How Science Works (HSW) & Math skills Flashcards
Valid conclusions need……
Need:
- Large sample size SO representative
- Long study SO can allow…. / see effect of X
- Control used SO comparison can be made.
*Mean & SD SO significant differences can be determined.
When the patients recorded the intensity of pain, suggest two reasons why it was important to use a statistically valid scale.
- Pain perception is subjective / pain threshold varies
- To ensure that differences (in pain detection) were (statistically) significant / differences not due to chance
- For (valid) comparison;
Limitations:
You can only use the information provided.
- Small sample size, not representative;
- Only sampled males, females may respond differently to treatment;
- Only tested on …….. in a lab, in the wild, may obtain different pattern in data;
- Only tested on …….. species, might not be true for all species;
- No STATS test so differences could be due to chance;
- Data is SUBJECTIVE, some people may have lied
Null hypothesis (How to write one)
- [x] will have no effect on [y]
- E.g. Temperature will have no effect on rate of reaction
- There will be no correlation between age and weight
- There will be no difference between the observed and expected ratio of 3:1 brown eyes to blue eyes
Explain why a log scale is used to record the number of cells/bacteria.
- Large range/difference/increase in numbers;
- Accept reference to exponential (increase)
In the UK in 2017, there were 805 000 deaths.
Cancer caused 29% of all deaths.
Throat cancer caused 4% of all deaths from cancer.
Calculate the mean number of people who died of throat cancer per month in 2017.
778
(805 000 x 0.29 x 0.04) / 12
Information travels at 120 metres per second in neurones.
Calculate the time it would take for the information to travel 1.8 m along a neurone.
Give your answer in milliseconds (2 sig fig)
15 ms
(1.8/120) x 1000
A ruler has an error of ± 1 mm.
An object’s length was 5.7 mm.
Calculate the % error of uncertainty.
to 2 DP
17.54 %
What is the equation for uncertainty of a measurement?
Reading: (half of smallest interval / reading) * 100
Meauremement: (one interval / actual measurement) *100
Calculate the percentage change in mass [grams]:
Mass before = 6.3 g
Mass after = 2.4 g
(Difference / Original) x 100
(3.9 / 6.3) *100
= 61.9 %
Calculate the mean value:
8.4, 2.5, 4, 1.1, 8.5, 8.5, 7, 2.5, 7.9
8.4+2.5+4+1.1+8.5+8.5+7+2.5+7.9
________________________________________
9
= 5.6
Which P value(s) shows a difference is significant.
a) P=0.06
b) P>0.05
c) P<0.05
d) P<0.50
c) P<0.05
The probability that the difference is due to a random chance event is less than 5%
A scientist determined the volume of a plant cell and the volume of organelles it contained.
They found:
- the volume of a plant cell is 18 500 µm3
- the volume of all the mitochondria in a plant cell is 262.5 µm3
- the volume of all the mitochondria and all the chloroplasts in a plant cell is 46.1% of the volume of a plant cell.
Use this information to calculate the volume of all the chloroplasts in a plant cell.
8266 µm3
18 500 x 0.461 = 8528.5;
8528.5 - 262.5;
Define Standard Deviation.
The spread of data around the mean
Large SD bars indicate…….
A large range of variation in the data.
Less reliable mean value.