--- marp: true theme: default html: true --- # Where does the energy go? Year 7 Biology · Food webs and ecosystems --- ## Today **We are learning to** energy enters a food web as sunlight captured by producers and flows one way along the arrows. At each step only about 10% is passed on; the rest is used for living or lost as heat. Matter is different: decomposers return it to be used again. - I can trace the direction of energy through at least three levels of a food web. - I can explain that energy is lost at each level. - I can explain the difference between energy flow and matter cycling. --- ## Why it matters > A field of grass can feed many grasshoppers, which feed fewer lizards, which feed a couple of kookaburras, which feed perhaps one eagle. Why the shrinking numbers? --- 💬 Discussion ## Engage: predict **Grass captures 10 000 kJ of energy from sunlight. A grasshopper eats grass, a lizard eats grasshoppers, a kookaburra eats lizards. About how much of that energy reaches the kookaburra?** - Almost all of it, 10 000 kJ - About 10 kJ - It goes round and comes back to the grass - About half --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fbiology-7%2Fenergy-flow%2Fstep-2&code=widget%3A+foodweb%0Amode%3A+trace%0Aenergy%3A+10000%0Aorganism+G%3A+Grass%0Aorganism+H%3A+Grasshopper%0Aorganism+R%3A+Kangaroo%0Aorganism+L%3A+Lizard%0Aorganism+B%3A+Kookaburra%0Aorganism+D%3A+Dingo%0Aorganism+E%3A+Wedge-tailed+eagle%0Aeats+H%3A+G%0Aeats+R%3A+G%0Aeats+L%3A+H%0Aeats+B%3A+L%2C+H%0Aeats+D%3A+R%0Aeats+E%3A+L%2C+B%0A&fresh=1}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/biology-7/energy-flow/?full=step-2#step-2) --- ✅ Check ## What happened? * About 10 kJ. Roughly 90% is used or lost as heat at each step, so only about 10% passes on: 10 000 → 1 000 → 100 → 10. --- ✅ Check ## Down the levels **A lizard gets 100 kJ from the grasshoppers it eats. About how much reaches a kookaburra that eats the lizard, in kJ?** * Answer: 10 --- ✅ Check ## Where it goes **Where does the other 90% go at each step?** Groups: Not passed to the next level · Passed to the next level Heat given off by the animal's body · Energy used for moving, breathing and keeping warm · Parts not eaten (bones, fur, roots) · Energy stored in the eaten animal's body * Answer: Heat given off by the animal's body → Not passed to the next level; Energy used for moving, breathing and keeping warm → Not passed to the next level; Parts not eaten (bones, fur, roots) → Not passed to the next level; Energy stored in the eaten animal's body → Passed to the next level --- ✅ Check ## Energy and matter **Which statement is true?** - Energy is recycled by decomposers; matter is lost - Energy and matter are both recycled - Energy flows one way through a web and is lost as heat; matter (the atoms) is recycled by decomposers * Answer: Energy flows one way through a web and is lost as heat; matter (the atoms) is recycled by decomposers --- ✅ Check ## Mix it up **Looking back at food webs: in the chain grass → grasshopper → lizard → kookaburra, which is the secondary consumer?** - The grasshopper - The grass - The kookaburra - The lizard * Answer: The lizard --- ✅ Check ## Elaborate: why so few eagles? **Why are there far fewer wedge-tailed eagles than grasshoppers in an ecosystem?** - Eagles have fewer babies - So little energy reaches the top of the food chain that it can only support a few large predators - Grasshoppers are easier to see * Answer: So little energy reaches the top of the food chain that it can only support a few large predators --- ✅ Check ## Elaborate: a desert and a rainforest **A rainforest's plants capture far more energy each year than a desert's. What would you predict about their food webs?** - They would be the same size - The rainforest can support more organisms and more levels of consumers - The desert would have more top predators * Answer: The rainforest can support more organisms and more levels of consumers --- ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - **Energy** enters as sunlight captured by producers and **flows one way** along the arrows. - At each step only about **10%** is passed on; about **90%** is used for living or lost as **heat**. - That's why there are **few top predators**. - **Matter cycles**: decomposers return atoms to the soil and air, and producers use them again. Energy does not cycle. --- ✅ Check ## Exit ticket **Why does a food chain rarely have more than four or five levels?** * Only about 10% of the energy passes to each level, so after four or five steps there is too little left to support another population.