Bio Practicals 1

Question 1

Preparing & observing an onion cell

Answer 1

1. Place a drop of water in the centre of the slide
2. Using tweezers , take a thin layer of onion skin
3. Place the onion skin in middle of slide
4. Add drop of iodine to stain cell structures so they are visible
5. Use tweezers to slowly lower a cover slip over the onion skin so there are no air bubbles

Question 2

Enzyme activity

Answer 2

• IV-> pH of solutions
• DV-> time taken for iodine to stop turning blue black
• CV-> volume of starch, volume of pH, temperature

1. Place drop of iodine into each area of simple tray
2. Measure 2cm3 of amylase solution into test tube with pipette
3. Add 1cm3 drops of pH solution to the test tube
4. Record pH of solution
5. Add 2cm3 of starch solution to mixture & stir
6. Mix solution into test tube test tube & place in water bath at 35•C for 5 mins
7. Every 20s use pipette to take a sample of mixture
8. Add sample to iodine solution on spotting tile
9. If iodine turns black turn repeat step 5 if its still yellow then the starch has been broken down to glucose
10. Record the time
11. Repeat experiment using different pH solutions

Question 3

Osmosis in plant cell

Answer 3

• IV-> concentration of sugar solution
• DV-> change in mass
• CV-> volume of sugar solution, length of potato chips, time left in solution, amount of drying

1. Label boiling tubes with concentrations of sugar solution (0M, 0.25M, 0.5M)
2. Measure 15cm3 of each concentration of sugar solution using a measuring cylinder ; add to labelled tube
3. Bore potato using cork borer
4. City of any potato skin , measure 3cm long slingers with. Scalpel
5. Weigh the potato using balance
6. Record starting masses
7. Leave potato chips in sugar solution for 15 mins
8. Remove potato from boiling tubes, dry it, reweigh it and record the results

Question 4

DNA extraction from fruits

Answer 4

1. Collection solution A which has been made by dissolving 3G of salt for every 100cm3 of water & adding 10cm3 of washing up liquid
2. Crush strawberry using pestle & mortar. Put them into a large empty beaker & add the solution A. stir slowly for 1 min.
3. Place the beaker in water bath for 15 mins to increase rate of reaction
4. Filter the mixture & pour the filtrate into a boiling tube
5. Add 2 drops of enzyme solution . Swirl boiling tubes carefully & leave in rack for 1 min
6. Tilt tube slightly & pour ice cold ethanol dow the side. Leave the tube for a few mins. Then you should see a white layer between juice and ethanol which is the DNA

Question 5

DNA extraction from fruits-> why is salt, detergent, mash fruit, leave in water bath, ethanol used

Answer 5

• salt-> DNA clumps together
• Detergent-> breaks down cell surface & nuclei membranes
• mash-> increases surface area & breaks down cell wall
• water bath-> increasing temperature increases rate of reaction
• ethanol-> DNA is insoluble in ethanol so it forms a precipitate