Chapter 55

Write the equation for photosynthesis here:

6CO2 + 6H2O + Light energy -> C6H12O6 + 6O2

What is a LIMITING NUTRIENT? What is the limiting nutrient off the shore of Long Island, New York? In the Sargasso Sea?

A limiting nutrient is the element that must be added for production to increase. Nitrogen is the limiting nutrient off the shore of Long Island, and, iron, the limiting nutrient in the Sargasso Sea.

What is an ECOSYSTEM?

An ecosystem is the sum of all the organisms living within a given area as well as the abiotic factors with which they interact.

What are some factors that limit primary productivity in aquatic ecosystems?

Both light and nutrients limit primary productivity in aquatic ecosystems.

Write the equation for cellular respiration here:

C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)

Review the CASE STUDY: NUTRIENT CYCLING IN THE HUBBARD BROOK EXPERIMENTAL FOREST. What effect has deforestation been shown to have on chemical cycling?

Deforestation has been shown to increase water runoff by 30-40% and increase the amount of minerals lost from the watershed.

What are DETRITIVORES? What is their importance in chemical cycling? Give some examples of detritivores.

Detritivores, or decomposers, are consumers that get their energy from detritus, which is nonliving organic material. Detritivores convert organic materials from all trophic levels into inorganic compounds usable by primary producers, closing the loop of an ecosystem's chemical cycling. Producers can then recycle these elements into organic compounds. Two important groups of detritivores are prokaryotes and fungi. These organisms secrete enzymes that digest organic material; they then absorb the breakdown products, linking the consumers and primary producers in an ecosystem. In a forest, for example, birds eat earthworms that have been feasting on leaf litter and its associated prokaryotes and fungi

Where does energy enter most ecosystems? How is it converted to chemical energy and then passed through the ecosystem? Remember is this: ENERGY CANNOT BE RECYCLED.

Energy enters most ecosystems as sunlight. It is converted to chemical energy by autotrophs, passed to heterotrophs in the organic compounds of food, and dissipated as heat. Energy flowing through the ecosystem is ultimately dissipated into space as heat, so if the sun were not continuously providing energy to Earth, most ecosystems would vanish.

What is EUTROPHICATION? What are factors that contribute to eutrophication?

Eutrophication is a process by which nutrients, particularly phosphorus and nitrogen, become highly concentrated in a body of water, leading to an increased growth of organisms such as algae or cyanobacteria. Adding a nonlimiting nutrient even one that is scarce, will not stimulate production. Conversely, adding more of the limiting nutrient will increase production until some other nutrient becomes limiting.

What is contributing to the great increase in atmospheric carbon dioxide? What are potential effects of the increase?

Fossil fuel burning is contributing to the great increase in atmospheric carbon dioxide. Potential effects of this increase are global warming, an increased likelihood of fires, alteration of the geographic distribution of precipitation, and dramatic changes in plant communities.

Write an equation here that shows the relationship between gross and net primary production.

NPP=GPP-R (In many ecosystems, NPP is about 1/2 of GPP)

Why do people who have limited diets in overpopulated parts of the world eat low on the food chain?

People who have limited diets in overpopulated parts of the world eat low on the food chain because plants, which provide more energy than meat, are found there. Crops are more available and more efficient for people under these conditions.

List three groups of organisms that are PHOTOSYNTHETIC AUTOTROPHS.

Plants, algae, and photosynthetic prokaryotes are three groups of organisms that are photosynthetic autotrophs.

State the trophic level of a COW.

Primary consumer.

State the trophic level of a MUSHROOM.

Primary consumers (detritivores).

State the trophic level of GRASS.

Primary producer.

State the trophic level of MAN.

Secondary/tertiary consumers.

In what ways have human activities contributed to acid precipitation? What are some negative consequences of acid precipitation?

The burning of wood and fossil fuels (especially in ore smelters and electrical generating plants), including coal and oil, releases oxides of sulfur and nitrogen that react with water in the atmosphere, forming sulfuric and nitric acid, respectively. The acids eventually fall to Earth's surface as acid precipitation. Acid precipitation lowers the pH of some streams and lakes and affects soil chemistry and nutrient availability. Nutrient deficiencies affect the health of plants and limit their growth.

Pay particular attention to the nutrient cycles in Figure 55.14. Note the key processes in each cycle. Use the figure below to describe the water cycle. Specify the roles of EVAPORATION, TRANSPRIATION, and RAINFALL.

The main processes driving the water cycle are evaporation of liquid water by solar energy, condensation of water vapor into clouds, and precipitation. Transpiration by terrestrial plants also moves significant volumes of water into the atmosphere. Surface groundwater flow can return water to the oceans, completing the water cycle. The width of the arrows in the diagram reflect the relative contribution of each process to the movement of water in the biosphere.

Both energy and matter can be neither ___________ nor __________.

created, destroyed

Besides the energy flow that you described in "Where does energy enter most ecosystems? How is it converted to chemical energy and then passed through the ecosystem?", chemicals such as carbon and nitrogen CYCLE through ecosystems. So energy __________ through an ecosystem and matter __________.

flows, cycles within them

Generally, what percentage of energy available at one trophic level is available at the next? THIS IS IMPORTANT! REMEMBER IT.

10%

Notice that most biomass pyramids have greatest biomass on the bottom of the pyramid. Label the trophic levels on the figure. Explain why the second pyramid of biomass is inverted.

The second pyramid of biomass is inverted because the producers-phytoplankton-grow, reproduce, and are consumed so quickly by the zooplankton that they never develop a large population size, or standing crop. In other words, the phytoplankton have a short turnover time, which means they have a small standing crop compared to their production. Because the phytoplankton continually replace their biomass at such a rapid rate, they can support a biomass of zooplankton bigger than their own biomass. Nevertheless, because phytoplankton have much higher production than zooplankton, the pyramid of production for this ecosystem is still bottom-heavy.

We can measure the efficiency of energy conversion in an ecosystem as well as whether a given nutrient is being gained or lost from an ecosystem. Let us take a second look at TROPHIC LEVELS. What trophic level supports all others?

The trophic level that ultimately supports all others consists of autotrophs, also called the primary producers of the ecosystem.

You may recall from Chapter 54 that BIOMASS is the total mass of all individuals in a trophic level. Another way of defining net primary production is as the amount of NEW biomass added in a given period of time. Why is net primary production, or the amount of new biomass/unit of time, the key measurement to ecologists?

To ecologists, net primary production is the key measurement because it represents the storage of chemical energy that will be available to consumers in the ecosystem.

What is TROPHIC EFFICIENCY?

Trophic efficiency is the percentage of production transferred from one trophic level to the next.

This concept reviews trophic relationships. Know all terms in your textbook that are bolded. What are TROPHIC LEVELS? What is always at the first trophic level?

Trophic levels are the levels of different feeding relationships in an ecosystem that make up the ecosystem's trophic structure. The first trophic level is always the primary producers.

Explain the process of biological magnification. Discuss at least one example.

Biological magnification is a process in which retained substances become more concentrated at each higher trophic level in a food chain. This occurs because the biomass at any given trophic level is produced from a much larger biomass ingested from the level below. One class of industrially synthesized compounds that have demonstrated biological magnification are the chlorinated hydrocarbons, which include the industrial chemicals called PCBs (polychlorinated biphenyls). Biological magnification of PCBs has been found in the food web of the Great Lakes, where the concentration of PCBs in herring gull eggs, at the top of the food web, is nearly 5,000 times that in phytoplankton, at the base of the food web.

What are the PRIMARY PRODUCERS of the deep-sea vents?

Chemosynthetic prokaryotes are the primary producers of the deep-sea vents.

Phytoplankton growth can be increased by additional nitrates and phosphates. What are common sources of each of these?

Common sources of nitrates and phosphates are farm fertilizer, sewage, and windblown dust.

How has agriculture affected nitrogen cycling? What are some negative consequences of nutrient enrichment?

Nitrogen is the main nutrient lost through agriculture; thus, agriculture has a great impact on the nitrogen cycle. Plowing mixes the soil and speeds up decomposition of organic matter, releasing nitrogen that is then removed when crops are harvested. Applied fertilizers make up for the loss of usable nitrogen from agricultural ecosystems. Recent studies have shown that human activities have more than doubled Earth's nitrogen supply of fixed nitrogen available to primary producers. However, nutrient enrichment has caused nitrogen levels to increase and exceed safe levels for drinking in some groundwater in some agricultural regions. It also allows for a bloom pf phytoplankton and when they die, they create an extensive "dead zone" of low oxygen availability. This zone threatens the survival of other organisms.

What is PRIMARY PRODUCTION? Distinguish between GROSS PRIMARY PRODUCTION and NET PRIMARY PRODUCTION.

Primary production is the amount of light energy converted to chemical energy (organic compounds) by autotrophs during a given time period. Gross primary production (total primary production) is the amount of light energy that is converted to chemical energy by photosynthesis per light time, while net primary production is the gross primary production of an ecosystem minus the energy used by the producers for respiration.

Pay particular attention to the nutrient cycles in Figure 55.14. Note the key processes in each cycle. Use the second figure on the following page to describe the carbon cycle. In doing so, explain how carbon enters the living system and how it leaves, indicate the role of microorganisms in the cycle, and identify the reservoir for carbon.

Photosynthesis by plants and phytoplankton removes substantial amounts of atmospheric CO2 each year. This quantity is approximately equaled by CO2 added to the atmosphere through cellular respiration by producers and consumers. Over geologic time, volcanoes are also a substantial source of CO2. The burning of fossil fuels is adding significant amounts of additional CO2 to the atmosphere. The widths of the arrows reflect the contribution of each process. Photosynthetic organisms utilize CO2 during photosynthesis and convert the carbon to organic forms that are used by consumers, including animals, fungi, and heterotrophic protists and prokaryotes. The major reservoirs of carbon include fossil fuels, soils, the sediments of aquatic ecosystems, the oceans (dissolved carbon compounds), plant and animal biomass, and the atmosphere (CO2). The largest reservoir is sedimentary rocks such as limestone; however, this pool turns over very slowly.

Which ecosystem would tend to have a greater biomass/unit area, a prairie or tropical rain forest? Explain.

Prairies tend to have a greater biomass/unit area than tropical rainforests. Although a forest has a very large standing crop, its net primary production may actually be less than that of some grasslands. (prairies) which do not accumulate much vegetation because animals consume the plants rapidly and because grasses and herbs decompose more quickly than trees do.

How is atmospheric ozone depleted? What are projected effects of this depletion?

The destruction of atmospheric ozone results mainly from the accumulation of chlorofluorocarbons (CFCs), chemicals used in refrigeration and manufacturing. When the breakdown products from these chemicals rise to the stratosphere, the chlorine they contain reacts with the ozone (O3), reducing it to the molecular O2. Potential effects of this depletion are increases in both lethal and nonlethal forms of skin cancer, increases in cataracts among humans, as well as unpredictable effects on crops and natural communities, especially the phytoplankton that are responsible for a large proportion of Earth's primary production.

What is meant by the GREENHOUSE EFFECT? What would life on Earth be like without this effect?

The greenhouse effect is the warming of Earth due to the atmospheric accumulation of carbon dioxide and certain other gases, which absorb reflected infrared radiation and radiate some of it back toward Earth. Without this effect, the average air temperature at Earth's surface would be a frigid -18^C (-2.4^F), and most life as we know it would not exist.

Use the diagram below to describe the nitrogen cycle. In doing so, indicate the role of microorganisms in NITROGEN FIXATION, NITRIFICATION, and DENITRIFICATION.

The major pathway for nitrogen to enter an ecosystem is via nitrogen fixation, the conversion of N2 by bacteria to forms that can be used to synthesize nitrogenous organic compounds. Some nitrogen is also fixed by lightning. Nitrogen fertilizer, precipitation, and blowing dust can also provide substantial inputs of NH4+ and NO3- to ecosystems. Ammonification decomposes organic nitrogen to NH4+. In nitrification, NH4+ is converted to NO3- by conditions nitrifying bacteria. Under anaerobic conditions, denitrifying bacteria use NO3- in their metabolism instead of O2, releasing N2 in a process known as denitrification. The widths of the arrows reflect the relative contribution of each process.