Food Webs and Energy — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. In an ocean food web, tiny floating plants called phytoplankton are the main producers.
Phytoplankton are microscopic plant-like organisms that float near the ocean surface and use sunlight to make food. They are the base of nearly every ocean food web.
2. A hawk that eats a snake that ate a mouse is a tertiary consumer.
Count the steps: the mouse eats plants (primary), the snake eats the mouse (secondary), and the hawk eats the snake (tertiary, meaning third-level consumer).
3. Trees, grasses, and shrubs are all producers in a forest food web.
Trees, grasses, and shrubs all make their own food through photosynthesis, which is exactly what producers do. They form the foundation of a forest food web.
4. Small fish that eat zooplankton are secondary consumers in an ocean food web.
Zooplankton are primary consumers because they eat phytoplankton. Small fish that eat zooplankton are one step higher, making them secondary (second-level) consumers.
5. Energy is lost as heat when organisms use it for movement and body heat.
Every time an organism moves, digests food, or keeps its body warm, some energy escapes as heat into the surroundings and cannot be used again by other organisms.
6. A omnivore is an organism that eats both producers and other consumers.
An omnivore feeds at multiple levels of the food web by eating both plants (producers) and animals (consumers). Bears and raccoons are common examples of omnivores.
7. Bacteria on the ocean floor act as decomposers by breaking down dead organisms.
Bacteria on the ocean floor break down dead organisms into simple nutrients, which is the key job of decomposers. These nutrients then become available for producers to use again.
8. The transfer of energy from one organism to another is called energy flow.
Scientists call this process energy flow because energy moves in one direction through a food web, passing from producers to consumers and never cycling back.
9. Owls, foxes, and wolves are examples of predators in a forest ecosystem.
Owls, foxes, and wolves all hunt and catch other animals for food, which makes them predators. They help keep prey populations in balance within the forest ecosystem.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each organism to its role in a food web.
oak tree
→ producer
secondary consumer
caterpillar
→ primary consumer
decomposer
owl
→ secondary consumer
producer
mushroom
→ decomposer
primary consumer
Correct matches: oak tree → producer; caterpillar → primary consumer; owl → secondary consumer; mushroom → decomposer.