Energy Flow, Food Chains & Food Webs — Practice · Grade 7 Science

Chapter: Ecosystems, Matter & Energy

What this practice covers

By the end of Energy Flow, Food Chains & Food Webs you should be able to:

8 questions, written answer and multiple choice, each with a worked explanation.

Vocabulary used: ecosystem, producer, consumer, food web, decomposer.

Problem 1

Why is a decomposer not outside the food system?
Answer and explanation

It obtains and transfers organic matter and energy from dead material and wastes within connected pathways.

Problem 2

Which way should an arrow point from an eaten seed to a seed-eating bird?
Answer and explanation

From seed to bird, because the bird receives matter and stored energy from the seed.

Problem 3

Why might a consumer persist after one food source declines?
Answer and explanation

It may use other resources, migrate, or respond over time; the web shows possible connections rather than an immediate fixed outcome.

Problem 4

Do decomposers recycle all usable energy back to plants?
Answer and explanation

No. They recycle matter into other forms while energy transfers and much dissipates as heat.

Problem 5

Illustrative web: grass feeds insects and rabbits; insects and seeds feed mice; mice and rabbits feed foxes. An insect decline is recorded, but other resource counts are missing. Trace one affected pathway and explain why the exact mouse or fox change cannot be determined.
Answer and explanation

The insect decline can affect the mouse pathway and indirectly foxes, but mice also have seeds and foxes also have rabbits. The web does not give dependence strengths, alternative resource changes, movement, or timing. It supports a conditional mechanism, not an exact population forecast.

Follow insect→mouse→fox under the stated arrows.

Identify seeds as another mouse resource and rabbits as another fox resource.

Request counts, rates, and interval information.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

Why can one organism have more than one feeding position?
Answer and explanation

It can eat resources from different positions, such as both producers and other consumers. The web must show its actual resource relationships.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

In the stated convention, grass→rabbit means what?
  1. Grass hunts rabbits
  2. Rabbit receives food matter and energy from grass
  3. Rabbits create sunlight
  4. Grass becomes a whole rabbit instantly
Answer and explanation

Rabbit receives food matter and energy from grass

The arrow tracks transfer from the eaten resource toward the consumer.

Problem 8

Name information missing from a web that prevents an exact population prediction.
Answer and explanation

Feeding rates, dependence on each resource, initial counts, movement, and environmental conditions are examples of needed information.

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