Biology Required Practicals B1 to B9

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  • Created by: Dene3
  • Created on: 12-05-18 14:42

Preparing and observing a slide

  • Add a drop of water onto middle of a cleant slide
  • Cut up an onion and separate it into layers. Use tweezers to pull out a layer from the lower epidermis
  • Using the tweezers, place it on the drop of water on the slide
  • Add a drop of staining Iodine solution. A stain is used to highlight objects in a cell by adding colour 
  • Place a coverslip using a needle. Stand the coverslip next to the specimen and lower it. Make sure no air bubbles are captured as they will obstruct the view of the specimen. 

Looking at the slide

  • Clip the slide onto the stage
  • Select the lowest-powered objective lens
  • Adjust the coarse adjustment knob until the image is roughly in focus
  • Use the fine adjustment knob to change the focus until the image is clear
  • If a higher magnification is needed, switch to a higher-powered objective lens and adjust the focusing knobs 
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Culturing Microorganisms

Bacteria need to grow in a culture medium which contains carbohydrates, proteins, minerals and vitamins required for growth. The culture medium can be an agar jelly plate or a nutrient broth solution. Backteria grown on agar plates will form visible colonies on the surface of the jelly, or will spread out to give an even covering of bacteria. 

  • Sterilise everything by heating it
  • To make an agar plate, hot agar jelly is poured into a petri dish 
  • When the jelly is cooled, inoculating loops can be used to transfer microorganisms
  • The inoculation loop is passed through a bunsen burner fro sterlisation
  • Alternatively, a sterile dropping pipette and spreader can be used to get an even coverage of bacteria 

In school, the culture is kept at 25 degrees celsius so that harmful patthogens do not grow

In industry, they multiply much quicker because cultures are kept in higher temperatures

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Effect of Antibiotics on Bacterial Growth

  • Prepare a culture of bacteria 
  • Place paper discs soaked in different antibiotics in a sterile agar plate with an even coverage of bacteria. Leave some space between the discs. 
  • A control paper disc with distilled water should also be added. This is to ensure that the changes are occuring as a result of the IV (different antibiotics) and not something else. 
  • The antibiotic should diffuse into the agar jelly.
  • Antibiotic resistant bacteria are unaffected but non-resistant strains will die. This will result in a clear section around the paper disc called the inhibition zone
  • A lid is taped onto the petri dish to ensure bacteria from the air does not get in
  • It is stored upside down so that condensation does not fall onto the agar surface
  • Leave the plate for 48 hours in 25 degrees
  • The larger the inhibition zone, the more effective the antibiotic against bacteria
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Food tests for reducing sugars and starch

Get a piece of food and break it up using a pestle and mortar. Add some distilled water and mix it with a glass rod. Filter the solution using a funnel and filter paper to remove the solid bits. 

Test for Reducing Sugars:

  • Prepare a food sample and transfer 5cm3 to a test tube and place it in a water bath set to 75 degrees celsius 
  • Add some Benedict's solution to the test tube using a pipette (about 10 drops)
  • Place the tube in the water bath and make sure it is faced away from you 
  • If a reducing sugar is present, then the solution will change from blue to green, yellow or brick-red depending on how much sugar there is 

Test for Starch 

  • Make a food sample and transfer 5cm3 of the sample to a test tube
  • Add a few drops of iodine solution and shake it gently 
  • If starch is present the solution will change from browny-orange to black or blue-black
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Food tests for proteins and lipids

Get a piece of food and break it up using a pestle and mortar. Add some distilled water and mix it with a glass rod. Filter the solution using a funnel and filter paper to remove the solid bits. 

Test for Proteins

  • Prepare a sample of 2cm3 of food in a test tube
  • Add 2cm3 of biuret solution and mix the contents by gently shaking it
  • If the food sample contains protein, the solution will change from blue to pink or purple

Test for Lipids

  • Prepare a sample of 5cm3 of food in a test tube and do not separate it from the distilled water
  • Add 3 drops of Sudan III stain solution and mix the contents by gently shaking it
  • If the food sample contains lipids, the mixture will separate into two layers. The top layer will be bright-red
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Effect of pH on amylase

Amylase= breaks down starch into maltose/simple sugars

  • Iodine is put into a spotting tile, a drop in each well
  • In three test tubes there is 2cm of starch solution, amylase solution and pH 5 buffer solution (used to control the pH)
  • All three are placed in a water bath of 30 degrees so they reach the correct temperature for 10 minutes
  • Combine the three solutions into a test tube and mix with a stirring rod
  • Immediately, it is put into the water bath and the stopwatch is started
  • After 30 seconds, one drop of solution is added to a well in the spotting tile using the stirring rod which has iodine
  • The iodine should turn blue-black and this is continued every 30 seconds until the iodine remains orange-the reaction is complete
  • The experiment is repeated for different buffer solutions
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Effect of light intensity on photosynthesis

Canadian pondweed can be used to mesure the effect of light intensity on photosynthesis. 

  • A source of white light is placed at a specific distance from the pondweed
  • The pondweed is left to photosynthesise for a set amount of time. As it photosynthesises, the oxygen released will collect in the capillary tube 
  • At the end of the experiment, a syringe is used to draw gas bubbles in the tube up alongside a ruler and the length of the gas bubble is measured. This is proportional to the volume of oxygen produced 
  • For this experiment, any variables that could affect the results should be controlled (can you think of any examples?)
  • The experiment is repeated twice with the light source at the same distance and the mean volume of oxygen produced is calculated 
  • Then the whole experiment is repeated with the light souce at different distances from the pondweed

The appratus can be altered to measure the effect of temperature or CO2. The test tube of pondweed can be put in water bath of set temperature, or a measured amount of sodium hydrogencarbonate can be dissolved. The experiment can be don with different temps or concs

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