Primary productivity - Lab Report Example

Lab report 13 November Primary productivity Introduction Primary productivity is the measure of the rate of carbon assimilation by plants. Carbon is assimilated into the plants tissues in the form of carbohydrates with the concomitant release of oxygen according to the following equation:6 H2O(l) + 6 CO2 (g)+ energy → C6H12O6+ 6O2(g)The oxygen released is dissolved in water to form molecular oxygen which can then be utilized by aquatic organisms. The respiration done by plants and animals reduces the concentrations of oxygen while photosynthesis increases the oxygen concentrations.

Therefore the primary productivity of an ecosystem can be measured over time by calculating the amount of oxygen produced which is directly proportional the amount of carbon bound to organic compounds such as carbohydrates in photosynthesis. In this experiment the light and dark bottle method was used.2. Materials and MethodsA set of 24 clean bottles each with a capacity 300ml were prepared. Twelve of the bottles were covered with aluminum foil and a black tape while the other twelve were not covered.

All the 24 bottles were then filled with algae water. All the bottles were then exposed to light for a period of 1 hour. Dissolved oxygen probes were prepared and allowed to stay in water for 5 minutes as the probe warmed up and the initial dissolved oxygen concentration recorded. Data in each bottle was collected by gently stirring the probe in the water sample until the readings were relatively stable for about 30 seconds and the values recorded. The values for the light and the dark bottles were recorded and the means calculated.

The respiration rate, gross productivity and net productivity were then calculated. The means were compared using student’s t-test and considered significant at P < 0.05.3. Results The data obtained for the dissolved oxygen concentrations in the light and dark bottles were subjected to paired student’s t- test. The results obtained indicated that there was a significant (P < 0.05) increase in dissolved oxygen concentrations for the algae in the light bottles compared to those in the dark bottles.

DiscussionThe algae in the bottles exposed to light predominantly carry out photosynthesis as they trap light energy which is converted into chemical energy in the form of sugars. Photosynthesis leads to the production of O2 and thus explains the increased concentrations of the dissolved oxygen. In the dark bottle only respiration occurs since algae are C3 plants. Since there was no sunlight the plants did not manufacture more sugars but rather there was breakdown of the sugars to provide energy for cellular activities with the production of carbon dioxide and water according to the equation below.

The dissolved oxygen in the water was thus used up and led to decreased oxygen concentrations.C6H12O6+ 6O2 ⇒6CO2+ 6H2O + ATPThe rate of respiration was calculated as follows:= (9.15-7.69)/1=1.46Gross primary productivity (GPP) is the rate at which the primary producers, in this case the algae, in a particular community turn solar energy into stored chemical energy via the process of photosynthesis and thus measures the rate of energy accumulation. This occurred mainly in the algae contained in the light bottle.

This was calculated as follows:= (12.97-7.69)/1= 5.29The net primary productivity (NPP) which is the rate at which energy is incorporated into the primary producers’ bodies through growth and reproduction was also calculated. Not all the GPP is incorporated in to the primary producers since they utilize some of the energy for respiration and other metabolic activities (Solomon, Berg and Martin 1169) The NPP was thus calculated as follows:=(12.97-9.15)/1=3.82.In conclusion, the dark bottle was used to measure the rate of respiration in algae while the light bottle was used to measure the rate of photosynthesis.

The difference in respiration and photosynthesis gave the NPP. As it can be seen from the results the NPP is greater than that of respiration and thus allows for the increase in size among the plants as they store the extra energy in form of carbohydrates. Work citedEldara, P. Solomon, Linda R. Berg and Diana W. Martin. Biology. United States 8th ed Thomson Brooks/cole 2008. Print.