AP Lab 5 Cellular Respiration

Overview Seeds are dormant until the right conditions are met and then they germinate.

In this lab the goals are: Germinating Peas!! When germinations occurs, the rate of cellular respiration greatly increases. In this lab the goals are: Measure oxygen consumption by measuring the change in gas volume in respirometers containing either germinating or nongerminating peas. Measure the rate of germinating peas at two different temperatures. Hint: your hypothesis and prediction should be based on the goals of the lab.

Introduction Cellular Respiration is the release of energy (ATP and heat) from organic compounds, such as glucose (C6H12O6), by metabolic chemical oxidation in the mitochondria within a cell. The transfer of electrons during oxidation-reduction chemical reactions releases energy stored in organic molecules. This released energy is ultimately used to synthesize ATP.

Cellular Respiration Formula C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat) In the equation, glucose is oxidized in the presence of oxygen. There are three ways to measure cellular respiration: Consumption of O2 Production of CO2 Release of energy In this experiment, the volume of O2 consumed by germinating and nongerminating peas at two different temperatures will be measured.

Using Respirometers To understand how this apparatus works, it is important to understand ideal gas laws. PV=nRT If T and P remain constant, then V is directly proportional to n. If T and V remain constant, then P changes in direct proportion to n. If n and T remain constant, then P is inversely proportional to V. If T changes and n stays constant , then either P or V (or both) will change in direct proportion to T.

How will we know that the change in volume will measure the oxygen and not the CO2? CO2 produced during respiration by the peas will be removed by potassium hydroxide (KOH) and will form solid potassium carbonate (K2CO3): CO2 + 2KOH K2CO3 + H2O Since the CO2 is being removed, the change in the volume of gas in the respirometer will be directly related to the amount of oxygen consumed.

Measuring Respirometers If water temperature and volume remain constant, the water will move toward a region of lower pressure. Oxygen will be consumed during respiration. Its volume will be reduced because CO2 is turning into a solid. The result is a decrease in gas volume within the tube, and a decrease in pressure in the tube. Control: Glass BEADS The glass beads will let us know if any changes in volume are due to atmospheric pressure changes or temperature changes.

Example with crickets!

Let’s get Started! First write your hypothesis and prediction for each: How will the amount of oxygen consumption compare in germinating versus nongerminating peas? Hypothesis: The amount of oxygen consumption will be _______________ in _________________ peas than in _____________ peas because during germination, oxygen consumption increases. Prediction: If _____________ peas consume ____________ oxygen than _____________ peas, then the _________ peas will show a ___________ in gas volume. How does temperature affect the rate of respiration in germinating peas? Hypothesis: Prediction:

Procedures Both a room-temperature (approx. 25°C) bath and a 10°C bath should be set up. Obtain 6 vials and label them 1-6. they should represent the table on pg. 56. Respirometer 1:Obtain a 100-mL graduated cylinder and fill it with 50 mL of water. Drop in 25 germinating peas and measure the displacement of water which will equal the volume of the peas.