Practical Required Knowledge

Question 1

Purification of DNA

Answer 1

1. Add in small species to a mixture of slay water and washing up liquid (damaged cells membranes)
2. Stand in hot water for 15 mins (speed up breakdown)
3. Cool mixture
4. Blend mixture for no more than 5 seconds
5. Filter pieces from the liquid
6. Add protease (breaks down protein)
7. Add an equal volume of ice cold ethanol
8. See layer of DNA that isn’t dissolved in the ethanol

Question 2

Wet mount for light microscope
(Live species and aquatic animals)

Answer 2

1. Use a pipettes to put a drop of water on the slide
2. Use tweezers to place the specimen in the water
3. Stand the cover slip upright on the slide next to the water droplet and carefully tilt it down onto the specimen (avoid any air bubbles)
4. Add a stain on the edge of the cover slip with a paper towel on the opposite edge to absorb it

Question 3

Dry mount for light microscope
(Used for specimens such as hairs, pollen)

Answer 3

1. Slice the specimen into a thin OOVE so light can pass through
2. Use tweezers to place it in the centre of the slide
3. Place a cover slip on top

Question 4

Drawings requirements

Answer 4

• No shading
• Take up at least half the page
• Label lines must be horizontal, drawn with a ruler, cannot overlap and exactly touch the object they are labelling
• A scale given for magnification
• Drawn in pencil

Question 5

Using a colorimeter

Answer 5

1. Switch on and leave to stabilise for 5 mins
2. Select appropriate filter for positive result to test (centrifuge out any ppt)
3. Set the colorimeter to 0 using blanking solution of distilled water
4. Fill cuvette With sample
5. Read absorbante of light (%)
6. Do for known concs of substrate and plot calibration curve
7. Compare absorbance to curve to find exact conc of substrate in solution

Question 6

Using a potometer

Answer 6

1. Cut shoot underwater at a slant (to increase SA) to prevent air entering the xylem
2. Assemble under water and insert the shoot underwater
3. Remove from water but keep end of capillary tube submerged in a beaker of water
4. Dey leaves
5. Allow time to acclimatise then shut the tap
6. Form an air bubble in the capillary tube
7. Record the starting position of the air bubble
8. Start the stopwatch and record distance moved at regular time intervals (eg every 30 mins)
9. Calculate rate of bubble movement (mm min-1)