Ecosystem Characteristics and Producers

Ospreys are birds that eat fish. Where would an osprey MOST likely live?

• near a marsh

• near a forest

• near a desert

• near a prairie

Answer explanation

An osprey would most likely live by a marsh because it primarily feeds on fish, and marshes provide a rich source of fish and other aquatic life. Marshes also offer tall trees or structures for nesting, as well as an undisturbed environment where they can raise their young.

What do the following ecosystems: reef, pond, marsh, and prairie have in common?

• fish

• salt water

• sunlight

• tall grasses

Answer explanation

Reefs, ponds, marshes, and prairies all have sunlight in common because they are all ecosystems that rely on sunlight as the primary source of energy. Sunlight is essential for photosynthesis, which allows plants and algae to produce food, supporting the entire food web in these environments.

Which characteristic differs the MOST between a forest and a grassland ecosystem?

• the amount of sunlight

• the amount of organisms

• the amount of salt

• the amount of trees

Answer explanation

The characteristic that differs the MOST between a forest and a grassland ecosystem is the amount of trees.

Explanation:

• Amount of Trees (Correct Answer) → Forests have a large number of trees, creating a dense canopy, while grasslands have few to no trees, mainly consisting of grasses and small shrubs. This is the most significant difference between the two ecosystems.

• Amount of Salt → Neither forests nor grasslands are typically saltwater environments, so salt levels do not significantly differ between them.

• Amount of Sunlight → Both ecosystems receive similar amounts of sunlight, though forests may have more shade due to tree cover, while grasslands have direct sunlight reaching the ground. However, this difference is not as drastic as the presence or absence of trees.

• Amount of Organisms → Both ecosystems support diverse life, but the number of organisms depends on various factors like climate and food availability. While their species differ, the total number of organisms is not the most defining characteristic between the two.

The amount of trees is the most significant difference between a forest and a grassland.

The main function of a producer in an ecosystem is to

• absorb minerals from the soil.

• change water vapor into a liquid.

• make a sugar through photosynthesis.

• break down dead plant and animal matter.

Answer explanation

The main function of a producer in an ecosystem is to make sugar through photosynthesis, which provides energy for the entire food chain.

Explanation:

• Producers (such as plants, algae, and some bacteria) use sunlight, carbon dioxide, and water to produce glucose (a type of sugar) through photosynthesis.

• This sugar stores chemical energy, which the plant uses for growth and survival.

• Consumers (herbivores, omnivores, and carnivores) depend on producers because they cannot make their own food.

• When animals eat plants (or eat other animals that ate plants), they gain energy that originally came from the sun.

In short, producers are the foundation of the food web because they convert sunlight into usable energy, making life possible for all other organisms in the ecosystem.

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Which pair of organisms benefits each other the MOST?

• squirrels burying seeds from a tree

• birds building a nest in a bush

• worms eating the roots of a plant

• deer scraping their antlers on a tree

Answer explanation

The pair of organisms that benefit each other the MOST is squirrels burying seeds from a tree.

Explanation:

• Squirrels bury seeds (such as acorns and nuts) as a food source, but they often forget to dig them up.

• These forgotten seeds can germinate and grow into new trees, helping the tree species reproduce and spread.

• The tree benefits by having its seeds dispersed, and the squirrel benefits by having a food source.

Why the Other Pairs Do Not Benefit Each Other Equally:

• Birds building a nest in a bush → The bird benefits from shelter, but the bush does not receive a clear benefit. This is commensalism, not mutualism.

• Worms eating the roots of a plant → The worms benefit by getting food, but the plant is harmed, making this a harmful relationship (parasitism).

• Deer scraping their antlers on a tree → The deer remove bark, which can damage the tree, so this relationship is also harmful rather than beneficial.

Thus, squirrels burying seeds from a tree is the best example of mutualism, where both organisms benefit from the interaction.

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Why are salt marshes and estuaries important for ocean life?

• They minimize damage to oceans during hurricanes.

• They filter salt out of river water before it enters the oceans.

• The provide safe, nutrient-rich breeding areas for ocean organisms.

• They increase the amount of sediment able to settle on the ocean floor.

Answer explanation

Salt marshes and estuaries serve as nurseries for many marine species, providing a safe environment for fish, shellfish, and other aquatic life to grow and develop before moving into open ocean habitats. These areas are rich in nutrients, which support a high level of biodiversity and productivity. Additionally, estuaries act as transition zones between freshwater and saltwater ecosystems, offering a mix of conditions that many marine species rely on for breeding and early life stages.

4o

The picture shows a polar bear. Which change in the environment would MOST likely decrease the ability of this animal to survive?

• decrease in yearly rainfall

• increase in yearly rainfall

• increase in Earth's temperature

• decrease in Earth's temperature.

Answer explanation

Polar bears depend on sea ice for hunting, resting, and breeding. As Earth's temperature rises due to climate change, sea ice melts at a faster rate, reducing the bear's hunting grounds and making it harder to find food, especially seals. A decrease in ice cover forces polar bears to swim longer distances, leading to exhaustion, starvation, and a decline in their population. Therefore, an increase in Earth's temperature would most likely decrease their ability to survive.

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Which pair of organisms will MOST likely compete for the similar food source?

• A

• B

• C

• D

Answer explanation

Explanation:

Organisms compete for resources when they have similar diets and habitats. The two deer shown in option B are both herbivores that likely eat the same types of plants, grasses, and leaves. Since they live in the same environment and rely on the same food sources, they would most likely compete for food.

Other choices are less likely to compete:

• A (eagle and small bird): They have different diets—eagles are predators that eat meat, while small birds often eat seeds or insects.

• C (frog and crab): They live in different environments (land vs. water) and eat different foods.

• D (bobcat and lion): They are both carnivores, but they live in completely different habitats (one in forests, the other in savannas).

Thus, the two deer (B) will most likely compete for a similar food source.

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Which will most likely cause a decrease in predator populations?

• a decrease in decomposers

• an increase in producers

• a decrease in prey populations

• an increase in prey populations.

Answer explanation

Predators rely on prey as their primary food source. If the prey population decreases, predators will have less food available, leading to starvation, lower reproduction rates, and eventually a decline in the predator population. This is a direct example of how food availability impacts ecosystems.

Other choices are less likely to cause a decrease in predator populations:

• An increase in prey populations would actually benefit predators, leading to more food and possibly an increase in their numbers.

• A decrease in decomposers could affect nutrient cycles but wouldn’t directly impact predator populations as quickly.

• An increase in producers (plants) might help prey populations grow, which could actually lead to an increase in predator populations rather than a decrease.

Thus, the most direct cause of a decrease in predator populations is a decrease in prey populations.

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