Biology Paper 1 Required Practicals Flashcards
(24 cards)
Describe the steps for the culturing microorganisms practical
- Clean the bench with disinfectant solution to kill unwanted bacteria
- Sterilise an inoculating loop by passing it through a bunsen burner
- Open a sterile agar gel petri dish near a bunsen burner flame (the bunsen burner will kill bacteria in the air)
- Use the inoculating loop to spread the bacteria evenly over the plate
- Place sterile filter paper containing antibiotics on the plate
- Incubate the plate at 25°C
What is the area called where there is no bacteria grown
The zone of inhibition
Describe the steps of the osmosis practical
- Peel the potato, this is because the skin affects osmosis
- Use a Cork borer to produce three cylinders of equal diameter and use a scalpel to trim the potato to an equal length (3cm)
- Measure the length with a Ruler and the mass with a mass balance
- Place each cylinder in a test tube. Add 10cm^3 of a 0.5 molar solution to the first test tube 0.25 to the second and the third with distilled water
- Leave the cylinders overnight to allow osmosis to take place
- Remove the cylinders and roll them on a paper towel to remove surface moisture
- Measure he length and mass of the cylinders again and calculate the percentage change
How to calculate percentage change
(Change in value ÷ original value)× 100
What happens to the potato in high salt / water concentrations
High salt : loses mass because water moves out of the cells
High water : gains mass because water moves into the cells
Why would there be no change in mass?
Because the concentration outside the cells and inside the cells are the same so no overall osmosis takes place
Name the microscope parts
Stage, lamp/ mirror, objective lenses, eyepiece, eyepiece lense, coarse focus, fine focus
Describe the steps for the “using a microscope” practical
- Place he prepared slide onto a stage and use the clips to hold it in place
- Select the lowest power objective lense
- Position it so it almost touches the slide by turning the coarse focusing dial. Look at he microscope from the side.
- Look down the eypeice and turn the coarse focusing dial slowly until the cells come into focus
- Use the fine focus to bring it into clear focus
How to calculate magnification
Magnification = image size ÷ actual size
How do you find the total magnification
Eyepiece lense (10x) × objective lense
What can/cannot we see in a light microscope?
Nucleus,cytoplasm,cell membrane, vacuoles and chloroplasts, but NOT ribosomes
Describe the steps of the food testing practical
- Take food sample and grind it with distilled water using a mortar and pestle
- Transfer the paste to. Beaker and add distilled water do the chemicals in the food dissolve in the water
- Filter the solution to remove suspended food particles
How to test for starch
Place 2cm cubed of solution into a test tube, add a few drops of iodine solution. If starch is present it will turn from orange to blue black. If not it will stay orange
How to test for sugars
Place food solution into a test tube, add ten drops of benedicts solution. Place it into a beaker of hot water from a kettle. Leave for five minutes. If sugars are present, the solution will change colour, giving us the approximate amount of sugar present.
To test for sugars, what do the colours mean?
Green = small amount of sugar
Yellow = more sugar present
Brick red = lots of sugar
How to test for protien
Take food solution and add biuret solution. If protein is present it will change from blue to a purple or lilac colour
How do you test for lipids
For this test DO NOT filter the solution because lipid molecules can stick to filter paper. Add a few drops of distilled water and a few drops of ethanol. Gently shake the solution. If lipids are present a white cloudy emulsion forms.
Describe the steps for the Effect of pH on amylase practical
- Place 1 drop of iodine solution in each well of a spotting tile
- Take three test tubes, 2 cm cubed of starch solution, two of the amalayse solution, and two of a pH 5 buffer solution
- Place all three test tubes in a water bath at 39°C and allow them to reach the correct temperature
- Combine the three solutions and mix with a stirring rod. Return them to the water bath and start a stopwatch
- After 30 seconds use the stirring rod to transfer 1 drop of solution in the spotting tiles the iodine should turn blue black
- Continue adding iodine every 30s until the iodine remains orange, this shows the total time for the reaction to take place, which we record
- Repeat the whole experiment using different pH buffers
What are the problems of the pH experiment and how would we address these problems?
- we only take samples every 30s - we only have the approximate time for the reaction to complete - take samples from every 10s
- We are looking for when the iodine doesn’t go blue black. This isn’t always obvious because the colour change is gradual - ask several people to look at the spotting tile
3.
Describe the photosynthesis practical
- Take a boiling tube and place it 10cm away from an LED light source LEDs are used because they don’t release much heat
- Fill the tube with sodium hydrogen carbonate solution because it releases carbon dioxide which is needed for photosynthesis
3.Put a piece of pond weed inside with the cut end on the top
- Leave it for 5 minutes to acclimatise to the conditions of the boiling tube. we should see bubbles of oxygen produced from the cut end
- Start a stopwatch and count the number of bubbles produced in one minute.
- repeat this twice and calculate the mean
- Do it all again but this time place the boiling tube 20cm away, the 30 the 40 ect.
What are the problems of the photosynthesis practical
- Bubbles come up too quickly to count
- The bubbles are not always the same size
we can fix these by calculating the volume of oxygen produced.
How do you calculate the volume of oxygen (for the photosynthesis practical)
Place the pond weed under a funnel and catch them under a measuring cylinder
what is the inverse-square law
If you double the distance, the number of bubble decreases by a factor of 4
Why does the inverse-square law happen
Because if you double the distance the light intensity falls by 4 times
