Texas Grab-and-Go Substitute Packet

Energy Flow in Ecosystems

Course: Biology (Grades 9–12) Subject: Science Time: ~50 min standard · ~90 min block Science

Overview

This is a self-contained, no-technology substitute packet in which students analyze how energy flows through an ecosystem. Working alone with a pencil, students read a short original passage on producers, consumers, decomposers, trophic levels, energy pyramids, and the ~10% rule of energy transfer; study an original labeled energy-pyramid diagram; analyze an original energy-data table; classify organisms by trophic level; calculate energy passed and percent transfer using the 10% rule; interpret the pyramid's shape; predict the effect of removing a trophic level; and write an evidence-based explanation (CER) of why top-level consumers are limited. It is a paper investigation with no lab materials and no hazards. Runs in a ~50-minute standard period; a ~90-minute block adds a multi-step energy-loss calculation.

At a glance

Course: Biology (Grades 9–12)

Subject: Science

Time: about 50 minutes standard, or a ~90-minute block (block adds a calculation extension)

Materials: printed packet and a pencil (no calculator, computer, or lab materials)

Work mode: independent

Product: a data analysis and a claim–evidence–reasoning explanation (CER)

Standards (provisional): 19 TAC §112.42 (Biology) — energy flow through trophic levels, energy pyramids and the ~10% rule, and ecosystem relationships. Provisional — pending educator verification against the current official TAC source. Standards are paraphrased, not quoted. This packet does not claim formal alignment to the TEKS.

Accessible version of the student activity

The full student activity is reproduced below in plain, screen-reader-friendly HTML. It reflows on phones and at 200% zoom. Write your answers on the printed packet.

Start (5 minutes) — Notice & Wonder

Ecosystems have huge numbers of plants, far fewer plant-eaters, and only a few top predators such as hawks or wolves. Write one thing you notice and one thing you wonder about why there are so few top predators compared with plants.
Where do you think the energy in a grassland originally comes from, and what happens to most of it as it moves from grass, to grasshoppers, to the animals that eat grasshoppers?

Build (8–12 minutes) — Read the science

Energy enters most ecosystems as sunlight. Producers (plants, algae) capture it through photosynthesis. A trophic level is a feeding step in a food chain. Primary consumers (herbivores) eat producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers. Decomposers (bacteria, fungi) break down dead matter and return nutrients to the soil.

An energy pyramid shows the energy (kcal) available at each trophic level. The ~10% rule: only about 10% of the energy at one level is passed to the next; the other ~90% is lost as heat and to life processes. Matter cycles (reused by decomposers), but energy flows one way — in as sunlight, out as heat — so the pyramid is wide at the bottom and narrow at the top.

Word bank

producer: an organism that makes its own food from sunlight (autotroph); the 1st trophic level.
consumer: an organism that gets energy by eating other organisms (heterotroph).
decomposer: bacteria/fungi that break down dead matter and return nutrients to the soil.
trophic level: a feeding step in a food chain that shows where an organism gets its energy.
energy pyramid: a diagram of the energy (kcal) available at each trophic level.
10% rule: about 10% of the energy at one level is passed to the next; ~90% is lost as heat.

Figure 1 — full text alternative. An energy pyramid for a grassland ecosystem, drawn as four stacked bands from a wide base to a narrow apex. From bottom to top the levels and their energy values are: Level 1, Producers (grass) — 10,000 kcal; Level 2, Primary consumers (grasshoppers) — 1,000 kcal; Level 3, Secondary consumers (shrews) — 100 kcal; Level 4, Tertiary consumers (hawk) — 10 kcal. Each level upward holds about one tenth (~10%) of the level below it, and roughly 90% of the energy is lost as heat at each step. An arrow at the base shows sunlight energy entering the producers. In the printed packet this is a labeled line drawing with real text labels and grayscale-safe patterns (dots, hatching) rather than color.

Using Figure 1, name the trophic level with the most energy available and the one with the least, and explain in one sentence why the pyramid narrows as you go up.

Apply (20–25 minutes) — Use the data

Energy available at each trophic level of a grassland ecosystem (original data):

Table 1. Energy available at each trophic level of a grassland ecosystem, in kilocalories per square meter per year (original data).
Trophic level	Example organism	Energy available (kcal/m²/yr)
1 — Producers	Grass	10,000
2 — Primary consumers	Grasshoppers	1,000
3 — Secondary consumers	Shrews	100
4 — Tertiary consumers	Hawk	10

Classify each organism by trophic level number and role (producer, primary/secondary/ tertiary consumer, or decomposer): a) grass, b) grasshopper, c) hawk, d) soil fungi.
Calculate energy passed with the 10% rule (show work): 5a) about how much energy passes from producers (10,000 kcal) to primary consumers? 5b) from primary consumers to secondary consumers? 5c) do your values match Table 1, and what does that tell you?
Percent transfer: the hawk has 10 kcal and the shrews below have 100 kcal. Calculate the percent of energy transferred (energy passed ÷ energy in lower level × 100).
Observation vs. inference — mark O (read directly) or I (a reasoned conclusion):
- a) The producers have 10,000 kcal available.
- b) There can only be a few hawks because so little energy reaches the top.
- c) The hawk level has 10 kcal available.
- d) Most energy at each level was lost as heat before reaching the next level.
Interpret the pyramid shape: explain what the wide-bottom, narrow-top shape tells you about energy flow, using the terms trophic level and 10% rule.
Predict the effect of removing a trophic level: if a disease kills almost all the grasshoppers, what happens to (a) the grass and (b) the hawks, and why?

Explain (7–10 minutes) — Claim, Evidence, Reasoning

Question 10. Write a claim explaining why top-level consumers such as hawks are limited in number, support it with two pieces of numeric evidence from Table 1 or Figure 1, and explain your reasoning using trophic levels and the 10% rule.

Sentence stems you may use: "Top-level consumers are limited because…"; "One piece of evidence is… (from Table 1 / Figure 1)."; "A second piece of evidence is…"; "This limits top consumers because the 10% rule says…"

Close (5 minutes) — ACE

Articulate: explain the 10% rule in your own words.
Connect: point to one row of Table 1 or one band of Figure 1 that shows the 10% rule; name the numbers.
Extend: give a new (non-grassland) food chain and label at least three trophic levels.

Continue (optional) — Early finisher & block extension

Early finisher: design a four-level energy pyramid for a new ecosystem, labeling each trophic level with a real organism and filling in energy values using the 10% rule.

Block extension (~+30 min): for an ocean chain starting with phytoplankton at 50,000 kcal, apply the 10% rule through phytoplankton → zooplankton → small fish → tuna → shark, then find the percent of the original producer energy that reaches the shark.

Turn in

Hand in the whole packet with your name, class period, and date, with questions 1–10 and the ACE box answered. Include the optional pyramid and block calculation if you did them.

HS_BIO_EnergyFlow_01 — Energy Flow in Ecosystems Accessible landing page