1. IB Biology Topic 2 Internal Assessment
Osmosis in Potatoes
IB Biology
Topic 2
Internal Assessment

2. Internal Assessment Timetable
Tuesday 18th Sept:
-pre-lab
-carrying out a standardised practical using handouts I will give you
-familiarising yourself with working in a lab and thinking about how you could adapt the experiment for an Internal Assessment
Friday 21st Sept:
-Using your Design Lab Training Sheet you will work in teams to design a practical investigating an aspect of osmosis.
-all pupils will write up a design INDIVIDUALLY (to be completed for homework)
Monday 24th Sept:
-You will carry out the practical and collect data as a team
-no completed Design booklet = no data collection for your team and an automatic fail
-you MUST organise your data tables onto an excel spreadsheet and bring them to class the following day
Tuesday 25th Sept:
-I will show you how to process your data with statistics
-specifically using Excel to calculate means, standard deviations and draw graphs
-your homework will be to write up your design and your raw data FORMALLY for the following Tuesday
Monday 1st October:
-we will continue processing data
Tuesday 2nd October:
-I will guide you on how to write up a conclusion and evaluation
-you will complete the write up for homework
Tuesday 9th October
-you will bring your COMPLETED IA to class printed out in its proper format
Internal Assessment Timetable

3. Pre-lab
3 cm

4. Writing A Statement of the Problem for the Experiment
What should it state?
It should state: “The Effect of the Independent Variable on the Dependent Variable”.
A good statement of the problem for “Rate of photosynthesis” would be
The effect of light intensity on the rate of photosynthesis

5. More about our variables:
The independent variable is the variable that is purposely changed. It is the manipulated variable.
The dependent variable changes in response to the independent variable. It is the responding variable.
What is the “photosynthesis” independent variable?
Light intensity measured in Lux
What is the dependent variable?
Volume of O2 produced per minute

6. Title for the photosynthesis experiment
The effect of light intensity on the rate of photosynthesis of Elodea

7. Another Look at Our Hypothesis
INDEPENDENT VARIABLE
If the light intensity increases,
DEPENDENT VARIABLE
then the rate of photosynthesis will increase.
To make this IB worthy you MUST:
a)Include a sketch graph of your predicted results
b) Give SCIENTIFIC reasoning as to why you predict this

8. Controls in an Experiment
Factors that are kept the same and not allowed to change
What should be kept constant in the experiment?
CONSTANTS
Type of plant
C02 concentration
Time the experiment runs for
Time intervals at which the DV is measured
Wattage of light bulb
Colour of bulb
Temperature of experiment
Time of day

9. Values of the Independent Variable
How many different values of the independent variable should we test?
Enough to clearly illustrate a trend in the data –always use the 5x5 rule for continuous data
e.g. 10cm, 20cm, 30cm, 40cm, 50cm

10. Repeated Trials How many repeated trials are needed in the experiment
At least 5, then calculate n mean value for each level of the independent variable
(this will also give enough data to calculate standard deviation)

11. Drawing of Experiment

12. Now complete your Design Lab sheet as a team!