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?

   • Stay level, because insects get their energy from the sun
   • Rise, because the frogs send energy back to the insects
   • Fall, because less energy passes from grass to insects
   • Rise, because the arrow shows the insects are the food source
3. 2.

   Line Caterpillars: (1, 500), (2, 520), (3, 480), (4, 500). Line Songbirds: (1, 50), (2, 52), (3, 48), (4, 50). In model data, Bo sees the songbird line stay far below the caterpillar line in every year. Which reason fits the web and the graph?

   • About 10% of energy passes up, so fewer songbirds are supported
   • The top level should have the most energy, so the graph is wrong
   • Energy cycles back to the caterpillars, so songbirds keep little
   • The songbirds are the food source, so they run out of energy first

4. 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).

5. 3.

   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?

   • Less energy passed from the sedge to the beetles after the sedge fell
   • 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
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?

   • About 10% passes up, so the insects should hold about 1,000 units
   • 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
7. 5.

   Jun writes: energy and matter both cycle around the rainforest. Which fix is right?

   • Nothing needs fixing, since both cycle around through the trees
   • Matter cycles through decomposers; energy flows one way
   • Matter flows one way, but energy cycles through the trees
   • Both flow one way, so the decomposers are not really needed
8. 6.

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

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

   • Grass takes its food from the soil, so light changes nothing
   • Each level uses most of its energy, and much leaves as heat
   • The rest goes back to the sun to be used again
   • The rest passes on to the frogs, so it is not lost
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 send energy back to the trees
    • Fungi are not needed: trees get their food from the soil
    • Fungi are needed: they return nutrients for producers to reuse
    • Fungi are not needed: fallen leaves would break down without them
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 owls hold the most, because they are at the top
    • The sedge holds the most, because energy moves in a circle
    • The sedge holds the most, because about 10% passes up each level
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
    • Neither: the arrows should loop, because energy is reused
    • Diagram 1: the arrow points to the beetles, which get the energy
    • Both: arrows may point either way in a food web