Year 8 Science · Unit 1 · Lesson 20
Foundation Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. In a food chain, the arrow points from the predator to its prey.
Correct it:
2. A food web is made of many food chains joined together.
Correct it:
3. A caterpillar that eats gum leaves is a primary consumer.
Correct it:
4. Energy is recycled round a food chain, just like matter is.
Correct it:
5. Producers are at the bottom of an energy pyramid.
Correct it:
6. Most of the energy in the leaves a caterpillar eats does not end up in the caterpillar’s body.
Correct it:
Put the food chain in order
Number these five organisms from 1 (the producer) to 5 (the top predator). Beside each, write producer or consumer.
| Position (1–5) | Organism | Producer or consumer? |
|---|---|---|
| Eagle | ||
| Grasshopper | ||
| Snake | ||
| Grass | ||
| Frog |
1. Write the whole food chain on one line, using arrows (→).
2. Draw a food web from these facts. Grasshoppers eat grass. Caterpillars eat gum leaves. Lizards eat grasshoppers and caterpillars. Magpies eat grasshoppers and caterpillars. Hawks eat lizards and magpies. Use arrows that show the direction of energy flow. Then, under your web, name one animal that would still have food if all the grasshoppers died, and say why.
Using the 10 percent rule
About 10 percent (one tenth) of the energy at one trophic level passes to the next. Table 1 applies this to grass → grasshopper → lizard → hawk.
| Trophic level | Organism | Energy available (kJ) |
|---|---|---|
| 1. Producer | grass | 20 000 |
| 2. Primary consumer | grasshoppers | 2 000 |
| 3. Secondary consumer | lizards | |
| 4. Tertiary consumer | hawks |
Source: numbers worked out from the one-tenth rule; not measured.
3. Fill in the two empty cells in Table 1. Show your working.
Hawks kJ
4. Use Table 1 to explain why a patch of bushland has lots of grass but only a few hawks.
5. Where does the energy in a kangaroo’s muscles come from? Trace it back to the sun. Then explain why only a small part of the energy the grass captured ends up in the kangaroo.
True or false
1. False: the arrow points from the prey (the organism eaten) to the predator, showing the direction of energy flow. 2. True. 3. True. 4. False: energy flows one way and is lost at each level; matter is recycled, but energy is not. 5. True. 6. True.
Put the food chain in order
Reading down the table as printed: 5, 2, 4, 1, 3. Grass is the producer; eagle, grasshopper, snake and frog are consumers.
1. grass → grasshopper → frog → snake → eagle. [1 mark]
2. Arrows: grass → grasshopper; gum leaves → caterpillar; grasshopper → lizard; grasshopper → magpie; caterpillar → lizard; caterpillar → magpie; lizard → hawk; magpie → hawk. Still has food: the lizard or the magpie, because each also eats caterpillars. [4 marks: 1 all organisms placed; 1 all links present; 1 every arrow points from eaten to eater; 1 animal with a second food source]
Use the 10 percent rule
3. Lizards: 10% of 2 000 = 200 kJ. Hawks: 10% of 200 = 20 kJ. [2 marks: 1 each]
4. The grass has 20 000 kJ but only 20 kJ reaches the hawks, because about 90% of the energy is lost as heat, movement and waste at each level. There is only enough energy at the top for a few hawks. [2 marks: 1 data quoted, 1 energy lost at each level]
Show What You Know
5. Marking guide (points expected): 1 the sun’s energy is captured by grass (the producer) by photosynthesis; 1 sun → grass → kangaroo, with the kangaroo a primary consumer (trophic level 2); 1 only about 10% of the grass’s energy passes to the kangaroo; 1 the rest is lost as heat, movement and waste (for example, parts of the grass that are not eaten or not digested). [4 marks]
Common error to watch for: drawing arrows from eater to eaten (“the eagle eats the snake”). The arrow means “energy goes to”.