Required Practical

Question 1

Describe how to use aseptic techniques to transfer bacteria from bottle to agar plate (3)

Answer 1

• wash hands with SOAP and wipe surfaces with disinfectant
• use sterilised unopened pipette
• use sterile spreader

Question 2

Describe and explain 3 ways the scientist ensure he used aseptic techniques? (3)

Answer 2

• wash hands before and after experiment to remove microbes
• flame equipment and neck of bottle to kill microbes to prevent contamination
• life lid slightly at small angle to prevent entry of microbes of the plate

Question 3

Explain how a control group is needed/ used by scientists? (2)

Answer 3

1) allow comparison effects of other experimental conditions
2) allow measuring effect of independent variables (cause and effect)

Question 4

Suggest why number of E coli in culture will decrease if the student did not use a steriliser pipette (2)

Answer 4

1) unknown microorganisms introduced to the pipette
2) these microorganisms can use up food and space so more competition for growth of E coli

Question 5

Suggest what students added to well to get positive control and negative control results (2)

Answer 5

PC= add disinfectant/ antibacterial substance
NC= add water

Question 6

Describe an experiment to investigate whether a plant have a lower w.p than sea water (4)

Answer 6

1) record mass of before and after
2) place plant in sea water for specific time
3) use tissue paper to dry out the excess water when take the plant out
4) increase in mass shows water been absorbed by osmosis showing w.p of plant is lower than sea water

Question 7

Describe what scientist should add in control tube when investigating PH of enzyme activity (3)

Answer 7

1) same volume of buffer
2) same conc of denatured enzymes
3) same conc. of substrate

Question 8

Describe how can the student use a calculated changes ratio to determine w.p of cell (3)

Answer 8

1) plot a calibration curve
2) interpolate from ratio of 1
3) change IV into w.p in another graph or table to identify exact w.p

Question 9

Explain why scientists use percentage values rather than range (2)

Answer 9

1) number of sample collected is different every time ( unless stated standardised)
2) allow a valid comparison

Question 10

Point for criticisms for evaluate questions

Answer 10

1) criticise sample size if stated
2) representativeness of experiment setting not showing in real life situation
3) no stats test done
4) whether sample of animals are same age
5) other environmental impact the experiment

Question 11

Describe how the student should ensure she handled the scalpel safely during this procedure (2)

Answer 11

1) cut away from body
2) on a hard flat surface

Question 12

What to include in conclusion questions?

Answer 12

1) crticise SD to see over lapp pf sig difference
2) so …. What does the sig difference shows about the data
3) then e.g. what else is affecting the data

Question 13

Describe how students could use an eyepiece graticule to determine mean diameter of cells (3)

Answer 13

1) measure using eyepiece graticule
2) calibrate eyepiece graticule against ruler or graph paper
3) take a number of measurements to calculate mean

Question 14

Describe how to produce calibration curve to find conc of one particular substance (4)

Answer 14

1) produce range of known conc of substances
2) measure absorbance values of each conc
3) plot a graph of absorbance with conc against then draw curve
4) use absorbance of sample to find conc of the substance from curve

Question 15

Suggest why students soaked the root tips in hydrochloric acid before looking it under microscope (2)

Answer 15

1) to hydrolyse cellulose cell wall to break open cells
2) so allow stains to diffuse into cells

Question 16

Suggest why other students using the same procedure still get different mitotic index (2)

Answer 16

1) not obtained a large enough representative sample of field of view
2) cells undergo mitoiss differently at different rate

Question 17

Describe how a sample of chloroplast could be isolated from leaves (4)

Answer 17

1) break open cells and filter
2) in cold buffer isotonic solution
3) centrifuge and spin at increasing speed to remove nucleus
4) higher speed will get chloroplast settle out

Question 18

Describe 4 precautions when cleaning away after dissection

Answer 18

1) wash scalpel by holding handle, away from body
2) disinfect surface and equipment
3) disinfect hands, wash hands with soap
4) put organs and gloves in sperate bag to dispose