Starter
What are the dependent and
independent variables from our
experiment with photosynthesis?
What is the next step now that we
have collected the data?
How are we going to process the data?
How do we present the processed data?
Outcomes – Data processing
You should all be able to:
• Calculate the mean from the results collected.
• Construct graphs of the mean number of leaves
floating vs. time.
• Identify the time at which half of the leaves were
floating: the “ET50” for each concentration.
Look at the results we have…
1. How many repeats are there?
2. What still needs to be calculated?
3. How are you going to calculate it?
Step 1 - we need to calculate the mean number of
leaves floating per minute.
• Now that you have the mean, let’s graph the results.
• What type of graph do we need? Why?
• NOTE: these are not the final graphs but we need
them to calculate the rate of photosynthesis.
ET50
Step 2 – Calculate the ET50 using our graphs of the results…
The point at which 50% of
the leaf disks are floating
(the median) is the point
of reference for this
procedure and is known
as ET50.
Using your graph,
estimate the time at
which 50% of the disks
are floating.
What are our ET50 values?
Step 3 – put our ET50 values into a table.
Sodium bicarbonate concentration (mol/dm3)
ET50 (min)
0.3
10
0.6
7
0.9
8
1.2
8
1.5
5
How do we interpret ET50?
• In a low concentration of sodium bicarbonate
photosynthesis would proceed at a relatively slow rate. We
would expect the rate of oxygen produced to be low, and
the time at which 50% of the disks are floating to be
relatively long.
• In a high concentration of sodium bicarbonate,
photosynthesis would proceed more rapidly. We would
expect the rate of oxygen produced to be high and the time
at which 50% of the disks are floating to be comparatively
short.
How do we interpret ET50?
We can conclude that the ET50 statistic is
indirectly proportional to the rate of
photosynthesis, the higher the rate of
photosynthesis, the smaller the ET50 statistic.
Concentration of sodium bicarbonate
0.3
0.6
0.9
1.2
1.5
Concentration of sodium bicarbonate (mol/dm3)
How do we interpret ET50?
To correct for this representation of the data and present a
graph that shows increasing rates of photosynthesis with a
positive slope the ET50 term can be modified by taking the
inverse or 1/ET50. This creates a graph like this (data from
Steucek, et al. 1985.):
Concentration of sodium bicarbonate
0.3
0.6
0.9
1.2
1.5
Concentration of sodium bicarbonate (mol/dm3)
What are our 1/ET50 values?
Step 4 – We need to calculate the 1/ET50 in order to get the
rate of photosynthesis
Sodium bicarbonate concentration (mol/dm3)
Rate of photosynthesis 1/ET50
0.3
0.10
0.6
0.14
0.9
0.13
1.2
0.13
1.5
0.20
Now we need to present our
processed data…
Step 5 – we need to graph our final results
What type of graph will we use? Why?
To Excel!
What do we need to include in the write-up
when presenting our tables and graphs?