Ecosystems — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A disease kills most of the rabbits in a meadow ecosystem. What is the most likely effect on the fox population?
A) Fox numbers would increase because there is less competition.
B) Fox numbers would decrease because they lost a major food source.
C) Fox numbers would stay the same because they can eat grass instead.
D) Fox numbers would increase because the disease makes rabbits easier to catch.
Foxes depend on rabbits as prey. Fewer rabbits means less food for foxes, so fox numbers would decline.
2. A new factory begins releasing warm water into a lake. How would this most likely affect the lake ecosystem?
A) All fish would grow larger because warm water helps them digest food faster.
B) Some organisms that need cool water could die while warm-water species might thrive.
C) The ecosystem would not change because water temperature does not affect organisms.
D) All plants in the lake would grow faster because warmer water has more nutrients.
Temperature is an abiotic factor. Warm water reduces oxygen levels and harms cold-water species, while favoring heat-tolerant species.
3. Why would removing all the decomposers from a forest ecosystem cause the greatest damage?
A) Predators at the top of the food chain would have nothing to eat.
B) Dead matter would build up and nutrients would stop cycling back into the soil for plants.
C) All the trees would immediately die without decomposers living near their roots.
D) Herbivores would run out of food because decomposers are their main prey.
Decomposers are essential for nutrient cycling. Without them, nutrients stay locked in dead matter and producers starve.
4. An invasive plant species grows faster than native plants and takes over a field. Which effect is most likely?
A) Animals that depended on native plants for food or shelter would decline in number.
B) The soil would become richer because the invasive plant adds extra nutrients.
C) Predators in the area would increase because the new plant attracts more prey.
D) Nothing would change because all plants provide the same resources to animals.
Native animals evolved with native plants. If native plants disappear, animals that need them for food or habitat will decline.
Part B: Fill in the Blank
Write the correct answer on each line.
1. When one species is removed from a food web, other species that depend on it are affected.
Food webs show interdependence. Removing one species creates a cascade — predators lose food, prey population may surge.
2. An invasive species is a non-native organism that harms the ecosystem it enters.
Invasive species often lack natural predators in their new environment, allowing them to outcompete native species.
3. Cutting down large areas of forest is called deforestation and destroys many habitats.
Deforestation removes habitat, destroys food webs, increases carbon in the atmosphere, and reduces biodiversity.
4. Pollution is a human activity that can change the abiotic factors of an ecosystem.
Pollution changes water chemistry, air quality, and soil health — all abiotic factors that affect living things.
5. All organisms in an ecosystem are interdependent, meaning they rely on one another to survive.
Interdependence means every organism plays a role. Changes to one species ripple through the entire ecosystem.