(c) Bio molecules, (d) Movement substances in & out of cells

• Which chemical elements do carbohydrates contain?

  Carbon, hydrogen, oxygen
• Which chemical elements do lipids contain?

  Carbon, hydrogen, and oxygen.
• Which chemical elements does protein contain?

  Carbon, oxygen, hydrogen, nitrogen and small amounts of sulphur
• Carbohydrates contain the elements carbon, hydrogen, and oxygen
• A monosaccharide is a simple sugar, for example, glucose (C6H12O6) or fructose
• Glucose molecules contain lots of energy which can be released in respiration by breaking the bonds between the carbon atoms
• A disaccharide is formed when two monosaccharides join together
• Maltose is formed from two glucose molecules
• Sucrose is formed from one glucose and one fructose molecule
• A polysaccharide is formed when lots of monosaccharides join together
• Starch, glycogen, or cellulose are all formed when lots of glucose molecules join together
• Polysaccharides are insoluble and therefore useful as a storage molecule
• Fats

  • Most fats (lipids) in the body are made up of triglycerides
  • Their basic unit is one glycerol molecule chemically bonded to three fatty acid chains
  • The fatty acids vary in size and structure
  • Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)
• Proteins

  • Proteins are formed from long chains of amino acids
  • There are 20 different amino acids
  • When amino acids are joined together a protein is formed
  • Amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins
  • Examples of proteins include enzymes, haemoglobin, ligaments and keratin
• Proteins structure

  A) amino acids

  B) peptide

  C) protein

  
• Different proteins have different amino acid sequences, resulting in them having different shapes
• Before most food tests:

  • Break up the food using a pestle and mortar
  • Transfer to a test tube and add distilled water
  • Mix the food with the water by stirring with a glass rod
  • Filter the mixture using a funnel and filter paper, collecting the solution
  • Proceed with the food tests
• Benedict’s test (for glucose):

  • Add Benedict's solution, using a pipette, to the sample solution in a test tube
  • Heat in a boiling water bath for 5 minutes
  • Take the test tube out of the water bath and observe the colour
  • A positive test will show a colour change from blue to orange / brick red
• Iodine test (for starch):

  • Add drops of iodine solution to the food sample
  • A positive test will show a colour change from orange-brown to blue-black
• Biuret test (for protein):

  • Add drops of Biuret solution to the food sample
  • A positive test will show a colour change from blue to violet / purple
• Ethanol test (test for lipids):

  • Mix the food sample with 4cm3 of ethanol and shake
  • Allow time for the sample to dissolve in the ethanol
  • Strain the ethanol solution into another test tube
  • Add the ethanol solution to an equal volume of cold distilled water (4cm3)
  • A positive test will show a cloudy emulsion forming
• colour of reagents

  A) orange-brown

  B) light - blue

  C) colourless

  D) blue

  
• Positive test result colours

  A) blue-black

  B) green to brick red

  C) cloudy emulsion

  D) lilac purple

  
• What are the hazards involved in the foot test experiments?

  Answers:

  
• Apparatus for investigating the effect of temperature on enzyme activity:

  • Spotting tile
  • Measuring cylinder
  • Test tube
  • Syringe
  • Pipette
  • Stopwatch
  • Water
  • Thermometer
  • Water bath
  • Iodine
  • Starch solution
  • Amylase solution
• Method for investigating the effect of temperature on enzyme activity:

  1. Add 5cm3 starch solution to a test tube and heat to a set temperature using a beaker of water with a Bunsen burner

  2. Add a drop of Iodine to each well of a spotting tile

  3. Use a syringe to add 2cm3 amylase to the starch solution and mix well

  4. Every minute, transfer a droplet of solution to a new well of iodine solution (which should turn blue-black)

  5. Repeat this transfer process until the iodine solution stops turning blue-black (indicating all starch has been broken down)

  6. Record the time taken for the reaction to be completed

  7. Repeat the investigation for a range of temperatures (from 20°C to 60°C)
• Results and Analysis of the investigation:

  • Amylase is an enzyme that breaks down starch
  • The quicker the reaction is completed, the faster the enzyme is working
  • At the optimum temperature, the iodine stopped turning blue-black the fastest because the enzyme is working at its fastest rate and has digested all the starch
  • At colder temperatures (below optimum), the iodine took a longer time to stop turning blue-black due to the amylase enzyme working slowly
  • At hotter temperatures (above optimum), the iodine turned blue-black throughout the investigation because the amylase enzyme became denatured and could no longer bind with the starch or break it down
• Limitations of the investigation:

  • The method described for controlling temperature is not very precise; using water baths kept at each temperature would be an improvement
  • Starch and amylase solutions should be placed in a water bath and allowed to reach the temperature before use
  • A colorimeter can be used for more accurate measurement of the reaction progress
  • The absorbance or transmission of light through the coloured solution can be measured using a colorimeter
• Factors affecting enzyme function related to pH:

  • The optimum pH for most enzymes is 7
  • Enzymes produced in acidic conditions, like the stomach, have a lower optimum pH (pH 2)
  • Enzymes produced in alkaline conditions, like the duodenum, have a higher optimum pH (pH 8 or 9)
  • pH levels too high or too low can disrupt/destroy bonds holding the amino acid chain together, changing the shape of the active site and reducing activity
  • Moving away from the optimum pH can cause enzyme denaturation and stop activity
• Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration
• Molecules move down a concentration gradient due to their random movement
• Living cells have a cell membrane that can restrict the free movement of molecules
• The cell membrane is partially permeable, allowing some molecules to cross easily while others with difficulty or not at all
• Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane
• In osmosis, water moves down its concentration gradient
• In animal cells, osmosis can lead to cell shrinkage (crenation) or bursting if placed in different solutions
• In plant cells, osmosis can result in the cell becoming flaccid or turgid based on the solution it is placed in
• Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
• Active transport involves protein carrier molecules embedded in the cell membrane
• Factors affecting the rate of diffusion include surface area to volume ratio, diffusion distance, temperature, and concentration gradient