Core Practicals🦠

Question 1

Core practical- using microscopes

Answer 1

Magnification = eyepiece lens times objective lense

• use your own cheek cells or pieces of tissue from onion bulbs, rhubarb stems or leaves.
• collect a small specimen of the cells
• add drop of water or stain to centre of microscope slide. Record the name of the stain you use.
• place your specimen on the water or stain
• use toothpick to lower a coverslip onto the specimen. This keeps the specimen flat, holds it in place and stops it dying out.
• examine under microscope- start with lowest magnification and work up to higher
• draw one or more of the cells you see and annotate drawing

Question 2

Core practical- PH and enzymes

Answer 2

• set up tripod, gauze, heat-resistant mat, Bunsen burner and beaker half filled with water. Heat water to 40 degrees and use the collar of Bunsen to produce a flame that keeps the water at this temp.
• place one drop of iodine solution into each depression of a spotting tile (well tray)
• measure 2cm cubed of amylase solution into tube
• add 1cm cubed of a solution with a particular PH into a tube
• add 2cm cubed of starch solution to the tube and place it carefully into the water bath. Start the stopwatch and stir the mixture
• every 20 secs, take a small amount of mixture and place one drop into a drop of iodine solution. Stop repeating this when the iodine stops changing colour. When the solution is blue/ black starch is present but when it’s yellow/ orange the reaction is complete.
• repeat experiment with different PH solution

Question 3

Osmosis in potato slices

Answer 3

• label separate boiling tubes with the sucrose concentration of each solution you’ll test. Place all the tubes in a rack. The concentrations should be 0, 10,30 and 50.
• cut similar sized pieces of potato, enough for one per tube.
• blot each piece dry and measure and record its mass and put it in an empty tube.
• fill each tube with the solution of the appropriate concentration + cover potato with the solution.
• after 15 mins remove each piece of potato and blot dry. Measure and record it’s mass again.
• the higher the sucrose concentration, the more the mass of the potato decreases. The potato with distilled water increases in mass.

Question 4

Core practical- light intensity and photosynthesis

Answer 4

Place 6 clear plastic bottles 10-15cm away from each other along a meter rule.
Add 20 algal balls to each bottle and the same amount of indicator solution to each bottle and put on the bottle caps.
Work out the PH of each indicator at the start by comparing with PH range bottles.
At one end of meter rule put a lamp and between the first bottle of indicator and the lamp place a tank of water so the heat coming from the lamp doesn’t interfere with the results.
Cover one bottle with kitchen foil- this is the CONTROL.
place the control next to the bottle that’s closest to the lamp.
Turn on the lamp and wait (1 hour) to see the changes in colours in the bottles.
Compare the colours of bottles with PH range bottles and write down PH of solutions.
Calculate the change in PH/hour for each bottle.

As the bottles get further away from light, rate of photosynthesis decreases + solution is more yellow. This is because more carbon dioxide is present so the solution is more acidic.