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Biology > Topic 1: Daphnia core practical > Flashcards

Topic 1: Daphnia core practical Flashcards

1
Q

what is the Independent variable? (1 point)

how would you vary it? (1 point)

A
  1. Caffeine concentration

1. 5 solutions with different caffeine concentrations

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2
Q

what is the control? (1 point)

What is the point of the control? (2 points)

A
  1. {distilled/pond} water for comparison (both 0% caffeine)
  2. for comparison
  3. to prove that any change in heart rate is due to caffeine, not anything in the distilled water that was used to make up caffeine solutions
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3
Q

what is the dependent variable? (1 point)

how do you measure it? (1 point)

Describe the method to measure it (3 steps)

A
  1. HEART RATE
  2. COUNT heart rate
  3. use a microscope to magnify the heart,
  4. COUNT heart beats for 15 seconds and, using a pen, make a dot on paper for each heart beat.
  5. count dots and *4 to give heart rate in bpm
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4
Q

To calculate the heart rate in a daphnia, the heart beats are counted for 15 seconds, and a dot is made on paper for each heartbeat.

The dots are then counted and multiplied by 4 to give heart rate in bmp.

Why is the heart rate obtained this way? (2 points)

A
  1. very high heart rete makes it difficult to count

2. less chance of error if count in 15 seconds

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5
Q

what are the organism controlled variables? (3 controlled variables)

A
  1. DAPHNIA same age (hatched from eggs at the same time)
  2. species
  3. gender
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6
Q

What are the environmental variables? (2 controlled variables + how for each)

A
  1. SAME TEMPERATURE of pond water and caffeine solutions - use a heat shield and turn microscope lamp off when not counting
  2. SAME pH of pond water and caffeine solutions - use a buffer
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7
Q

(for 2 controlled procedural variables)

State the procedural variable? (1 point)

How? (1 point)

Suitable measurement? (1 point)

+ why (only for one of the variables) (1 point)

A
  1. Same volume of caffeine solution or pond water on slide
    How? - graduated pipette
    Suitable volume? - 0.5cm^3
  2. Same acclimatisation time in caffeine solution
    How? - stopwatch
    Suitable time? - 2 minutes
    Why? - To allow time for caffeine to diffuse from solution into Daphnia and have an effect on the heart rate
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8
Q

Describe steps for preparation of slide and daphnia

4 steps

A
  1. On a CAVITY SLIDE spread a FEW STRANDS OF COTTON WOOL
  2. Using a CUT OFF PLASTIC PIPETTE, carefully transfer Daphnia in a drop of pond water onto the cotton wool on the slide
  3. Place slide on the microscope stage – use x4 lens and focus
  4. Locate the Daphnia heart (on the back of the Daphnia - like a clear bean)
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9
Q

(Collecting data - heart rate in pond water/control)

how to measure it the heart rate in pond water? (1 point)

what next? (1 point)

why? (3 points)

A

How to measure it?
1. Count heart rate in pond water – 15 seconds, dots on paper, x4

What next?
1. Repeat 5 times

Why?

  1. To identify anomalies, discard and repeat those results until 3 concordant results are obtained
  2. To calculate a MEAN and {RANGE / STANDARD DEVIATION}
  3. To increase RELIABILITY (remember Repeats = Reliability)
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10
Q

How do you prepare the caffeine solution with the daphnia (3 steps)

A
  1. remove pond water
  2. add required caffeine solution
  3. leave Daphnia to acclimatise for 2 minutes before counting the heart rate
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11
Q

Key Summary: Explain the method for the daphnia practical (exam method)
(9 steps)

A
  1. Heart rate determined in control solution (pond water)
  2. Daphnia put into caffeine solution on slide and allowed to acclimatise for 2 minutes
  3. Place slide under microscope
  4. Count heart {rate/beats}, by putting dots on paper, in 15 seconds and x4
  5. (Name controlled variables) same volume of solution on slide, same Daphnia age species & gender, same temperature, same acclimatisation time
  6. Carry out for 5 different caffeine concentrations
  7. Repeat 5 times for each caffeine concentration
  8. identify and discard anomalies
  9. calculate mean heart rate to increase reliability
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12
Q

Heart rate determined in control solution (pond water)

What is the purpose of this step? (1 point)

A
  1. (control) To give a resting heart rate for comparison to see if caffeine has an effect
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13
Q

Daphnia put into caffeine solution on slide and allowed to acclimatise for 2 minutes

What is the purpose of this step? (1 point)

A
  1. (acclimatisation) Allows time for caffeine to diffuse from solution into Daphnia in order for it to have an effect on the heart rate
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14
Q

What is the purpose of using a cavity slide? (1 point)

A
  1. depression (the cavity) helps drop of solution stay on slide
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15
Q

What is the purpose of using cotton wool strands on the slide? (1 point)

A
  1. To restrict daphnia movement
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16
Q

What is the purpose of using a microscope? (1 point)

A
  1. Heart can be seen more clearly so counting can be more accurate
17
Q

Carry out for 5 different caffeine concentrations

What is the purpose of this step? (2 points)

A
  1. To allow a trend to be established

2. which improves validity

18
Q

Key Summary: Why is Daphnia a good organism to use for this experiment?
(4 points)

A
  1. invertebrates have a simple nervous system - so unlikely to feel pain
  2. transparent - so heart is easy to see without need for dissection
  3. abundant in nature - so no threat to it or its dependent species (food chains)
  4. bred for fish food - will thus die anyway
19
Q

List the 3 risks to daphnia during the experiment (1 point) & how to minimise each risk (1 point)

A

RISK: Lack of solution on slide or solution evaporating may kill Daphnia
MINIMISE: Check solution on slide at intervals and turn off lamp between counts

RISK: Temperature increase caused by microscope lamp may kill Daphnia
MINIMISE: Turn off lamp between counts and use a heat shield

RISK: Daphnia {may be injured/may die} when taken up into a pipette
MINIMISE: Cut off the end of the pipette

20
Q

Key Summary: Ethical reasons for use of invertebrates (1 point for)

A
  1. Daphnia are very simple organisms with a basic nervous system, so are UNLIKELY to feel pain
21
Q

Key Summary: Ethical reasons against use of invertebrates (3 points against)

A
  1. Use of any animal is wrong (absolutism)
  2. We cannot be sure whether or not Daphnia can feel pain
  3. Possibility that the Daphnia could die
22
Q

Explain Absolutism viewpoint (1 point)

A
  1. Organisms should never be used for scientific experiments
23
Q

Explain {Utilitarianism/relativism} viewpoint (1 point)

A
  1. Organisms should only be used if the benefits of the investigation outweigh the potential harm to the organism
24
Q

How do you draw a bar chart for the daphnia experiment? (7 steps)

A
  1. Paper portrait
  2. Four bars should be SAME WIDTH and SHOULD NOT TOUCH each other (evenly spaced)
  3. Suitable scale on axes (1, 2, 5, 10, 20 etc)
  4. Label BOTH axes fully – with UNITS
  5. Draw bars using a sharp pencil - plot mean heart rate
  6. Calculate standard deviation for the data for each solution
  7. Add standard deviation bars to your graph – evenly spaced above and below the top of the bar/mean (so divide your SD by 2)
25
Q

how to calculate standard deviation

5 steps

A
  1. First, calculate the mean of your values
  2. FOR EACH VALUE, subtract the mean from the value, then square
  3. Calculate the sum of these square numbers
  4. Divide this by the number of values: (n – 1)
  5. Square root your answer
26
Q

How to plot standard deviation onto graph

2 steps

A
  1. For SD the length of the bar IS EQUAL above and below the mean.
  2. ADD BARS TO YOUR GRAPH which are of equal length above and below the mean value - so DIVIDE SD BY 2 and plot this both above and below.
27
Q

What do standard deviation bars tell you? (1 point)

A
  1. Standard deviation bars tell you how far on average any data point is from the mean

NOTE: Standard deviation does not have to be bars, in can be written (e.g. 44 +- 0.6) so lowest value is 43.4 and highest 44.6

28
Q

What do range bars show you? (3 points)

NOTE: Range bars are also known as Error bars

A
  1. Range bars show you the highest and lowest values in a data set
  2. If the range bars OVERLAP, it indicates there is NO SIGNIFICANT DIFFERENCE BETWEEN THE SETS OF DATA
  3. If the range bars DO NOT OVERLAP, it indicates that THERE IS A SIGNIFICANT DIFFERENCE BETWEEN THE SETS OF DATA

NOTE: Overlapping also goes for standard deviation between the sets of data

29
Q

How can the investigation (of caffeine on daphnia heart rate) be made reliable? (1 point)

A
  1. Carry out repeats to calculate a mean
30
Q

How can the investigation (of caffeine on daphnia heart rate) be made valid? (4 points)

A
  1. CONTROLLED VARIABLES – state each controlled variable and explain how it is controlled
  2. Make it RELIABLE – carry out repeats
  3. Use a CONTROL for comparison
  4. Include extra caffeine concentrations between the ones suggested by a {table/graph/exam question}
31
Q

List experimental design question checklist

7 points

A
  1. Independent variable
  2. Control
  3. Dependent variable
  4. Controller variables
  5. Method
  6. Repeats
  7. Safety

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