UNIT 1 bio

Question 1

define the term limitation?

Answer 1

limitations are factors that have not been controlled or taken into account of in the design of the experiment.

Question 2

How do limitations effect each replicate?

Answer 2

limitation effect each replicate equally

Question 3

Why are experimental errors?

Answer 3

Experimental errors are caused by a single one-off incident or event caused by THE PERSON CARRYING OUT THE EXPERIMENT

Question 4

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

Answer 4

explanation
- substances are not uniformly distributed

modification:
- reference to a standardised mixing procedure

Question 5

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

Answer 5

temperature effects enzyme controlled reactions

modification:

• use a thermostatically controlled water bath
• non-heat emitting light source
• heat screen

Question 6

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

Answer 6

pH effects enzyme controlled reactions

modification
use a buffer to keep pH constant

Question 7

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

Answer 7

explanation
external light sources might effect the results

modification
- use a dark chamber with a single light source

Question 8

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

Answer 8

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

Question 9

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

Answer 9

explanation

reaction and products may escape thus affecting readings for the dependent variable

modification
grease bung/ syringe plunger

Question 10

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

Answer 10

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

Question 11

An example of a limitation is the following, explain how it will effect the experiment and what modification should take place?

no control readings

Answer 11

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

Question 12

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

Answer 12

explanation:

• this may introduce inconsistency in the results

modification:
- use plant material that is the same age/ variety/ same tissue type/ thickness

Question 13

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

Answer 13

explanation

-cannot determine accurately between the temperatures used

modification:

• take observations more frequently at smaller intervals

Question 14

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

Answer 14

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

Question 15

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

Answer 15

explanation
- there is no data for high and/or low temperatures

modification
- increase range at upper and lower end of readings

Question 16

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

Answer 16

explanation

• inaccurate amount of substance added/ inconsistency between readings

modification

• use a graduated pipette

Question 17

What determines accuracy?

Answer 17

whether an individual test result is in close agreement with the true value

Question 18

what is validity?

Answer 18

a measurement is valid if it ‘MEASURES WHAT IS IT SUPPOSED TO BE MEASURING’

Question 19

How can validity be reduced?

Answer 19

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

Question 20

HOW TO ANSWER EXPERIMENTAL DESIGN QUESTIONS?

Answer 20

A Small Measure Vodka And Redbull

1. what is the Aim of your experiment?
   - clearly identify IV and DV and Control group
2. 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

3. 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

4. Validity:
   name which variables need to be controlled
   in ecological sampling use a standardised sampling technique
5. 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
6. 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