Lab 5: Photosynthesis

Objectives:

Design and conduct an experiment to explore the effects of certain factors, including different environmental variables, on the rate of cell respiration.
Conduct and apply concepts, including the relationship between cell structure and function (chloroplasts); strategies for capture, storage, and use of free energy; diffusion of gases across cell membranes; and the physical laws pertaining to the properties and behaviors of gases.

Things to note in this lab:

Make sure you answer the questions for each section of the lab (if called for).
Don't forget to create graphs in addition to data tables!
You will be completing a poster with your group for part 2. Part 1 will be graded in your notebook.
Please be careful with the leaves! If you damage your leaf, you may not get good results! Follow all precautions mentioned in the procedures!!
For part 2, each group will be doing a different experiment. NO 2 groups can do the SAME experiment!!!

Part 1 Procedures:

Prepare a solution of 0.2% bicarbonate. It will serve as the source of CO2.
Pour the bicarbonate solution into a clear plastic cup labeled "w/ CO2." Fill a second cup with water and label it "w/o CO2." The water cup is the control.
Using a pipette, add 1 drop of dilute liquid dish soap to each cup. AVOID SUDS!! Dilute with more bicarbonate or water if suds form.
Using a hole punch, cut 10 uniform disks for each cup. AVOID LEAF VEINS!!

5. Draw the gases out of the spongy mesophyll tissue and infiltrate the leaves with sodium bicarbonate:

Remove the plunger from both syringes
Place 10 leaf disks into each barrel.
Replace plunger, but DO NOT CRUSH DISKS! Depress until only a small volume is left.
Pull a small volume of sodium bicarbonate into 1 syringe and a small volume of water into the other syringe.
Tap each syringe to suspend disks. Make sure NO AIR REMAINS in the syringe!
Create a vacuum in the plunger to draw the air out of the leaf tissue. Hold 1 finger over the syringe opening while pulling back the plunger. Hold for 10 seconds and swirl to make the disks float. Let go of the plunger to release the vacuum and the solution to sink into the leaf. Disks should sink. Repeat 2-3 times if disks do not sink or add more soap.

6. Pour disks into their solution labeled cups.

7. Place both cups under a light source and start timing.

8. Record the # of disks floating after each minute until all disks are floating in the cup with sodium carbonate. Dislodge disks after each minute by gently swirling cup.

9. Find the standard point of reference, which is the time it takes for 50% of the leaf disks to float (ET50).

Part 2 Procedures:

Test another variable that might affect photosynthesis rate.
Follow similar procedures for part 1 but changing 1 variable picked out.
Record data.
Present data as poster presentation.

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