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A LEVEL BIO > AS practicals > Flashcards

AS practicals Flashcards

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Biology 101 flashcards
1
Q

RP1 - measuring enzyme activity*

A
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2
Q

how can the progress of enzyme-catalysed reactions can be investigated by?

A

1) by measuring the rate of formation of a product using a catalyst

2) by measuring the rate of disappearance of a substrate using a catalyst

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3
Q

common factors to investigate and how to investigate them:

A

-temperature
-pH
-substrate concentration
-enzyme concentration
-inhibitors

(the effect of each of these can be determined by changing a single variable and measuring its effect on the rate of reaction. it is important to keep all other variables constant so that they do not influence the results)

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4
Q

common enzymes to investigate:

A

-amylase
-catalase
-protease
-trypsin

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5
Q

trypsin practical

A
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6
Q

trypsin practical equipment:

A

-powdered milk suspension
-trypsin solution (0.5%)
-distilled water
-hydrochloric acid
-5cm³ syringe
-flat bottomed tubes
-timer

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7
Q

what is the independent variable in the trypsin practical?

A

temperature

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8
Q

method of trypsin practical:

A

1) take three test tubes and measure 5cm³ milk into each. place in water bath at
10°C for 5 minutes to equilibrate

2) add 5cm³ trypsin to each test tube simultaneously and start the timer immediately

3) record how long it takes for the milk samples to completely hydrolyse and become colourless

4)) repeat steps 2-3 at temperatures of 20°C, 30°C, 40°C and 50°C

5) find the mean time for the milk to be hydrolysed at each temperature and use this to work out the rate of reaction

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9
Q

rate of reaction formula:

A

1/ mean time

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10
Q

risk assessment: hazards

A

-broken glass
-hydrochloric acid
-hot liquids
-enzymes

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11
Q

broken glass
(risk, safety precaution, in emergency)

A

risk: cuts from sharp object

safety precaution: take care when
objects; keep away from edge of desk

in emergency: elevate cuts; apply pressure; do not remove glass from wound; seek medical assistance

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12
Q

hydrochloric acid
(risk, safety precaution, in emergency)

A

risk: may cause harm/irritation to eyes or in cuts

safety precaution: wear eye protection; avoid contact with skin, tie up long hair

in emergency: wash off skin immediately;
flood eye/cuts with cold water

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13
Q

hot liquids
(risk, safety precaution, in emergency)

A

risk: scalding

safety precaution: handle with care; use tongs to remove boiling tubes from water bath; wear eye protection, keep away from the edge of the desk

in emergency: run burn under cold water; seek medical assistance

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14
Q

enzymes
(risk, safety precaution, in emergency)

A

risk: allergies

safety precaution: avoid contact with skin/eyes; wear eye protection

in emergency: seek assistance

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15
Q

milk & colourlessness

A

-milk contains a protein called casein which, when broken down, causes the milk to turn colourless
-trypsin is a protease enzyme which hydrolyses the casein protein

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16
Q

method limitations:

A

-the end-point was subjective which leads to inaccurate ‘time taken’ measurements

-the water bath was not thermostatically controlled and therefore the temperature decreased during the practical

-the range of tested pH values was not wide enough as the point at which trypsin denatures was not identified (e.g. test beyond pH 11)

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17
Q

RP2 - root tips

A
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18
Q

plant mitosis

A

plant cells undergo mitosis at shoot and root tips in areas called ​meristems

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19
Q

equipment of root tip practical:

A

-100ml beaker
-hydrochloric acid
-microscope slide & cover slip
-acetic orcein stain
-filter paper
-mounted needle
-scalpel
-distilled water
-watch glass
-forceps
-onion
-paper towel
-light microscope

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20
Q

method of root tip practical:
(part 1)

A

1) heat 1 mol dm HCl at 60°C in a water bath

2) cut a small sample of the root tip using a scalpel

3) transfer root tip to HCl and incubate for 5 minutes

4) remove from HCI and wash sample in cold distilled water, remove the tip using a scalpel

5) place tip on a microscope slide and add a few drops of stain

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21
Q

method of root tip practical:
(part 2)

A

6) lower the cover slip down carefully onto the slide. make sure there are no air bubbles in the slide which may distort the image, and that the coverslip doesn’t slide sideways which could damage the chromosomes

7) place under a microscope and set the objective lens on the lowest magnification

8) use the coarse adjustment knob to move the lens down to just above the slide

9) use the fine adjustment knob to carefully re-adjust the focus until the image is clear (you can use a higher magnification if needed)

10) to calculate mitotic index, cells undergoing mitosis must be counted (cells with chromosomes visible), as well as the total number of cells.

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22
Q

why is hydrochloric acid used?

A

it softens and loosens the root tissues

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23
Q

why is acetic orcein stain used?

A

it makes the chromosomes visible and will show which cells are undergoing mitosis

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24
Q

why is a mounted needle used?

A

to lower the cover slip and prevent air bubbles under the cover slip

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25
Q

why was motion tip used?

A

the tip is the growing region, therefore mitosis should be occurring here

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26
Q

risk assessment: hazards

A

-hydrochloric acid
-stain
-scalpel
-broken glass

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27
Q

hydrochloric acid
(risk, safety precaution, in emergency)

A

risk: may cause harm/irritation to eyes or in cuts

safety precaution: wear eye protection; avoid contact with skin, tie up long hair

in emergency: wash off skin immediately; flood eye/cuts with cold water

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28
Q

stain
(risk, safety precaution, in emergency)

A

risk: may cause harm/irritation to eyes or in cuts

safety precaution: wear eye protection; avoid contact with skin

in emergency: wash off skin immediately; flood eye/cuts with cold water

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29
Q

scalpel
(risk, safety precaution, in emergency)

A

risk: cuts from sharp object

precaution: cut away from fingers; use forceps to hold sample whilst cutting, keep away from the edge of the desk

in emergency: elevate cuts; apply pressure; seek medical assistance

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30
Q

broken glass
(risk, safety precaution, in emergency)

A

risk: cuts from sharp object

safety precaution: take care when handling slides and coverslips; keep glassware away from edge of desk

in emergency: elevate cuts; apply pressure; do not remove glass from wound; seek medical assistance

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31
Q

what is mitotic index?

A

the proportion of cells (in a group of cells or a sample of tissue) that are undergoing mitosis

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32
Q

mitotic index: formula

A

number of cells with visible chromosomes ÷ total number of cells

(x100 if percentage is needed)

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33
Q

a student who wanted to observe mitosis prepared a sample of cells. they counted a total of 42 cells in their sample, 32 of which had visible chromosomes. calculate the mitotic index for this sample of cells (give your answer to 2 decimal places)

A

mitotic index = 32 ÷ 42

mitotic index = 0.76

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34
Q

how can root tip slides be prepared?

A

squash technique
(root tips are stained and then gently squashed, spreading the cells out into a thin sheet and allowing individual cells undergoing mitosis to be clearly seen)

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35
Q

mm → µm

A

x1000

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36
Q

RP3 - water potential

A
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37
Q

what are calibration curves?

A

graphs used to determine an unknown concentration of a sample by comparing the unknown to a set of standard samples with known concentrations

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38
Q

hypotonic

A

-lower concentration
-higher water potential

(water moves out of cell)

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39
Q

isotonic

A

-same concentration
-same water potential

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40
Q

hypertonic

A

-higher concentration
-lower water potential

(water moves in)

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41
Q

equipment of water potential practical:

A

-large potato
-cork borer
-1 mol dm-3 sucrose solution
-distilled water
-boiling tube rack
-six boiling tubes
-marker pen
-thermometer
-10cm measuring cylinder
-white tile
-scalpel
-ruler
-paper towels
-stop clock
-digital balance
-forceps

42
Q

method of water potential practical:

A

1) make a series of dilutions of 1M sucrose solution
↳ these should be at 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0M sucrose
↳ dilute using distilled water

2) measure 10cm³ of each dilution into separate test tubes and label them

3) use a cork borer to cut out six potato chips and cut down the sections into identically lengthed chips (with ruler)
↳ dry each chip using a paper towel to remove excess water but do not squeeze

4) weigh each before the start of the experiment and put into graph

5) place a potato chip in each test tube (one per sucrose concentration) and leave for 20 minutes

6) remove each potato chip, dry gently using paper towel, and weigh them in turn, put this into a table

7) calculate the percentage change in mass for each sucrose solution

43
Q

risk assessment: hazards

A

-scalpel
-broken glass

44
Q

scalpel
(risk, safety precaution, in emergency)

A

risk: cuts from sharp object

safety precaution: cut away from fingers; use forceps to hold sample whilst cutting, keep away from the edge of the desk

in emergency: elevate cuts; apply pressure; seek medical assistance

45
Q

broken glass
(risk, safety precaution, in emergency)

A

risk: cuts from sharp glass

safety precautions: take care when handling glass objects; keep glassware away from edge of desk

in emergency: elevate cuts; apply pressure; do not remove glass from wound; seek medical assistance

46
Q

osmosis analysis:

A

calculate the percentage change in mass for each potato cylinder

47
Q

percentage change in mass
(formula)

A

change in mass/initial mass

x100

48
Q

what does a positive percentage change in mass entail?

A

the potato has gained water by osmosis
↳ the solution had a higher water potential than the potato
↳ this would make the potato cells turgid
↳ the water exerts turgor pressure (or hydrostatic pressure) on the cell walls

49
Q

what does negative percentage change in mass entail?

A

the solution had a lower water potential than the potato
↳ the potato cylinder in the strongest sucrose concentration will have decreased in mass the most
↳ more water molecules will move out of the potato cells by osmosis, making them flaccid

50
Q

what does no change in mass entail?

A

-no overall net movement of water into or out of the potato cells
-the solution that this particular potato cylinder was in had the same water potential as the solution found in the cytoplasm of the potato cells

51
Q

the format of the calibration curve graph:

A

-plot a graph of change in mass against concentration of sucrose solution
-the point at which the line of best fit crosses the x axis indicates the point at which the solution is isotonic

52
Q

RP4 - permeability

A
53
Q

what are cell membranes comprised of?

A

-a phospholipid bilayer which makes them selectively permeable
-this permeability can be changed by different variables

54
Q

examples of variables that permeability is affected by:

A

-temperature
-concentrations of solvents (ethanol)

55
Q

beetroot components:

A

-beetroot cells contain a purple pigment called betalain (in the vacuole)
↳ betalain can’t cross the plasma membrane unless the membrane is damaged
-when the cell-surface membrane has a higher permeability, more pigment leaks out of cells

56
Q

why is beetroot used in the practical?

A

permeability can be measured by the amount of pigment leaked from beetroot cells into an aqueous solution using a colorimeter

57
Q

equipment of permeability practical:

A

-beetroot
-scalpel
-forceps
-ruler
-tongs
-distilled water
-boiling tube & boiling tube rack
-colorimeter
-cuvettes
-filter paper
-timer
-water bath
-thermometer
-ethanol

58
Q

method of permeability practical:
(temperature)

A

1) coloured agar is made up and cut into equal-sized cubes (a cork borer can also be used, as long as the cores are cut to the same length)

2) rinse the beetroot pieces

3) place each of the cubes of beetroot in an equal volume of distilled water (eg: 5ml)

4) place each test tube in a water bath at a range of temperatures (20, 30, …)

5) leave the samples for 20 minutes - the pigment will leak out of the beetroot

6) remove the beetroot pieces, leaving just the coloured liquid in the five test tubes

7) set the colorimeter to a blue filter and zero using a cuvette with distilled water

8) filter each sample of water into a cuvette using filter paper

9) use a colourimeter to measure how much light is absorbed as it passes through each of the five samples of coloured liquid

10) measure the absorbance for each solution. a higher absorbance indicates higher pigment concentration, and hence a more permeable membrane

59
Q

the method of the permeability practical:
(ethanol)

A

1) coloured agar is made up and cut into equal-sized cubes (a cork borer can also be used, as long as the cores are cut to the same length)

2) rinse the beetroot pieces

3) create a dilution series of ethanol using distilled water. ethanol concentrations should range from 0-100% ethanol.

5) leave the samples for 20 minutes - the pigment will leak out of the beetroot

6) remove the beetroot pieces, leaving just the coloured liquid in the five test tubes

7) set the colorimeter to a blue filter and zero using a cuvette with distilled water

8) filter each sample of water into a cuvette using filter paper

9) use a colourimeter to measure how much light is absorbed as it passes through each of the five samples of coloured liquid

10) measure the absorbance for each solution. a higher absorbance indicates higher pigment concentration, and hence a more permeable membrane

60
Q

ethanol
(risk, safety precaution, in emergency)

A

risk: irritant/ flammable

safety precaution: wear eye protection; keep away from naked flames

in emergency: wash eyes and skin with cold water

61
Q

what to plot for permeability practical:

A

absorbance (y) against ethanol concentration/temperature (x)

62
Q

why are equal sized beetroot cubes used?

A

the pieces must have the same dimensions so that they all have equal surface areas and volumes, as these factors could affect the rate at which the pigment leaks out

63
Q

why are the beetroot cubes rinsed?

A

to remove excess pigment

64
Q

conclusions of the practical:
(permeability)

A

as temperature increases, membrane permeability also increases
↳ phospholipids in cell membrane move more because they have more energy
↳ phospholipids are not as tightly packed together → permability increases

65
Q

permeability at very high temperatures:

A

-the phospholipid bilayer may even to melt and breakdown, further increasing the permeability of the membrane
-the volume of water inside the cells expands, putting pressure on the membrane, causing channel and carrier proteins to deform → they can’t control what enters and leaves the cell
↳ increased permeability

66
Q

how high temperatures affect proteins

A

-affects the conformation (3D shape) of proteins
-at high temperatures the intermolecular forces between amino acids are broken which affects the protein’s specificity and function

67
Q

cell membranes at very low temperatures (below 0):

A

membrane permeability may also be increased (once the cells have thawed again)

-channel or carrier proteins deform at these low temperatures
-ice crystals that form can also pierce the cell membrane, making it highly permeable

68
Q

how does ethanol affect permeability?

A

-ethanol causes the cell-surface membrane to rupture, releasing the betalain pigment from the cell
-higher concs of ethanol cause more disruption to the membrane → more gaps form
-as concentration of ethanol increases, the permeability of the cell-surface membrane also increases

69
Q

limitations of the permeability practical:

A

-cuvette
-beetroot pieces

70
Q

limitations: cuvettes
(+ how to rectify)

A

cuvettes may differ in thickness (slightly):
↳ a thicker (or scratched) cuvette will absorb slightly more light than a thinner unscratched cuvette
↳ this can be overcome by using the same cuvette for every reading, or repeating the investigation many times and finding a mean

71
Q

limitations: beetroot
(+ how to rectify)

A

the beetroot pieces may not be identical in size and shape, meaning some test tubes could contain slightly more beetroot tissue than others
↳ this can be overcome by cutting the discs as accurately as possible using a scalpel and ruler, and by repeating each investigation several times to find a mean

72
Q

RP5 - dissection

A
73
Q

the importance of dissections:

A

-essential for understanding the function of internal biological functions

74
Q

what are the issues with dissections?

A

ethical issues

75
Q

examples of the ethical issues of dissections:

A

-people worry about how the animals for dissections are raised and killed
-it goes against the religious beliefs of some individuals

76
Q

equipment for the dissections:

A

-scalpel
-scissors
-tweezers
-pins & labels
-dissection tray
-newspaper/paper towels
-specimen’s heart
-camera
-plastic gloves
-disinfectant spray

77
Q

the method of the dissection:

A

1) take a picture of the outside, identify the coronary arteries

2) place the specimen on the dissecting board

3) make a cut along each side of the heart to see inside of the four chambers

4) look for the atrioventricular valve, there will be tendinous cords attached to these
↳ use a dissection needle to pull on these cords to feel how strong they are. lift the valves to see how thin they are.

5) examine the thickness of the walls of the chambers.

6) observe how much thinner the muscular walls of the atria are than the ventricles

78
Q

what can scissors be used for?

A

cutting large sections of tissue (cuts do not need to be precise)

79
Q

what do scalpels enable?

A

finer, more precise cutting
(it needs to be sharpe to ensure this)

80
Q

how to clean up after the dissection:

A

-place all dissection equipment in a beaker of disinfectant.
-place the heart, gloves and any paper towels in disposal bags
-clean your work surface with a disinfectant spray and clean and disinfect the dissecting

81
Q

what are the hazards of the practical?

A

-biohazard
-disinfectant
-sharp tools

82
Q

biohazard
(risk, safety precaution, in emergency)

A

risk: contamination

precautions: use disinfectant; keep sample on dissection board; wash hands with soap after dissection

in emergency: seek assistance

83
Q

disinfectant
(risk, safety precaution, in emergency)

A

risk: flammable

safety precaution: keep away from naked flame

in emergency: out of fire

84
Q

what should be worn during the dissection?

A

-lab coat
-eye protection
-gloves

85
Q

tips for drawing a labelled diagram:

A

-use a sharp HB pencil
-add labels to all structures (lines should be drawn with a ruler)
-no shading
-use single and continuous lines (no sketching
-no colour
-include a magnification/scale

86
Q

limitations of dissection practical:

A

-it can be hard to see some of the smaller, finer structures within organs
-the specimens do not reflect how the tissue would look in a living organism
-if only a single specimen is dissected then anomalies found within that specimen may be ignored or glossed over

87
Q

RP6 - aseptic techniques

A
88
Q

what are aspetic techniques?

A

they ensure that the microbes being investigated don’t escape or become contaminated with another unwanted, and possibly pathogenic, microbe

89
Q

examples of aseptic techniques:

A

-washing hands thoroughly to disinfect them
-no food or drink allowed in the lab
-disinfecting work surfaces with disinfectant or alcohol

90
Q

aseptic techniques before the practical:

A

-sterilise all equipment
-sterilise work surfaces with disinfectant
-wash hands with soap
-close windows and doors to reduce draughts

(to kill microbes)

91
Q

equipment of the aseptic practical:

A

-petri fish with agar
-diluted bacterial broth
-pipettes
-plastic spreader
-bunsen burner
-gloves
-goggles
-virkon disinfectant
-heatproof mat
-loop
-antibiotic disc

92
Q

steps of aseptic practical:

A

1) sterilise the equipment (spreader, work surface, loop)

2) turn a bunsen burner on (keep it on the whole time)

3) open a bottle (containing bacteria) & flame the bottleneck

4) use an inoculating loop to transfer broth onto the agar plate (flame the wire hoop before using it to transfer bacteria)

4) spread a sample of the diluted bacterial broth onto the surface of the sterile agar plate (only open the petri dish quickly & slightly, when necessary)

5) use sterile forceps to put an antibacterial disc onto the agar plate

6) lightly tape a lid on, invert and incubate at 25°C for 48 hours

7) put all of the used equipment into virkon & disinfect the work surface

93
Q

steps of aseptic practical:
(after incubation)

A

1) measure the diameter of the inhibition zone (clear circle) for each antibiotic.
↳ don’t remove the lid from the agar plate

2) work out the area of the inhibition zone using the formula

94
Q

why is a bunsen burner used?

A

so that convection currents draw microbes away from the culture

95
Q

why are bottles flamed?

A

air moves out so unwanted organisms don’t move in

96
Q

clear zones:
(extra)

A

-the clear area will end when the conc of antibiotic reaches a level that the bacteria are no longer susceptible to
-more effective antibiotics need a lower concentration to kill bacteria and so they will produce larger clear zones
-if a bacteria is completely resistant to an antibiotic then there will be no clear zone around that particular paper disk

97
Q

hazards:

A

-disinfectant
-biohazard
-naked flame

98
Q

disinfectant
(risk, safety precaution, in emergency)

A

risk: flammable

safety precaution: keep away from naked flame

in emergency: put out fire; seek assistance

99
Q

biohazard
(risk, safety precaution, in emergency)

A

risk: contamination; infection

safety precaution: use disinfectant; wash hands with soap; do not incubate at human body temperature

in emergency: seek assistance

100
Q

naked flame
(risk, safety precaution, in emergency)

A

risk: fire hazard, burns

safety precaution: keep away from flammable materials; tie up long hair, wear goggles

in emergency: put out fire; seek assistance; run burns under cold water immediately

101
Q

how do you tape an agar plate?

A

don’t tape around the entire dish, this prevents oxygen from entering and so promotes the growth of more harmful anaerobic bacteria

A LEVEL BIO (12 decks)

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