required practicals

Question 1

how do you prepare you slide for microscopy if an onion?

Answer 1

1. add a drop of water to clean the slide
2. cut open onion and separate it out into layers then use tweezers to peel off some epidermal tissue from the bottom of the layers
3. using tweezers, put the epidermal tissue in the water on the slide
4. add a drop of iodine solution to stain
5. place a cover slip on top (square thin piece of plastic or glass)
   - try not to get any air bubbles

Question 2

describe the process of preparing your petri dish to grow bacteria

Answer 2

1. sterilise the workspace
2. sterilise the inoculating loop
3. let the loop cool down
4. dip it into the culture and streak in in the petri dish in a zigzag motion
5. make sure you only tilt the lid when doing this
6. then put it in the incubator at 25 degrees celsius (prevent harmful bacteria growing)

Question 3

describe how you would test the effect of antibiotics on bacterial growth

Answer 3

1. get a pre sterilised dish with the bacteria on it
2. add the antiseptic chads into the different sections labelled A B and C
3. this will show us which is best at killing bacteria
4. sellotape the petri dish north east south and west
5. put in the incubator at 25 degrees celsius

Question 4

describe the method for photosynthesis with potato chips

Answer 4

• put one potato chip in a high sugar or salt solution and the other one in pure water
• the one in the sugar solution should loose mass as water will move out of the chip from a high concentration to a low
• the one in the water solution should gain mass as the water in the beaker will move for a high concentration to a low, therefore moving into the chip

Question 5

describe the food test for sugars?

Answer 5

Benedict- in a test tube and put in water bath and add 10 drops of Benedict solution and leave in water bath for 5 mins

should turn green, yellow or brick-red if contains sugars

Question 6

describe food test for starch?

Answer 6

Iodine- put in test tube, add few drops of solution and shake

it should from browny-orange to
black, or blue-black if contains starch

Question 7

describe food test for proteins

Answer 7

Biuret- put in test tube add 2cm cubed of solution and shake

should go from blue to pink and purple

Question 8

describe test for lipids in foods

Answer 8

sudan III- put in test tube add three drops of solution and shake

should make a bright red ring at the top

Question 9

describe the practice to investigate the effect of pH on enzyme activity for amylase

Answer 9

• put a drop of iodine into every well of the spotting tile
• place bunsen burner, heat proof mat, tripod and gauze over the bunsen burner and put a beaker of water on top to heat the water until it’s 35 degrees-try to keep temp constant throughout practical
• use a syringe to add 1cm cubed of amylase solution and 1cm cubed of a buffer solution with a pH of 5 to a boiling tube
• use test tube holders to put the tube into the beaker and wait for five mins
• use a different syringe to add 5cm cubed of a starch solution to the boiling tube
• immediately mix the contents and start stop clock
• use continuous sampling to see how fast the amylase breaks down the starch, do this by taking a fresh sample every 30 secs and drop into a well
• repeat using different pH’s to see the affects
• remember to keep control variables to make it a fair test like volume of amylase solution

Question 10

explain pondweed experiment

Answer 10

• a source of white light is placed at a specific distance from the pondweed behind a sheet (to prevent heat getting to it)
• the pondweed is left to photosynthesise for a set amount of time, as this happens, oxygen will be collected in the capillary tube, also oxygen bubbles will be produced so you need to count the amount of bubbles
• at the end, record total amount of bubbles produced
• then repeat again with the light the same distance away to get a mean of your results
• then repeat changing the distance the light source is from the pondweed