Required practicals

Question 1

How do you use an optic microscope?

Answer 1

• Place the slide onto the stage and clip it in,
• Select the smallest magnification lens
• Turn the dial to bring the lens close to the slide, look form the side to make sure the slide is not broken,
• Focus the microscope,
• Calculate the magnification by multiplying the magnification of the objective lens and the magnification of the eye piece,
• Draw an accurate representation of what you see, this should include a magnification scale.

Question 2

How do you investigate the effect of osmosis in a plant tissue?

Answer 2

• Peel the potato
• Use a cork borer to create 3 identical potato cylinders of length 3 cm,
• Weigh the potato cylinders,
• Add 10cm^3 of 0.5 mol/dm^3 of sugar solution to the first test tube, 0.25 mol/dm^3 to the second and distilled water to the third,
• Add the potato cylinders to a test tube and leave them for 24 hrs,
• Remove the potato cylinders and gently roll them on a paper towel, this takes of surface water,
• Measure the mass and length of the potato cylinders and find the percentage change,
• If the mass or length increased, Osmosis bought water into the potato because the potato had a lower concentration of water than the solution in the test tube,
• If the mass of length decreased then osmosis transferred water from the potato into the solution because it had a higher concentration of water than the solution in the test tube.

Question 3

How do you make a food sample for the food tests?

Answer 3

• Grind up the food with a mortar and pestle,
• Add the ground food to distilled water to create a paste,
• Keep adding more distilled water until it is a thin solution,
• Filter the solution to catch any suspended food particles.

Question 4

What are the food tests?

Answer 4

Take 2cm^3 food sample:

> Carbohydrates/starch:

• Add iodine solution
• If it turns from orange to blue/black then starch is present.

> Sugars:

• Add 10 drops of Benedict’s solution,
• Heat the solution to 80(),
• If sugar is present it will go from Blue to Brick red if a lot of starch is there (or to green if only slightly present or yellow if present).

> Protein:

• Add biuret solution,
• If it turns from blue to purple then protein is present,

> Lipids/fat

• Add ethanol and water to your food sample,
• Shake,
• If the solution goes cloudy and a layer of emulsion forms then lipids are present.

Question 5

Effect on pH on amylase

Answer 5

• Amylase breaks strach into simple sugars
• Put a drop of iodine in each well of the spotting tile
• take three test tubes 1 with 2cm^3 of starch solution 1 with 2cm^3 of amylase solution 1 with 2cm^3 of pH5 buffer solution
• place all test tubes in a bath of 30 degrees leave them 10 minutes so they all reach the correct temperature.
• Combine the three solutions and return this test tube to the water bath after 30 seconds use the stirring rod to transfer the solution into one well.
• The iodine should turn blue black we continue this every thirty seconds.
• When one well remains orange, which means no starch is present
• Record the time it took them repeat the experiment with different buffers the one that takes the least time is the optimum pH for amylase.

Question 6

What are the issues with the photosynthesis practical and how are they solved?

Answer 6

• You cant count the bubbles fast enough sometimes and small bubbles are equal to big bubbles even though they are a different volume of gas.
• In order to fix this, catch the bubbles in a measuring cylinder filled with water, this is upside down over a funnel that should be over the pond weed upside down so that no bubbles are lost,
• The decrease in volume of water is the volume of oxygen that is produced in the minute of timing.

Question 7

Culturing Microorganisms

Answer 7

Use an agar plate which contains nutrient broth for bacteria to grow and bacteria colonies are easy to view on this.
Sterilise the broth, agar and petri dish by opening them near a flame so unwanted bacteria in the air cannot get in.
- Sterilise the inoculating loop by using a bunsen burner flame
- add the bacteria using the loop to the agar jelly evenly across the plate
- Tape the lid on so no unwanted bacteria get in and leave the dish upside down in an incubator this is so no moisture from condensation disrupts the results.
- It is at 30 degrees so no harmful bacteria grow.
- You can use this to show the effectiveness of antibiotics
- Place sterile antibiotic covered paper disc to corners of the dish
- After culturing there will be a zone of inhibition around the antibiotic this is where the bacteria was killed the larger the inhibition area the more effective the antibiotic.

Question 8

Culturing Microorganisms

Answer 8

Use an agar plate which contains nutrient broth for bacteria to grow and bacteria colonies are easy to view on this.
Sterilise the broth, agar and petri dish by opening them near a flame so unwanted bacteria in the air cannot get in.
- Sterilise the inoculating loop by using a bunsen burner flame
- add the bacteria using the loop to the agar jelly
- Tape the lid on so no unwanted bacteria get in and leave the dish upside down in an incubator this is so no moisture from condensation disrupts the results.
- It is at 30 degrees so no harmful bacteria grow.