# 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.