Required Practical 1-6 & How Science Works Flashcards
RP1 (Enzymes)
Concentration of substrate solution
Concentration of enzyme solution
pH
RP1 (Enzymes)
Calculate the rate of reaction at 25°C.
DY (change in Y) / DX (change in X = time)
RP1 (Enzymes)
Describe the differences between the two curves (2 marks)
- Initial rate of reaction faster at 37 °C;
- Graph reaches plateau at 37 °C;
RP1 (Enzymes)
Explain the differences between the two curves (3 marks).
(Initial rate of reaction faster at 37 °C);
- Because more kinetic energy;
- So more enzyme substrate complexes formed;
(Graph reaches plateau at 37 °C);
- Because all substrate used up.
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?
.
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.
RP1 (Enzymes)
What is a common control condition that proves a specific enzyme is needed for a reaction?
- Boiled enzyme
- At same concentration & volume
- This denatures the enzyme and the reaction will not take place in this condition
RP1 (Enzymes)
Mark in pairs, 1 and 2 OR 3 and 4 OR 5 and 6
- Boil OR Add (strong) acid/alkali;
- Denatures the enzyme/ATP synthase;
- Put in ice/fridge/freezer;
- Lower kinetic energy so no enzyme-substrate complexes form;
- Add high concentration of inhibitor;
- Enzyme-substrate complexes do not form;
RP1 (Enzymes)
- Same volume of (each) buffer/pH solution;
- Same concentration/mass of substrate (at start);
- Same concentration/mass of denatured enzyme;
RP2 (Mitosis)
What is the equation for the mitotic index?
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).
- Count cells in mitosis in field of view;
- Divide this by total number of cells in field of view;
- Repeat many/at least 5 times
(to calculate a reliable mean mitotic index)
OR Select (fields of view) at random;
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?
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
RP2 (Mitosis)
State two precautions required when working with hydrochloric acid.
- Eye protection;
- Gloves;
- Add water to spills (immediately);
- Do not pour away down sink
RP2 (Mitosis)
Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly.
Explain why (2 marks).
- To create a single/thin layer of cells
OR to spread out cells;
- So that light could pass through;
RP2 (Mitosis)
Where dividing cells are found / mitosis occurs;
OR
No dividing cells / mitosis in tissue further away / more than 5 mm from tip;
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).
Description and explanation required, so mark as pairs only
- Examine large number of fields of view / many cells;
- To ensure representative / reliable sample;
OR
- Method to deal with part cells shown at edge /count only whole cells;
- To standardise counting;
RP2 (Mitosis)
- Stops anaphase / cell division / mitosis;
Accept prevents telophase / cytokinesis
- (By) stopping / disrupting / spindle fibres forming / attaching / pulling;
- Preventing separation of (sister) chromatids;
Accept chromatids split
- (So) no new cells added (to root tip);
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.
28.8 minutes
Working out:
6 / 200 = proportion in anaphase
Multiply this answer by 16 x 60 (convent into minutes).
RP2 (Mitosis)
When comparing the mitotic index in the roots of two different species.
Give two considerations to ensure this comparison is valid.
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;
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.
Differences in base sequences
OR
Differences in histones/interaction with histones
OR
Differences in condensation/(super)coiling;
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 = 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
RP3 (Osmosis)
Calculations made (from raw data)
OR raw data would have recorded initial and final masses.
RP3 (Osmosis)
- Water potential of solution is less than / more negative than that of potato tissue;
Allow Ψ as equivalent to water potential
- Tissue loses water by osmosis (so masses decreases).
RP3 (Osmosis)
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).
RP4 (Membrane damage)
What is uncertainty?
The amount of error your measurements might contain
RP4 (Membrane damage)
How do you calculate uncertainty?
Is always HALF of the smallest interval you can read with the measuring equipment you are using.
RP4 (Membrane damage)
What is the uncertainty of a measuring cylinder where the smallest interval is 20mls?
10mls
Uncertainty is always HALF of the smallest interval
RP4 (Membrane damage)
What is the uncertainty of a ruler and why?
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
RP4 (Membrane damage)
What is the equation for percentage error?
RP4 (Membrane damage)
Calculate the percentage error when measuring 50mls using a cylinder with the smallest interval of 5mls.
(2.5 / 50) x 100 = 5%
RP4 (Membrane damage)
What is the uncertainty of this measuring cylinder in mls?
1 ml
RP4 (Membrane damage)
What is the percentage error if measuring 15mls using this measuring cylinder? (to 1dp).
(1 / 15) x 100 = 6.7%
RP4 (Membrane damage)
Suggest how you could reduce the uncertainty calculated using this measuring cylinder
Use instrument with smaller intervals
RP4 (Membrane damage)
Give one way in which a student could ensure their beetroot cylinders were kept at 25 °C throughout the experiment.
Measure temperature (in tube) at intervals and use appropriate corrective measure (if temperature has fluctuated);