UNIT 1 bio Flashcards
define the term limitation?
limitations are factors that have not been controlled or taken into account of in the design of the experiment.
How do limitations effect each replicate?
limitation effect each replicate equally
Why are experimental errors?
Experimental errors are caused by a single one-off incident or event caused by THE PERSON CARRYING OUT THE EXPERIMENT
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
insufficient mixing of enzyme and substrate… the suspension of yeast or chloroplasts was not stirred before each reading
explanation
- substances are not uniformly distributed
modification:
- reference to a standardised mixing procedure
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
temperature was not controlled
temperature effects enzyme controlled reactions
modification:
- use a thermostatically controlled water bath
- non-heat emitting light source
- heat screen
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
pH was not controlled
pH effects enzyme controlled reactions
modification
use a buffer to keep pH constant
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
light was not controlled
explanation
external light sources might effect the results
modification
- use a dark chamber with a single light source
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
it was difficult to add a solution to start the reaction AND start the stopwatch at the same time
explanation
- this would affect the time the enzyme and substrate have been reacting
modification
- e.g. introduced solution to reaction vessel using a syringe and sealed bung
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
the reaction vessel was not completely sealed e.g. gas may escape dure to a leaky bing/ syringe plunger
explanation
reaction and products may escape thus affecting readings for the dependent variable
modification
grease bung/ syringe plunger
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
There were no repeat readings taken
explanation
- Unable to identify anomalies, thus decreasing the accuracy and repeatability of any conclusion
modification:
- take at least 3 repeat readings for each value of the independent variable to then calculate and mean, SD
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
no control readings
explanation
- unable to be sure if it was the independent variable alone effecting the dependent variable
why do you need a control group?
- to compare your experimental treatment to see if there is any difference
modification depend on the reaction you are doing:
enzyme reactions:
- use same volume of water instead of enzyme to show that enzyme is required to change pH etc
DCPIP and light reactions:
I) tube containing DCPIP alone to see if DCPIP decolourises in light alone
II) leaf extract alone to determine whether leaf extract decolourises in light alone
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
for each reading we do not known if the plant tissue used varied in its:
- age
- variety of plant
- tissue type
- thickness of disc
explanation:
- this may introduce inconsistency in the results
modification:
- use plant material that is the same age/ variety/ same tissue type/ thickness
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
readings were only taken at an interval of x min/s
explanation
-cannot determine accurately between the temperatures used
modification:
- take observations more frequently at smaller intervals
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
- end point is subjective
explanation
- variation in judgement as to when end-point has been reached
modification
reference to either:
- comparison to a colour standard
- use a colorimeter/ pH meter
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
- the range of the independent variable used is too limited
explanation
- there is no data for high and/or low temperatures
modification
- increase range at upper and lower end of readings
An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?
- a syringe is not sufficiently precise for measuring small volumes
explanation
- inaccurate amount of substance added/ inconsistency between readings
modification
- use a graduated pipette
What determines accuracy?
whether an individual test result is in close agreement with the true value
what is validity?
a measurement is valid if it ‘MEASURES WHAT IS IT SUPPOSED TO BE MEASURING’
How can validity be reduced?
validity is reduced if not all variables have been effectively controlled or
if it was an investigation into the efficacy of a therapeutic drug if no negative control is included
HOW TO ANSWER EXPERIMENTAL DESIGN QUESTIONS?
A Small Measure Vodka And Redbull
- what is the Aim of your experiment?
- clearly identify IV and DV and Control group - Sampling
- to sample a random subset of the population in an unbiased manner use a grid and a random number generator etc
- or systematic - if looking at how species abundance changes in relation to physical factor
- name sampling apparatus
- sample must be large in order to be representative of total population
- sample at different times of year/day/weather conditions
- MARK-RELEASE-RECAPTURE
- measurements:
- must specify what you will actually measure and how
- in ecological sampling use ACFOR scale/ use a key to identify species/ percentage cover/ species richness
- Validity:
name which variables need to be controlled
in ecological sampling use a standardised sampling technique - accuracy:
accuracy is generally improved by taking readings at more frequent intervals/ at intermediate temperatures
IF EXPERIMENT IS VALID, more repeats will get you closer to the true value - Repeatability/ reproducibility
repeatability - same person takes at least 3 readings at each temp
more than one transect
large sample size
with repeats you can calculate mean and SD
reproducible
- if a different person reaches same conclusion but not necessarily using same equipment or in same place
