Food webs: where energy and matter go in an ecosystem

Grade 7 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   Use this

   Marsh web with a graph, not to scale (model data). Graph (model data): x axis Year, ticks every 1 year from 1 to 4; y axis Population size (model units), ticks every 20 from 0 to 100. Line Marsh grass: (1, 80), (2, 80), (3, 50), (4, 30). Line Marsh insects: (1, 60), (2, 60), (3, 60), (4, 58).

2. 1.

   Ari sees the marsh grass line fall after year 2 while the insect line has not changed. If the grass stays low, what will the insect line do next, and why?

   • Fall, because less energy passes from grass to insects
   • Rise, because the frogs send energy back to the insects
   • Stay level, because insects get their energy from the sun
   • Rise, because the arrow shows the insects are the food source

3. Use this

   Graph (model data): x axis Year, ticks every 1 year from 1 to 5; y axis Population size (model units), ticks every 20 from 0 to 80. Line Tundra sedge: (1, 70), (2, 70), (3, 35), (4, 30), (5, 30). Line Tundra beetles: (1, 50), (2, 50), (3, 50), (4, 25), (5, 25).

4. 2.

   In model data, Luz sees the sedge line fall in year 3 and the beetle line fall in year 4. Which explanation fits the web and the graph?

   • Both take their food from the soil, so they fell together
   • The beetles' energy returned to the sedge, so the sedge fell first
   • The sedge gets energy from the beetles, so the beetles' drop came first
   • Less energy passed from the sedge to the beetles after the sedge fell
5. 3.

   Esme draws an orchard web. One arrow, labeled energy, runs from the fungi back to the apple tree. Which fix does Esme's web need?

   • Add an arrow carrying food from the soil to the apple tree
   • Label it nutrients, since energy does not return to the tree
   • Remove the fungi, because an orchard has no use for decomposers
   • Turn around the arrow that runs from the apple tree to the beetles
6. 4.

   Bo draws a marsh energy pyramid (model data) and says about 90% of the energy passes up each level. What is the flaw?

   • Energy should return to the grass, so each level equals 10,000 units
   • The grass is not a level, because it makes its own food
   • The top level should hold the most energy units
   • About 10% passes up, so the insects should hold about 1,000 units
7. 5.

   Tala counts three levels in a tundra chain: sedge, lemmings and owls. Light reaches the sedge for weeks, yet no fourth level exists. Why?

   • The top level gets the most energy, so no more levels are needed
   • Energy cycles back to the sedge, so nothing moves up
   • Decomposers use the energy before a fourth level can
   • About 10% passes up each level, so too little reaches a fourth
8. 6.

   Zee reads that fungi and bacteria were removed from one orchard plot. After a year, fallen leaves piled up and the apple trees grew less. Why?

   • Apple trees take their food from the soil, which the leaves used up
   • Nutrients stayed locked in the leaves, not back in the soil
   • The leaves blocked the sun, so the soil lost its energy
   • Decomposers were not needed; the trees just needed more time
9. 7.

   Kira reads that a sunny week gives marsh grass extra energy, yet the insects still get about 10% of it. Why does the share passed on stay about 10%?

   • Each level uses most of its energy, and much leaves as heat
   • The rest passes on to the frogs, so it is not lost
   • The rest goes back to the sun to be used again
   • Grass takes its food from the soil, so light changes nothing
10. 8.

    Pia and Jun disagree about fungi in a rainforest web. Fallen leaves have an arrow to the fungi. Which claim and reason fit best?

    • Fungi are needed: they return nutrients for producers to reuse
    • Fungi are not needed: trees get their food from the soil
    • Fungi are not needed: fallen leaves would break down without them
    • Fungi are needed: they send energy back to the trees
11. 9.

    Milo and Ren compare a tundra energy pyramid (model data): sedge 5,000 units, lemmings 500 units, owls 50 units. Which claim and reason fit best?

    • The three levels hold equal energy, because each passes it on in full
    • The sedge holds the most, because about 10% passes up each level
    • The sedge holds the most, because energy moves in a circle
    • The owls hold the most, because they are at the top
12. 10.

    not to scale. Noah's class shows two diagrams of one orchard. Diagram 1 has arrow X from apple leaves to beetles. Diagram 2 has arrow Y from beetles to apple leaves. Which is right?

    • Diagram 2: the arrow points to the food, which is the apple leaves
    • Diagram 1: the arrow points to the beetles, which get the energy
    • Neither: the arrows should loop, because energy is reused
    • Both: arrows may point either way in a food web