required practicals

Question 1

Practical 1: Investigating the effect of a named variable on the rate of an enzyme-controlled reaction

Answer 1

Prepare a range of substrate concentrations using serial dilutions (e.g. starch for amylase).

Add equal volumes of buffer solution to maintain constant pH.

Add a fixed volume of enzyme to each tube and start a stopwatch.

Take samples at regular intervals and test with iodine on a spotting tile.

Record the time when iodine no longer turns blue-black (reaction complete).

Repeat at least 3 times and calculate mean time or rate for each concentration.

Question 2

Practical 3: Investigating the effect of a named variable on the permeability of cell-surface membranes

Answer 2

Cut equal-sized beetroot cylinders and rinse to remove surface pigment.

Place them in test tubes containing equal volumes of distilled water.

Vary one condition, e.g. temperature using water baths or solvent concentration.

After a set time, remove beetroot and mix solutions.

Measure absorbance of each solution using a colorimeter.

Plot absorbance vs. temperature or concentration to assess permeability.

Question 3

Practical 2: Observing mitosis in root tips

Answer 3

Cut 5 mm of root tips (e.g. garlic/onion), place in HCl at 60°C for 5 minutes.

Rinse and place on a microscope slide; add stain (e.g. toluidine blue) to highlight chromosomes.

Gently macerate the tissue with a mounted needle.

Add a coverslip and squash gently to produce a single layer of cells.

View under a microscope at high power and identify mitotic stages.

Count cells in each stage and calculate mitotic index = (cells in mitosis ÷ total cells) × 100.

Question 4

Practical 4: Investigating the effect of a named variable on the movement of substances by osmosis

Answer 4

Cut equal-sized cylinders or discs of plant tissue (e.g. potato).

Blot dry and weigh each piece before placing in different sucrose concentrations.

Leave samples for a set time (e.g. 20 minutes).

Remove, blot dry again, and reweigh to calculate percentage change in mass.

Plot results on a graph of percentage change vs. concentration.

Identify the concentration where mass doesn’t change — the tissue’s water potential

Question 5

Practical 5: Dissection of animal or plant gas exchange system (e.g. lungs/heart)

Answer 5

Examine and identify the trachea, bronchi, and lungs.

Use scissors to cut open the trachea to observe cartilage rings.

Follow bronchi into lung lobes and note alveolar structure.

Use appropriate dissection tools and techniques for safety and accuracy.

Record labelled drawings and observations of internal structures.

Dispose of biological waste according to safety guidelines.

Question 6

Practical 6: Using aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Answer 6

Sterilise the agar plate surface and equipment using aseptic techniques.

Inoculate a bacterial lawn evenly using a sterile pipette or spreader.

Place paper discs soaked in different antimicrobial agents onto the agar.

Seal the Petri dish with tape (not all the way around) and incubate at 25°C.

Measure the diameter or area of clear zones after incubation.

Compare zones to determine effectiveness of each antimicrobial.

Question 7

define independent variable

Answer 7

variable that you are changing

Question 8

define controlled variable

Answer 8

variable that you are controlling (keeping the same) to ensure that your experiment is not affected by outside sources

Question 9

define dependent variable

Answer 9

the variable that is being measured

Question 10

purpose for a control in an experiment? (2)

Answer 10

• to ensure that the factor you are investigating is causing the observed results
• to allow comparison of your results

Question 11

describe why we would need to repeat an experiment? (2)

Answer 11

-to allow you to calculate a reliable mean

• to identify any anomalies in your data

Question 12

risk posed by broken glass?

Answer 12

cuts from sharp objects

Question 13

risk posed by hydrochloric acid?

Answer 13

can cause irritation to eyes or skin

Question 14

risk posed by naked flame?

Answer 14

burns and fire hazard

Question 15

risk posed by scalpel?

Answer 15

cuts from sharp object

Question 16

risk posed by disinfectant?

Answer 16

flammable

Question 17

safety precaution for broken glass?

Answer 17

handle glass with care

Question 18

safety precaution for hydrochloric acid

Answer 18

wear eye protection and gloves to prevent contact

Question 19

safety precaution for naked flame?

Answer 19

tie up long hair, wear goggles and keep flammable objects away

Question 20

safety precaution for scalpel?

Answer 20

cut away from fingers

Question 21

safety precaution for disinfectant?

Answer 21

keep away from flame