Do the following lab activity, "Primary Productivity." Read the information below and on the following pages in order to answer the questions on your worksheets. There are worksheets for this activity in your worksheet packet. When you have completed each step of the activity, check your answers online.

Remember, the material covered in this optional activity will be on your Unit 2 test.

• This is a virtual lab activity that can be completed anywhere that you have internet access.

Primary productivity is the rate at which plants make organic material (sugar) from inorganic carbon (carbon dioxide gas: CO2) through the process of photosynthesis minus the rate at which they use up organic material during cellular respiration. Marine biologists are very interested in (and concerned with) primary productivity because it directly indicates the robustness of the base of marine food webs: the producers.

As a quick review, here are the formulas for photosynthesis and respiration; both of which enter into determining primary productivity.

Photosynthesis: CO2 + H2O (+ nutrients) + sunlight --> C6H12O6 + O2

Respiration: C6H12O6 + O2 --> energy + CO2 + H2O

Plants use the energy of sunlight to make sugar from water and CO2. Oxygen is given off as a by-product. The sugar, a form of stored chemical energy, supplies the plant’s immediate needs for growth and reproduction and is converted into the structural components of the plant.

Note that primary production has a dual meaning. Oceanographers generally express primary production in terms of the amount of organic carbon produced from CO2 per unit time (e.g., grams of carbon per day), but it is equally valid to consider primary production as the rate at which chemical energy is produced from sunlight energy.

Who are the primary producers in the ocean?

More than 90% of the production in the sea is due to phytoplankton, a diverse group of microscopic organisms that includes tiny, single-celled photosynthesizing organisms and even smaller bacteria. For years, oceanographers focused on the single-celled organisms but it is becoming clear that the bacteria play a much greater role in marine production. The macroscopic algae, also called sea weeds, also contribute to the primary productivity of coastal regions.

Recent expeditions to mid-ocean ridges have discovered unusual communities that exist entirely on energy derived not from the sun, but from chemical reactions. In the process of chemosynthesis, bacteria are the primary producers. These genetically unique microbes appear to be ancient life forms that are specialized to break down the methane and sulfide compounds spewing from hot water vents, releasing the energy needed to convert inorganic nutrients into living tissue. Unique communities supported by chemosynthesis also have recently been found surrounding hot water vents and methane seeps in other environments. Again, specialized bacteria play the major role as the base of the food chain. These alternative production schemes exist in the absence of sunlight and in environments that, until recently, were considered barren and hostile to life as we know it. It is not yet known how much chemosynthesis contributes to the overall production of the ocean.

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