles are found in it.
• Cell membrane


  Contains receptor molecules to identify and selectively control what enters and leaves the cell
• Mitochondria


  Where aerobic respiration reactions occur, providing energy for the cell
• Ribosomes


  Where protein synthesis occurs. Found on a structure called the rough endoplasmic reticulum.
• Chloroplasts


  Where photosynthesis takes place, providing food for the plant. Contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis.
• Permanent vacuole


  Contains cell sap. Found within the cytoplasm. Improves cell's rigidity.
• Cell wall


  Made from cellulose. Provides strength to the cell.
• Cell differentiation


  A process that involves the cell gaining new sub-cellular structures in order for it to be suited to its role.
• Stem cells

  Undifferentiated cells which can undergo division to produce many more similar cells. Some will differentiate to have different functions.
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
  • Meristems in plants
• Embryonic stem cells


  • Form when an egg and sperm cell fuse to form a zygote. They can differentiate into any type of cell in the body. Scientists can clone these cells (though culturing them) and direct them to differentiate into almost any cell in the body.
• Adult stem cells


  • If found in bone marrow they can form many types of cells (not any type, like embryonic stem cells can) including blood cells.
• Meristems in plants


  • Found in root and shoot tips. They can differentiate into any type of plant, and have this ability throughout the life of the plant. They can be used to make clones of the plant.
• Benefits of stem cells in medicine

  • Can be used to replace damaged cells
  • Bone marrow transplants for adult stem cells can be used to treat blood cell cancers
  • Can grow whole organs for transplants
  • No rejection, if it is made from the patient's own cells
  • Can allow for the testing of millions of potential drugs without animal testing
• Risks of stem cells in medicine

  • Ethical issues of destroying unused embryos
  • No guarantee in how successful these therapies will be and if there will be any long term effects
  • Mutations could occur in cultured stem cells
  • Difficult to find suitable stem cell donors
• Carbohydrates


  They are made of carbon, oxygen and hydrogen. They are polymers that break down into simple sugars.
• Proteins


  They are made of carbon, oxygen, hydrogen, sulfur, nitrogen and phosphorous. They are polymers that are broken down into its monomers: amino acids.
• Lipids


  Lipids (fats and oils) are made of carbon, oxygen and hydrogen. They are large polymers that are broken down into 3 fatty acids molecules and a glycerol molecule.
• Test for glucose


  1. Add the sample solution into a test tube

  2. Add drops of Benedict's solution into the test tube

  3. Heat in a water bath at 60-70°C for 5 minutes

  4. Brick red colour indicates glucose is present
• Test for starch


  1. Pipette the sample solution into wells or on a tile

  2. Add drops of iodine solution and leave for 1 minute

  3. Blue-black colour indicates starch is present
• Test for protein


  1. Add the sample solution into a test tube

  2. Add drops of Biuret solution into the test tube

  3. Purple colour indicates protein is present
• Test for fat


  1. Add 2cm3 of ethanol to the test solution

  2. Add 2cm3 of distilled water

  3. Milky white emulsion indicates fat is present
• Enzymes


  Biological catalysts (a substance that increases the rate of reaction without being used up). They are protein molecules and the shape of the enzyme is vital to its function. Each enzyme has its own uniquely shaped active site where the substrate binds.
• Lock and Key Hypothesis


  The shape of the substrate is complementary to the shape of the active site (enzyme specificity), so when they bond it forms an enzyme-substrate complex. Once bound, the reaction the reaction takes place and the products are released from the surface of the enzyme.
• As temperature increases


  The rate of reaction increases up to the optimum temperature of around 37°C, but above this temperature it rapidly decreases and eventually the reaction stops.
• When the temperature becomes too hot, the bonds in the structure will break, changing the shape of the active site, so the substrate can no longer fit in. The enzyme is said to be denatured and can no longer work.
• As pH changes


  If the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected, changing the shape of the active site, so the substrate can no longer fit in. The enzyme is said to be denatured and can no longer work.
• Investigating how enzyme activity is affected by changes in temperature

  1. Starch solution is heated to set temperature

  2. Amylase is added

  3. Iodine is added to each well after a minute

  4. Measure the time it takes until the iodine stops turning blue-black (this means that starch is not present as amylase has broken the starch down into glucose)

  5. Repeat the test with different temperatures
• Investigating how enzyme activity is affected by changes in pH

  1. Place a beaker of water on a gauze above a Bunsen burner

  2. Place single drops of iodine solution on each well of a tray

  3. Add 2cm3 of amylase solution, 2cm3 of starch solution and 1cm3 of pH solution in a test tube and mix

  4. Put this test tube into the water beaker and start a stopwatch

  5. Every 10 second use a pipette to place a drop the solution into one of the wells containing iodine solution

  6. Continue repeating until the solution stops turning black and becomes orange and record the time taken

  7. Repeat with different pH solutions

  8. Record results on a graph of pH (x-axis) and time taken to complete reaction (y-axis)
• The optimum pH for most enzymes is 7, but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH.
• Experiment procedure


  1. 2cm³ of amylase solution, 2cm³ of starch solution and 1cm³ of pH solution in a test tube and mix

  2. Put test tube in water beaker above Bunsen burner to keep temperature controlled

  3. Every 10 seconds use pipette to place drop of solution in iodine solution well

  4. Continue until solution stops turning black and becomes orange, record time

  5. Repeat with different pH solutions

  6. Record results on graph of pH vs time taken for reaction
• The optimum pH of amylase is around pH 7.0 as this is where the reaction is completed fastest
• Diffusion


  The spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration
• Diffusion is a passive process as no energy is required
• Molecules that can move by diffusion

  • Oxygen
  • Glucose
  • Amino acids
  • Water
• Larger molecules such as starch and proteins cannot move by diffusion
• Single-celled organisms


  • Can use diffusion to transport molecules into their body from the air due to their large surface area to volume ratio
  • Their low metabolic demands mean diffusion is sufficient to meet their needs
• Multicellular organisms


  • Cannot rely on diffusion alone due to their small surface area to volume ratio
  • Have adaptations to allow molecules to be transported in and out of cells, e.g. alveoli, villi, root hair cells