Prac

Question 1

Testing for fat

a

Answer 1

add ethanol then water, shake

Question 2

Describe a control experiment involving enzymes.

Answer 2

boiled pectinase, denatured pectinase

Question 3

Reagent for CO2?

a

Answer 3

Limewater

Question 4

Hazards

a

Answer 4

breakage of glass equipment

pectinase, gloves and goggles (handle carefully)

Question 5

Kept constant in human experiment?

a

Answer 5

environment, age, sex of participants

Question 6

Agar jelly conclusions (monkey)

a

Answer 6

huddling reduces heat loss, as time increases temperature falls

Question 7

Kept constant in insulation investigation?

Answer 7

size and kind of test tubes, all placed in a beaker, same time intervals

Question 8

Errors

a

Answer 8

no repeat, volume vary, temp at start, bands for insulation, band tightness, dough not flat/uneven

Question 9

Improvement to method?

a

Answer 9

repeat investigation twice more, (things to fix errors), use clean rod, no 10-minute cut-off

foam is uneven, measure volume of gas produced

Question 10

Things to mention in experiment with enzymes and disappearance.

a

Answer 10

Method: white tile, buffer colorimeter, maintaining temperature using water bath

Question 11

Why a large number sampled?

a

Answer 11

To get a representative sample. To avoid bias. To identify anomalies.

Question 12

Why temp of water bath change not significant error?

a

Answer 12

would effect the tubes equally

Question 13

(Agar jelly) Control experiment?

a

Answer 13

use water instead of acid, only add water to agar jelly

Question 14

Kept constant in plant growth experiment?

Answer 14

plant species, number of leaves, humidity, soil type, water supplied, time, wind-speed

Question 15

(Vit C) Reason for wrapping beaker in foil?

Answer 15

Insulation, decrease heat loss, maintain temperature

Question 16

Explain why it is important to rinse the outside of the dialysis tubing.

Answer 16

to ensure no starch is left

Question 17

Why repeating two more times is an improvement to method?

Answer 17

identify any anomalies

Question 18

Explain why it is important to take measurements from the same place

Answer 18

so differences between measurements can be compared accurately

Question 19

Conclusion of dialysis tubing experiment.

Answer 19

osmosis allows water to move across a semi-permeable membrane down a concentration gradient

Question 20

Explain why percentage change in mass is more useful than change in mass.

Answer 20

Allows comparison, as initial masses were different

Question 21

Results not the same. Did not wash syringe.

Answer 21

contamination of new substance

Question 22

Explain why it is important to stir the yeast suspension.

Answer 22

ensures yeast cells are uniformly distributed

Question 23

Improving an investigation including color change.

Answer 23

place a white card behind the test tube to identify color change easily

Question 24

Compare the volumes produced at 20 degrees and 30 degrees

Answer 24

COICC

Question 25

Temp was a source of error. Give improvement.

Answer 25

bunsen burner to heat and thermometer to monitor water bath

Question 26

Test tubes were covered in foil. Predict and explain the effect.

Answer 26

If room temp was lower, temp of test tube would be lower. More heat loss.

Question 27

Obtain a more accurate value for optimum pH.

Answer 27

use a set of pH values with shorter intervals between pH 7 and pH 9

Question 28

Describe variables that scientists should have considered when selecting women.

Answer 28

age, calcium intake from their diets and their health status

Question 29

State one way this study is not representative of the population.

Answer 29

only women, not done on people younger than 50

Question 30

"More women were losing bone mass than gaining" Why this may not be correct?

Answer 30

the number of women in each category is unknown

Question 31

(Experiment of potatoes, dye and light) Independent, dependent and kept constant?

Answer 31

potato sa percentage of light absorbed type of dye and length of times

Question 32

Independent variable for agar jelly?

Answer 32

size of blocks

Question 33

(Effect of temperature on osmosis in plant tissue) What is the dependent variable?

Answer 33

volume/mass of tissue before and after immersion measuring volume of water before and after immersion

Question 34

Describe the relationship between pulse rate and time after exercise

Answer 34

biggest decrease.. return to pre-exercise pulse rate at 2 mins

Question 35

(Potato cylinders and diffusion) Suggest improvements to the method used.

Answer 35

-measure mass instead of length -more intermediate concentrations -extend the range of concentrations used -repeat 2 more times -same temp -dry before measuring

Question 36

State one safety precaution that the students would take when evaporating substances containing ethanol.

Answer 36

not using a bunsen burner or water bath

Question 37

Suggest why repeating the procedure several times would improve the investigation

Answer 37

anomalous result identified

Question 38

Suggest why some named factors were same for all experiment?

Answer 38

so the results are comparable

Question 39

How to maintain temperature of water bath?

Answer 39

1. use thermostatically controlled water-baths ; 2. use a Bunsen burner AND thermometer (method outlined) / use a Bunsen burner and monitor the temperature ; 3. top up with, hot water / cold water / ice, and monitor /use a thermometer ; 4. insulate the container / AW ;

Question 40

How to decrease humidity around plant?

Answer 40

dehumidifier

Question 41

How to increase humidity around plant?

Answer 41

bowls of hot water around apparatus / place in plastic bag

Question 42

Error and improvement for any experiment involving indicators.

Answer 42

Error → Judgement of endpoint is subjective and qualitive Improvement → Compare to a colorimeter

Question 43

Error and improvement for any experiment involving drops of a liquid.

Answer 43

Error → Volume of drops size is inconsistent or unknown or different Improvement → Use syringe/ burette/ graduated pipette to measure volume

Question 44

Error and improvement for any experiment involving shaking or stirring a liquid.

Answer 44

Error → different degree of, shaking / mixing / stirring Improvement → shake at a fixed speed or use a (mechanical) stirrer Error → different time of, mixing or shaking Improvement → shake or stir, for a fixed time ;

Question 45

Error and improvement for any experiment involving hot or cold water.

Answer 45

Error → temperature of the water not controlled / temperature changes Improvement → thermostatically controlled water-bath / insulation / Bunsen burner

Question 46

Error and improvement for any experiment involving unknown volume of a liquid.

Answer 46

Error → volume of starch not measured Improvement → measuring cylinder

Question 47

Explain why a control group was used in this investigation

Answer 47

to show that the beetroot causes the effect

Question 48

Describe suitable apparatus that could be used to collect and measure the volume of carbon dioxide produced.

Answer 48

gas syringe upturned measuring cylinder with delivery tube

Question 49

Carbon dioxide gas was bubbled through hydrogencarbonate indicator solution. The indicator was red before the gas was bubbled through. State the colour change that would occur.

Answer 49

Red to Yellow

Question 50

DCPIP colour change.

Answer 50

blue to colourless

Question 51

What is the dependant and independant variable in determining the rate of breakdown?

Answer 51

dependant- temperature independant- time taken for the negative result for starch

Question 52

Method basics.

Answer 52

-maintaining 2 temp, thermostat and water bath -iodine test - pH - buffer

Question 53

Method relating to plants.

Answer 53

- medium for keeping moist - variety of tomato seed - soil type - pH - cut sections of stalk to see distance moved by dye

Question 54

Method relating to general preparation.

Answer 54

cutting measuring

Question 55

Method methods..

Answer 55

method of measuring gas method to check end-point