Required Practical 1-6 & How Science Works

Question 1

RP1 (Enzymes)

Answer 1

Concentration of substrate solution

Concentration of enzyme solution

pH

Question 2

RP1 (Enzymes)

Calculate the rate of reaction at 25°C.

Answer 2

DY (change in Y) / DX (change in X = time)

Question 3

RP1 (Enzymes)

Describe the differences between the two curves (2 marks)

Answer 3

1. Initial rate of reaction faster at 37 °C;
2. Graph reaches plateau at 37 °C;

Question 4

RP1 (Enzymes)

Explain the differences between the two curves (3 marks).

Answer 4

(Initial rate of reaction faster at 37 °C);

1. Because more kinetic energy;
2. So more enzyme substrate complexes formed;

(Graph reaches plateau at 37 °C);

3. Because all substrate used up.

Question 5

RP1 (Enzymes)

When investigating factors that affect enzyme-controlled reactions, enzymes are often ‘isolated’ from a cell (e.g. a bacterial cell).

Explain why this is a limitation?
.

Answer 5

The process of isolation may change the enzyme’s activity

Outside the optimum conditions of the host cell, the enzyme’s activity may also change.

Question 6

RP1 (Enzymes)

What is a common control condition that proves a specific enzyme is needed for a reaction?

Answer 6

1. Boiled enzyme
2. At same concentration & volume
3. This denatures the enzyme and the reaction will not take place in this condition

Question 7

RP1 (Enzymes)

Answer 7

Mark in pairs, 1 and 2 OR 3 and 4 OR 5 and 6

1. Boil OR Add (strong) acid/alkali;
2. Denatures the enzyme/ATP synthase;
3. Put in ice/fridge/freezer;
4. Lower kinetic energy so no enzyme-substrate complexes form;
5. Add high concentration of inhibitor;
6. Enzyme-substrate complexes do not form;

Question 8

RP1 (Enzymes)

Answer 8

1. Same volume of (each) buffer/pH solution;
2. Same concentration/mass of substrate (at start);
3. Same concentration/mass of denatured enzyme;

Question 9

RP2 (Mitosis)

What is the equation for the mitotic index?

Answer 9

Question 10

RP2 (Mitosis)

Describe how you would determine a reliable mitotic index (MI) from tissue observed with an optical microscope.

Do not include details of how you would prepare the tissue observed with an optical microscope (3 marks).

Answer 10

1. Count cells in mitosis in field of view;
2. Divide this by total number of cells in field of view;
3. Repeat many/at least 5 times
   (to calculate a reliable mean mitotic index)

OR Select (fields of view) at random;

Question 11

RP2 (Mitosis)

A student prepared a plant root to observe cells undergoing mitosis.

He put the root in a small bottle of hydrochloric acid in a 40 °C water bath.

Why did he put the plant root in acid?

Answer 11

To stop mitosis

To break down links between cells/cell walls

To separate cells/cell walls

To break down/hydrolyse cellulose/cell wall

Allowing the stain to pass/diffuse into the cells

Allowing the cells to be (more easily) squashed

Question 12

RP2 (Mitosis)

State two precautions required when working with hydrochloric acid.

Answer 12

1. Eye protection;
2. Gloves;
3. Add water to spills (immediately);
4. Do not pour away down sink

Question 13

RP2 (Mitosis)

Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly.

Explain why (2 marks).

Answer 13

1. To create a single/thin layer of cells

OR to spread out cells;

2. So that light could pass through;

Question 14

RP2 (Mitosis)

Answer 14

Where dividing cells are found / mitosis occurs;

OR

No dividing cells / mitosis in tissue further away / more than 5 mm from tip;

Question 15

RP2 (Mitosis)

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate (2 marks).

Answer 15

Description and explanation required, so mark as pairs only

1. Examine large number of fields of view / many cells;
2. To ensure representative / reliable sample;

OR

3. Method to deal with part cells shown at edge /count only whole cells;
4. To standardise counting;

Question 16

RP2 (Mitosis)

Answer 16

1. Stops anaphase / cell division / mitosis;

Accept prevents telophase / cytokinesis

2. (By) stopping / disrupting the spindle fibres forming / attaching / pulling;

3. Preventing separation / splitting of (sister) chromatids;

4. So no new cells added (to root tip);

Question 17

RP2 (Mitosis)

The student counted the number of cells she observed in each stage of mitosis.

Of the 200 cells she counted, only six were in anaphase.

One cell cycle of onion root tissue takes 16 hours.

Calculate how many minutes these cells spend in anaphase.

Answer 17

28.8 minutes

Working out:
6 / 200 = proportion in anaphase

Multiply this answer by 16 x 60 (convent into minutes).

Question 18

RP2 (Mitosis)

When comparing the mitotic index in the roots of two different species.

Give two considerations to ensure this comparison is valid.

Answer 18

1. Roots/plant of the same age;

2. Same growing conditions (for all roots);

3. Same distance from root tip;

4. Same time in acid
OR Same temperature of acid;

5.Same concentration of acid;

6. Several fields of view (for each species) to calculate a mean / reliable mitotic index;

Question 19

RP2 (Mitosis)

The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped appearance.

Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas.

Answer 19

Differences in base sequences

OR

Differences in histones/interaction with histones

OR

Differences in condensation/(super)coiling;

Question 20

RP3 (Osmosis)

Describe how you would use a 1.0 mol dm−3 solution of sucrose to produce 30cm3 of a 0.15 mol dm−3 solution of sucrose.

Clue: C1 x V1 = C2 x V2

Answer 20

Answer = Add 4.5 cm3 of (1.0 mol dm–3) solution to 25.5 cm3 (distilled) water.

Step-by-step working:
C1 x V1 = C2 x V2
1 x V1 = 0.15 x 30
V1 = (0.15 x 30) / 1
V1 = 4.5cm3

Question 21

RP3 (Osmosis)

Answer 21

Calculations made (from raw data)

OR raw data would have recorded initial and final masses.

Question 22

RP3 (Osmosis)

Answer 22

1. Water potential of solution is less than / more negative than that of potato tissue;

Allow Ψ as equivalent to water potential

2. Tissue loses water by osmosis (so masses decreases).

Question 23

RP3 (Osmosis)

Answer 23

1. Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;

2. Find concentration where curve crosses the x-axis / where percentage change is zero;

3. Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis).

Question 24

RP4 (Membrane damage)

What is uncertainty?

Answer 24

The amount of error your measurements might contain

Question 25

RP4 (Membrane damage)

How do you calculate uncertainty?

Answer 25

Is always HALF of the smallest interval you can read with the measuring equipment you are using.

Question 26

RP4 (Membrane damage)

What is the uncertainty of a measuring cylinder where the smallest interval is 20mls?

Answer 26

10mls

Uncertainty is always HALF of the smallest interval

Question 27

RP4 (Membrane damage)

What is the uncertainty of a ruler and why?

Answer 27

1mm

This is because you measure twice at both ends with a ruler. So you add the uncertainties together:

0.5mm + 0.5mm = 1.0mm

Question 28

RP4 (Membrane damage)

What is the equation for percentage error?

Answer 28

Question 29

RP4 (Membrane damage)

Calculate the percentage error when measuring 50mls using a cylinder with the smallest interval of 5mls.

Answer 29

(2.5 / 50) x 100 = 5%

Question 30

RP4 (Membrane damage)

What is the uncertainty of this measuring cylinder in mls?

Answer 30

1 ml

Question 31

RP4 (Membrane damage)

What is the percentage error if measuring 15mls using this measuring cylinder? (to 1dp).

Answer 31

(1 / 15) x 100 = 6.7%

Question 32

RP4 (Membrane damage)

Suggest how you could reduce the uncertainty calculated using this measuring cylinder

Answer 32

Use instrument with smaller intervals

Question 33

RP4 (Membrane damage)

Give one way in which a student could ensure their beetroot cylinders were kept at 25 °C throughout the experiment.

Answer 33

Measure temperature (in tube) at intervals and use appropriate corrective measure (if temperature has fluctuated);

Question 34

RP4 (Membrane damage)

In an experiment investigating the impact of increasing temperature on the permeability of beetoot.

List the key control variables.

Answer 34

1. (Of beetroot cylinders):

Length and diameter

OR Surface area

OR Volume

OR Mass/weight (of cylinders);

2. Time in water/solution;
3. The volume of water/solution used
   (so they complete submerge the cylinder)

Question 35

RP4 (Membrane damage)

Answer 35

1. Water/25oC caused no damage/no pigment release (in E);
2. (Damage to) cell(-surface) membrane / phospholipid bilayer;
3. Ethanol/acid caused some/similar/identical damage

OR 70oC caused most damage;

Accept description of ‘pigment release’ for ‘damage’

4. (By) ethanol dissolving phospholipid bilayer
5. (By) 70oC denaturing/altering membrane protein

OR (By) 70oC increasing fluidity/permeability of membrane;

Question 36

RP4 (Membrane damage)

The cells of beetroot contain a red pigment. A student investigated the effect of temperature on the loss of red pigment from beetroot. He put discs cut from beetroot into tubes containing water. He maintained each tube at a different temperature.

After 25 minutes, he measured the percentage of light passing through the water in each tube.

(a) The student put the same volume of water in each tube.

Explain why it was important that he controlled this experimental variable.

Answer 36

1. (If) too much water the concentration of pigment (in solution) will be lower / solution will appear lighter / more light passes through (than expected);

OR

(If) too little water the concentration of pigment (in solution) will be greater / solution will appear darker / less light passes through (than expected);

2. So results (from different temperatures) are comparable;

Question 37

RP4 (Membrane damage)

The decrease in the percentage of light passing through the water between 25 °C and 60 °C is caused by the release of the red pigment from cells of the beetroot.

Suggest how the increase in temperature of the water caused the release of the red pigment (2 marks).

Answer 37

1. Damage to (cell surface) membrane;
2. (membrane) proteins denature;
3. Increased fluidity / damage to the phospholipid bilayer;

Question 38

How science works (AO3)

Suggest appropriate units the student should use to compare the distribution of stomata on leaves.

Answer 38

Stomata per mm^2 or cm^2

Question 39

How science works (AO3)

Give two reasons why it was important that the student counted the number of stomata in several parts of each piece of leaf tissue.

Answer 39

1. Distribution may not be uniform

OR So it is a representative sample;

2. To obtain a (reliable) mean;

Question 40

RP5 (Dissection)

Give three control measures to reduce the risks associated with carrying and using a scalpel.

Answer 40

1. Carry with blade protected

OR carry pointing down

OR Do not carry if likely to be jostled;

2. Cut away from body;

3. Cut onto hard surface / tile / board;

4. Use sharp blade;

5. Disinfect/dispose of used scalpel (blade) as instructed;

Question 41

RP5 (Dissection)

Answer 41

1. Only use single lines/do not use sketching (lines)/ensure lines are continuous/connected;

2. Add labels/annotations/title;

3. Add magnification/scale (bar);

4. Draw all parts to same scale/relative size;

5. Do not use shading/hatching;

Question 42

RP5 (Dissection)

Describe two precautions the student should take when clearing away after a heart dissection.

Answer 42

1. Carry/wash scalpel / sharp instruments by holding handle

OR Carry/wash scalpel / sharp instruments by pointing away (from body)/down;

2. Disinfect instruments/surfaces;

3. Disinfect hands

OR Wash hands with soap (and water);

4. Put organ/gloves/paper towels in a (separate) bag/bin/tray to dispose;

Question 43

RP5 (Dissection)

Give two safety precautions that should be followed when dissecting a heart.

Answer 43

1. Use a sharp scalpel/scissors

2. Wash hands with soap / wear gloves

3. Disinfect bench/equipment

4. Cover any cuts

5. Cut away from self AND on a hard surface

6. Safe disposal (of scalpel / biological waste)

Question 44

RP5 (Dissection)

Scientists dissected gills from several species of fish. They recorded:

*   the mass of the whole fish
*   the total number of gill filaments
*   the mean length of one filament
*   the mean number of lamellae per mm
*   the mean surface area of one lamella.

It was not possible for the scientists to measure the length of every filament and the surface area of every lamella.

Suggest how they collected data to give a reliable mean for these variables (2).

Answer 44

1. Random samples;
2. Large sample size;

Question 45

How science works (AO3)

The scientists estimated the mean mass of fibre eaten per day using a food frequency questionnaire (FFQ).

The FFQ asks each person how often they have eaten many types of food over the past year.

An alternative method to calculate fibre eaten is for a nurse to ask each person detailed questions about what they have eaten in the last 24 hours.

Suggest one advantage of using the FFQ method and one disadvantage of using the FFQ method compared with the alternative method.

Answer 45

Advantage
Over longer period so more representative;

OR Diet may vary during the year/from day to day;

OR More cost effective because fewer people/nurses required;

Disadvantage
Relies on (long term) memory so may not be accurate

OR Recall of 24 hr diet likely to be more accurate

Question 46

How science works (AO3)

Blood cells can be counted using a haemocytometer (see below). When counting, cells that touch top or left lines are counted but cells that touch right or bottom lines are not counted.

Suggest two reasons for this rule.

Answer 46

1. To avoid dealing with parts of cells;

2. To avoid counting same cells twice / more than once;

3. To be consistent / get comparable results;

OR more accuracy

Question 47

How science works (AO3)

A doctor used a haemocytometer (see below) to count white blood cells per mm3.

When counting white blood cells, the doctor only diluted the blood sample by a factor of 20 times, instead of 200 times when counting red blood cells.

Suggest why he only diluted the sample by a factor of 20 times.

Answer 47

There are fewer white cells, so no need to dilute (further to see enough);

OR accept converse i.e. too few to see if greater dilution / at 200 times;

Question 48

How science works (AO3)

Explain how a stain allowed doctor to count the white blood cells amongst all the red blood cells in a blood sample.

Answer 48

White blood cells have a nucleus (that stains but red cells do not);

Question 49

How science works (AO3)

Answer 49

Median

Reason
Presence of outliers / anomalies e.g. 80, 70

OR small sample size/8 (measurements);

Question 50

How science works (AO3)

Suggest why the scientist made repeat measurements.

Answer 50

Increases reliability (of results)

OR

Anomalous results can be identified;

Question 51

How science works (AO3)

The scientist used the reduction in total leaf area of the experimental plants as an indicator of plant growth.

Outline a method by which you could find the area of a plant leaf.

Answer 51

Draw around leaf on graph paper and count squares;

Question 52

How science works (AO3)

The scientists’ hypothesis at the start of the investigation was that crop plants genetically engineered to produce the protein GB would become more resistant to high environmental temperatures.

The scientists developed this hypothesis on the basis of previous research on crops that are grown in hot climates.

Suggest how the scientists arrived at their hypothesis.

Answer 52

1. Looked for information / journals / research, on crop plants that grow at high temperatures;

2. Crop plants cited in this research contain / make GB;

3. So assumed making plants produce GB makes them resistant to high temperatures;

Question 53

RP6 (Aseptic Techniques)

What is an antimicrobial?

Answer 53

A molecule / drug / chemical that inhibits the growth OR causes the cell death of a microorganism

Micoorganisms are often referred to as ‘microbes’

Question 54

RP6 (Aseptic Techniques)

Antimicrobial examples

Answer 54

Antibiotics
Antivirals
Antifungals
Antiparasitics

Question 55

RP6 (Aseptic Techniques)

Main goal of using aseptic techniques

Answer 55

Prevent contamination from unwanted microorganisms / microbes

Question 56

RP6 (Aseptic Techniques)

A student added 100 mm^3 of a bacterial culture from its glass bottle onto a separate agar plate.

They spread each bacterial culture evenly over the agar using a spreader.

Describe the aseptic techniques they should use (3).

Answer 56

Any 3 from:
1. Wash hands with soap OR Disinfect surfaces;
2. Use sterile pipette/syringe (to transfer bacteria);
3. Remove bottle lid and flame neck of bottle;
4. Lift lid of (agar) plate at an angle;
5. Work close to upward air movement / convection current;
6. Use sterile spreader / flame spreader;
7. Place pipette/spreader into disinfectant immediately after use;

Question 57

RP6 (Aseptic Techniques)

Explain the purpose of washing hands with soap

Answer 57

To remove/kill microbes

Question 58

RP6 (Aseptic Techniques)

Explain the purpose of working close to a bunsen burner

Answer 58

to create an upward current of air
(that moves away contaminating microbes)

Question 59

RP6 (Aseptic Techniques)

Explain the purpose of disinfecting the work bench

Answer 59

To kill microbes and prevent contamination

Question 60

RP6 (Aseptic Techniques)

Explain the purpose of flaming the equipment (e.g. spreader / innoculation loop) when transferring bacteria from culture bottles to an agar plate.

Answer 60

sterilise / kill microbes / prevent contamination

Question 61

RP6 (Aseptic Techniques)

Explain the purpose of lifting the lid of the petri dish at angle

Answer 61

prevent entry of microbes

Question 62

RP6 (Aseptic Techniques)

What is a colony?

Answer 62

1 bacteria that has multiplied many times via binary fission to form a visible colony

Question 63

RP6 (Aseptic Techniques)

Purpose of ‘broth’ AND ‘agar’ in bacterial cultures

Answer 63

Provides named nutrients for microbe growth e.g., galactose, glucose, amino acids, mineral ions

Question 64

RP6 (Aseptic Techniques)

A student used a dilution series to investigate the number of cells present in a liquid culture of bacteria.

Describe how he made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original liquid culture of bacteria.

Answer 64

1. Add 1 part bacteria culture to 9 parts sterile liquid (e.g. broth/water) to make 1 in 10 dilution;
2. Mix well;
3. Add 1 part of 1 in 10 and 9 parts fresh sterile liquid to make 1 in 100 dilution;
4. Mix well;
5. Add 1 part of 1 in 100 and 9 parts fresh sterile liquid to make 1 in 1000 dilution;

Question 65

RP6 (Aseptic Techniques)

A student transferred 0.5 cm^3 of a 1 in 10,000 dilution to an agar plate and after a 24-hour incubation counted 57 colonies.

How many bacteria are present in the original culture of 1cm^3?

Answer 65

57 x 10000 = 570,000 in 0.5cm^3

570,000 x 2 in 1cm^3

= 1.14 x 10^6

Always multiply the dilution factor!

Question 66

RP6 (Aseptic Techniques)

Answer 66

Always multiply by the dilution factor!

Question 67

RP6 (Aseptic Techniques)

Why did the student transfer the same volume of bacteria culture onto each agar plate.

Answer 67

So same number of bacteria transferred to allow comparison

Question 68

RP6 (Aseptic Techniques)

Explain why agar was boiled before adding to the petri dish

Answer 68

So no contamination / other bacteria present

Question 69

RP6 (Aseptic Techniques)

Equation for estimating population of cells that double each division e.g. bacteria, cancer cells.

Answer 69

Question 70

RP6 (Aseptic Techniques)

Starting with one bacteria cell, how many bacteria would be present after 17 divisions.

Give your answer in standard form.

Answer 70

Question 71

RP6 (Aseptic Techniques)

Starting with 17 bacteria cells, how many bacteria would be present after 30 divisions.

Give your answer in standard form.

Answer 71

Question 72

RP6 (Aseptic Techniques)

Equation for determining how many divisions produced a total number of cells e.g. bacteria.

Answer 72

Question 73

RP6 (Aseptic Techniques)

Answer 73

Question 74

RP6 (Aseptic Techniques)

Answer 74

Question 75

RP6 (Aseptic Techniques)

Why use a logarithmic scale on a graph?

Answer 75

Allows numbers with a large range or differences to be presented

Question 76

RP6 (Aseptic Techniques)

What are logs?

Answer 76

Question 77

RP6 (Aseptic Techniques)

Answer 77

Question 78

RP6 (Aseptic Techniques)

A student investigated cinnamon oil as an antimicrobial.

Suggest exactly what the student added to the petri dish as a positive control AND negative control.

Answer 78

(Positive control = will decrease microbe numbers)

1. Antimicrobial / antibacterial (solution)

OR Antibiotic OR Antiseptic/disinfectant;

(Negative control = no effect on microbe numbers)

2. Sterile water

OR Oil (without cinnamon);

Question 79

RP6 (Aseptic Techniques)

Explain the below clear zones OR zones of inhibition around the antibiotic disks after 24 hours.

Answer 79

Antibiotic diffuses from disk into agar;

Bacteria resistant to antibiotic A so no clear zone;

Antibiotic B prevents growth of bacteria as shown by clear zone / zone of inhibition;

Anitibiotic C the most effective against bacterial growth as shown largest clear zone / zone of inhibition;

Question 80

How Science Works (AO3)

Why should sampling be random?

Answer 80

To reduce bias

This also make the results / experiment more reliable

Question 81

How Science Works (AO3)

Why should a sample be large?

Answer 81

To ensure it is representative;

To calculate a mean so results are more reliable;

Identify anomolus results;

Question 82

How Science Works (AO3)

The scientists’ hypothesis at the start of the investigation was that crop plants genetically engineered to produce the protein GB would become more resistant to high environmental temperatures.

The scientists developed this hypothesis on the basis of previous research on crops that are grown in hot climates.

Suggest how the scientists arrived at their hypothesis.

Answer 82

1. Looked for information / journals / research, on crop plants that grow at high temperatures;

2. Crop plants cited in this research contain / make GB;

3. So assumed making plants produce GB makes them resistant to high temperatures;

Question 83

How Science Works (AO3)

Suggest how the scientist measured the rate of water flow in a river.

Answer 83

Movement of (floating) object over known distance and over given time

OR Time to fill container of known volume

OR Use of data logging device;

Question 84

How Science Works (Maths)

Answer 84

Hint: C1 x V1 = C2 x V2