required practicals biology

• How would you perform Required Practical 1 about microscopy?


  Place the prepared slide onto the stage

  
  

  Then select lowest power objective lens and slowly turn the coarse focussing dial

  
  

  When the objective lens almost touches the slide ,stop turning the dial

  
  

  Now look down through the eyepiece and slowly turn the coarse focussing dial until the cells come into focus

  
  

  Then use the fine focussing dial to bring the cells into a clear focus

  
  

  calculate total magnification

  
  

  Finally select a higher power objective lens, adjust the fine focussing dial and sketch the cells
• How do you prepare a slide?


  Place the specimen onto slide

  
  

  Add two drops of iodine

  
  

  Place cover slip over stained specimen
• Why is iodine put on the slide?


  It stains the cell so parts can be seen under a microscope
• How do you calculate total magnification?

  eyepiece lens x objective lens
• How do you calculate magnification?

  Image size/actual size
• What is the purpose of the coarse focussing dial?

  It is used to move the objective lens towards or away from the specimen
• What is the purpose of the fine focussing dial?


  Used to fine tune the focus on the specimen

  
  

  Used to focus on various parts of specimen
• Why would you look at the microscope from the side when adjusting the object lens position?


  Because there is a risk of damaging the slide if you look through the eyepiece
• How would you perform Required Practical 2 about culturing microorganisms?


  First clean bench with disinfectant solution

  
  

  Next sterilise an inoculating loop by passing it through a Bunsen burner flame

  
  

  Then open a sterile agar gel plate best a Bunsen burner flame and use the loop to evenly spread bacteria over the plate

  
  

  Next place sterile filter discs containing antibiotic onto the plate

  
  

  Finally incubate the plate at 25°C for 48 hours
• Why is the bench cleaned with disinfectant solution?

  To kill microorganisms that could contaminate the culture
• Why is the agar gel plate opened near a Bunsen burner flame?


  The flame kills bacteria in the air
• Why is the plate incubated at 25°C?


  Higher temperatures increase the risk of growing harmful pathogens
• What is the independent variable for the culturing microorganisms practical ?

  Antibiotic disks
• What is the dependent variable for the culturing microorganisms practical ?

  Area of the zone of inhibition
• What are the control variables for the culturing microorganisms practical ?

  Incubation temperature, same agar gel plate
• What is the method for performing Required Practical 3 about the effects of osmosis?


  Firstly peel potato skin and use a cork borer to produce 3 cylinders of the potato

  
  

  Then measure the length and mass of each cylinder using a ruler and a balance

  
  

  Next place each cylinder in a test tube and add 10cm³ of a 0.5 molar sugar solution to the first test tube, 10cm³ of 0.25 molar sugar solution to the second and 10cm³ of distilled water to the third.

  
  

  Leave the potato cylinders overnight to allow osmosis to take place

  
  

  Then remove the cylinders and gently roll them on paper towel

  
  

  Finally remeasure the length and mass of the cylinders and compare results
• Why is the potato skin peeled?

  It can affect osmosis
• Why is distilled water used?

  It contains no dissolved substances(normal water does) and dissolved substances can affect the rate of osmosis
• Why are potato cylinders gently rolled on paper towels?

  To remove surface moisture
• What is the independent variable for the Osmosis practical?

  Concentration of salt solution
• What is the dependent variable for the Osmosis practical ?

  Change in length and mass of potato cylinders
• What are the control variables for the Osmosis practical ?

  Same type of potato, same balance, same ruler
• What is the test for starch?

  Iodine solution turns blue-black if starch is present
• What is the test for glucose?


  Blue Benedict's solution turns brick-red on heating if a sugar like glucose is present
• What is the issue with the glucose test?


  It works for reducing sugars like glucose but does not work for non-reducing sugars like sucrose
• What is the test for protein?

  Blue biuret reagent turns purple is protein is present
• What is the test for lipids?


  Sudan 3 added to a solution gives a red oil layer which floats to the top if a lipid is present
• What safety issues are there about Required Practical 4 about food tests?

  Biuret solution is corrosive

  Ethanol is highly flammable
• What is amylase?

  enzyme that breaks down starch into simple sugars
• What is the method for performing Required Practical 5 about the effect of pH on amylase?


  Firstly place one drop of iodine solution into each well of a spotting tile

  
  

  Get three test tubes - in the first, add 2cm³ of starch, in the second add 2cm³ of amylase solution and in the third add 2cm³ of a pH 5 buffer solution

  
  

  Next place all the three test tubes in a water bath at 30°C and leave for 10 minutes

  
  

  Then combine all three solutions into a test tube, return the test tube to the water bath and start a stopwatch

  
  

  After 30 seconds use a stirring rod to transfer one drop of solution into a well in the spotting tile containing iodine

  
  

  Next take a sample every 30 seconds until the iodine remains orange and finally repeat the whole experiment repeatedly with different pH buffers
• At what temperature and for how long do you leave the tubes in the water bath

  30 degrees Celsius for 10 mins
• What are the issues with Required Practical 5 about the effect of pH on amylase?


  Samples are only taken every 30 seconds so time taken for reaction is not precise

  
  

  Colour change tends to be gradual so it can be difficult to see when the reaction finishes
• How can the issues with Required Practical 5 be fixed?


  Take samples more frequently

  
  

  Ask several people to look at the spotting tile and decide when the reaction is done
• Why is a water bath used?


  To make sure the amylase and starch are the same temperature
• How would you know when the temperatures are equal?

  Use a thermometer
• What is the independent variable for the Amylase practical?

  Temperature
• What is the dependent variable for the Amylase practical?

  Time taken for amylase to break down
• What are the control variables for the Amylase practical?

  Concentration of amylase and starch solution
• What is the method for performing the Photosynthesis practical ?


  First get a boiling tube and place it 10cm away from an LED light source

  
  

  Next fill the boiling tube with sodium hydrogen-carbonate solution and put a piece of pondweed into the boiling tube

  
  

  Leave the boiling tube for 5 minutes to acclimatise

  
  

  Start a stopwatch, count the number of bubbles produced in a minute and repeat twice more to calculate a mean produced

  
  

  Finally repeat the whole experiment several times from further distances
• Why is LED used for the Photosynthesis practical?

  They do not generate a lot of heat