Advanced Biology/AP Biology Senegar-Mitchell NAME DATE PERIOD Introduction Floating Leaf Disk Photosynthesis Lab Adapted from Brad Williamson's Leaf Disk Lab (http://www.elbiology.com/labtools/Leafdisk.html) Light is a part of a continuum of radiation, or energy waves. Shorter wavelengths of energy have greater amounts of energy. For example, high-energy ultraviolet rays, with wavelengths of approximately 1 nanometer (nm) to 380 nm, can harm living tissues due to the large amount of energy they carry. Wavelengths of light within the visible part of the light spectrum power photosynthesis. The visible light spectrum is from about 400 to 750 nm (1 billionth of a meter). Only visible light, with its intermediate wavelengths, has enough energy to cause chemical change without destroying biological molecules. The short, high frequency waves of gamma rays (10"5 nm) have too much energy and break the hydrogen bonds found within biological molecules such as proteins and nucleic acids like DNA. The longer waves of heat, microwaves and radio waves (103 nm to 103 meters) do not possess enough energy and are absorbed by the water molecules in a plant. When light is absorbed by leaf pigments such as chlorophyll a or b, electrons within each Photosystem are boosted to a higher energy level. This energy is used to produce ATP, to reduce NADP to NADPH and then used to incorporate carbon dioxide (CO2) into organic molecules in a process called carbon fixation. Leaf disks float, normally. When the air spaces are infiltrated with a solution the overall density of the leaf disk increases and the disk sinks. The infiltration solution includes a small amount of sodium bicarbonate (NaHCO3) thus enabling the bicarbonate ion to serve as the carbon source for photosynthesis. As photosynthesis proceeds, oxygen is released into the interior of the leaf which changes its buoyancy causing the disks to rise. Since cellular respiration is taking place at the same time within the leaf, consuming the oxygen generated by photosynthesis, the rate that the disks rise is an indirect measurement of the net rate of photosynthesis. In this lab, you will measure the net rate of photosynthesis for several plants under various lighting conditions. Bubbles of O2 forming CO2 in solution 1 2 Solution
Advanced Biology/AP Biology Senegar-Mitchell Materials NAME DATE PERIOD · Sodium Bicarbonate (baking soda) · Liquid soap · Plastic syringe (10 cc or larger) · Leaves (i.e. spinach, ivy, pokeweed) · 4 clear, plastic cups · Timer · Light source · Hole punch · 2 small beakers · 1 ml or 5 ml plastic disposable pipette · Metric ruler Procedure 1) Label 4 cups with the following: 30 cm CO2 Light, CO2 dark, Water/soap Light, 50 cm CO2 Light 2) Mix 1/8t of baking soda and mix it in 300 ml of water in one of the beakers provided. (Fig. 1) 3) Add a squirt of soap to the beaker and add 200ml of water. 4) Using the plastic pipette, add one drop of the dilute liquid soap to the baking soda solution. Avoid suds. If your solution