Required Practicals

Question 1

Tell me about microscopy.

Answer 1

Start with the lowest-powered lens then move the stage up with the coarse adjustment knob > look down the eyepiece and adjust the focus with the adjustment knobs (use the coarse one first) > to see the slide with a greater magnification, swap to a higher-powered lens and refocus

Question 2

What are 4 things to remember in microscopy?

Answer 2

1: use a sharp pencil
2: draw unbroken lines
3: label important features
4: include a magnification scale

Question 3

What are the 4 steps to investigate the effects of different concentrations of sugar or salt solutions on plant tissue?

Answer 3

1: cut a potato into identical cylinders
2: measure the mass of each cylinder
3: prepare beakers containing different concentrations of sugar or salt solution and one of pure water. Put one cylinder into each beaker
4: leave for 24 hours and then take out the cylinders and gently dry them with a paper towel. Measure their masses again.

Question 4

What are the independent and dependent variables of the osmosis practical?

Answer 4

Independent: concentration of sugar/salt solution
Dependent: potato cylinder mass

Question 5

How do you calculate % change in mass?

Answer 5

New mass - original mass / original mass x 100

Question 6

What are the 5 steps to prepare an uncontaminated culture of bacteria in a lab?

Answer 6

1: a Petri dish and some agar jelly are sterilised (heated to a high temperature) to kill any unwanted microorganisms in them
2: hot agar jelly is poured into the Petri dish and allowed to cool and set
3: an inoculating loop is passed through a hot flame to sterilise it
4: the inoculating loop is used to transfer bacteria to the agar jelly
5: the Petri dish is lightly taped shut to stop microorganisms in the air getting in. It is stored at 25C and upside down to stop drops of condensation falling on the agar surface

Question 7

What are the independent and dependent variables for the bacteria growing practical?

Answer 7

Independent: type or concentration of antibiotic or antiseptic
Dependent: width of inhibition zone

Question 8

Tell me about the effect of pH on amylase activity.

Answer 8

1cm^3 of amylase and 1cm^3 of pH buffer solution are added to a tube of 5cm^3 of starch solution (added 5 minutes after other solutions). Put this into a water bath at 35C
The amylase enzyme breaks down the starch.
Sample the mixture every 30 seconds (after starch is added) on a spotting tile into drops of iodine solution.

Question 9

When do you record the time?

Answer 9

When iodine solution remains browny-orange after sample is added

Question 10

What are the independent and dependent variables of amylase?

Answer 10

Independent: pH of solution
Dependent: time taken for amylase to break down starch

Question 11

How do you work out rate of reaction?

Answer 11

Rate of reaction = 1000 / time (s)

Question 12

Talk to me about Benedict’s test.

Answer 12

It is a test for sugars.
Add about 10 drops of Benedict’s solution to a 5cm^3 food sample and leave for 5 minutes at 75C
It gives a rainbow of results but should go from blue to either green, yellow or brick-red depending on the amount of sugar

Question 13

Talk to me about iodine test.

Answer 13

It’s a test for starch
Add a few drops of iodine solution to a 5cm^3 food sample and mix
A positive result is it turning from a browny-orange to blue-black

Question 14

Talk to me about Biuret test

Answer 14

It is a test for proteins
Add 2cm^3 of biuret solution to a 2cm^3 food sample and mix
Positive result is blue to purple

Question 15

Talk to me about the Sudan III test.

Answer 15

Test for lipids
Add 3 drops of Sudan III stain solution to a 5cm^3 food sample and mix
Positive result is that the mixture separates into two layers - top layer bright red

Question 16

What are the independent and dependent variables for the light intensity photosynthesis practical?

Answer 16

Independent: distance from light
Dependent: length of bubble

Question 17

What is reaction time?

Answer 17

The time it takes to respond to a stimulus

Question 18

What are the 4 steps to investigate reaction time?

Answer 18

1: hold a ruler between the thumb and forefinger of the person being tested
2: drop the ruler without warning and record the distance it falls before it’s caught
3: repeat the test several times then calculate the mean distance that the ruler fell
4: repeat the experiment to investigate the effect of a factor on reaction time (eg, caffeine)

Question 19

Which variables should you control in an experiment for plant growth responses?

Answer 19

number and type of seeds
water
temperature
light intensity

Question 20

what are the independent and dependent variables?

Answer 20

indedpendent: direction of light
dependent: direction of growth

Question 21

what are the 4 steps to estimate the population size of small organisms using quadrats?

Answer 21

1: place a 1m^2 quadrat at random in a field
2: count all the daisies within it
3: repeat several times
4: multiply the size of the entire area by the number of organisms per 1m^2

Question 22

what are 3 steps to find out how organisms are distributed across an area using transects?

Answer 22

1: mark out a line using a tape measure
2: count the daisies in quadrats placed at regular intervals along the line
3: draw a graph to show how the daisies are distributed

Question 23

what are the 6 steps to investigate the effect of temperature on the rate of decay of fresh milk?

Answer 23

1: Put 5cm^3 of lipase solution into a labelled test tube and 5cm^3 of milk into a different test tube
2: use a pipette to add 5 drops of phenolphthalein indicator to the milk
3: then add 7cm^3 of sodium carbonate solution and the milk becomes alkaline (turns pink)
4: use a thermometer to monitor temperature and add it to a water bath at certain temperature
5: transfer 1cm^3 of lipase solution to milk when solutions have reached water bath temperature
6: start a stop watch immediately, stir with a glass rod. Lipase decompoeses milk so the milk becomes white since is no longer alkaline, stop stopwatch now.

Question 24

what are the independent and dependent variables of the milk experiment?

Answer 24

independent: temperature
dependent: time taken for colour change