Spinach plants grown under low irradiance reduced biomass production and redirected the photoassimilates to leaves to optimize light interception. This change occurred without effects in the functionality of the photosynthetic process, and the reduction of photosynthetic rate was due essentially to the low radiative energy available for low light leaves. In our experiment, low light intensity significantly reduced the CO2 assimilation of spinach plants (A), without changes in stomatal conductance (gs).

Living leaves, such as baby spinach from the grocery store, are used with a hole punch, clear cups, aluminum foil, a timer, and a light source. A grow light is used, but a desk lamp with a super bright 100 W bulb is also suitable, and for comparing results across multiple experimental setups, the light source must have the same wattage.

The floating leaf disk assay (FLDA) measures the rate of oxygen production or consumption for photosynthesis and respiration. After leaf disks are vacuum-infiltrated and sink, photosynthesis in light causes oxygen accumulation, making them float. Conversely, in the dark, oxygen is consumed by respiration, causing the floating leaf disks to sink.

When you see tiny bubbles forming on the leaf disks during this experiment, you're actually observing the net production of O2 gas as a byproduct of photosynthesis. Accumulation of O2 on the disks causes them to float. The rate of production of O2 can be affected by the intensity of the light source, but there is a maximum rate after which more light energy will not increase photosynthesis. When you put floating leaf disks in the dark, they will eventually sink. Without light energy, no photosynthesis will occur, so no more O2 gas will be produced. However, respiration continues in the dark, so the disks will use the accumulated O2 gas.

This experiment uses the floating disk leaf assay to explore the process of photosynthesis in plants. As photosynthesis takes place, oxygen is released into the interior of the leaf which changes the buoyancy and causes the disks to rise. Since cellular respiration takes place and also consumes oxygen, the rate that the disks rise is an indirect measurement of the net rate of photosynthesis. Graph 1 Result - In this graph, the cup with its floating disks (spinach) was placed under the light source 15 cm away. The number of floating disks was recorded at the end of each minute until all of the disks were floating.

The floating leaf disk assay technique is both reliable and understandable. Once familiar with the technique, students can design experiments to answer their own questions about photosynthesis. For a control, infiltrate leaf disks with a solution of only water with a drop of soap (no bicarbonate). For another control, complete steps 1-5 as directed above, but place cup in the dark. This will deplete your leaf disks of air (you'll see it come out!), causing your leaf disks to sink. Place under a light source and time each leaf disk as it photosynthesizes and floats to the top of the solution!

In the leaf disc assay, the median time for 50% of leaf discs to float in a sodium bicarbonate solution represents the amount of oxygen gas released per unit of time. To establish a negative control, a leaf disc setup with sodium bicarbonate solution should be placed in the dark for the experiment's duration, as negative controls are conditions where no photosynthesis is expected to occur.

For extensions of this lab, you can try different light bulbs (i.e., red) for the lamps, put the lamps at different heights to simulate different light intensities, or put filters between the light and the beaker to see the effects of different colored light on photosynthesis and respiration. As photosynthesis proceeds, the oxygen gas produced will displace the liquid from the intracellular space, and the specific gravity will decrease, and the disks will float. Respiration occurs in all cells all the time, but we can only measure it in plants that are not photosynthesizing. You will need to experimentally stop photosynthesis in your leaf disks to measure respiration.

This video is about photosynthesis and covers the AP Biology lab 'What factors affect the rate of photosynthesis in living leaves'. More light equals more photosynthesis equals more oxygen produced equals less density which equals more float. The analysis comes from taking a look at this and charting how many discs float versus time. You can adjust that distance, you can measure that, you can keep track of it as it relates to what is your light intensity. And ultimately what is your estimated time 50, so how long did it take for 50% or five out of 10 of your leaf discs to start floating.

As oxygen is produced by photosynthesis, it comes out of solution and infiltrates the leaf tissue, replacing some of the water. This decreases the density of the disks, and they begin to float. The number of disks that float per unit of time gives a measure of the rate of photosynthesis. Students can also use the time needed to float half of the disks for their measurement. The exact distance is not critical, but it should be the same for all student groups unless they are testing to see if the distance from the light to the disks influences the rate of photosynthesis.

The floating leaf disc experiment indirectly measures the rate of photosynthesis by observing oxygen production under different light intensities. Results typically show that leaf discs in a dark environment eventually sink, as photosynthesis is not occurring to produce oxygen.

The biology behind the procedure: Leaf disks float, normally. When the air spaces are infiltrated with solution the overall density of the leaf disk increases and the disk sinks. As photosynthesis proceeds oxygen is released into the interior of the leaf, which changes the buoyancy--causing the disks to rise. Since cellular respiration is taking place at the same time, consuming oxygen, the rate that the disks rise is an indirect measurement of the net rate of photosynthesis. For a control infiltrate leaf disks with a solution of only water with a drop of soap--no bicarbonate. Place under the light source and start the timer. At the end of each minute, record the number of floating disks.

The experiment tested the effect of varying light intensities on the photosynthesis rate in spinach leaves by measuring the time it took for spinach disks to float in a sodium bicarbonate solution. The key findings showed that stronger light intensity led to a faster rate of photosynthesis, as indicated by shorter flotation times for the spinach disks. Specifically, the shortest time was 352 seconds at 13 cm, and the longest was 1327 seconds at 33 cm. The results showed that higher light intensities (closer lamp positions) led to faster floating times, demonstrating that increased light intensity increases the rate of photosynthesis.

In a leaf disc experiment, one beaker of leaf discs should be covered to prevent light from reaching them, while a second beaker is placed under a light source approximately 15 centimeters away, with timing beginning when the light is turned on. It is important to explain why the covered beaker is necessary and to observe if any leaf discs float in the dark.

The floating leaf disk assay allows investigation into factors affecting photosynthesis, such as light intensity, chlorophyll content, and light color. After all leaf disks float, covering the cup with aluminum foil and leaving it for 30 minutes to an hour will demonstrate cellular respiration, where disks will sink as oxygen is consumed without photosynthesis.

The cups were then exposed to light for 20 minutes, and the number of disks floating in each cup was measured every minute. Results were calculating by finding the ET50 for each concentration. The ET50 is the time it takes for 50% of the leaf disks to float and is a good indicator of the rate of photosynthesis. The experiment found that there was a connection between the two and that the rate of photosynthesis is affected by an increased concentration of carbon dioxide.