REQUIRED PRACTICALS PAPER 1 Flashcards
Describe the test for sugars (a type of carbohydrate)
- Grind up food and add Benedict’s reagent
- Boil tube to a heat above 65°C) in a water bath
- Sugar turns solution (from blue to) green / yellow / orange / brick red
Describe the test for starch a type of carbohydrate
: give colour change
- Grind up food
- add iodine solution
- If starch present than
orange/brown to blue black
Describe the test for lipids (fats
- Grind up food and add ethanol, then add water
- Fat turns solution milky | cloudy white
Describe the test for proteins
• Grind up food and add Biuret reagent
• Protein turns solution (from blue to) purple / lilac
practical:
how to prepare a slide to view onion cells
1) add a drop of water to the middle of a Clean slide
2) cut up an onion and use tweezers to peel off epidermal tissue
3) place the epidermal tissue into the water on the slide
4) add a drop of iodine solution
5) place a cover slip on top by carefully tilting and lowering it so it covers the specimen
How to use a light microscope to look at your slide
clip the prepared slide onto the stage
• select the lowest powered objective lens
• use the coarse adiustment knob to
move the stage downwards until the image is in focus
• adjust the focus with the fine adiustment knob until you get a clear image of what’s on the slide
• if higher magnification is needed swap to a higher-powered objective lens and refocus
Investigate the effect of antiseptics or antibiotics on bacterial growth using agar
plates and measuring zones of inhibition
- sterilise glass Petri dishes and agar gel in an autoclave
- Pour the sterile agar gel into the Petri dish and allow time to set
- sterilise the inoculating loop by passing it through a Bunsen burner flame
- dip the inoculating loop into the solution of microorganisms and make streaks with the loop on the surface of the agar
- Place sterile filter paper discs containing antibiotic onto the plate
- put the lid on the Petri dish and secure it with tape. Label accordingly then turn and store upside down
- Incubate the culture at 25oC in school laboratories
- Measure the zone of inhibitions to find the most effective antiseptic
Describe the practical to observe the effect of sugar solution son plant tissue:
- give the method
- independent variable
- dependent variable
- peel the potato
- use a cork borer to produce three cylinders of potato
- use a scalpel to trim the cylinders to the same length
- measure the length of each cylinder using a ruler and the mass of each cylinder using a balance
- Now place the cylinders into the test tubes. Add varying concentrations of sugar solution into each sylinder-
- one test tube must be of distilled water
- leave the potato cylinders overnight to allow osmosis to take place
- remove the potato cylinders and gently roll them on paper towel to remove any surface mositure
- measure the length and the mass of the cylinders again
- calculate the percentage change of the mass using the equation: percentage change = change in value/ original value x 100
IV: concentration of sucrose solution
DV: mass and length of potato
CV: volume of solute, temperature , time
required practical - investigating the effect of pH on enzyme activity:
- place one drop of iodine solution into each well of a spotting tile
- Add 2 cm3 of amylase enzyme solution and starch solution and pH buffer solution to three separate test tubes.
- Place all 3 test times in a water bath at 35 degrees
- leave for 10 minutes to allow solutions to reach correct temperature
- Combine the three solutions into one test tube and mix with a stirring rod
- return to water bath and start a stopwatch
- after 30 secs, use the stirring rod to transfer one drop of solution to a well containing iodine
- iodine should turn blue black as starch is present
- take a sample every 30 secs until the iodine remains orange
- this tell us that starch is no longer present
- repeat this experiment several times using different pH buffers
give two problems and solutions to the enzyme practical
problems:
- taking samples every 30 secs so only have an approximate time for the reaction to complete
- gradual colour change and so difficukt to see when reaction is ended
solutions
- shorter sample time like 10 secs
- have several people to look at the spotting tile and decide when the reaction is completed
required practical 6 : photosynthesis
- take a boiling tube and place it 10cm away from an LED light source
- LED is used as they do not release much heat thus not affecting the experiment to a great degree
- fill the boiling tube with sodium hydrogen carbonate solution, this releases carbon dioxide which is needed for photosynthesis
- put a piece of pondweed into the boiling tube with the cut end at the top
- leaf for 5 minutes to acclimatise to the boiling tube
- bubbles of gas are produced from the cut end , these are oxygen bubbles
- start a stopwatch and count the number of bubbles produced in one minute
- repeat the two more times and calculate the mean number of bubbles produced in 1 minute
- repeat the experiment again with different distances in 10cm increments
what are the 2 problems and solutions to the photosynthesis practical
problems:
- number of bubbles may be counted inaccurately
- bubbles not always same size
solutions:
- measuring the volume of oxygen produced by placing the pondweed under a funnel and catch the bubbles using a measuring cylinder
