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biology year 13 > required pracs > Flashcards

required pracs Flashcards

(52 cards)

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1
Q

Describe how pigments from a leaf of a plant can be isolated withe paper chromatography:

A

Crush leaves with solvent to extract pigments
Draw a pencil line on filter/chromatography paper, 1 cm above bottom
Add a drop of extract to line (point of origin)
Stand paper in boiling tube of organic solvent below point of origin
Add lid and leave to run
Remove before solvent reaches top and mark solvent front with pencil

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2
Q

Explain why the origin should be drawn in pencil rather than ink:

A

Ink is soluble in solvent
So ink would mix with pigments/line would move

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3
Q

Explain why the point of origin should be above the level of the solvent:

A

Pigments are soluble in solvent
So would run off paper/spots dissolve into solvent

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4
Q

Explain why a pigment may not move up the chromatography paper in one solvent:

A

May be soluble in one solvent but insoluble in another

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5
Q

Describe how pigments can be identified:

A

Rf value= distance moved by spot/ distance moved by solvent front

Compare Rf value to published value

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6
Q

Explain why the solvent front should be marked quickly once chromatography paper is removed:

A

Once solvent evaporates, solvent front not visible

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7
Q

Explain why the centre of each pigment spot should be measured:

A

Standardises reading as pigment is spread out
So allows comparisons to be made

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8
Q

Explain why the obtained Rf values were similar but not identical, to the published values:

A

Different solvent/paper/running conditions may affect Rf value

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9
Q

Explain why Rf values are used and not the distances moved by pigment spots:

A

Solvent/pigment moves different distances
Rf value is constant for same pigment/can be compared

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10
Q

Describe the role of the enzyme dehydrogenase in photosythesis:

A

Catalyses the reaction of NADP in the light-dependent reaction
- NADP accepts (gains) electrons from photoionisation of chlorophyll/photolysis of water

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11
Q

Describe how rate of dehydrogenase activity in extracts of chloroplasts can be measured:

A
  1. Extract chloroplasts from a leaf sample using the cell fractionation
  2. Set up test tubes as follows
    - A Control 1: set volume of DCPIP, water and chloroplasts in isolation medium, cover in foil to block light
    - B Control 2: set volume of DCPIP, water and isolation medium with NO chloroplasts
    - C Standard: set volume of water and chloroplasts in isolation medium without DCPIP
    - D Experiment: set volume of DCPIP, water and chloroplasts in isolation medium
  3. Shine light on test tubes and time how long it takes for DCPIP to turn blue to colourless in tube D
    - Compare to colour standard to identify end point
  4. Rate of dehydrogenase activity = 1/time taken
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12
Q

Give examples of variables that could be controlled when measuring the effect on dehydrogenase activity:

A

Source of chloroplasts, volume of chloroplast suspension, volume/conc. of DCPIP

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13
Q

Explain the purpose of control 1 (A):

A

Shows light is required for DCPIP to decolourise
Shows that chloroplasts alone do not cause DCPIP to decolourise

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14
Q

Explain why DCPIP in control 1 stays blue:

A

No light so no photoionisation of chlorophyll
So no electrons released to reduce DCPIP

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15
Q

Explain the purpose of control 2 (B):

A

Shoes chloroplasts are required for DCPIP to decolourise
Shows that light alone does not cause DCPIP to decolourise

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16
Q

Explain why DCPIP changes from blue to colourless:

A

DCPIP is a redox indicator/ DCPIP gets reduced by electrons
From photoionisation of chlorophyll

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17
Q

Suggest a limitation with the method to measure effect on rate of dehydrogenase and how the experiment could be modified to overcome this limitation:

A

End point is subjective
Use a colorimeter
Measure light absorbance of sample at set time intervals
Zero colorimeter using the colour standard

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18
Q

Describe how a respirometer can be used to measure the rate of aerobic respiration:

A

Add set mass of single celled organism
Add a buffer to keep pH constant
Add a set volume/conc. of a chemical that absorbs CO2
Place in water bath at a set temperature and allow to equilibrate
Measure distance moved by coloured liquid in a set time

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19
Q

Explain why the liquid moves in a respirometer:

A

Organisms aerobically respire so take in O2
CO2 given out but absorbed by sodium hydroxide solution
So volume of gas and pressure in container decrease
Fluid in tube moves down pressure gradient towards organism

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20
Q

Explain why the respirometer apparatus is left open for 10 minutes:

A

Allow apparatus to equilibrate
Allow for overall pressure expansion/change throughout
Allow respiration rate of organisms to stabilise

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21
Q

Explain why the respirometer apparatus must be airtight:

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A

Prevent air entering/leaving
Would change volume and pressure, affecting movement of liquid

22
Q

Describe a more accurate way to measure volume of gas than a respirometer:

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A

Use a gas syringe

23
Q

Suggest a suitable control experiment and explain why it is necessary:

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A

No organisms OR use inert objects Or use dead organism AND all other condition/apparatus/equipment same To show that organisms are causing liquid to move/taking up oxygen/causing the change in volume/pressure

24
Q

Describe how a respirometer can be used to measure the rate of anaerobic respiration:

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A

Repeat experiment as above but remove chemical that absorbs CO2
Make conditions anaerobic
- layer of oil above yeast to stop O2 diffusing in
- add a chemical that absorbs O2
- leave for an hour to allow O2 to be respired and used up

25
Explain why the liquid moves when measuring anaerobic respiration:
Yeast anaerobically respire so release CO2 So volume of gas and pressure in container increase So fluid in capillary tube moves down a pressure gradient away from organism
26
Explain why the respirometer apparatus is left for an hour after the culture has reached a constant temperature:
Allow time for oxygen to be used/repired
27
Describe how rate of respiration can be calculated:
1. Calculate volume of O2/CO2 consumed/released - calculate cross-sectional area of capillary tube using πr^2 - multiply by distance liquid has moved 2. Divide by mass of organism and time taken 3. Units - unit for volume per unit time per unit mass
28
Describe how redox indicators such as methlyene blue can be used to measure rate of respiration:
1. Add set volume of organism and a set volume of respiratory substrate 2. Add a buffer to keep pH constant 3. Place in water bath at a set temp and allow to equilibrate for 5 mins 4. Add a set volume of methylene blue, shake for a set time 5. Record time taken for colour to disappear in tube 6. Rate of respiration = 1/time
29
Give two examples of control variables when measuring the rate of respiration:
Volume of single celled-organism Volume/conc/type of respiratory substrate Temp pH Volume of redox indicator
30
Why leave tubes in water bath for 5 mins?
Allow for solutions to equilibrate and reach same temp as water bath
31
Suggest a suitable control experiment and explain why it is necessary (redox indicators for measuring respiration):
Add methylene blue to dead/inactive/boiled yeast All other conditions the same To show change is due to respiration in organisms
32
Suggest and explain why you must not shake tubes containing methylene blue:
Shaking would mix solution with oxygen Which would oxidise methylene blue/cause it to lose its electrons So methylene blue would turn back to its original blue colour
33
Suggest one source of error in using methylene blue and explain how this can be reduced:
Subjective as to when endpoint is Compare results to a colour standard OR use a colorimeter for quantitative results
34
Describe how the effect of an environmental variable on the movement of an animal can be investigated using a choice chamber:
1. Set up a choice chamber to create different environmental conditions - humidity: add drying agent to one side and damp filter paper to other - light: shine light but cover half with black card 2. Control other environmental conditions - if investigating humidity control light intensity 3. Use a teaspoon to place a set number of animals on centre of mesh platform and cover with lid 4. After a set amount of time record the animals in each section 5. Repeat after gently moving woodlice back to centre
35
Explain why the animals were left for 15 mins before recording their movement:
Time to establish humidity/substance to absorb water/water to evaporate Woodlice no longer affected by handling So that behaviour is typical of that humidity
36
Explain how you would ensure the safe and ethical handling of animals:
Safely- cover open wounds/wash hands with soap after - minimise risk of infection Ethical- handle carefully/return to habitat ASAP
37
Explain why a mesh platform is used when investigating the effect of humidity:
To keep woodlice a safe distance from drying agent
38
Describe how the effect of an environmental variable on the movement of an animal can be investigated using a maze:
Change environment at one end of T shape Place animal in stem of T Record whether animal turns towards/away from food source Repeat with a large number of maggots - wipe/clean maze between trials Repeat with food on other side of T
39
Explain why the same organism is not used more than once:
Reduces stress on maggots Prevents chance of learned behaviours
40
Explain why a clean petri dish/maze is used each time:
Animals may leave chemicals/scents Which influence behaviour of other animals
41
Describe how a calibration curve could be produced for glucose:
1. Use distilled water and a glucose solution of known conc. to produce a dilution series 2. Heat a set volume of each solution with a set volume of Benedict's solution 3. Measure absorbance of each solution using a colorimeter 4. Plot a graph of absorbance against conc. of glucose solution and draw a line/curve of best fit
42
Describe how the conc. of glucose in an unknown urine sample can be identified using a calibration curve:
1. Perform Benedict's test on sample using same volumes of solutions used in producing calibration curve 2. Measure absorbance using a colorimeter 3. Absorbance value for urine sample read off calibration curve to find associated glucose conc.
43
Give examples of variables that should be controlled:
Volume of sample Volume of Benedict's Temp of water bath Time samples were heated for in water bath
44
Explain why a high blood glucose conc. can cause glucose can be present in the urine of a diabetic person:
Not all glucose reabsorbed at PCT As glucose carrier/cotransporter proteins are saturated/working at max rate
45
Describe how you could investigate the effect on an environmental factor on the distribution of a species in a habitat:
1. Divide two areas into grids/squares 2. Generate a pair of co-ordinates using a random number generator 3. Place a quadrat here and count number/frequency of species 4. Repeat a large number of times and calculate a mean per quadrat for both areas 5. Measure environmental factor in each area
46
Suggest why percentage cover may be used rather than frequency:
Too difficult to count individual organisms/individual organisms are too small to count
47
Explain why random sampling is used:
To avoid sample bias
48
Explain the importance of a large sample size:
Minimises the effect of anomalies Ensures sample is representative of the pop.
49
Describe how you could decide the number of quadrates that should be used in order to collect representative data:
Calculate a running mean When enough quadrats, this shows little change Enough to carry out a stats test
50
Describe how you could investigate the effect of a factor on the distribution of a species in a habitat:
Place a transect line across an area with an environmental gradient place quadrats at regular intervals and record the number of organisms of species and named environmental factors Repeat in other parallel areas and calculate mean number of plants at each point along the transect
51
Explain the limitations of using systematic sampling to estimate the population of a species in a field:
Not appropriate unless an environmental gradient Transects run in one direction but to cover the entire field, they would need placing in multiple directions
52
Which stats test should be used to determine abundance and an environmental factor?
Correlation coefficient

biology year 13 (10 decks)

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