Paper 1 Practicals Flashcards
How do you use an optical microscope to view a prepared slide?
1- place the slide onto the stage, use clips to hold slide in place
2- then select lowest power objective lense (gives lowest magnification), usually 4x
3- use the coarse adjustment knob to move the stage as if it is almost touching the objective lens, looking at it from the slide when adjusting
4- look down through the eye-piece, slowly turn the coarse adjustment knob, slowly increasing distance between objective lens until the cells come into focus
5- use fine adjustment knob to bring the cells into clear focus
6- now select higher power objective lens and adjust the fine adjustment knob to bring the image to focus again
7- can make clear, labelled drawing of the cells, including magnification scale
How do you prepare an uncontaminated bacterial culture, using aseptic technique?
- sterilise petri dishes, bacterial nutrient broth and agar plates, killing unwanted microorganisms and prevents contamination
- sterilise the inoculating loop, passing it through an open blue bunsen burner flame
-attach the lid of the petri dish with tape, stops lid from falling off - place agar plate upside down, reduces condensation
- culture at 25 degrees C, reduces chances of unwanted bacteria growth
How do you use agar plates to test the effect of antibiotics on bacterial growth?
1- clean the bench with disinfectant solution, kills any unwanted microorganisms (no contamination)
2- sterilise inoculating loop (bunsen burner flame)
3- open agar plate near + towards bunsen burner, killing bacteria in the air
4- use loop to spread chosen bacteria evenly over the plate
5- place sterile paper discs containing antibiotics onto the plate, including 1 control (sterile water)
6- incubate plate at 25 degrees C
7- after few days, around the discs, region of no growth, zone of inhibition
8- measure effect of antibiotic by finding area of zone of inhibition
How do you investigate the effects of osmosis on plant tissue?
- First peel potato/vegetable skin as the skin can affect osmosis
- Use a cork borer to produce 3 cylinders of potato with the same diameter + use a scalpel to trim the cylinders to the same length (around 3 cm)
- Measure length of each cylinder with a ruler + mass using a balance
- Place each cylinder into a test tube and add 10cm^3 of 0.5 molar sugar solution to the first test tube
- Add 10cm^3 of 0.25 molar sugar solution to the second test tube + 10cm^3 of distilled water to the third test tube (contains no dissolved substances)
- Leave potato cylinders overnight to allow osmosis to take place
- Remove potato cylinders and gently roll them on paper towel to remove any surface moisture
- Re measure and weigh the cylinders using a ruler and a balance
- Calculate percentage change in length and mass
- Plot the change in mass against the concentration of sugar solution on a graph (shows negative correlation)
FINDINGS:
water- potato cylinder gains mass (from area of high conc to area of low conc)
concentrated sugar solution- cylinder loses mass (from area of high conc to area of low conc)
What is Osmosis?
The diffusion of water from an area of high concentration to an area of low concentration through a partially permeable membrane
What happens when a plant cell is placed in water?
Water will move into the cell, and the cell will expand and become turgid
What happens if a plant cell is placed in a concentrated solution?
Water moves out of the cell, the cell will shrink and become flaccid
How do you prep for a food test (protein and carbohydrates)?
- Take a food sample and grind with distilled water using a pestle and mortar to make a paste
- Transfer paste to beaker + add distilled water, stir to dissolve food into the water
- Filter solution to remove suspended food particles
Describe the chemical test for starch (carbohydrate)?
- place 2cm^3 of food solution into test tube + add few drops of iodine solution (orange)
- if starch is present, the solution will go turn from orange to blue black
if no starch is present, the solution will stay orange
Describe the chemical test for sugars?
- place 2cm^3 of food solution into a test tube
- add 10 drops of Benedict’s solution (blue)
- place test tube into water bath of hot water, leaving it for 5 minutes
- if sugars present, solution changes colour, indicating amount of sugar present in solution
- green= small amount of sugar
- yellow= more sugar present
- brick red= lots of sugar present
ONLY WORKS FOR CERTAIN SUGARS ie glucose (reducing sugars
non reducing sugars= NOT WORK ie sucrose
Describe the chemical test for proteins?
- place 2cm^3 of food solution into a test tube
- add 2cm^3 of Biuret solution (blue)
- If proteins present, solution goes from blue to purple/ lilac
Describe the chemical test for lipids (fats)?
to prepare= grind food with mortar and pestle BUT don’t filter solution before testing-> lipid molecules can stick to filter paper
- place 2cm^3 of the food solution into a test tube
- add a few drops of distilled water + few drops of ethanol
- gently shake solution
- if lipids present-> white, cloudy emulsion forms
Describe how to investigate the effect of pH on amylase?
Amylase= carbohydrase enzyme, breaks down starch molecules into simple sugars
- place 1 drop of iodine solution into each well of a spotting tile
- take 3 test tubes: in the first test tube, add 2cm^3 of starch solution, in the second test tube, add 2cm^3 of amylase solution, in the third test tube, add 2cm^3 pH 5 buffer solution (used to control pH)
- Place all 3 test tubes in a 30 C water bath for 10 mins to reach the correct temperature
- Combine the 3 solutions into 1 and mix using a stirring rod, return to the water bath and start a stopwatch.
- After 30 seconds, use a stirring rod to transfer 1 drop of solution to a well in the spotting tile (containing iodine)-> should turn blue black, showing starch is present
- take a sample every 30 seconds until the iodine remains orange-> showing starch is no longer present
- record the time for this in results
- Repeat the experiment with different pH buffer solutions (ie pH 6, 7, 8)
What are the problems with the experiment for testing for amylase?
Only taking samples every 30 seconds- time for reaction to be completed ends up being approximate-> can take samples at smaller intervals (ie every 10 seconds)
Looking for time iodine stops turning blue-black- may not be obvious, colour change is gradual-> peer review the colour change to decide whether reaction is complete
Describe the investigation on the effect of light intensity on the rate of photosynthesis (by counting bubbles)?
- Take a boiling tube and place it 10cm away from the LED light source (LED don’t release lots of heat, too much would change the temp of the experiment)
- Fill boiling tube with Sodium hydrogen carbonate solution (released CO2, needed for photosynthesis)
- Place a piece of pondweed into the boiling tube with the cut end at the top-> leave for 5 mins to acclimatise to the boiling tube conditions
- Begin to see bubbles of oxygen gas being produced from the cut end of the pondweed from photosynthesis
- Start a stopwatch and count the number of bubbles produced in a minute
- Repeat 2 more times, calculate mean number of bubbles produced in 1 minute
- Then, repeat experiment again but at different distances from the light (20 cm, 30 cm etc)
