Energy Flow through Organisms
Every bite of food carries energy that started with the Sun.
Topic 3 of 5Grade 6 · Life Science
- Teacher:
- Mr. Mohamed Fawzy
- School:
- Oceans Academy
- Unit:
- From Cells to Ecosystems
How this topic is built
- Covers workbook pages 80 to 82 (Week 8: What is an Ecosystem, the food web passage, and the Chesapeake Bay Waterbird Food Web) and all six workbook questions.
- Added beyond the workbook, because they are core to energy flow in middle school: decomposers and the 10% energy rule. Both are marked in their notes.
What is an ecosystem?
Where did your last meal come from? Maybe a grocery store, your own garden, or a local farm share (community-supported agriculture). Trace it back far enough, and most of it came from a farm. But wild animals can't shop for food. So how do they find what they need to survive?
An ecosystem is an area of land or water whose conditions meet the needs of the living things there.
Abiotic factors are the nonliving parts: temperature, air, water, sunlight, wind, rocks, and space. Biotic factors are the living or once-living parts: animals, plants, trees, bugs, sticks, logs in a stream, and fallen leaves.
Corrections from the workbook (page 80)
- The workbook defines ecosystems as "areas of land." Ecosystems can be land or water (the Chesapeake Bay is one). The slide says both.
- The workbook lists "water" twice in the abiotic list; it appears once here.
- The workbook puts sticks, logs and leaf litter under biotic but calls biotic "the living parts." They are once-living, so the slide says "living or once-living."
Sort it: biotic or abiotic?
Is each thing living (or once-living), or nonliving?
The planted mix-ups
- Fallen log and leaf litter: dead, but once living, so biotic.
- Mushroom: many students think fungi are not alive.
Quick Check 1
From the workbook, page 80, question 2.
Workbook question, unchanged
Answer D. "Hills" are landforms made of rock and soil, so they are abiotic.
What living things need
To survive, an organism needs food (plants need sunlight to make their food), water, air, and shelter: a safe place with enough space. A species is one kind of living thing, like all red foxes. A species also needs other members of its kind so it can continue into the future.
An organism can live in an ecosystem only if the ecosystem meets these needs. This topic focuses on food, because food is where an organism gets its energy: the ability to move, grow, and do work.
Correction from the workbook (page 80)
- The workbook says ecosystems must meet the five needs "equally." There is no such rule; the needs must simply be met. The word is dropped.
- "Other members of their species" is needed for the species to continue, not for one animal to stay alive. The slide words it that way, at the workbook's level.
Quick Check 2
From the workbook, page 80, question 1.
Workbook question, unchanged
Answer C. Mention that "land" here should be read as "land or water."
Food webs: who eats whom
A food web shows which organisms eat which others in an ecosystem. Its arrows point from the food to the eater, showing the way energy moves.
Almost all of that energy starts with the Sun. Producers capture sunlight and use it to make their own food. They include plants, algae (like seaweed), and phytoplankton (tiny producers that float in water). Consumers can't make food, so they eat other organisms.
Primary consumers eat producers. They are herbivores (eat only plants) or omnivores (eat plants and animals). Secondary consumers eat primary consumers; they are omnivores or carnivores (eat only animals). Tertiary and then quaternary consumers come next, and are usually carnivores.
An apex predator has no natural predators: great white sharks, orcas, tigers, lions, grizzly bears, and wolves.
Corrections from the workbook (page 81)
- "All energy on Earth begins with plants." The energy in food webs begins with the Sun, and producers include algae and phytoplankton, not only plants.
- "Plants are known as Producers because they get their energy from the sun." More exactly: they make their own food using the Sun's energy.
Extra fact
Orcas sometimes hunt great white sharks, so "apex" can depend on the ocean area. Students love this.
Energy levels, step by step
Tap each level to see where it gets its energy.
Teaching tip
Ask: "Could a lion be a primary consumer?" No, it doesn't eat plants. "Could a bear?" Yes, when it eats berries. Many animals eat at more than one level.
Quick Check 3
From the workbook, page 81, question 2.
Workbook question, unchanged
Answer D, all of the above: producers make food, carnivores eat only animals, and secondary consumers eat primary consumers.
Home experiment 1: do producers need light?
Producers make food using sunlight. Test what happens without it.
Expected result
After a week, the plant in the dark is pale yellow, thin, and often taller and floppy as it stretches to find light. The window plant is green and sturdy.
Word for curious students
Plants grown in the dark are called "etiolated."
A real food web: the Chesapeake Bay
Arrows point from the food to the eater. Tap any organism to see what it eats and what eats it.
Corrections to the workbook's food web (page 82)
- The workbook's chart has separate rows for "Herbivores" and "Primary Consumers," but page 81 says herbivores are primary consumers. In the chart, zooplankton sit in "Herbivores" while small fish that eat zooplankton sit in "Primary Consumers," which contradicts page 81. This redrawn web places each organism by what it eats.
- One arrow between Herbivorous Ducks and Bivalves appears to point the wrong way in the workbook picture (as if clams ate ducks). It is not included.
- All other feeding links from the workbook are kept, plus phytoplankton → zooplankton, which the workbook implies.
Teaching tip
Many animals eat at more than one level. The tundra swan eats plants (primary) and clams (secondary).
Quick Check 4
Use the Chesapeake Bay food web.
What this checks
Counting levels along one food chain. Students often count the osprey as "secondary" because it is the second animal they think of.
Where does the energy go?
Each time one organism eats another, only about 10% of the energy moves up to the next level. The rest is used by the organism to move, grow, and stay alive, and much of it escapes as heat.
That's why a food web has lots of producers, fewer consumers at each level, and only a few apex predators at the top.
When plants and animals die, decomposers go to work. Bacteria, fungi (like mushrooms and mold), and earthworms break down dead organisms and wastes.
This returns nutrients to the soil and water, where producers can use them again. Nutrients are materials living things need to grow, like the minerals in plant food. Without decomposers, dead things would pile up everywhere.
Added content (not in the workbook)
The 10% rule and decomposers are part of the standard grade 6 food-web content (energy flow and cycling of matter). You asked me to use my judgment on additions; this slide and experiment 2 are the only additions in this topic.
Common mistake
"Energy is recycled like nutrients." Nutrients are recycled; energy is not. It leaves as heat and new energy keeps arriving from the Sun.
Energy pyramid simulator
Bar widths are not to scale; the numbers are.
How to use it
- Start at 10,000 units with 4 levels: the top gets only 10 units.
- Add a fifth level: now only 1 unit reaches it. Ask why food chains rarely have more than 4 or 5 levels.
Accuracy note
"About 10%" is an average; real transfers range roughly from 5% to 20%.
Quick Check 5
From the workbook, page 81, question 3.
Workbook question, unchanged
Answer C. The osprey and bald eagle in the Bay web are quaternary consumers and also have almost no natural predators as adults.
Home experiment 2: decomposers at work
Mold is a fungus, a decomposer. Does it need water to break down food?
Expected result
The damp slice shows fuzzy mold spots within about 4 to 7 days; the dry slice changes little. Bread without preservatives molds faster.
Safety for class
Bags stay sealed the whole time and go in the trash sealed. Students with mold allergies or asthma should watch a classmate's photos instead.
Energy flow in everyday life
Menhaden: a small fish with a big job
Atlantic menhaden eat plankton in the Chesapeake Bay, and they are a main food for striped bass and ospreys. They pass the Sun's energy up the food web.
Ospreys come back every March
Ospreys return to the Chesapeake Bay each spring to nest. They eat almost only fish, so they need plenty of fish below them in the food web.
Farms and farm shares
Many families in Loudoun and Fairfax counties buy vegetables from local farms. Crops are producers: they turned sunlight into the energy in your food.
Compost bins and fallen leaves
Earthworms, fungi, and bacteria in a compost pile break down food scraps and leaves into rich soil for gardens.
Sources for the local examples
- Menhaden as a key forage fish for striped bass and ospreys: Chesapeake Bay Program.
- Ospreys return to the Bay around mid-March: Chesapeake Bay Program, Virginia DWR.
Vocabulary flip cards
Say the meaning out loud, then tap the card to check.
Game idea
Build a human food web: each student holds a card, and a ball of yarn passes from food to eater.
Final quiz: Energy Flow through Organisms
Answer all 8, then check your answers. Every answer comes with an explanation.
Answer key
1 B · 2 A · 3 A · 4 B · 5 A · 6 B · 7 C · 8 D
Question 1 is the workbook's page 80, question 3. Question 2 is page 81, question 1 (written as multiple choice; in class it can stay an open question).