Paper 1 Required Practicals

Question 1

1. Describe how you would prepare a microscope slide for anyalsis?

Answer 1

• 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

Question 2

1. Why is a thin sample of tissue required ?

Answer 2

Allows light to pass through so internal structures can be observed

Question 3

1. Why is water added to the slide before the sample is mounted ?

Answer 3

Allows the sample to be suspended between the slide and the cover slip, and ensures the cover slip stays in place

Question 4

1. Why is iodine solution added to stain the cells ?

Answer 4

Iodine solution adds contrast - reacts with starch in plant cells and turns blue-black; allows internal structures (e.g. nucleus ) to become more visible

Question 5

1. Why is the cover slip lowered using a mounting needle ?

Answer 5

Ensures that no air bubbles are trapped

Question 6

1. How would you calculate the magnification of an image ?

Answer 6

Magnification = observed cell length / actual cell length

Question 7

1. What safety precautions should be taken during this expermient ?

Answer 7

Wear safety goggles when handling iodine solution

Question 8

2. What is osmosis ?

Answer 8

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

Question 9

2. Describe how you would carry out an investigation into osmosis using potato tissue

Answer 9

• 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)

Question 10

2. Why is it necessary to use a cork borer to cut the the cylinders ?

Answer 10

Results in equal size samples so changes in length and mass can be compared easily

Question 11

2. Why is it necessary to blot the cylinders with paper after removing them ?

Answer 11

Each cylinder may have a different amount of water on its surface, so masses may vary. Blotting cylinders allows masses to be comparable

Question 12

2. What safety precautions should be taken with the osmosis experiment ?

Answer 12

Handle cork borer with care

Question 13

3. Describe how you would prepare a sample of food to be tested

Answer 13

Grind up food samples using pestle and mortar

Mix with water

Filter with funnel and filter paper

Question 14

3. Describe how you would test for the presence of starch in a sample

Answer 14

Add iodine solution to sample

If starch is present , solution turns from brown to blue-black

Question 15

3. Describe how you would test for the presence of a reducing sugar in a sample

Answer 15

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

Question 16

3. Describe how you would test for the presence of protein in a sample

Answer 16

Add Biuret reagent

Shake mixture

If protein is present, solution turns from blue to purple

Question 17

3. Describe how you would test for the presence of lipids in a sample

Answer 17

Add ethanol to the sample
Add water to sample
Shake test tube
White emulsion formed if lipid present

Question 18

4. Describe how you would investigate the effect of pH on the rate of reaction of the amylase enzyme

Answer 18

• 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)

Question 19

4. Which enzymes catalyses the breakdown of starch in the human digestive system ?

Answer 19

Amylase - catalyses breakdown of strach to maltose

Question 20

4. Why must samples be left in the water bath before solutions are mixed ?

Answer 20

To allow temperatures to equilibrate

Question 21

4. What is a buffer solution ?

Answer 21

A solution which can resist changes in pH

Question 22

5. What is photosynthesis ?

Answer 22

The process by which plants synthesise glucose using light energy from the sun

Question 23

Describe how you would investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant

Answer 23

• 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)

Question 24

Why is it best to use an LED light source rather than a lamp ?

Answer 24

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

Question 25

How can the measurement of oxygen production be made more accurate ?

Answer 25

If the pondweed is placed under a filter funnel with an inverted measuring cylinder over the spout, the volume of oxygen produced can be determined

Question 26

Why is sodium hydrogen carbonate solution used during this expermient ?

Answer 26

It releases carbon dioxide , which is used by the pondweed during photosynthesis

Question 27

Why can the number of bubbles produced be used to calculate the rate of photosynthesis ?

Answer 27

Oxygen bubbles are formed as a product during photosynthesis. The number of bubbles produced in a given time is proportional to the rate of photosynthesis