biology homework

Assays of Metabolism Lab

Exergonic and Endergonic Reactions

Chemical reactions can consume energy (endergonic) or release energy (exergonic). In cells. The most common form of cellular energy is ATP. Catabolic reactions break down macromolecules and yield a net release of energy. Anabolic reactions build up molecules and require a net input of energy. Catabolism and anabolism are couple because there are component reactions in both that yield or require energy,

Materials per station for protocol 1:

2 tubes of Ammonium chloride (NH4Cl)

2 tubes Calcium chloride (CaCl2).

Squirt bottle dH20

Protocol 1:

Endergonic Reaction:

1. Obtain 1 50 ml plastic centrifuge tube containing ~ 5g of Ammonium chloride (NH4Cl)

2. Add about 15 ml of water. Place cap on securely and shake the tube.

Exergonic Reaction:

1. Obtain 1 50 ml plastic centrifuge tube containing ~ 5g Calcium chloride (CaCl2).

2. Add about 15 ml of water. Place cap on securely and shake the tube.

Cellular Respiration: Redox Reactions

Germinating seeds activate dormant metabolic reactions, especially cellular respiration. The viability of a seed collection is measured by the percentage of germinated seeds that have activity for cellular respiration.

A common chemical used to assay seed viability is tetrazolium. In its oxidized state tetrazolium is clear, but in its reduced state (accepted electrons), tetrazolium is red (Figure 1).

For this activity, iodine is used to identify the part of the germinated corn seed that is the endosperm, which is rich in starch, a storage carbohydrate (Figure 2). If cellular respiration is occurring in the embryo of the germinating seed, then the tetrazolium will become reduced by the electrons transferred during the cellular respiration reactions.

Figure 1. Geminating corn seeds assayed for viability with tetrazolium. The embryo is red , indicating that the tetrazolium has been reduced. The source of electrons that reduce tetrazolium come from cellular respiration pathways. Image: C. MacKinnon

Figure 2. The iodine assay stains starch-rich regions a black color. The part of the corn seed that contains starch is called endosperm. When the seed is hydrated, the carbohydrate is used as the energy source needed for growth and development. Image: C. MacKinnon

Materials per station for protocol 2:

2 razor blades

2 petri dishes

microfuge tubes tetrazolium solution (wrapped in foil)

1 dropper bottle of iodine

Squirt bottle dH20

Protocol 2 Tetrazolium Assay:

1. Use a razor blade to cut three corn seeds longitudinally.

2. Place each cut corn seed in a petri dish, numbered 1-3.

3. Add about two drops of water on seed #1.

4. Add about two drops of iodine on seed #2.

5. Add about two drops of Tetrazolium on seed #3; if needed, add two or more drops.

6. Incubate the seeds at room temperature for ~10-30 minutes.

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