Biology topic 2

• 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 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 it rapidly decreases and eventually the reaction stops as the enzyme becomes denatured.
• Investigate how enzyme activity can be affected by changes in temperature

  1. Heat starch solution to set temperature

  2. Add amylase

  3. Add iodine after a minute

  4. Measure time until iodine stops turning blue-black

  5. Repeat with different temperatures
• 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 becomes denatured.
• Investigate how enzyme activity can be affected by changes in pH

  1. Place amylase, starch and buffer solutions of different pH in a test tube

  2. Heat in water bath to control temperature

  3. Every 10 seconds, take a drop and test with iodine

  4. Record time until iodine stops turning blue-black

  5. Plot a graph of pH vs time taken

  
• 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


  Spreading out of particles resulting in net movement from higher to lower concentration, passive process requiring no energy
• Molecules that can diffuse

  • Small molecules like oxygen, glucose, amino acids, water
  • Larger molecules like starch and proteins cannot
• Diffusion in living organisms

  • Single-celled organisms can use diffusion to transport molecules
  • Multicellular organisms cannot rely on diffusion alone and have adaptations like alveoli, villi, root hair cells
• Factors affecting rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area:volume ratio
  • Distance
• Osmosis


  Movement of water from less concentrated to more concentrated solution through partially permeable membrane, passive process
• Isotonic, hypertonic, hypotonic

  Isotonic - no net movement, hypertonic - water moves out, hypotonic - water moves in
• Osmosis in animals

  • Dilute external solution causes cells to burst, concentrated external solution causes cells to shrivel
• Osmosis in plants

  • Dilute external solution causes turgor pressure, concentrated external solution causes plasmolysis and cell death