Question

In this activity we will measure the rate of cellular respiration using bean seeds. Seeds contain a plant embryo and all the necessary nutrients for plant growth. When seeds germinate, the stored sugars are used in cellular respiration to produce ATP needed for plant development. In this lab activity, you will germinate bean seeds to measure cellular respiration. We know from the equation above that cellular respiration produces carbon dioxide. Carbon dioxide is also a compound that has the ability to change the pH of a solution. So if we place beans in solution and measure any change in pH, we will be measuring carbon dioxide production and as a consequence respiration. In order to have a reference point, you will first manipulate the pH of a solution using Sodium Bicarbonate and then perform the cellular respiration experiment using beans. Materials: 1) Small bag of Lima Beans 2) Paper cups 3) Grape Juice 4) Sodium Bicarbonate 5) Plastic Wrap

Experimental Procedure: 1) Take a small paper cup and add grape juice (3/4 of the volume). 2) Add 1 tablespoon of sodium bicarbonate and mix.

OBSERVATIONS. Describe your observations below (what was the color of the juice before and after mixing carbon dioxide? Can you give any tentative explanation to this?):

Take another paper cup and add enough lima beans to cover the bottom of the cup. Add then grape juice to the cup (3/4 of the volume).

Cover it with plastic wrap

Leave the beans in solution for 24 hours.

After 24 hours write your observations

The purpose of this activity is to collect the products of cellular respiration in solution and measure them by a color change. The mitochondria in our beans will be activated when placed in solution and perform the reactions of cellular respiration. The sugars in the juice will nurture them to perform the pathway efficiently.

Describe your observations below (Is there any change in the color of the juice now? How can you explain this? Please review the equation for cellular respiration above and try to find a link between the bean and the carbonate mediated change).

Answer 1

The equation for cellular respiration is

C6H12O6 + 6O2 ------> 6CO2 + 6 H2O + Energy.

The colour of juice after mixing sodium bicarbonate will be redder as sodium bicarbonate will dissociate and release carbon dioxide in the solution which in turn will decrease the pH of the juice making it look darker in colour.

In case of Lima beans after 24 hours, enough cellular respiration have taken place and all the CO2 produced will be trapped inside the cup and due to partial pressure, it will be present in the solution. There will be similar change in colour as in the case of sodium bicarbonate. In this case it will be due to release of carbon dioxide by Lima beans as a by product of cellular respiration.

The beans undergo respiration as they take up oxygen from the surrounding to undergo aerobic respiration which include the following pathways in the sequence- Glycolysis, Citric Acid Cycle, Electron Transport change(ETC) or Oxidative phosphorylation.
the last step of aerobic respiration I.e. ETC requires oxygen as an electron acceptor and in turn produces ATP. It takes place inside mitochondria and is ver essential for survival of any cell.

However, in case of sodium bicarbonate the release of CO2 is because of decomposition of NaHCO3. This is not at all relayed to cellular respiration. This is used only to have an idea of what colour change of grape juice looks like when Carbon dioxide is present in the solution. This is useful for comparing the colour of juice in the Lima bean experiment.