1. ccc system models which model best illustrates the flow of energy and matter in an ecosystem—a food chain or a food web? explain.
2. sep evaluate information a student says an organism that is both a first - level and second - level consumer is an omnivore. is that student correct? explain.
3. ccc energy and matter suppose a rancher wants to buy some grassland to raise cattle. what should she know about energy flow before she invests in the land or the cattle?
4. ccc patterns in massachusetts, a team of scientists studying great white sharks estimates that a population of 15,000 seals supports fewer than 100 sharks during the summer. why are there so few top - level consumers in this system?
5. sep construct explanations human activity can affect ecosystems by removing producers, consumers, and decomposers. what limiting factors may result from human actions, and what effects might they have on the flow of energy and matter in an ecosystem?

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Accepted Answer

### Question 1
# Brief Explanations:
A food web is a better model for showing energy and matter flow in an ecosystem. A food chain is a simple linear sequence of who eats whom, while a food web consists of multiple interconnected food chains. Ecosystems have complex feeding relationships, and a food web can represent the multiple prey and predator relationships of different organisms, thus providing a more comprehensive view of how energy and matter move through the various trophic levels and different populations. So it captures the complexity of real - world ecosystems better than a single food chain.
# Answer:
A food web best illustrates the flow of energy and matter in an ecosystem. Because a food web shows the complex, interconnected feeding relationships (multiple food chains linked together) in an ecosystem, while a food chain is a simple, linear sequence. This complexity in the food web better represents how energy and matter move through different trophic levels and organisms in a real - world ecosystem.

### Question 2
# Brief Explanations:
First - level consumers eat producers (plants), and second - level consumers eat first - level consumers. An omnivore is an organism that eats both plants (producers) and animals (which can be first - level consumers). So if an organism is a first - level consumer (eating producers) and a second - level consumer (eating first - level consumers), it is consuming both producers and other consumers, which fits the definition of an omnivore. For example, a bear eats berries (producers, acting as a first - level consumer) and also eats fish (which may be first - level consumers, so the bear acts as a second - level consumer in that relationship).
# Answer:
The student is correct. A first - level consumer eats producers (e.g., plants), and a second - level consumer eats first - level consumers (e.g., herbivores). An omnivore is an organism that eats both producers (plants) and other consumers (animals). So an organism that is both a first - level and second - level consumer is consuming both producers and consumers, which means it is an omnivore.

### Question 3
# Brief Explanations:
Energy flow in an ecosystem follows the 10% rule, where only about 10% of the energy from one trophic level is passed on to the next. Producers (grass in the grassland) capture energy from the sun. Primary consumers (cattle, as herbivores) eat the producers, and only a small portion of the energy from the grass is available to the cattle. The rancher should know that the amount of grass (producers) will limit the number of cattle (primary consumers) she can raise, because the energy transfer is inefficient. Also, if she plans to sell the cattle or use them for other purposes, she needs to consider the carrying capacity of the grassland, which is related to the energy flow and the amount of available producers. Additionally, she should be aware of the trophic levels and how energy is lost at each level (through respiration, waste, etc.), so that she can manage the grassland and the cattle population in a sustainable way.
# Answer:
The rancher should know about the 10% energy transfer rule (only about 10% of energy is passed from one trophic level to the next). Producers (grass) capture solar energy. Cattle (primary consumers) eat grass, but only a small fraction of the grass's energy is available to the cattle. She should know the carrying capacity of the grassland (how much grass is available to support the cattle population), as the energy available from the grass will limit the number of cattle she can raise. Also, she should be aware that energy is lost at each trophic level (through processes like respiration, heat loss, and waste), so managing the grassland (e.g., ensuring enough grass growth) and the cattle population is crucial for a sustainable cattle - raising operation.

### Question 4
# Brief Explanations:
In an ecosystem, energy transfer between trophic levels is inefficient, following the 10% rule. Producers capture energy from the sun, primary consumers (seals) eat producers, and top - level consumers (sharks) eat primary consumers. At each trophic level, most of the energy is lost (through respiration, heat, waste, etc.), and only about 10% is passed on. So to support a top - level consumer like a shark, a large number of lower - level consumers (seals) are needed, but since energy transfer is so inefficient, the number of top - level consumers is much smaller than the number of lower - level consumers. For example, if a seal has 100 units of energy from eating producers, only about 10 units will be available to the shark that eats the seal. So with 15,000 seals, the total energy available to sharks is limited, resulting in a small number of sharks.
# Answer:
There are few top - level consumers (sharks) because of the inefficiency of energy transfer in ecosystems. Only about 10% of the energy from one trophic level is passed to the next. Seals (primary consumers) get energy from producers, and sharks (top - level consumers) get energy from seals. Most of the energy at each trophic level is lost (through respiration, heat, waste, etc.). So even with a large population of seals (15,000), the amount of energy available to support sharks is relatively small, leading to a small number of top - level consumers.

### Question 5
# Brief Explanations:
Human actions like deforestation (removing producers), overfishing (removing consumers), or using pesticides that kill decomposers can act as limiting factors. If producers are removed, there is less energy available at the base of the food web, which affects all other trophic levels. Fewer producers mean fewer primary consumers can be supported, and this cascades up to higher trophic levels, reducing the flow of energy and matter. If consumers are removed, the population of their prey may increase uncontrollably, and the predators of the removed consumers may have less food. Removing decomposers slows down the recycling of nutrients back into the soil, which affects producer growth (since producers need nutrients), thus disrupting the flow of matter and energy as well. For example, if we overfish a certain species of fish (a consumer), the population of the fish's prey may explode, and the fish's predators may struggle to find food, altering the energy and matter flow in the aquatic ecosystem.
# Answer:
Limiting factors from human actions:
1. **Removing producers**: For example, deforestation or over - farming removes plants. This reduces the energy available at the base of the ecosystem. With fewer producers, primary consumers have less food, so their populations decrease. This reduction in primary consumers then affects secondary and higher - level consumers, reducing the overall flow of energy and matter through the ecosystem. Matter cycling is also affected as there are fewer plants to take in carbon dioxide and release oxygen, and to cycle nutrients.
2. **Removing consumers**: Overfishing or hunting can remove consumer species. If a primary consumer is removed, its prey (producers) may overpopulate, and its predators (secondary consumers) may have less food. This disrupts the balance of the ecosystem and the flow of energy and matter. For example, if we remove a species of herbivorous fish, the algae (producers) it ate may grow out of control, and the carnivorous fish that ate the herbivorous fish may decline.
3. **Removing decomposers**: Using chemicals like pesticides or polluting the soil can kill decomposers (like bacteria and fungi). Decomposers break down dead organisms and waste, returning nutrients to the soil. Without them, nutrients are not recycled, so producers have less access to nutrients, which limits their growth. This in turn affects all other trophic levels as energy and matter flow starts with producers.

These actions disrupt the normal flow of energy (less energy available at each trophic level due to imbalances) and matter (nutrient cycling is disrupted) in the ecosystem.

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