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Required practicals Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

RP1: What are the factors that affect the rate of enzyme activity?

A
  1. Enzyme concentration
  2. Substrate concentration
  3. Temperature
  4. pH
  5. Concentration of competitive and non-competitive inhibitors
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2
Q

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

A

Replace the enzyme solution with distilled water or boiled enzyme solution

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3
Q

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

A

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

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4
Q

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

A
  • 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
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5
Q

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

A

Rate of reaction = 1/time

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6
Q

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

A

As temperature increases, KE increases so more ES complexes form. The rate of reaction increases up to the optimum temperature.

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.

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7
Q

RP1: What is the independent variable?

A

It will be one of the five factors that affect the rate of an enzyme-controlled reaction

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8
Q

RP1: What is the dependent variable?

A

Will be a measurement of the time taken for the reaction to complete. This will either be the time taken for the substrate to be used up, or the time take for the product to form

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9
Q

RP1: You used a buffer solution in your investigation. What are buffer solutions used for?

A

Maintain constant pH 1

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10
Q

RP1: You left the test tubes in the water bath for 10 minutes before you added the enzyme to the milk powder solution. Explain why

A

To equilibrate/reach temperature at which reaction will take place

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11
Q

RP1: Why is a water bath needed?

A

Water bath keeps test tubes at constant temperature

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12
Q

RP1: Explain why you set up three experiments at each temperature

A

Enables calculation of a more reliable mean, so that anomalous data can be identified

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13
Q

RP2: Where in plants can cells undergo mitosis be found?

A

Meristem tissue at shoot and root tips

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14
Q

RP2: What is the mitotic index?

A

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

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15
Q

RP2: Outline the procedure to prepare a root tip slide

A
  1. Warm 1M HCl to 60C in a water bath
  2. Cut a root tip using a scalpel and add to the HCl. 3. 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
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16
Q

RP2: State the formula for the mitotic index

A

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

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17
Q

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

A

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

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18
Q

RP2: Why can’t you let the coverslip move from side to side

A

Could damage/break the chromosomes

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19
Q

RP3: What is the purpose of calibration curves?

A

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

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20
Q

RP3: How is a calibration curve used to find the concentration of plant tissue?

A

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

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21
Q

RP3: What occurs when plant tissue is placed in a hypotonic solution?

A

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

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22
Q

RP3: Why are the potato discs left in solution for 20 minutes?

A

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

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23
Q

RP3: What is water potential determined by?

A

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

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24
Q

RP3: Outline the procedure of investigating osmosis using potato tissue

A
  1. Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5 cm^3 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 % change in mass
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25
Q

RP3: Why is the % change used rather than the actual change in mass?

A

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

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26
Q

RP3: What is indicated by the x-intercept of the calibration curve?

A

The concentration that is isotonic to the solution tested

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27
Q

RP3: Explain the change in mass in the potato chips

A

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 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.

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28
Q

RP3: Why are the potato chips dabbed dry after removing from the sucrose solution?

A

To remove any excess water clinging to its surface

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29
Q

RP3: What are the controlled variables of this practical?

A
  • Volume of sucrose solution
  • Size of potato chips
  • Length of time left in solution
  • Dab each potato disc with paper towels
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30
Q

RP4: State 2 factors that affect the permeability of cell membranes

A
  • Temperature
  • Concentration of solvents (ethanol)
31
Q

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

A

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

32
Q

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

A
  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 30-80C. Leave for 20 minutes
  4. Filter each solution out into a cuvette and measure the absorbance using a colorimeter
33
Q

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

A
  • 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
34
Q

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

A

Increasing temperature results in increase membrane permeability

35
Q

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

A

Increasing ethanol concentration leads to increased membrane permeability

36
Q

RP4: You were provided with beetroot discs that were washed thoroughly before the start of the investigation. Explain why it was important to wash the beetroot discs.

A

To wash off any pigment, to show any pigment released is from the effect of alcohol

37
Q

RP4: Describe a suitable control for your investigation, explain why this control would be necessary

A

Distilled water and discs of beetroot
To show that the alcohol was causing the leakage of pigment/ to compare it with the effects of the alcohol

38
Q

RP4: Explain why you were instructed to shake the test tubes every minute

A

Increase the contact of all surfaces with the alcohol

39
Q

RP4: Explain why you were instructed to pour the alcohol immediately from the experimental test tube into a clean test tube

A

Heating/cooking would damage the membranes - disrupts phospholipid bilayer/denatures proteins

40
Q

RP4: You were given discs taken from fresh beetroot in your investigation. Explain why your results would have been different if you had used cooked beetroot

A

Less kinetic energy
Molecules move slower
Lower rate of diffusion
Membranes less fluid

41
Q

RP4: You used a water bath in this investigation. Explain why a decrease in temperature of 5C would affect the results

A

Variation in beetroot/variation in judging colour

42
Q

RP6: State 6 aseptic techniques

A
  • 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
43
Q

RP6: Why is bacteria incubated at 25C?

A

To prevent the growth of pathogens, which occurs at higher temperatures

44
Q

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

A

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

45
Q

RP6: What does the zone of inhibition indicate?

A

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

46
Q

RP6: State the hazards and precautions of this practical

A

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

47
Q

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

A

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

48
Q

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

A

A bar chart of zone of inhibition against antibiotic

49
Q

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

A

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

50
Q

RP5: How should a diagram be drawn?

A

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

51
Q

RP7: What is the purpose of chromatography?

A

To separate different components in a sample

52
Q

RP7: State the factors affecting the rate of migration of different pigments

A
  • Solubility
  • Mass
  • Affinity to the paper
53
Q

RP7: What is the formula of the RF value?

A

Distance moved by pigment/distance moved by solvent

54
Q

RP7: What is the purpose of finding the RF value of a pigment?

A

Experimental RF value can be compared to a standard value in a database to identify the pigment.
The standard value should be measured using the same paper and solvent

55
Q

RP7: Outline the procedure of using chromatography to separate photosynthetic pigments

A
  1. Draw a horizontal pencil line 1cm above the bottom of the filter paper
  2. Add some acetone and use the mortar and pestle to grind up the leaf sample and release the pigments
  3. Use a capillary tube to transfer the pigment onto the pencil line
  4. Suspend the paper in the solvent so that the level of the liquid does not lie above the pencil line and leave the paper until the solvent has run up the paper to near the top
  5. Remove the paper from the solvent and draw a pencil line marking where the solvent moved up to
  6. Calculate the Rf value for each spot
56
Q

RP7: State the hazards and precautions in this practical

A

Solvents are irritant and flammable.
Keep away from naked flames, wear eye protection and avoid contact with skin.
Leaf extract may be a biohazard. Wash hands after use

57
Q

RP8: What is the function of dehydrogenase in chloroplasts?

A

It catalyses the acceptance of electrons by NADP in the light dependent reactions

58
Q

RP8: What is the purpose of DCPIP?

A

It is a redox indicator dye and acts as an alternate electron acceptor instead of NADP. It turns from blue to colourless when reduced

59
Q

RP8: Why is the plant extract chilled in an ice-water bath?

A

To lower the activity of enzymes to prevent them from breaking down the chloroplasts

60
Q

RP8: How is the control set up?

A

Fill a cuvette with chloroplast extract and distilled water

61
Q

RP8: How is light intensity controlled?

A

Adjust the distance of the lamp from the set up. Perfrom the practical in a dark room so that the only light source is the lamp

62
Q

RP8: Why are the stalks of leaves removed before grinding?

A

The stalks do not contain many chloroplasts

63
Q

RP8: Outline the procedure of investigating the effect of light intensity, after chloroplast extract has been obtained

A
  1. Set the colorimeter to the red filter. Zero using a cuvette containing chloroplast extract and distilled water
  2. Place test tube in the rack 30cm from light source and add DCPIP. Immediately take a sample and add to cuvette. Measure the absorbance of the sample
  3. Take a sample and measure its absorbance every 2 minutes for 10 minutes
  4. Repeat for different distances from lamp up to 100cm
64
Q

RP9: What is the function of methylene blue in this practical?

A

It is a redox dye and acts as an alternate electron acceptor of the electrons transferred during ATP synthesis.
It turns from blue to colourless, indicating the end point

65
Q

RP9: Outline the procedure to investigate the effect of temperature on the rate of respiration of yeast

A
  1. Set up a water bath at 35C
  2. Add equal volumes of the yeast and glucose solution to 3 test tubes. Place test tubes in the water bath and leave them to equilibrate for 10 minutes
  3. Add 2 cm^3 of methylene blue to the test tubes and start the timer. Shake for 10 seconds and place test tube back in water bath. Record how long it takes for the methylene blue to turn colourless for each test tube
  4. Repeat the experiment using temperatures of 40,50,60 and 70C
66
Q

RP9: How are the results used to calculate the rate of respiration at each temperature?

A

Rate = 1/taken for methylene blue to decolourise

67
Q

RP9: Why does the yeast solution need to be buffered?

A

To maintain a constant pH so that the enzymes are functioning at their optimum pH

68
Q

RP9: What is the effect of temperature on the rate of respiration?

A

As temperature increases, the rate of respiration increases to an optimum. This is because the rate of enzyme activity increases.
Beyond the optimum, enzyme activity decreases as enzymes denatures with high temperature

69
Q

RP10: How can a choice chamber be used to measure the favourable environment of a small organism?

A

By setting up chambers in different quadrants with different environmental conditions: dark + dry, dark + damp, light + dry, light + damp
- Organisms will move to the quadrant they find favourable

70
Q

RP10: What factors must be controlled when repeating the experiment?

A
  • Number of animals
  • Environmental conditions
  • Time allowed for animals to choose
71
Q

RP10: Which statistical test is used to analyse the results of this practical and why?

A

Chi squared
- Compares the expected and observed values, and tests if there is a significant difference

72
Q

RP10: What is the conclusion drawn if the calculated value is greater than the critical value?

A

Null hypothesis is rejected
- Less than 5% probability that the difference is due to chance alone
- These is a statistically significant difference between the expected and observed values

73
Q

RP10: What do animals do when they are in unfavourable environments?

A

They move faster and change direction more frequently to increase their chances of survival

74
Q

RP10: State the hazard and precaution involved in this practical?

A

The live organisms used are a biohazard.
Wash hands after handling

Biology (47 decks)

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