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What is an independent variable

Something that is changed or controlled in a scientific experiment to test the effects on the dependant variable


What is a dependant variable

Something that is being measured in a scientific experiment


What axis does the independent variable always go on

X axis


What axis does the independent variable always go on

Y axis


What are key variables?

Something that must be kept constant


What is a control variable

Something that stops other factors influencing the results of the experiment


How to increase the reliability of an experiment

Complete it at least 3 times to get an average


What are the different types of safety procedures for an experiment

- Goggles
- Gloves
- Appropriate clothing
- No trip hazards etc etc etc


What are some examples of key variables

- Temperature
- C02
- Chloroplasts
- Mass
- Piece of something


How to increase the accuracy of an experiment

- Stopwatch (time it)
- Ruler for measurements etc


How can data be obtained

By taking measurements and can lead to an explanation of why materials have different properties


When are measuring cylinders used

When measuring liquids


What is a burette

A long glass tube with volume marking and a stopclock at the bottom to start and stop liquid flow


How many ml of liquid can a burette hold



How can gas be measured through a gas syringe

A string is attached to the gas syringe and on the other side there is a test tube with a gas about to be realised inside
The string will move the syringe if gas is present and it can be used to measure how much gas is there
Stopwatch can be used to measure the rate of the reaction


Line Graphs

- Series of points plotted on grid and then connected together point by point by a line
- Only used when BOTH variables are quantitative
- Shows trends, such as how many things change over time


Bar Charts

- Designed to make comparisons of data
- Bars DO NOT touch
- Does not depend on other veriable


Pie Charts

- Designed to show a percentage of a whole where the whole equals 100%
- Used to compare data but cannot be sued to see how manipulated variable effects a responding variable


What are the parts of a Palisade (top to bottome)

- Epidermis
- Palisade
- Mesophyll
- Most Air (in mesophyll)
- Vein
- Atoma
- Guard Cells


What comes in and out of palisades

- OUT - CO2
- IN - O2


Accuracy of data

- Accuracy of each measurement depends on quality of the measuring apparatus and the skill of the scientists taking the measurements
- If apparatus is faulty or the scientists make a mistakes the results will be inaccurate


Reliability of data

- For the data to be reliable, the variation within the values must be small.
- There may be small differences in the composition of the rubber or the way the measuring apparatus is used.


How to measure the tenstile strength of samples

- Measure each sample length.
- Hang a mass from the bottom of each sample and record the new length.
- Increase the mass in increments and continue to -measure the length, until the rubber snaps.


Ways of improving the accuracy of an experiment

- Sing a larger sample
- Using lid and polysterine cup in heating experiment using data logger and timer and stopwatch
- To be fair and keep factors measuring the cylinder
- Common one to repeat and take avarage
- Same apparatus and instruments
- Control temp and PH
- Make sure apparatus is working


EXAM QUESTION - The students were given a hypothesis that said
“the activity of catalase increases with increasing temperature”.
Describe a similar investigation to the one carried out in (a) to test this hypothesis.

give a range of at least 4 temperatures;
describe how temperature would be changed / water-bath;
describe the use of a controlled equilibration time to reach temperature;
control stated as: an inert cube / boiled cube or same volume of water as hydrogen
appropriate description of how volume of gas will be measured / bubbles counted;
appropriate statement regarding time;
surface area of potato controlled;
another controlled variable stated, e.g. pH / same potato;
repeat and calculate mean;


EXAM QUESTION - Outline one safety precaution that you would need to take when performing this

safety goggles / gloves;
reference to temperature and safety;


EXAM QUESTION - A student criticised the results by saying that the loss in mass does not allow for a fair
comparison between leaves.
Suggest a more appropriate calculation and explain why it gives a fairer compariso

(iv) percentage change in mass = (change in mass ÷ starting mass) × 100;
different original mass would affect result / to take into account the starting mass


EXAM QUESTION - i) Explain why the bung of the delivery tube must fit tightly into the test-tube

prevents leakage of oxygen/ all oxygen collected ;
increases accuracy /results will be comparable/ consistent/
reliable/ valid;
allow a pressure to build up/ bubbles to form;


EXAM QUESTION - Suggest why the free end of the delivery tube was placed in the water before adding the
potato slice to the hydrogen peroxide solution and connecting the test-tube to the bung
of the delivery tube.

prevents leakage of oxygen/ all oxygen collected;
can observe reaction/bubbles as soon as it starts /AW