Section 2: Structure and functions in living organisms

• LEVELS OF ORGANISATION

  ORGANELLES: Cell structures specialised with a specific function.CELLS: Basic functional and structural units in a living organism.TISSUES: Composed of same cells carrying out same functionORGANS: Composed of different tissues carrying out a particular function.SYSTEMS: Composed of organs carrying out body function.
• Nucleus: Membrane-bound organelle that contains genetic material.
• Cytoplasm: Material that fills cell to facilitate chemical reactions and hold organelles in place.
• Cell membrane: Phospholipid bilayer that controls the movement of substances into and out of cell.
• Cell wall: External to cell membrane that protects and maintains the shape of cell (prevents cell from bursting).
• Mitochondria: Membrane-bound organelle that carries out cellular respiration.
• Chloroplast: Plastid in plants that carries out photosynthesis.
• Ribosome: Site of protein synthesis.
• Vacuole: Storage organelle in plants to store Water and dissolved substances.
• SIMILARITIES AND DIFFERENCES IN PLANT AND ANIMAL CELLS

  Same:

  Multicellular organism

  Nucleus

  Mitochondria

  Cytoplasm

  Cell membrane

  Only plant cell:

  Fixed shape

  Large vacuole

  Cell wall

  Stores carbohydrates as Starch

  Contains Chloroplasts to conduct photosynthesis

  Only animal cell:

  No fixed shape

  Little or no vacuole

  No cell wall

  Stores carbohydrates as Glycogen

  Does not contain Chloroplasts (cannot conduct photosynthesis)
• CHEMICAL ELEMENTS

  Carbohydrate: Carbon, Oxygen and Hydrogen

  Protein: Carbon, Oxygen, Hydrogen, Sulfur and Nitrogen

  Lipids: Carbon, Oxygen and Hydrogen
• TEST FOR GLUCOSE

  METHOD:

  • Add a few drops of Benedict's solution into test tube of test solution
  • Heat test tube placed in a water bath set at 60 - 70 °C for 5 minutes
  • Remove test tube from water bath and observe colour change

  RESULT:

  • If Glucose is present, solution will turn brick red
  • If Glucose is not present, solution will stay blue

  
• TEST FOR STARCH

  METHOD:

  • Use pipette to transfer sample solution into wells on tile
  • Add a few drops of Iodine solution and observe colour change

  RESULT:

  • If Starch is present, solution will turn blue-black
  • If Starch is not present, solution will stay brown

  
• TEST FOR PROTEIN

  METHOD:

  • Add a few drops of Biuret solution into test tube of sample solution
  • Observe colour change

  RESULT:

  • If Protein is present, solution will turn violet
  • If Protein is not present, solution will stay blue

  
• TEST FOR FAT

  METHOD:

  • Test tube of sample solution is mixed with 2cm3 of Ethanol and 2cm3 of distilled water
  • Observe colour change

  RESULT:

  • If Fat is present, a milky - white emulsion will form
  • If Fat is not present, solution will remain colourless

  
• STRUCTURE OF MOLECULES

  Starch and Glycogen: Composed of simple sugars.

  Protein: Composed of amino acids.

  Lipid: Composed of fatty acids and glycerol.
• ROLE OF ENZYMES

  ENZYMES: Protein molecule that acts as a biological catalyst by speeding up the rate of specific reaction without being used up or affected.

  • Enzymes are biological catalyst in metabolic reactions (digestion) as they allow substrates to bind onto their active site, breaking them down into products

  Diagram:

  
• COMMON ENZYMES

  Amylase/Maltase: Starch → Glucose

  Protease: Protein → Amino Acids

  Lipase: Lipids → Fatty Acids & Glycerol
• As the temperature increases towards optimum, the rate of enzyme activity increases.
• This is because as temperature increases, enzymes and substrates will gain kinetic energy, vibrating and moving faster.
• Increasing the frequency of enzyme-substrate collisions increases the rate in which substrates are broken down, hence increasing enzyme activity.
• As temperatures exceed optimum, enzymes will denature due to high temperatures causing bonds to vibrate more, increasing the chance of bonds within enzyme breaking.
• Enzymes denature and metabolic reactions cannot take place when bonds in enzymes break.
• When bonds in enzymes break, the shape and structure of the active site change, diminishing the ability of the substrate to bind to the active site of the enzyme.
• The independent variable in the experiment is the temperature of the starch solution which is tested at 0, 10, 20, 30, 40, 50, 60°C.
• The method involves placing a test tube of starch solution in a water bath of set temperature for several minutes.
• Amylase enzyme is added into the test tube of starch solution immediately after it is placed in the water bath.
• Immediately after Amylase is added into the test tube, droplets of the mixture are added into wells using a pipette.
• Iodine solution is added into the wells immediately after the droplets of the mixture are added.
• The process is repeated in increments of fixed time until Iodine turns orange, indicating that Starch has completely broken down into Glucose.
• As temperature increases towards optimum (37°C), the rate of amylase activity increases as shown with the decrease in time taken for Iodine solution to turn orange.
• This is because as temperature increases, Amylase and Starch gain kinetic energy, vibrating and moving faster, allowing more frequent successful enzyme-substrate collisions to occur, increasing the rate in which Starch is broken down into Glucose, which causes Iodine solution to turn orange quicker, hence increasing enzyme activity.
• However, as temperature exceeds optimum, Amylase denatures as shown with the increase in time taken for Iodine solution to turn orange.
• High temperatures cause bonds to vibrate more, increasing the chance of bonds within Amylase enzyme to break.
• When bonds in enzyme break, the shape and structure of the active site will change, diminishing the ability of Starch (substrate) to bind to the active site of Amylase.
• Amylase denatures and Starch cannot be broken down into Glucose, which causes Iodine solution to turn orange slower, hence decreasing enzyme activity.
• As the pH increases towards optimum, the rate of enzyme activity increases.
• This is because as pH increases, the shape and structure of the active site, and the charge of substrate molecule will both be optimal to allow the substrate to bind to the active site of enzyme.
• This allows more frequent successful enzyme-substrate collisions to occur, increasing the rate in which substrates are broken down, hence increasing enzyme activity.
• However, as pH exceeds optimum, enzymes will denature.