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BIO 2 - foundations in biology > REQUIRED PRACTICALS > Flashcards

REQUIRED PRACTICALS Flashcards

1
Q

outline the method to investigate cell membrane permeability

A
  1. place 5 equally cut beetroot pieces into separate test tubes
  2. place each test tube in a water bath at different temperatures for 20 minutes
  3. remove beetroot piece from each tube, leaving only the colored liquid
  4. using the blue filter on a colorimeter, add distilled water to a cuvette and calibrate it
  5. using pipettes, transfer liquid from first test tube into a clean cuvette and add to colorimeter
  6. read/record absorbable of solution
  7. repeat readings for the remaining test tubes
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2
Q

what do higher levels of absorbance show in the membrane permeability experiment?

A
  • more pigment released
  • higher the permeability of the membrane
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3
Q

what filter is used on the colorimeter during the membrane permeability experiment?

A
  • blue filter
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4
Q

explain the results of the membrane permeability experiment show?

A
  • as temperature increases, membrane permeability increases (shown by higher absorbance readings)
  • phospholipids have more energy at high temps, so move more
  • phospholipid bilayer may begin to melt
  • volume of water inside cells expands, putting pressure on membrane
  • causes transport proteins to deform
  • transport proteins become denatured, so can’t control substances entering or leaving the cell
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5
Q

state 3 limitations of the membrane permeability experiment

A
  1. some cuvettes may be thicker or scratched, so absorb slightly more light
  2. beetroot pieces may not be identical in size
  3. some parts of the beetroot may contain more pigment than others
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6
Q

how to ensure the unidentifiable sizes of beetroot doesn’t effect the membrane permeability experiment results

A
  • cut as accurately as possible, using a scalpel and a ruler
  • repeat multiple times and calculate a mean average
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7
Q

state the independent variable in the membrane permeability experiment

A

temperature

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8
Q

state the dependent variable in the membrane permeability experiment

A

percentage absorbance

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9
Q

state 5 control variables of the membrane permeability experiment

A
  • same SA:V ratio of beetroot pieces
  • length of time in the water bath
  • volume of water on the surface of the beetroots after rinsing
  • volume of water in each boiling tube
  • same type + age of beetroot
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10
Q

how to ensure each beetroot has the same SA:V ratio in the membrane permeability experiment

A

use a ruler to ensure all pieces are the same length

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11
Q

how to ensure each beetroot spends the same length of time in their water bath during the membrane permeability experiment

A

use a stopwatch to time 20 minutes

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12
Q

how to ensure each beetroot has the same volume of water on it after rinsing initially, during the membrane permeability experiment

A

roll over a paper towel 3 times

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13
Q

how to ensure each boiling tube has the same volume of water in it during the membrane permeability experiment

A

use a 5cm3 syringe to measure 5cm3 of water for each tube

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14
Q

how to ensure each beetroot piece has the same age/type, during the membrane permeability experiment

A

all cylinders should be from the same beetroot/same type of beetroot

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15
Q

describe the test and positive result for proteins

A

BIURET TEST
1. add sodium hydroxide to sample
2. add a few drops of copper (ll) sulfate solution
POSITIVE: blue to purple

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16
Q

why is sodium hydroxide added to the sample during the Biuret test?

A

to make the solution alkaline

17
Q

describe the test and positive result for starch

A

IODINE TEST
1. add iodine dissolved in potassium iodide solution to the sample
POSITIVE: orange to blue-black

18
Q

what is the iodine dissolved in and why during the iodine test?

A
  • potassium iodide
  • it is insoluble in water
19
Q

describe the food test and the positive result for presence of lipids

A

EMULSION TEST
1. add ethanol to sample and shake
2. add the mixture to a sample of water
POSITIVE: clear solution forms a milky white emulsion layer

20
Q

explain the positive result of the emulsion test

A
  • lipids are non-polar
  • can only dissolve in organic solvents e.g. ethanol
  • cannot dissolve in water
21
Q

describe the test and positive result for the presence of reducing sugars

A

BENEDICT’S TEST
1. add benedict’s reagent to sample, heat gently
POSITIVE: blue solution turns green/orange/brick red

22
Q

explain the positive result for the benedict’s test - reference Cu ions

A
  • Cu2+ ions in the Benedict’s are reduced into Cu+ ions (CuO)
  • these are insoluble in water, so form a brick-red precipitate
  • the more sugars present, the closer the solution becomes to brick- red
23
Q

describe the test and positive result for non-reducing sugars

A

HCl + NEUTRALISE + BENEDICT’S
1. add dilute HCl to a new sample and heat gently
2. neutralize the sample using sodium hydrogencarbonate
3. add drops of Benedict’s reagent, heat gently
POSITIVE RESULT: blue to green/yellow/brick red

24
Q

explain the method for the test for non-reducing sugars

A
  • addition of HCl breaks non-reducing sugars into monosaccharides by hydrolysing any glycosidic bonds present
  • these monosaccharides have functional groups which can reduce the Cu2+ ions into Cu+ ions
25
state examples of reducing sugars
MONOSACCHARIDES, SOME DISACCHARIDES - galactose - glucose - fructose - maltose
26
state examples of non-reducing sugars
- sucrose
27
describe how to perform a wet mount
1. pipette a drop of water onto slide 2. use tweezers to place specimen on the water 3. stand coverslip next to droplet, carefully lower onto specimen to avoid air bubbles 4. add drop of stain on one edge, place paper towel on opposite edge to draw the stain across the specimen
28
describe how to perform a dry mount
1. take thin enough piece of specimen to allow light through 2. use tweezers to place specimen in middle of the slide 3. place coverslip on top
29
describe how to use a light microscope
1. clip slide onto stage 2. switch to lowest powered objective lens 3. use coarse adjustment knob to move the stage just below the objective lens 4. look down the eyepiece lens and use to fine adjustment knob to gain a clear image 5. if needed, switch to higher powered magnification, refocus
30
describe how to calibrate an eyepiece gratitule
1. set to required magnification (must be re-calibrated for each magnification) 2. place stage graticule on stage 3. line up the scales 4. count how many eyepiece graticule divisions equal one division on the stage micrometer 5. use the already known scale of micrometer to calculate the length of one eyepiece division
31
Outline the method for viewing mitosis (practical 2.6)
1. Cut off tips from roots of an onion/garlic 2. Add HCl and place in a water bath for 10 minutes 3. Rinse off sample and add a stain (acetic orecin) 4. Use a blunt item to squash the roots against a glass slide 5. View under a microscope
32
Why is HCl added to the root tips (MITOSIS PRACTICAL)
Softens tissues, allowing them to be more easily pushed down later
33
Why is acetic orecin used as a stain (MITOSIS PRACTICAL)
Stains chromosomes red/purple
34
Why is a mounted needle used (MITOSIS PRACTICAL)
Prevents air bubbles from underneath cover slip
35
Why is the root tip of an onion/garlic used (MITOSIS PRACTICAL)
This is the growing region, so mitosis should be occurring here
36
Why is the cover slip squashed down (MITOSIS PRACTICAL)
To get a thin layer of cells to allow light through
37
- risks present during mitosis practical - how to reduce
1. Cutting yourself with scalpel - cut away from you - cut on a white tile 2. HCl - irritant, so wear goggles - wash hands if contact was made
38
How can improvements be made to the end image (MITOSIS PRACTICAL)
- increase time in HCl - increase temperature in water bath - increase time in stain (acetic orecin)
39
What are 3 limitations of the mitosis practical
1. Hard to distinguish between prophase + telophase (look at nuclei number) 2. Size of cells may be inconsistent 3. Light microscopes do not have same magnification power as others, so some structures won’t be visible

BIO 2 - foundations in biology (8 decks)

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