PRACTICAL PAPER

Question 1

independent variable

Answer 1

the factor that changes in an investigation

Question 2

dependent variable

Answer 2

the factor that changes as a result.

Question 3

controlled experiment

Answer 3

experiment to ensure independent variable is causing results

Question 4

standardizing temperature

Answer 4

Thermo-statically controlled water bath

Question 5

standardizing pH

Answer 5

pH Buffer solution of known concentration

Question 6

standardizing light

Answer 6

Heat-shielded lamp set at constant

Question 7

standardizing intensity

Answer 7

Distance/power

Question 8

standardizing wind speed

Answer 8

Fan set at constant distance & power

Question 9

measuring temperature

Answer 9

Thermometer

Question 10

measuring colour

Answer 10

Colorimeter

Question 11

measuring pH

Answer 11

pH indicator / pH meter

Question 12

measuring mass

Answer 12

balance

Question 13

measuring length

Answer 13

Microscope with calibrated eyepiece graticule/Ruler.

Question 14

measuring volume

Answer 14

Beaker/Measuring cylinder/Burette/Pipette.

Question 15

measuring time

Answer 15

stopwatch

Question 16

how to read measuring cylinders accurately

Answer 16

Read from bottom of meniscus, perpendicular to scale

Question 17

accuracy

Answer 17

closeness to true value

Question 18

improving accuracy

Answer 18

better instruments

Question 19

precision

Answer 19

closeness to repeated readings

Question 20

improving precision

Answer 20

control all variables

Question 21

reliability

Answer 21

confidence in results

Question 22

improving reliability

Answer 22

repeat readings and take mean

Question 23

validity

Answer 23

agreement between hypothesis and investigation

Question 24

improving validity

Answer 24

check relation between key and derived variables

Question 25

systematic errors

Answer 25

result from uncertainties in measurements.

Question 26

random errors

Answer 26

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

Question 27

common error sources

Answer 27

- Anomalous readings (owing to inadequate technique/replicates) - Inadequate range and intervals. - Uncontrolled variables.

Question 28

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

Answer 28

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

Question 29

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

Answer 29

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

Question 30

observable features of Xerophytes

Answer 30

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

Question 31

counting bubbles sources of error and how to improve them?

Answer 31

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

Question 32

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

Answer 32

1) Species of potato have different enzyme catalase | - Use the same potato or same species of potato

Question 33

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

Answer 33

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

Question 34

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

Answer 34

1) Difficult to judge when the colour has changed | - Use a colour chart for comparison or use a colorimeter

Question 35

lack of precision or accuracy in measuring instruments

Answer 35

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

Question 36

when talking about modifications to experiment

Answer 36

- 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

Question 37

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

Answer 37

- count number of squares that cover more than half of the square improvement : count using a grid with smaller squares

Question 38

drops of milk sources of error + improvement

Answer 38

1) Different sizes of drop of milk | - Use a small syringe or graduated pipette

Question 39

when talking about enzymes ALWAYS mention

Answer 39

- enzyme substrate complexes - higher temp --> higher kinetic energy --> more collisions - denaturing

Question 40

reducing sugar test

Answer 40

- 80 degrees celsius in thermostatically controlled waterbath - Use benedict's solution - reducing sugar present - turns from blue to brick red

Question 41

non-reducing sugar test

Answer 41

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

Question 42

protein test

Answer 42

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