Paper 1 Required Practicals Flashcards
- Describe how you would prepare a microscope slide for anyalsis?
- peel off epidermal layer using forceps
- place sample on drop of water on microscope slide
- add drops of iodine solution sample
- lower cover slip onto sample using mounting needle
- Why is a thin sample of tissue required ?
Allows light to pass through so internal structures can be observed
- Why is water added to the slide before the sample is mounted ?
Allows the sample to be suspended between the slide and the cover slip, and ensures the cover slip stays in place
- Why is iodine solution added to stain the cells ?
Iodine solution adds contrast - reacts with starch in plant cells and turns blue-black; allows internal structures (e.g. nucleus ) to become more visible
- Why is the cover slip lowered using a mounting needle ?
Ensures that no air bubbles are trapped
- How would you calculate the magnification of an image ?
Magnification = observed cell length / actual cell length
- What safety precautions should be taken during this expermient ?
Wear safety goggles when handling iodine solution
- What is osmosis ?
The movement of water from a higher water potential to a lower water potential through a partially permeable membrane
equation for practical = (final mass - initial mass)/initial mass x 100
- Describe how you would carry out an investigation into osmosis using potato tissue
• Cut identical potato cylinders using a cork borer
• Measure and record the length and mass of cylinders using ruler and balance
• Add each cylinder to one of three solutions: 1M sugar solution, 0.5M sugar solution and distilled water
• Leave cylinders in tubes overnight
• Remove cylinders from tubes and blot them using paper towels
• Record length and mass of each cylinder
• Draw graph of change in mass in grams (y axis) against concentration of solution in mol dm^3 (x axis)
- Why is it necessary to use a cork borer to cut the the cylinders ?
Results in equal size samples so changes in length and mass can be compared easily
- Why is it necessary to blot the cylinders with paper after removing them ?
Each cylinder may have a different amount of water on its surface, so masses may vary. Blotting cylinders allows masses to be comparable
- What safety precautions should be taken with the osmosis experiment ?
Handle cork borer with care
- Describe how you would prepare a sample of food to be tested
Grind up food samples using pestle and mortar
Mix with water
Filter with funnel and filter paper
- Describe how you would test for the presence of starch in a sample
Add iodine solution to sample
If starch is present , solution turns from brown to blue-black
- Describe how you would test for the presence of a reducing sugar in a sample
Add Benedict’s reagent to sample
Boil test tube in a hot water bath
If reducing sugar is present, a brick red precipitate froms. If not, solutiom remains blue
- Describe how you would test for the presence of protein in a sample
Add Biuret reagent
Shake mixture
If protein is present, solution turns from blue to purple
- Describe how you would test for the presence of lipids in a sample
Add ethanol to the sample
Add water to sample
Shake test tube
White emulsion formed if lipid present
- Describe how you would investigate the effect of pH on the rate of reaction of the amylase enzyme
• Place starch solution, amylase solution and buffer solution in a water bath at 25°C for a few minutes
• Combine solutions and add a drop of the mixture to iodine solution on a tile
• Add the mixture to iodine solution drops on the tile at fixed 30s intervals until the iodine solution remains brown (does not turn blue-black)
• Calculate the rate of reaction using 1 / time taken for solution to remain brown
• Repeat at different pH values using different buffer solutions
• Plot graph of rate (y) against pH (x)
- Which enzymes catalyses the breakdown of starch in the human digestive system ?
Amylase - catalyses breakdown of strach to maltose
- Why must samples be left in the water bath before solutions are mixed ?
To allow temperatures to equilibrate
- What is a buffer solution ?
A solution which can resist changes in pH
- What is photosynthesis ?
The process by which plants synthesise glucose using light energy from the sun
Describe how you would investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant
• Place cut pondweed in a boiling tube (containing sodium hydrogen carbonate solution) at a fixed distance from a light source
• Count the number of bubbles produced in one minute using stopwatch
• Repeat several times at different distances/light intensities, and calculate a mean for each distance
• Plot a graph of light intensity (x) against rate of photosynthesis (bubbles per minute, y)
Why is it best to use an LED light source rather than a lamp ?
A lamp will emit more heat energy than a LED - therefore it may change the temperature of the experiment and affect the rate of photosynthesis
