Paper 1 Required Practicals Flashcards
Required practical activity 1: use a light microscope to observe plant cells.
How do you prepare a microscope slide?
- Specimens must be prepared on a microscope slide to be observed under a light microscope
- This must be done carefully to avoid damaging any biological specimen
- The most common specimens to observe under a light microscope are cheek cells (animal cells) and onion cells (plant cells)
- Stains are used to highlight structures within cells – methylene blue is used to stain cheek cells, iodine for onion cells
Required practical activity 1: use a light microscope to observe plant cells.
How do you use a Microscope?
- Understanding the main features of a light microscope is essential if you are to use it correctly
- ALWAYS TURN THE LIGHT ON
Required practical activity 1: use a light microscope to observe plant cells
What are the rules for a biological drawing?
- Producing biological drawings of what you see under the microscope is a key skill
- The key is not to try to be too artistic with your drawings – they are supposed to be scientific so make sure you follow the rules
Required practical activity 1: use a light microscope to observe plant cells
How do you calculate magnification?
Magnification of the microscope = magnification of eyepiece × magnification of objective
Watch Free Science lesson vid.
Required practical activity 3: investigate the effect of a range of concentrations of salt solution on the mass of plant tissue.
Method?
- Use a scalpel or cork borer to cut 5 pieces of the plant of the same diameter/size
- Use a scalpel to trim and cut each plant tissue so they are all equal in length
- Measure the initial mass of each potato cylinder in a table of results
- Measure 10cm^3 of each sugar or salt solution and pour into each boiling tube. Label the tubes clearly.
- Add one potato cylinder to each boiling tube and leave for a specified amount of time.
- Remove the potatoes. Blot dry and record the final mass and length of each
- You should measure both the mass and the length of each potato cylinder before and after it has been submerged in solution - these measurements are your dependent variables from which you will calculate the percentage change in mass and length
- The independent variable is the concentration of salt or sucrose solution in mol dm3
- Important control variables are type and volume of solute in solution, temperature, and time
Required practical activity 3: investigate the effect of a range of concentrations of salt solution on the mass of plant tissue.
Analysis?
Required practical activity 4: use qualitative reagents to test for a range of carbohydrates, lipids and proteins.
Preparing a sample
- Before you can carry out any of the food tests described below, you may need to prepare a food sample first (especially for solid foods to be tested)
- To do this:
- Break up the food using a pestle and mortar
- Transfer to a test tube and add distilled water
- Mix the food with the water by stirring with a glass rod
- Filter the mixture using a funnel and filter paper, collecting the solution so there are no suspended food particles
- Proceed with the food tests
Required practical activity 4: use qualitative reagents to test for a range of carbohydrates, lipids and proteins.
Test for sugars
- Set up a traditional water bath using a Bunsen burner
- Add food sample to test tube with a few drops of benedict’s solution
- Leave the test tube in the water bath at 80 degrees for 5 minutes
If sugar is present soloution will change colour.
A green colour tells us there is a small amount of sugar.
A Yellow colour tell us there is more sugar.
A Brick-red colour tells us there is lots of sugar.
If the test is negative the test tube should be light blue(the colour shouldn’t change.
Hazards
- Wear safety goggles.
- Benedict’s solution is an irritant.
- Avoid contact with skin and eyes.
Required practical activity 4: use qualitative reagents to test for a range of carbohydrates, lipids and proteins.
Test for Starch
- Add food sample to a test tube
- Add a few drops of iodine
If starch is present the colour will change to blue-black.
If it is not present the solution will have no colour change.
Hazards:
- Wear safety goggles.
- Iodine solution is an irritant.
- Avoid contact with skin and eyes.
Required practical activity 4: use qualitative reagents to test for a range of carbohydrates, lipids and proteins.
Test for Proteins
- Add 2cm^ 3 food sample to a test tube
- Add 2cm^3 biuret reagent and shake
- IF protein is present it will change from a blue to a Purple or lilac colour
Hazards
- Wear safety goggles.
- Biuret solution contains copper (II) sulphate which is dangerous particularly if it gets in the eyes, so always wear goggles
- Avoid contact with skin and eyes.
Required practical activity 4: use qualitative reagents to test for a range of carbohydrates, lipids and proteins.
Test for lipids/fats
- Add food sample to a test tube
- Add a few drops of distilled water and a few drops of ethanol
- Shake the solution gently
If lipids are present a white cloudy emulsion forms.
Hazards
- Wear safety goggles.
- Ethanol is flammable. It is very important that no naked flames are present
- Avoid contact with skin and eyes.
