Unit 2 - Practice Quiz

Abiotic components are the non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Biotic components are the living parts.

Decomposers, like bacteria and fungi, play a crucial role by breaking down dead plants and animals, returning essential nutrients to the soil for producers to use.

A terrestrial ecosystem is a land-based community of organisms. Ponds, rivers, and oceans are all examples of aquatic ecosystems.

Artificial ecosystems, such as aquariums, gardens, or crop fields, are man-made and require human management to sustain them.

Solar energy is captured by producers (plants) through photosynthesis, forming the base of the energy flow in most food chains and webs.

Herbivores are primary consumers that feed on producers (plants). Carnivores eat other animals, and omnivores eat both plants and animals.

A food web provides a more realistic representation of feeding relationships in an ecosystem, as most animals feed on more than one type of organism.

The base of the pyramid, representing producers (like plants), is the largest because it must support all other trophic levels above it.

The pyramid of energy is always upright because energy is lost as heat at each successive trophic level, so the energy at a lower level is always greater than the energy at a higher level.

Ecological succession describes how the mix of species and habitat in an area changes over time, for example, a bare rock being colonized by lichens, then mosses, grasses, shrubs, and finally trees.

Natural resources are materials or substances such as minerals, forests, water, and fertile land that occur in nature and can be used for economic gain.

Non-renewable resources, like fossil fuels (coal, oil, natural gas), exist in a fixed quantity and are consumed much faster than they can be formed, which takes millions of years.

Renewable resources like sunlight, wind, and biomass can be regenerated or replenished naturally, making them sustainable if managed properly.

Wind power is a renewable energy source because it is generated from wind, which is a naturally occurring and replenishing phenomenon. The others rely on finite resources.

Deforestation is the clearing of forests for other land uses like agriculture or urban development. Afforestation is planting trees where there were none, and reforestation is replanting a cleared forest.

Removing vegetation, such as through deforestation or overgrazing, exposes the topsoil to wind and water, leading to increased rates of erosion.

Burning fossil fuels like coal and oil releases large amounts of carbon dioxide, a greenhouse gas that contributes to global warming and climate change.

Fixing leaks is a simple remedial measure that can save a significant amount of water, helping to combat water scarcity on an individual level.

Turning off lights is a direct and easy action that reduces electricity consumption, thereby conserving the energy resources used to generate that electricity.

The '3 Rs' - Reduce, Reuse, Recycle - form a waste hierarchy for resource conservation. Reducing consumption is best, followed by reusing items, and finally recycling materials.

Decomposers play a crucial role in breaking down dead organic material and returning essential nutrients (like nitrogen and phosphorus) to the soil. Without them, this recycling process would stop, leading to a pile-up of dead organisms and a depletion of nutrients available for producers.

According to the 10% rule, only about 10% of the energy from one trophic level is transferred to the next.

• Energy from Grass (Producer) to Grasshopper (Primary Consumer): 10% of 10,000 kJ = 1,000 kJ.
• Energy from Grasshopper to Frog (Secondary Consumer): 10% of 1,000 kJ = 100 kJ.
• Energy from Frog to Snake (Tertiary Consumer): 10% of 100 kJ = 10 kJ.

An inverted pyramid of biomass is often found in aquatic ecosystems like the open ocean. This is because the producers (phytoplankton) have a very short lifespan and reproduce rapidly. At any given moment, their total mass (biomass) may be less than that of the primary consumers (zooplankton) that feed on them, even though the overall energy production of the phytoplankton over time is much greater.

This is secondary succession because the process starts on soil that is already present and was previously inhabited. Primary succession begins on bare rock or newly formed land where no soil exists (e.g., after a volcanic eruption). The abandoned field already has soil and residual life, allowing for a faster and different successional path.

This question highlights the nuance in resource classification. While the Earth's internal heat is virtually inexhaustible on a human timescale (making geothermal renewable overall), a specific local reservoir can be depleted if overused. This shows that the key factor in sustainability is managing consumption to be at or below the rate of natural replenishment.

Irrigation water, even freshwater, contains small amounts of dissolved salts. In arid climates, high evaporation rates cause the water to turn to vapor, but the salts are left behind in the soil. Over time, these salts accumulate in the root zone, making the soil toxic to many plants and reducing agricultural productivity.

This question addresses the concept of 'virtual water' or 'embedded water' – the water used to produce goods and services. The amount of water required to produce 1 kg of beef is exceptionally high (often estimated at over 15,000 liters) due to the water needed to grow feed crops for the cattle. This is significantly more water than is saved by most other direct household conservation efforts.

Estuaries are where rivers meet the sea. This location allows them to act as nutrient traps, receiving a constant supply of nutrients from terrestrial runoff. Additionally, their shallow depth allows sunlight to penetrate to the bottom, promoting abundant growth of producers like marsh grasses and phytoplankton, which form the base of a very productive food web.

This is a classic example of a trophic cascade. The sea otter is a keystone species. Its removal releases the sea urchin population from predation pressure, allowing their numbers to explode. The increased population of sea urchins then decimates the kelp forests, which are the primary producers and habitat for many other species, leading to a significant change in the ecosystem's structure.

The second law of thermodynamics states that during any energy conversion, some energy is lost as heat and entropy increases. In an ecosystem, as energy flows from one trophic level to the next, a significant portion (around 90%) is lost as metabolic heat. Therefore, the energy available at each successive level is always less than the level below it, resulting in an upright pyramid shape that cannot be inverted.

Dams trap sediments that would naturally flow downstream. This starves deltas and floodplains of the silt needed to replenish land and maintain fertility. The altered, controlled flow also changes the natural flood cycles that many downstream ecosystems and agricultural systems depend on, leading to habitat loss and reduced productivity.

Pioneer species are the first to colonize barren environments. They must be extremely hardy and adapted to conditions of low nutrients, high sun exposure, and temperature extremes. Species like lichens can chemically weather rock to start soil formation, and some pioneer plants can fix atmospheric nitrogen, enriching the substrate for later species that are less tolerant but better competitors in more developed soil.

The excess nutrients (nitrates/phosphates) first cause a massive, rapid growth of algae (an algal bloom). When these algae die and sink, bacteria and other decomposers multiply to break them down. This decomposition process consumes large amounts of dissolved oxygen in the water. The resulting low-oxygen condition (hypoxia or anoxia) is lethal to fish and other aquatic organisms.

This is a key distinction. Standing crop is a static measurement (e.g., kilograms of plant matter per square meter). Productivity is a dynamic measurement of flow (e.g., kilograms of new plant matter produced per square meter per year). An ecosystem can have a low standing crop but high productivity if the biomass is consumed or turned over very quickly (like phytoplankton in the ocean).

JFM moves away from a top-down, exclusionary conservation model. It recognizes that local communities have a stake in the health of the forest. The model involves them in protection and management, and in return, they get a share of the benefits, such as non-timber forest products and a portion of the income from timber harvesting. This creates a local incentive for conservation.

The main argument for nuclear power in the context of climate change is that the fission process itself does not produce CO2 or other greenhouse gases. While it is non-renewable and has significant issues with waste disposal and safety, its low carbon footprint during operation makes it an important part of the debate on transitioning away from fossil fuels like coal and natural gas.

Composting creates a nutrient-rich soil amendment (humus). Using this compost in gardens reduces the reliance on synthetic fertilizers, whose production is energy-intensive and whose overuse can lead to soil degradation and water pollution. Furthermore, by diverting organic waste from landfills, it reduces the volume of garbage, extending the life of landfill sites and reducing the need to use more land for waste disposal.

Tree canopies intercept a significant amount of rainfall, reducing its impact on the ground. The extensive root networks act like a net, holding the soil together and preventing erosion. The forest floor, rich in organic matter, acts like a sponge, absorbing water and releasing it slowly. When the forest is removed, rainwater hits the ground directly, dislodging soil, and runoff is rapid and uncontrolled, leading to landslides and flash floods.

The key characteristic described is permafrost, which is a layer of permanently frozen subsoil. This feature, along with a short growing season and the dominance of low-growing, cold-adapted plants like mosses, lichens, and sedges, is the defining feature of the Tundra biome.

The 'Tragedy of the Commons' describes a situation where a shared, unregulated resource (the 'commons') is depleted because individual users, acting independently according to their own self-interest, behave contrary to the common good of all users by depleting that resource. The open-access fishery is a classic example: if one fisherman doesn't catch the fish, another one will, creating a race to exploit the resource that ultimately harms everyone.

An inverted pyramid of biomass occurs when the total weight (biomass) of producers at any given time is lower than the total biomass of primary consumers. This is characteristic of many aquatic ecosystems. The reason is not that there are fewer producers overall, but that they have a very short lifespan and high reproductive rate (high turnover). Phytoplankton reproduce and are consumed so rapidly by zooplankton that their standing crop (biomass at one point in time) is low, even though their overall productivity over a year is massive. The other options are less accurate: individual size doesn't determine total biomass, biomass import describes an allochthonous system, and high energy transfer efficiency doesn't in itself cause an inversion.

This scenario demonstrates two distinct ecological models of succession. First, the presence of Balanus facilitates the arrival of Mytilus by creating a more suitable substrate (Facilitation model). However, once established, Mytilus actively outcompetes and eliminates the earlier species, Balanus, which is a form of the Inhibition model where one species prevents the persistence of another. The Tolerance model would imply that later species are simply better competitors for resources but are unaffected by earlier species, which is not the case here.

This question requires careful analysis of energy partitioning. First, determine the energy entering the Grazing Food Chain (GFC). Total NPP = 20,000 kcal/m²/year. Energy to detritus = 90%. Therefore, energy to GFC = 10% of NPP.
Energy for primary consumers (herbivores) = 10% of 20,000 = 2,000 kcal/m²/year.
Now, apply the 10% trophic efficiency rule up the GFC:

• Energy to secondary consumers (carnivores) = 10% of 2,000 = 200 kcal/m²/year.
  Let's recalculate carefully:
  1. Total NPP = 20,000 kcal/m²/year.
  2. Energy entering the detritus pathway = 0.90 * 20,000 = 18,000 kcal/m²/year.
  3. Energy entering the Grazing Food Chain (GFC) at the producer level for herbivores to eat = 20,000 - 18,000 = 2,000 kcal/m²/year.
  4. Energy assimilated by Primary Consumers (herbivores) = 10% of 2,000 = 200 kcal/m²/year.
  5. Energy assimilated by Secondary Consumers = 10% of 200 = 20 kcal/m²/year.
  6. Energy assimilated by Tertiary Consumers = 10% of 20 = 2 kcal/m²/year. The correct answer is 2 kcal/m²/year.

This is a classic problem in lake restoration. After external sources of phosphorus (P) are cut off, P that has accumulated in the lake sediments for years can be released back into the water column, a process called 'internal loading.' This is especially pronounced under anoxic (low oxygen) conditions at the sediment-water interface. This internal P source can fuel algal blooms for years. The most direct remedies are to either remove the P-rich sediment (dredging) or to oxygenate the bottom waters (hypolimnetic aeration) to keep the phosphorus locked in the sediment. Riparian buffers target external runoff, not internal loading. Increasing flushing rate is a different strategy, and biomanipulation addresses the food web structure, not the root chemical cause in this case.

Resistance is the ability of an ecosystem to withstand disturbance without changing. Resilience is the ability of an ecosystem to recover quickly after being disturbed. The redwood forest shows high resistance to low-intensity fires (its structure doesn't change much). However, if it suffers a catastrophic disturbance like clear-cutting, its recovery rate is extremely slow, indicating low resilience. The grassland shows low resistance (it burns completely) but high resilience (recovers quickly). The coral reef shows low resistance but high resilience to minor stress. The agricultural system is artificial and its 'recovery' is human-managed, not a natural process of resilience.

While edges can increase local species richness (the 'edge effect'), artificial edges created by fragmentation have well-documented negative impacts. One of the most significant is the increased vulnerability of forest-interior species. Predators and brood parasites (like the Brown-headed Cowbird) that thrive in open or edge habitats can more easily access the nests of birds adapted to the deep forest interior, leading to population declines. This is a more specific and critical ecological problem than a general decrease in productivity or an absolute halt to nutrient cycling or genetic flow, which are overstatements.

This question requires a nuanced understanding of LCA for different 'green' technologies. Corn ethanol requires large amounts of land and fertilizer (nitrogen, phosphorus), leading to runoff and high eutrophication potential. PV panel manufacturing, conversely, requires mining of silicon and other scarce minerals (abiotic resource depletion) and involves toxic chemicals in processing (human toxicity potential). While PV manufacturing has a carbon footprint, it is generally much lower over its lifecycle than burning biofuels, which also have associated emissions from farming and processing. Water consumption for corn agriculture is very high. The EROI for corn ethanol is notoriously low (around 1.3), whereas for PV it is significantly higher (often >10).

While all options are challenges, the issues of permanence (ensuring the saved carbon isn't released later) and leakage (deforestation moving elsewhere) are the most fundamental and difficult problems for REDD+. If a project protects a forest for 10 years but it's burned in year 11, the carbon benefit is lost (permanence). If protecting 'Forest A' causes loggers to simply move and clear 'Forest B' just outside the project boundary, there is no net global climate benefit (leakage). These conceptual and practical hurdles are harder to solve than the technical challenges of measurement, funding, or local participation.

The key requirement is providing power after sunset. While PV with batteries can do this, Concentrated Solar Power (CSP) is uniquely designed for it. CSP systems use mirrors to concentrate sunlight onto a receiver, heating a fluid (like molten salt) to very high temperatures. This heat can be stored efficiently in insulated tanks and used to generate steam to drive a turbine hours later, providing power on demand. This thermal storage is currently more cost-effective for large-scale, long-duration storage than batteries. PV with batteries is a valid solution, but CSP with thermal storage is a single, integrated technology designed specifically for this purpose and often seen as superior for grid stability.

This question tests the origin of energy in an ecosystem. 'Allochthonous' means the energy originates from outside the ecosystem (in this case, the terrestrial forest). 'Autochthonous' means the energy is produced within the ecosystem (e.g., by algae). Since the main energy source is external leaf litter, the system is allochthonous. 'Heterotrophic' means that the total ecosystem respiration is greater than its production (P/R < 1), which is typical for ecosystems that rely on subsidies of organic matter from elsewhere. Therefore, the stream is both allochthonous and heterotrophic.

The monoclimax theory, proposed by Frederic Clements, suggested that for any given climatic region, there was only one true, stable climax community that all successional pathways would eventually lead to. The polyclimax theory is a more modern and accepted view which recognizes that other local factors besides climate are critical. Factors like soil type (edaphic factors), topography (slope, aspect), and disturbance regimes (like frequent fires) can create a variety of different, stable climax communities within the same climatic region. For example, in one region you might find an oak-hickory climax on one soil type and a pine climax on a sandier, fire-prone soil.

A pyramid of energy depicts the flow of energy from one trophic level to the next. The Second Law of Thermodynamics states that during any energy transfer or transformation, some energy is degraded into a less useful form (usually heat) and the total entropy of the system increases. This means that the transfer of energy between trophic levels is inherently inefficient; only a fraction (typically 5-20%) of the energy from one level is converted into biomass at the next level. The rest is lost as heat during metabolic processes. Consequently, the energy available at each successive trophic level must be less than the level below it, preventing the pyramid of energy from ever being inverted.

The Ghyben-Herzberg relation describes the balance between freshwater and saltwater in coastal aquifers. It is based on their density difference. The principle states that for every unit drop (e.g., 1 meter) in the height of the freshwater table above sea level, the freshwater-saltwater interface will rise by approximately 40 units (40 meters). This is because the density of saltwater () is about 1.025 g/cm³ and freshwater () is 1.000 g/cm³. The relationship is , where is the height of the water table above sea level and is the depth of the interface below sea level. Therefore, a 2-meter drop in the water table () will cause an approximate 2 * 40 = 80-meter rise in the saltwater interface.

Laterization is characterized by intense weathering due to high temperatures and heavy rainfall. This causes water to percolate through the soil, dissolving and carrying away (leaching) soluble base cations (like calcium, magnesium, potassium) and even silica. What remains is a concentration of the least soluble compounds: iron and aluminum oxides (sesquioxides), which give the soil a reddish color. These soils are nutrient-poor because the nutrients are either leached away or locked up in the living biomass. When this soil is cleared of vegetation and exposed to the sun, it can undergo irreversible hardening, a process called plinthite formation, making it useless for agriculture.

This question targets the understanding of lifecycle emissions. While all are positive actions, their impacts vary dramatically. The production of meat, especially beef from ruminants, has an enormous 'Scope 3' carbon footprint due to methane emissions (a potent GHG), land-use change (deforestation for pasture), and the production of feed. Shifting dietary patterns away from red meat addresses this massive source of indirect emissions. Switching to LEDs and eliminating vampire power are 'Scope 2' actions (related to purchased electricity) and are effective, but typically have a smaller total impact than the dietary shift. Using recycled products is good, but its GHG reduction potential is also less than that associated with industrial-scale livestock agriculture.

Mycorrhizal fungi form symbiotic relationships with tree roots and are essential for nutrient uptake in nutrient-poor tropical soils. Clear-cutting removes all host trees simultaneously, starving the fungal network. It also drastically changes the soil temperature and moisture, further damaging the sensitive mycelium. This loss of the mycorrhizal network can severely inhibit the re-establishment of many native tree species that depend on it. Selective logging, while still damaging, leaves many host trees standing, allowing the network to persist and facilitate the regeneration of new seedlings in the logged gaps. Therefore, the impact of clear-cutting on this critical below-ground ecosystem component is far more severe and long-lasting.

EROI is the ratio of the amount of usable energy delivered from a particular energy resource to the amount of energy used to obtain that energy resource (Energy Output / Energy Input). If the EROI is 1:1, it means that one unit of energy is expended to produce one unit of energy. This results in no net energy gain for society, making the source effectively an energy sink or, at best, a form of energy storage, not a primary source. To be a viable energy source for society, an EROI significantly greater than 1 is needed. While some argue the minimum for a modern society is 3:1 or 5:1, the absolute threshold of sustainability is 1:1, below which the process consumes more energy than it produces.

This problem requires a step-by-step calculation of ecosystem production metrics.

1. GPP (Gross Primary Production) = 1500 gC/m²/year (given).
2. (Autotrophic Respiration) = 60% of GPP = 0.60 * 1500 = 900 gC/m²/year.
3. NPP (Net Primary Production) = GPP - = 1500 - 900 = 600 gC/m²/year. This is the energy available to heterotrophs.
4. (Heterotrophic Respiration) = 400 gC/m²/year (given).
5. NEP (Net Ecosystem Production) = NPP - = 600 - 400 = 200 gC/m²/year.
   A positive NEP value indicates that the ecosystem is capturing more carbon through photosynthesis (GPP) than it is releasing through total respiration (). Therefore, it is a net carbon sink, accumulating biomass.

IWRM emphasizes coordinated development and management of water to maximize economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems. A benefit-sharing agreement moves beyond simply dividing water volumes. It focuses on dividing the benefits derived from water use (like electricity, food production, and ecosystem services). This approach is more cooperative and economically efficient, as the upstream country can generate significant value from the dam, part of which can be used to compensate the downstream country for its losses or to fund mitigation measures. This creates a 'positive-sum' outcome rather than the 'zero-sum' conflict of litigation or purely independent actions.

This question contrasts the energy dynamics of lentic (still water) and lotic (flowing water) systems. Fast-flowing rivers, especially with a gravel bed and shaded canopy, often have low in-stream primary production (P). They receive significant energy subsidies from terrestrial organic matter (leaves, etc.), which is an allochthonous input. The respiration (R) of this external carbon often exceeds the in-stream production, making the system net heterotrophic (P/R < 1). In contrast, a deep, clear, oligotrophic lake, while low in nutrients, has a well-lit pelagic zone where phytoplankton production (P) can exceed the total ecosystem respiration (R), making it net autotrophic (P/R > 1), at least on an annual basis. The lake acts as a carbon sink, while the river acts as a processor of terrestrial carbon.