Required Practicals 1 - 6

Question 1

RP1 - What are the factors that affect enzyme activity (4)?

Answer 1

1. Enzyme concentration
2. Substrate concentration
3. Temperature
4. pH

Question 2

RP1- How is a control set up in a practical measuring enzyme activity?

Answer 2

Replace the enzyme solution with distilled water or boiled enzyme solution

Question 3

RP1 - How can the results of the practical measuring enzyme activity be used to find the initial rate of reaction?

Answer 3

Plot your results on a graph of ‘rate of reaction’ against ‘time’. Draw a tangent at time = 0 to find the initial rate.

Question 4

RP1 - Outline the practical procedure used to measure the effect of temperature on enzyme activity, using trypsin and milk.

Answer 4

• Immerse equal volumes of trypsin and milk, stored in different test tubes, in a water-bath for 5 minutes for the temperature to equilibrate.
• Mix together and immediately start timing, record the time taken for the milk to be completely hydrolysed (become colourless/same as the control standard set up).
• Test at least 5 temperatures, with at least 3 repeats at each temperature.

Question 5

RP1 - How is the rate of reaction calculated from time?

Answer 5

Rate of reaction = 1/time

Question 6

RP1 - What is the effect of temperature on enzyme activity?

Answer 6

• As temperature increases, kinetic energy increases so more ES complexes form. The rate of reaction increases up to the optimum temperature.
• Beyond that, bonds in the enzyme tertiary structure break, which changes the shape of the active site. The substrate and enzyme are no longer complementary, so rate of reaction decreases

Question 7

RP1 - What is the risk and level of risk associated with handling enzymes?

Answer 7

Students may have allergic reactions to enzymes, so avoid contact with skin and eyes, wear eye protection.
Low risk.

Question 8

RP2 - Where in plants can cells undergoing mitosis be
found?

Answer 8

Meristem tissue at shoot and root tips.

Question 9

RP2 - What is the mitotic index?

Answer 9

The ratio of cells undergoing mitosis to the total number of cells in a sample.

Question 10

RP2 - Outline the procedure to prepare a root tip slide.

Answer 10

RP2 - 1. Warm 1M HCl to 60°C in a water bath.
2. Cut a root tip using a scalpel and add to the HCl. Leave for 5 minutes.
3. Remove from HCl and wash with distilled water.
4. Cut the tip of the root tip sample and place on a slide.
5. Add a few drops of stain to make chromosomes visible.

Question 11

RP2 - State the formula for the mitotic index.

Answer 11

Mitotic index =
Number of cells with visible chromosomes /
Number of cells in sample

Question 12

RP2 - State the hazards and precautions for reagents used in this procedure.

Answer 12

HCl - corrosive, avoid contact with skin, wear eye
protection
Toluidine Blue O stain - irritant, avoid contact with
skin, wear eye protection
Scalpel - cut away from fingers

Question 13

RP 3 - What is the purpose of calibration curves?

Answer 13

They are used to determine the concentration of an unknown sample by
comparing it to a set of standard values with known concentrations

Question 14

RP 3 - How is a calibration curve used to find the concentration of plant tissue?

Answer 14

Plot a calibration curve of percentage change in mass against concentration.
Find the x-intercept where the plant tissue is isotonic to the sucrose solution

Question 15

RP 3 - What occurs when plant tissue is placed in a hypotonic solution?

Answer 15

Water moves into the plant tissue by osmosis, plant tissue increases in mass

Question 16

RP 3 - What occurs when plant tissue is placed in a hypertonic solution?

Answer 16

Water moves out of the plant tissue by osmosis, plant tissue decreases in mass.

Question 17

RP 3 - Why are the potato discs left in solution for 20 minutes?

Answer 17

To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution

Question 18

RP 3 - What is water potential determined by?

Answer 18

The concentration of solutes. The higher the solute concentration then Qthe lower the water potential

Question 19

RP 3 - Outline the procedure of investigating osmosis using potato tissue.

Answer 19

1. Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5 cm3 to 5 different test tubes.
2. Cut a potato into equal sized chips and weigh.
3. Place a chip in each test tube and leave for 20 minutes.
4. Take out, dab the excess water and weigh them again.
5. Calculate the percentage change in mass

Question 20

RP 3 - Why is the percentage change used rather than the actual change in mass?

Answer 20

Potato chips may not all have same starting mass.
Percentage change allows comparison.

Question 21

RP 3 - What is indicated by the x-intercept of the calibration curve?

Answer 21

The concentration that is isotonic to the solution tested.

Question 22

RP 3 - Explain the change in mass in the potato chips.

Answer 22

The potato chips with concentration lower than the sucrose solution (higher water potential) lose mass as there is a net movement of water out of the cells.

The potato chips with concentration higher than the sucrose solution (lower water potential) gain mass as there is a net movement of water into the cells.

Question 23

RP 3 - Why are the potato chips dabbed dry after removing
from the sucrose solution?

Answer 23

To remove any excess water clinging to its surface.

Question 24

RP 3 - What are the controlled variables of this practical?

Answer 24

Volume of sucrose solution
Size of potato chips
Length of time left in solution
Dab each potato disc with paper towels

Question 25

RP4 - State 2 factors that affect the permeability of cell membranes.

Answer 25

Temperature
Concentration of solvents (ethanol)

Question 26

RP4 - How is beetroot used to measure the permeability of cell membranes?

Answer 26

The higher the permeability, the more red pigment that leaks out into the surrounding solution within a given time. A colorimeter can be used to determine the absorbance, hence concentration of pigment

Question 27

RP4 - Outline the procedure to investigate the effect of temperature on permeability of cell membrane.

Answer 27

1. Cut beetroot into 6 identical cubes with a scalpel.
2. Place each cube in a different test tube with equal
   volumes of distilled water.
3. Place each test tube into water baths ranging from 30-80°
   C. Leave for 20 minutes.
4. Filter each solution out into a cuvette and measure the
   absorbance using a colorimeter

Question 28

RP4 - What are the safety hazards involved in testing the effect of ethanol concentration on membrane permeability?

Answer 28

Ethanol is an irritant and is flammable, keep away from naked flames, wear eye protection.
Keep sharp scalpel away from fingers.
Handle hot liquid with care.

Question 29

RP4 - What is the effect of temperature on membrane permeability?

Answer 29

Increasing temperature results in increase membrane permeability

Question 30

RP4 - What is the effect of ethanol concentration on membrane permeability?

Answer 30

Increasing ethanol concentration leads to increased membrane permeability.

Question 31

RP5 - How should label lines in a diagram be drawn?

Answer 31

With a ruler, no arrows, without crossing other label lines, in pencil

Question 32

RP5 - How should a diagram be drawn?

Answer 32

Large diagram - at least half the space given
No shading, single continuous lines (no sketching) with pencil

Question 33

RP6 - State 6 aseptic techniques.

Answer 33

● Wipe down surfaces with antibacterial cleaner, before and after experiment
● Use a Bunsen burner in the work space so that convection currents draw
microbes away from the culture.
● Flame the wire hoop before using it to transfer bacteria.
● Flame the neck of any bottles before using them to prevent any bacteria
entering the vessel.
● Keep all vessels containing bacteria open for the minimum amount of time.
● Close windows and doors to limit air currents.

Question 34

RP6 - Why is bacteria incubated at 25°C?

Answer 34

To prevent the growth of pathogens (harmful bacteria), which occurs at higher temperatures.

Question 35

RP6 - How can you compare the effectiveness of different antibiotics applied to the same bacteria?

Answer 35

Measure the diameter and calculate the area of the zone of inhibition (clear zone) on the agar.

Question 36

RP6 - What does the zone of inhibition indicate?

Answer 36

It indicates the bacteria killed by the antibiotic.
The larger the zone the more effective the antibiotic.
If an antibiotic has very little or no zone of inhibition, the bacteria is likely resistant to the antibiotic.

Question 37

RP6 - State the hazards and precautions of this practical.

Answer 37

Naked flame: keep away from flammable materials, tie hair up, wear goggles
Bacteria is a biohazard, use disinfect and wash hands, dispose of bacteria safely
Disinfectant is flammable, keep away from naked flame.

Question 38

RP6 - Why should the lid not be completely taped to the petri dish?

Answer 38

To allow oxygen to enter the petri dish, preventing the growth of harmful anaerobic bacteria.

Question 39

RP6 - Describe the graph that can be plotted from the results of this practical.

Answer 39

A bar chart of zone of inhibition against antibiotic.