Practical skills Flashcards
1
Q
What is a prediction?
A
- a statement about what you think might happen
- based on prior knowledge or an underlying hypothesis
2
Q
What is a hypothesis?
A
- a statement providing an explanation or prediction, ALWAYS based on prior knowledge and testable by an experiment
3
Q
State 5 components that should appear in a practical plan:
A
- Controlled variables
- Independent variables
- Dependent variable
- Improving reliability
- Safety
4
Q
How can reliability be improved?
A
- Repeat experiment 3-5 times and take mean value
- Identify and exclude anomalies
5
Q
How do you take safety into account?
A
- state a hazard and the level of risk
- state a safety precaution to take
6
Q
What are some common control variables?
A
- Temperature
- pH
- Volume
- Concentration
- Time
- Mass
7
Q
What are some sources of error when measuring length?
A
- Parallax error from vernier callipers
8
Q
How is a respirometer set up?
A
- two test-tubes, each with soda lime/KOH (absorbs CO2)
- so CO2 produced does not increase volume of air
- oxygen consumption read from fluid level on manometer
- temperature of surroundings must be kept constant, by a thermostatically controlled water bath
- pressure is controlled by using a second tube with no organism, but glass beads instead, same mass, temperature, light intensity etc.
- apparatus should be airtight
- air must be replaced between each set-up
- take care when assembling respirometer since capillary tubing can break and cause cuts
- soda lime is corrosive, wear gloves
9
Q
Outline the procedure to random sampling:
A
- Make a grid
- Random number generator to obtain a set of coordinates
- Place quadrats at coordinates
10
Q
What reagents can be used to measure the rate of respiration and photosynthesis?
A
- Redox indicators; a substance that changes colour when oxidized or reduced
- become colourless when reduced
- DCPIP or methylene blue
- the faster the rate of respiration, more hydrogens released per unit time, faster the dyes reduced
11
Q
What are two types of quantitative data?
A
- Continuous data: individual values can have any value between two extremes
- Discrete data: measurement can only belong to one of a limited number of values
12
Q
When should histograms be used?
A
- For continuous data divided into classes
13
Q
When should bar charts be used?
A
- when the independent variable is qualitative
14
Q
What are the two types of qualitative data?
A
- Ordinal data: values are not numerical, however can be arranged in sequence, CAN BE RANKED
- Nominal data: values cannot be arranged in sequence, instead each is assigned a distinct category
15
Q
How does repeating an experiment increase reliability?
A
- allows identification of anomalies
- minimize the effects of anomalies when taking a mean
16
Q
How can temperature be standardized?
A
- thermostatically-controlled water bath
17
Q
How can pH be controlled?
A
- Buffer solution
18
Q
How can accuracy of measurements be improved?
A
- By using apparatus with smaller divisions, e.g; vernier caliper instead of ruler
19
Q
What is the formula for percentage error?
A
((new value - original value) / original value) x 100
20
Q
State the four statistical tests:
A
- T-test
- Chi-squared
- Spearman’s rank correlation
- Pearson’s linear correlation
21
Q
When should T-test be used
A
- to compare two means
- sets of continuous normally distributed data
22
Q
When is Pearson’s linear correlation used?
A
- to correlate two sets of continuous, linear and normally distributed data
- scatter graph indicates there may be a LINEAR relationship
23
Q
When is Spearman’s rank used?
A
- to correlate ordinal data which can be ranked, NOT continuous
- one or both variables NOT normally distributed
24
Q
When is chi-squared used?
A
- to compare the observed against expected values
- nominal data
- discontinuous
25
How are degrees of freedom calculated for T-test?
(n1 - 1) + (n2 - 1)
26
How are degrees of freedom calculated for Pearson’s linear correlation?
No. of pairs of data - 2
27
How are degrees of freedom calculated for Spearman’s rank?
No. of pairs of data - 2
28
How are degrees of freedom calculated for chi-squared?
No. of categories - 1
29
How is a statistical conclusion written?
- state **calculated value is smaller/larger than critical value** at p = 0.05
- there is less/more than 5% probability that results are **due to chance** alone
- the results are/are not **statistically significant**
30
What does standard deviation measure?
- the spread of data from the mean
31
What does standard error measure?
- how close the calculated mean value is to the true mean value
- reliability of mean calculated
- formula:
SE = s / √n
s = standard deviation
n = sample size
32
What is the range of error bars?
+/– 2 x standard error
33
How is biodiversity assessed?
- Simpson’s Index of biodiversity
34
What does the calculated value of Simpson’s index indicate?
- it is between **0 and 1**
- close to 1: high biodiversity
- close to 0: low biodiversity
35
How is a 1% sugar solution made?
- 1% sugar solution means **1g of sugar for every 100g of water**
- 1cm3 of water has a mass of 1g
36
How is a 1 moldm-3 sucrose solution made?
- find Mr of sucrose - 342g
- put 342g of sucrose in 1dm3 volumetric flask
- add a small amount of distilled water and shake until completely dissolved
- add more distilled water until 1dm3 mark
37
Outline how chromatography can be used to identify chloroplast pigment:
- extract pigments by **crushing leaf in small amounts of solvent** (propanone or petroleum ether)
- **filter** extract to obtain dark green solution pigments
- ruler and **pencil used to draw baseline** 2cm from base of chromatography paper
- use capillary tube/pipette to place small drop of solution onto baseline and dry
- place paper in beaker with solvent such as ethanol BELOW baseline
- put lid to prevent evaporation of solvent
- pigments will rise, calculate Rf value
Rf = distance travelled by spot / distance travelled by solvent
38
How are factors of photosynthesis measured in aquatic plants?
light intensity
- altering distance from lamp
wavelength of light
- using colour filters (ensure same light intensity)
concentration of CO2
- adding different quantities of sodium hydrogencarbonate (NaHCO3) to water surrounding plant
temperature of water surrounding plant
- large container to maintain chosen temperatures
39
How are redox indicators used to determine rate of photosynthesis
- high energy electrons emitted in light dependent reactions
- electrons picked by electron acceptors and travel along ETC
- DCPIP and methylene blue take up electrons instead
- colour change from blue to colourless
- time taken for indicator to decolourise is an indication of the rate of photosynthesis
40
How do error bars show if data is significant?
- error bars overlap: NO significant difference
- no overlap: significant difference
