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AS Biology > PRACTICAL PAPER > Flashcards

Flashcards in PRACTICAL PAPER Deck (42)
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1
Q

independent variable

A

the factor that changes in an investigation

2
Q

dependent variable

A

the factor that changes as a result.

3
Q

controlled experiment

A

experiment to ensure independent variable is causing results

4
Q

standardizing temperature

A

Thermo-statically controlled water bath

5
Q

standardizing pH

A

pH Buffer solution of known concentration

6
Q

standardizing light

A

Heat-shielded lamp set at constant

7
Q

standardizing intensity

A

Distance/power

8
Q

standardizing wind speed

A

Fan set at constant distance & power

9
Q

measuring temperature

A

Thermometer

10
Q

measuring colour

A

Colorimeter

11
Q

measuring pH

A

pH indicator / pH meter

12
Q

measuring mass

A

balance

13
Q

measuring length

A

Microscope with calibrated eyepiece graticule/Ruler.

14
Q

measuring volume

A

Beaker/Measuring cylinder/Burette/Pipette.

15
Q

measuring time

A

stopwatch

16
Q

how to read measuring cylinders accurately

A

Read from bottom of meniscus, perpendicular to scale

17
Q

accuracy

A

closeness to true value

18
Q

improving accuracy

A

better instruments

19
Q

precision

A

closeness to repeated readings

20
Q

improving precision

A

control all variables

21
Q

reliability

A

confidence in results

22
Q

improving reliability

A

repeat readings and take mean

23
Q

validity

A

agreement between hypothesis and investigation

24
Q

improving validity

A

check relation between key and derived variables

25
Q

systematic errors

A

result from uncertainties in measurements.

26
Q

random errors

A

differ across investigation as they arise owing to difficulties in controlling standardised variables and measuring dependent variable.

27
Q

common error sources

A
  • Anomalous readings (owing to inadequate technique/replicates)
  • Inadequate range and intervals.
  • Uncontrolled variables.
28
Q

state the actual error in measuring an increase in temperature of 6 degrees celsius using a thermometer

A

1 degrees celsius

you can read reading 0.5 degrees out for one recording and 0.5 degrees out for the other recording so error would be 1 degrees

29
Q

measuring temperature from water in a beaker source of error and how to improve it?

A

1) energy may be transferred to the surroundings and won’t stay in the water
- Use insulation or lids

30
Q

observable features of Xerophytes

A

many air spaces - for buoyancy - and relatively small amount of xylem as water diffusing through epidermis

31
Q

counting bubbles sources of error and how to improve them?

A

1) Different sizes of bubbles released
- Use a gas syringe to measure volume of gas released in total

2) Too many bubbles so not all are counted
- Video in slow motion and count from the video so no bubbles are missed out

32
Q

getting enzymes from a fruit or vegetable (like potatoes) source of error and how to improve it?

A

1) Species of potato have different enzyme catalase

- Use the same potato or same species of potato

33
Q

describe how to standardise the position of the delivery tube in the test-tube of water

A

Make a mark on the delivery tube to standardise the position of delivery tube

34
Q

judging end points source of error and how to improve it?

A

1) Difficult to judge when the colour has changed

- Use a colour chart for comparison or use a colorimeter

35
Q

lack of precision or accuracy in measuring instruments

A

1) Measuring instrument (thermometer, colorimeter) is not properly calibrated (not accurate)
- Ensure calibration occurs or use alternate instruments that allow you to calibrate it

2) Using imprecise instruments / methods
- Use instruments that have smaller divisions E.g. using a graduated pipette instead of syringe
- Take measurements more often

36
Q

when talking about modifications to experiment

A
  • don’t forget to mention exactly how much of each sample. etc. like 5 different concentrations or 5 different sized cubes
  • mention an exact concentration as well
37
Q

using a grid to find area of a specimen - limitations and improvements

A
  • count number of squares that cover more than half of the square
    improvement : count using a grid with smaller squares
38
Q

drops of milk sources of error + improvement

A

1) Different sizes of drop of milk

- Use a small syringe or graduated pipette

39
Q

when talking about enzymes ALWAYS mention

A
  • enzyme substrate complexes
  • higher temp –> higher kinetic energy –> more collisions
  • denaturing
40
Q

reducing sugar test

A
  • 80 degrees celsius in thermostatically controlled waterbath
  • Use benedict’s solution
  • reducing sugar present - turns from blue to brick red
41
Q

non-reducing sugar test

A

sucrose is a non-reducing sugar made of glucose and fructose which are reducing sugars

  • add HCL and heat gently to break down non-reducing sugar into reducing sugars (glycosidic bonds)
  • neutralise the sample with sodium hydrogen carbonate solution
  • add benedict’s reagent (80 degrees in water bath)
  • observe colour change
42
Q

protein test

A
  • add sodium hydroxide and copper sulfate solution to sample (biuret solution)
  • if protein present solution turns from blue to purple