======Leaf Disk Photosynthesis======


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**Materials: **{{$demo.materials_description}}\\
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**Alternative titles:** Floating Leaf Disk Experiment
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====Summary====                   
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====Procedure====  
  -Prepare three clear cups with about 300 mL water each; dissolve a small pinch of baking soda and 1 drop of dish soap in each and stir gently.
  -Punch out 30 uniform disks from fresh spinach or ivy leaves, avoiding major veins.
  -Load 10 disks into a syringe (no needle), draw in a little of the baking soda solution, and hold the syringe upright.
  -Expel excess air, seal the tip with a finger, pull back the plunger to create a vacuum for about 10–15 seconds, then release; repeat until the disks sink.
  -Pour the sunken disks and solution into Cup 1 so the disks are covered by a few centimeters of solution; label the cup.
  -Repeat the infiltration for two more batches of 10 disks to prepare Cup 2 and Cup 3.
  -Place all cups under the same bright light from above; start a timer.
  -Each minute, note how many disks are floating in each cup; gently swirl to free any stuck disks.
  -Continue until all disks float; determine the time when 5 of 10 disks float (ET50) for each cup.
  -Average the three ET50 values, then compute 1/ET50 to compare photosynthesis rates between conditions.



====Links==== 
Measuring Photosynthesis: Leaf Disk Assay - LabXchange: 
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Leaf Disc Photosynthesis - Casey Tech School: 
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📄 Use Floating Leaf Disks to Study Photosynthesis - Science Buddies: [[https://www.sciencebuddies.org/science-fair-projects/project-ideas/PlantBio_p053/plant-biology/photosynthesis-leaf-disk-assay]]\\

====Variations====
  *Change light intensity by moving the lamp closer or farther.
  *Test different light colors using colored film (red, blue, green, etc.).
  *Compare light sources (LED, CFL, incandescent, halogen, sunlight).
  *Vary water temperature (for example, ~10°C, 20°C, 30°C, 40°C).
  *Adjust baking soda concentration (for example, 0 to 2 g per 100 mL).
  *Use different plant species or different leaf colors from the same plant.
  *After disks float, cover a cup with foil to observe sinking in the dark (cellular respiration).



====Safety Precautions====
  *Use a syringe without a needle; do not point the tip at eyes or face when releasing vacuum.
  *Do not drink the solutions; wash hands after the activity and clean spills promptly.
  *If using hot lamps or warm water, prevent burns and keep lamps a safe distance from cups.
  *Check for plant or soap sensitivities; avoid contact with eyes.
  *Work on a stable surface to prevent glass or cup tipping.




====Questions to Consider====
  *Why do the disks start to float in the light? (Oxygen from photosynthesis forms bubbles on the disks, increasing buoyancy.)
  *What role does baking soda play? (It provides dissolved carbon dioxide needed for photosynthesis.)
  *Why add a tiny drop of dish soap? (It reduces surface tension so bubbles form and release more consistently.)
  *How does temperature affect ET50? (Moderate warming speeds enzyme activity and lowers ET50; too hot can damage enzymes and increase ET50.)
  *Why use 1/ET50 as the “rate”? (Shorter ET50 means faster oxygen production; taking the reciprocal converts time-to-50% into a value proportional to rate.)
  *What would you expect in green vs. red leaves? (Leaves with more chlorophyll generally photosynthesize faster and reach 50% floating sooner.)