ECOSYSTEMS, NUTRIENT CYCLING AND CLIMATE CHANGE

What is primary production? Explain the difference between gross primary production (GPP) and net primary production (NPP).

Primary production is the amount of light energy converted to chemical energy (organic compounds) by autotrophs. Gross primary production (GPP) is the total energy captured, while net primary production (NPP) is the energy remaining after autotrophs use some for respiration (NPP = GPP - respiration). NPP represents the energy available to consumers.

Which terrestrial biomes contain ecosystems with the highest and lowest net primary production? Explain your answers with reference to the abiotic conditions of each.

Tropical rainforests have the highest NPP due to warm temperatures, high rainfall, and abundant sunlight. Deserts and tundra have the lowest NPP because of limited water, extreme temperatures, and poor nutrient availability.

Which aquatic biomes contain ecosystems with the highest and lowest net primary production? Explain your answers with reference to the abiotic conditions of each.

Coral reefs and estuaries have the highest NPP because they receive sunlight and nutrients from land and upwelling. Open oceans have the lowest NPP because they lack nutrients despite receiving ample sunlight.

What biotic factors are similar between the terrestrial biome with highest production and the aquatic biome with highest production?

Both have abundant producers—tropical plants in rainforests and algae or corals in marine systems—that efficiently capture sunlight and support complex food webs with many consumers.

What biotic factors are similar between the terrestrial biome with lowest production and the aquatic biome with lowest production?

Both have sparse producer populations (e.g., desert plants and open ocean phytoplankton) and limited food webs due to low nutrient availability, restricting consumer diversity.

Would all the ecosystems found within the most productive biomes also have high NPP? Would all the ecosystems found within the least productive biomes also have low NPP? Why or why not?

Not necessarily. Local conditions like soil fertility, water access, or pollution can increase or decrease NPP within a biome. For example, shaded areas in a rainforest may have lower productivity, and oases in deserts may have higher productivity.

For each of carbon, oxygen, nitrogen and phosphorus, explain its role in the formation of biological molecules and/or its role in biological functioning.

Carbon forms the backbone of organic molecules. Oxygen is essential for cellular respiration and water formation. Nitrogen is used in amino acids and nucleic acids. Phosphorus is vital for ATP, DNA, and cell membrane (phospholipid) structure.

Compare and contrast the flow of energy through an ecosystem and the flow of nutrients through an ecosystem.

Energy flows in one direction—from the sun to producers to consumers—and is lost as heat. Nutrients cycle repeatedly through biotic and abiotic components via decomposition, uptake, and release, allowing reuse by organisms.

For each of the four cycles (carbon, nitrogen, phosphorus, water), identify the main reservoirs for the nutrient, the forms available to life, and describe the key processes that drive the cycle.

Carbon: Reservoirs include the atmosphere, oceans, and fossil fuels. It cycles through photosynthesis and respiration. Nitrogen: Reservoirs include the atmosphere; it cycles via nitrogen fixation, nitrification, and denitrification. Phosphorus: Reservoirs are rocks and soil; weathering releases phosphate for uptake. Water: Reservoirs are oceans and freshwater; it cycles through evaporation, condensation, and precipitation.

Why does phosphorus generally cycle locally rather than globally?

Phosphorus lacks a gaseous phase, so it cycles mainly through soil, water, and organisms rather than through the atmosphere.

Why do nutrients cycle more quickly in warmer, wetter ecosystems than in colder, drier ecosystems? How does this affect net primary productivity?

Warm, moist conditions enhance microbial activity and decomposition, speeding up nutrient cycling. This increases nutrient availability for plants, boosting primary productivity.

Why do nutrients cycle more quickly in aerobic aquatic ecosystems than in anaerobic aquatic ecosystems? How does this affect net primary productivity?

Aerobic ecosystems support faster decomposition and nutrient recycling due to oxygen availability, promoting higher productivity. Anaerobic systems decompose slowly, limiting nutrient availability and productivity.

In both terrestrial and aquatic ecosystems, where are nutrients made available for uptake by plants (decomposed)?

Nutrients are released through decomposition in the soil of terrestrial ecosystems and in sediments or the water column of aquatic ecosystems.

In both terrestrial and aquatic ecosystems, where (in plants) are the nutrients used for photosynthesis?

Nutrients are used in leaves (chloroplasts), where they contribute to building chlorophyll, enzymes, and other molecules essential for photosynthesis.

How do nutrients move from the location of decomposition to the location of photosynthesis in terrestrial ecosystems?

Nutrients move from soil to leaves through the plant's vascular system (xylem) as they are absorbed by roots and transported upward.

How do nutrients move from the location of decomposition to the location of photosynthesis in aquatic ecosystems?

Nutrients released from decomposition in sediments or deeper water move upward through diffusion and water mixing (upwelling) to reach the photic zone where photosynthesis occurs.

Describe the effect of human activities on the composition of runoff and the function of plants as reservoirs for nutrients.

Human activities like agriculture and deforestation increase nutrient runoff, especially nitrogen and phosphorus, into water systems. Loss of vegetation reduces nutrient storage in plants and accelerates nutrient leaching and eutrophication.

Describe how agriculture leads to nitrogen enrichment of terrestrial and aquatic ecosystems.

Fertilizers add excess nitrogen to soil, which leaches into waterways. This causes eutrophication, algal blooms, and oxygen depletion, harming aquatic life.

In what ways would nitrogen enrichment change the abiotic and biotic environment of an oligotrophic lake?

Abiotic: Increased nutrient levels and decreased oxygen. Biotic: Algal blooms, decline in water clarity, and loss of fish and invertebrate species adapted to low-nutrient conditions.

Which carbon reservoirs do humans use for fuel and energy? Why does use of these reservoirs increase the amount of atmospheric carbon?

Humans burn fossil fuels such as coal, oil, and natural gas—carbon reservoirs formed from ancient organic matter. This releases carbon dioxide that had been stored underground, increasing atmospheric CO₂.

Describe how increased atmospheric carbon can influence primary productivity of ecosystems.

Higher CO₂ can enhance photosynthesis (CO₂ fertilization) in some plants but may be limited by nutrient or water availability. Long-term effects vary across ecosystems.

Explain how increased atmospheric carbon influences global climate.

Increased atmospheric CO₂ traps more heat through the greenhouse effect, raising global temperatures and altering precipitation, weather patterns, and sea levels.

Describe the implications of global climate change on ecosystems.

Global warming shifts biome distributions, alters species interactions, causes habitat loss, and increases extinction risk. Polar and coral reef ecosystems are especially vulnerable.

Does the graph showing increasing global CO₂ emissions and increasing global temperature illustrate a causative relationship between the two? Why or why not? What further evidence might be required?

The correlation suggests a strong link but doesn't prove causation alone. Evidence from climate models, isotopic analysis of CO₂ sources, and historical data supports that rising CO₂ from human activity causes temperature increases.