Habitats and Ecosystems — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. In a pond food web, what would happen if all the frogs disappeared?
A) Insect populations would increase.
B) Algae would stop growing.
C) Fish would have more insects to eat.
D) Nothing would change.
Frogs eat huge numbers of flies, mosquitoes, and other bugs every day, so without frogs to hunt them the insect population would grow quickly.
2. Which organism is both a consumer and prey in a grassland food chain?
A) grass
B) hawk
C) rabbit
D) mushroom
A rabbit is a consumer because it eats grass, but it is also prey because foxes, hawks, and coyotes hunt it — that puts it right in the middle of the food chain.
3. Why do food webs give a better picture of an ecosystem than a single food chain?
A) Food webs only show producers.
B) Food webs include nonliving things.
C) Food webs show that most animals eat more than one food source.
D) Food webs are shorter and simpler.
A single food chain shows only one path of who-eats-who, but real animals like bears munch berries, fish, and insects, so a web shows all those overlapping connections.
4. A forest is cut down to build houses. What is the most likely result for the animals?
A) Animals will find more food than before.
B) Animals must move, adapt, or they may not survive.
C) Animals will grow thicker fur.
D) Animals will start eating rocks.
Cutting down a forest destroys the animals' habitat — their food and shelter — so they must find a new home, change their habits, or they will not survive.
Part B: Fill in the Blank
Write the correct answer on each line.
1. When people cut down trees, animals lose their habitat and food sources.
A habitat is the home where an animal finds food, water, and shelter, so cutting down the trees that make up that home means the habitat is destroyed.
2. Pollution in a river can harm the entire aquatic ecosystem.
A river ecosystem includes fish, plants, insects, and the water itself, so pollution spreads through the whole network and hurts every living thing connected to it.
3. A species that many other organisms depend on is called a keystone species.
A keystone is the central stone that holds up a stone arch — pull it out and the arch falls — so a keystone species, like a sea otter, holds an entire ecosystem together.
4. Animals that are active at night are called nocturnal animals.
The Latin root "noct" means night, so nocturnal animals like owls, bats, and raccoons sleep during the day and hunt or move around after dark.
5. An invasive species can take over a habitat and push out native animals.
An invasive species is a plant or animal brought to a place where it does not belong; with no natural predators it can multiply fast and crowd out the local wildlife.