1. Post-Lab #4: Floating Leaf Disks and Photosynthesis
AP BIOLOGY
Ms. Day

2. the point at which 50% of the leaf disks are floating Called the ET-50
What is ET-50?
the point at which 50% of the leaf disks are floating
Called the ET-50
Estimated Time it takes 50% (1/2) of the disks to float

3. How do I find the ET-50? Using graph paper, plot your data…
Time (in minutes) on X-axis
Leaf disks floating (in number) on Y-axis
Connect data points to determine your 50% point (ET-50)
This is the point at which 50% of the leaf disks are floating
Since you used 10 disks per trial, you want to look at the time it took for half (5 disks) to float

4. How do I find the ET-50? EXAMPLE: For the Figure 4.1 below,
ET-50 = 11.5 minutes
Make 4 graphs…
50 cm light
30 cm light
Control
Dark
Leaf Disks (#) ( )

5. How do I use ET-50 to find the rate of photosynthesis?
The larger the ET-50, the slower the rate of Photosynthesis (PS)
Photosynthesis takes LONGER!
The smaller the PS ET-50, the faster the rate of Photosynthesis (PS)
Photosynthesis occurs FASTER!
RATE OF Photosynthesis  =  
1/ET-50
(expressed with a unit of min-1)
NOTE: You will NOT be using the typical rate equation (∆y/∆x) to find rates in this lab!

6. How do I use ET-50 to find the rate of photosynthesis?
EXAMPLE: For the Figure 4.1 below,
ET-50 = 11.5 minutes
So…rate of photosynthesis= 1/11.5 = min-1
Leaf Disks (#) ( )

7. Larger # for rate of photosynthesis
MEANS
FASTER rate
But…
smaller ET-50
Example:
1/5 min = 0.20 min-1
1/11 min = 0.09 min-1

8. What happens in the 30 cm light/Dark Treatment?
Complete is the following in your lab notebook:
1 graph for your data for ALL 30 minutes
Determine rate of photosynthesis (during first 15 minutes of this treatment) using ET-50PS
Use minute value at which 50% (5 disks) of disks are floating  complete the calculation (1/ET-50PS)….this is your rate of photosynthesis
Determine rate of cellular respiration (during last 15 minutes of this treatment) using ET-50CR
Use minute value at which 50% (5 disks) of disks have re-sunk (fallen back down to the bottom of the cup)
Then complete the calculation (1/ET-50CR)….this is your rate of cellular respiration

9. Rate of photosynthesis = 1/ 11 = 0
Rate of photosynthesis = 1/ 11 = min-1 Rate of cellular respiration = 1/ 32= min-1
O2 released by PS
O2 consumed by CR
Leaf Disks (#) ( )