Chapter 20 · Unit 7: Resources in Ecosystems · Segment 3

Resources in Living Systems

What do living things need from their surroundings, and what happens to organisms and populations when a needed resource runs short?

MS-LS2-1 · assessesMS-LS2-2 · practiceMS-LS2-4 · practiceMS-LS1-5 · supportsMS-ETS1-2 · practice Textbook pp. 262–271 1 presentation · 10 worksheets · 3 labs
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Overview

Students figure out that every living thing draws what it needs from its surroundings, that some of those needs are other living things (food) and some are nonliving (water, light, oxygen, nutrients, space), and that whichever needed resource runs short first puts a ceiling on how large a population can grow. They watch a carrying capacity appear in a bead-and-card deer simulation, grow real duckweed under different light and nutrient supplies, and work through case-study data to tell a pattern from a cause and to decide what a wildlife manager should do before the next drought. Along the way they learn why poison dart frogs raised in captivity are harmless: the poison is built from chemicals in their wild diet. The chapter prepares students for the predator, parasite and partner interactions of Lesson 21 and the changing ecosystems of Lesson 22.

Estimated class time: presentation about 134 minutes · worksheets about 395 minutes in total · labs 5 sessions. Seven 50-minute core periods for the presentation and the three labs, spread over about three weeks because the duckweed investigation (Lab 2) needs two weeks of growth. Set up Lab 2 in period 2 so that its final count lands in period 7. The ten worksheets add about 395 minutes (roughly eight more periods), so the sequence places each one, but most must go home, into extra periods or stations, or be chosen from.

Phenomenon

The frog that stops being poisonous

Some small, brilliantly colored frogs of Central and South American rainforests carry enough poison in their skin that hunters once wiped blowgun darts across their backs. Yet frogs of the same species hatched and raised in a zoo or a home terrarium can be handled safely, and wild-caught frogs kept in captivity slowly lose their poison over months and years. The captive frogs look the same, breathe the same air, and live at about the same temperature as wild frogs. Something a wild frog gets from its surroundings, and a captive frog does not, is missing.

Notice and wonder prompts

  • What do wild frogs get from a rainforest floor that a frog in a glass tank cannot get?
  • Why would the poison fade slowly instead of disappearing all at once when a frog is captured?
  • If a captive frog were fed exactly what wild frogs eat, would it become poisonous? How could you test that safely?
  • Resources usually change how many organisms live somewhere. Can a resource also change what an organism is like?

Learning targets

  • I can sort what an organism needs into living and nonliving resources and tell a resource apart from a condition such as temperature.
  • I can explain how competition for a limited resource changes how many individuals survive and reproduce, within one species and between species.
  • I can use data on a resource and a population to find a carrying capacity and predict whether the population will grow or shrink when the resource changes.
  • I can explain why a pattern in data is not by itself proof of cause and effect, and name the mechanism that links a resource to a population.
  • I can describe how water, light, nutrients and temperature shape biomes, and put organisms, populations, communities, ecosystems and the biosphere in order.

What shows the learning happened

  • A completed Lab 1 data table and graph for two meadows and a drought, with a written rule explaining why each herd stopped at exactly the number of patch cards plus the number of lush cards.
  • A duckweed growth graph (Lab 2) with four lines and a paragraph naming the limiting resource in each cup, backed by the growth factors the student calculated.
  • A management recommendation (Lab 3) that cites at least two numbers from the case file, states the mechanism connecting rainfall to deer, and explains why the deer-per-forage index fell after cattle arrived.
  • A Claim-Evidence-Reasoning paragraph (W6) that names the resource limiting three Daphnia jars, cites counts and days from the jars, rules out oxygen, light and temperature, and explains both the leveling off and the decline.
  • A correct sorting of a mixed list into biotic resources, abiotic resources and conditions, with temperature placed as a condition and the reason given.
  • A labeled nesting drawing (W10) that places an organism, a population, a community, an ecosystem and the biosphere in order.

Key vocabulary 12 terms

resourceAny material or energy a living thing must take in from its surroundings to stay alive, grow and reproduce, such as food, water, oxygen, sunlight, soil nutrients or space. A resource can be used up.For the duckweed in the sunny cup of plain water, dissolved nutrients such as nitrogen ran short first.
biotic and abioticBiotic means living or coming from living things; abiotic means nonliving. Grass is a biotic resource for a horse; water, oxygen and sunlight are abiotic resources.The ecologist listed the ants and mites the frog ate as biotic resources and the pool water as an abiotic one.
conditionA feature of the environment, such as temperature, that affects which organisms can live somewhere but is not consumed by them. Conditions are not resources, even though both set limits.Cold is a condition that keeps a wild horse off Arctic ice; the horse does not use up the cold the way it uses up grass.
organismOne individual living thing: one frog, one horse, one grass plant, one bacterium.The survey counted 286 organisms in the herd, each one an individual elk.
speciesA group of similar organisms whose members can mate with one another and produce offspring that can also reproduce. (A few different species can form hybrids, but those are usually infertile.)Mules exist, but a horse and a donkey are still different species because a mule cannot have foals.
populationAll the organisms of one species that live in the same area at the same time and can breed with one another.The duckweed population in cup B can grow from 10 fronds to several dozen in two weeks.
competitionAn interaction in which two or more organisms need the same resource that is in short supply, so what one takes, the other cannot have. It happens within a species and between species.Competition for grass meant that in a dry year neither the yaks nor the horses got enough to raise many young.
limiting resourceThe resource that is in shortest supply compared with how much organisms need, so it sets the limit on growth even when every other resource is plentiful.In the dark cup, light was the limiting resource, so the fertilizer in its water made no difference.
carrying capacityThe largest population of a species that an area's resources can support over time. A real population drifts above and below it, and it rises or falls when the resources change.After the drought dried up half of the lush patches, the bead meadow's carrying capacity dropped from 36 deer to 20.
communityAll the populations of different species that live and interact in one area; the living part of an ecosystem.The meadow community includes the grasses, the horses, the yaks, the insects and the soil bacteria.
ecosystemA community of living things together with the nonliving parts of its surroundings, such as water, soil, air and light, that it depends on.Rainfall is part of the grassland ecosystem because it controls how much grass grows for every grazer.
biomeA very large region of Earth defined by its climate and by the kinds of plants and animals that climate supports, such as a temperate grassland, a boreal forest or a coral reef.Savannas are a tropical grassland biome, while prairies and steppes are temperate grassland biomes.

Standards alignment

California NGSS, Grade 7 Preferred Integrated Course Model. Each entry says whether this chapter's work assesses the performance expectation, gives practice toward it, or supports it as background; the resource lists below repeat this for every worksheet and lab.

MS-LS2-1Assesses: the whole PE: analyzing and interpreting data on resource availability and its effects on individual growth and on population sizeCA Grade 7

Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem.

Lab 2 produces real duckweed counts and frond condition under different light, nutrient and crowding conditions, Lab 3 has students analyze a simulated twelve-year record of rainfall, forage, deer counts and fawn mass, and W5 a simulated record of rain, grass and pronghorn. Each asks students to use the data as evidence for how resource availability affects organisms and populations, which is the PE as written. Lab 1 builds the same analysis with model-generated data from abundant and scarce bead meadows.

MS-LS2-2Practice toward: the competition pattern onlyCA Grade 7

Construct an explanation that predicts patterns of interactions among organisms across multiple ecosystems.

Students see competition within a species (horses for grass), between species (yaks and horses; cattle and deer in Lab 3) and in a cup of duckweed, and they predict the same pattern in a new ecosystem. Predator and mutualist interactions are Lesson 21, so this chapter builds toward the PE rather than assessing it.

MS-LS2-4Practice toward: making warranted inferences from population data when a biological component (a competitor) is addedCA Grade 7

Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.

In Lab 3 students argue from simulated data that adding cattle to a range changed the deer population, and must separate the cattle effect from rainfall, recovery lag, water, predators and counting error. This is practice for the evidence-based argument the PE requires; Lesson 22 assesses it with real ecosystem changes.

MS-LS1-5Supports: environmental factors influencing the growth of individual organismsCA Grade 6

Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms.

Fawn mass in the Lab 3 case file and frond growth in Lab 2 show that resource supply affects how large individuals grow, not only how many there are. In the California integrated sequence this PE belongs to Grade 6, so it appears here as background that students should already have met, not as a target.

Assessment boundary: Assessment does not include genetic mechanisms, gene regulation, or biochemical processes.

MS-ETS1-2Practice toward: evaluating competing management plans against criteria and constraintsCA Grade 6-8

Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

The lesson has no engineering spread; this code comes in through W9, where pairs test four drought options for a fenced elk herd against criteria, constraints and a budget in a check table and defend a plan, and through the Lab 3 plan check, where groups test plans A to E against two criteria and two constraints. The options, criteria and checking steps are supplied in both, so this is practice rather than assessment.

Science and engineering practices

  • Analyzing and Interpreting Data. Students tabulate and graph population counts over rounds (Lab 1), frond counts over days (Lab 2) and twelve years of rainfall, forage and deer records (Lab 3), plus ten years of rain, grass and pronghorn records (W5); they compute growth factors and per-resource indices, and decide what the patterns do and do not show.
  • Developing and Using Models. The bead-and-card meadow is a model whose rules students can read, so they can explain exactly why the population stops growing and then say where the model stops matching real deer.
  • Engaging in Argument from Evidence. Students test five rival explanations and recommend a management plan against criteria and a budget (Lab 3), and write a CER (W6) that cites data, states the mechanism, and rules out a competing explanation.

Disciplinary core ideas

  • LS2.A Interdependent Relationships in Ecosystems. Organisms depend on living and nonliving parts of their environment; those with similar needs compete for limited resources; growth of individuals and of populations is limited by access to resources.
  • LS2.C Ecosystem Dynamics, Functioning, and Resilience. Only as a preview: a change in resource supply (a drought, a new competitor) shifts population size, and populations need time to recover when the resource returns.

Crosscutting concepts

  • Cause and Effect. Students learn that a resource-population graph shows a pattern, and that the cause-and-effect claim needs a mechanism (grass needs rain; deer eat grass) plus a check for other explanations such as a new competitor or a hard winter.
  • Patterns. Rainfall tracks forage, forage tracks deer numbers and fawn mass, and the same competition pattern shows up in a meadow, a cup of duckweed and a bead model.
  • Systems and System Models. Students place organisms inside populations, communities, ecosystems and the biosphere, and treat the meadow model and the duckweed cup as systems with inputs (resources) and outputs (population change).

Presentation 27 slides

Resources in Living Systems: what living things need and what happens when it runs short. Original, editable slides with speaker notes: a phenomenon opener, learning targets, the chapter's concepts with diagrams, vocabulary in context, 3 checks for understanding, 2 discussion prompts, an application task, a misconception check, a synthesis and an exit ticket.

PowerPoint (editable)Slides PDFSpeaker notes PDFSpeaker notes (web)

Worksheets 10 of 10

Ten different tasks, one per instructional blueprint. Each has a student PDF (low ink, US Letter), an editable DOCX, an HTML preview, and a separate teacher answer key with reasoning.

First page of Resource, Condition or Competitor? Sorting the Words of a Pond
Worksheet 2 · Vocabulary in action

Resource, Condition or Competitor? Sorting the Words of a Pond

I can tell resources apart from conditions, sort resources as living or nonliving, and use the terms population, competition, limiting resource, carrying capacity, ecosystem and biosphere correctly in new situations.

30 minindividualBuilds understandingIndependent practiceWriting MS-LS2-1 · supportsMS-LS2-2 · supports
Student PDFStudent DOCXPreview
Teacher only
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First page of Reading an S-Curve: Two Tubs of Duckweed
Worksheet 4 · Diagrams and models

Reading an S-Curve: Two Tubs of Duckweed

I can read a population growth curve, identify the phases of growth and the carrying capacity, connect the shape of the curve to a limiting resource, and draw a predicted curve for a new situation.

35 minindividualBuilds understandingVisual modelingIndependent practice MS-LS2-1 · practice
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First page of Rain, Grass and Pronghorn: Ten Years on the Sage Flats
Worksheet 5 · Data and graphing

Rain, Grass and Pronghorn: Ten Years on the Sage Flats

I can graph and calculate from a dataset to show how a resource (grass) depends on rainfall and how a population (pronghorn) depends on that resource, and I can say what the data can and cannot prove.

45 minindividualPracticeData analysisIndependent practice MS-LS2-1 · assesses
Student PDFStudent DOCXPreview
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First page of Ridgeback Reserve: Design a Drought Plan for a Fenced Elk Herd
Worksheet 9 · Transfer and design

Ridgeback Reserve: Design a Drought Plan for a Fenced Elk Herd

I can use resource data to find how many elk a fenced reserve can support in wet, average and drought years, identify the limiting resource in each, and design and justify a drought plan that meets criteria and constraints.

50 minpairsExtensionEngineering designData analysisWriting MS-LS2-1 · practiceMS-ETS1-2 · practice
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First page of Resources in Living Systems: Mastery Check
Worksheet 10 · Retrieval and mastery check

Resources in Living Systems: Mastery Check

I can tell resources from conditions, use data to show how a resource's availability affects individual organisms and populations, calculate a carrying capacity, and explain competition, biomes and the levels of organization.

35 minindividualAssessmentIndependent practiceWritingData analysis MS-LS2-1 · assessesMS-LS2-2 · practice
Student PDFStudent DOCXPreview
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Collaborative labs 3 of 3

Three different investigation approaches. Each has a teacher guide (purpose, materials with quantities, estimated cost, prep, safety, procedure, expected observations, debrief, answer key, assessment criteria, accessibility adaptations, low-cost alternative) and a student recording sheet.

First page of the The Bead Meadow: Deal the Grass, Count the Deer recording sheet
Lab 1 · Collaborative systems modeling

The Bead Meadow: Deal the Grass, Count the Deer

If every deer needs a patch of meadow to survive and only lush patches have enough grass to raise a fawn, how large can a herd grow, what sets that limit, and what happens when a drought dries up half of the lush grass?

Groups of 41 session42 min activityEst. 12 to 15 per class of 8 groups (estimate)Pony beads or dried beans of one color (the deer)Beads or beans of a second color (elk, for the optional two-species trial)Ordinary deck of playing cards (red = lush patch, black = thin patch) MS-LS2-1 · practiceMS-LS2-2 · practice
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First page of the Four Cups of Duckweed: Which Resource Runs Out First? recording sheet
Lab 2 · Classroom field investigation

Four Cups of Duckweed: Which Resource Runs Out First?

When a real duckweed population gets light but no added nutrients, nutrients but no light, or everything it needs but a crowded start, how does it change over two weeks, and which resource limits each cup?

Groups of 43 sessions75 min activityEst. 12 to 30 per class without a grow light; add about 15 to 25 for a clip-on LED grow light (estimates)Clear plastic cups, 9 oz (about 270 mL), all of the same brandCommon duckweed (Lemna minor), healthy green frondsAged tap water (left in an open jug for one to two days) or bottled spring water MS-LS2-1 · assessesMS-LS1-5 · supports
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First page of the The Cedar Hollow Case File: Deer, Cattle and the Next Dry Year recording sheet
Lab 3 · Data-driven decision

The Cedar Hollow Case File: Deer, Cattle and the Next Dry Year

Twelve years of monitoring records show rain, forage, cattle and deer in one valley. What limits the deer herd, did adding cattle change it, and what should the county do before a dry year that forecasters expect next spring?

Groups of 41 session46 min activityEst. 2 to 4 per class (estimate)Printed case file and recording sheetCalculatorRuler and two colored pencils (one for the years before cattle, one for after) MS-LS2-1 · assessesMS-LS2-4 · practiceMS-LS1-5 · supportsMS-ETS1-2 · practice
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Teacher guidance

Suggested sequence (7 steps)
  1. Period 1: Presentation slides 1-7 (frog phenomenon, targets, what counts as a resource, resources versus conditions, the grass-versus-horse comparison, first check). W1 phenomenon worksheet opens the period; W2 vocabulary relationships closes it or goes home.
  2. Period 2: Lab 2 session 1: set up the four duckweed cups and record day-0 counts and predictions (35 minutes). Then slides 8-11 (limited resources, competition within a species, the carrying-capacity graph, the second vocab set and check).
  3. Period 3: Lab 1, the bead-and-card meadow (one full session). Students run the abundant meadow, the scarce meadow and the drought rounds, then derive the carrying-capacity rule. Assign W5 (rain, grass and pronghorn on the Sage Flats) as follow-up data practice.
  4. Period 4: Slides 12-18 (competition between species, the two-grazer discussion, the rain-grass-grazer flow, pattern versus cause, the data task, the tule elk connection). Ten-minute day-7 duckweed count (Lab 2 session 2) at the start. W3 reading passage for homework; W4 diagram worksheet (reading and extending a duckweed S-curve) in an extra period or as homework.
  5. Period 5: Lab 3, the Cedar Hollow case file (one full session). Groups graph, compute the deer-per-forage index, run the skeptic's round and choose a plan. W6 CER (what limits the water fleas) practices the same claim-evidence-reasoning moves on a new dataset (homework or an extra period).
  6. Period 6: Slides 19-24 (biomes, the lake-light layers, the biome discussion, levels of organization, humans in the biosphere, back to the frogs). W7 misconception repair (Sam's packet: the frog, the Hollis Pond forecast and the pattern-versus-cause error from slides 15-16) as homework; W8, the twelve-card evidence jigsaw, needs a full period of its own.
  7. Period 7: Lab 2 session 3: final duckweed count, graphs and analysis (30 minutes). Slides 25-27 (misconception, synthesis, exit ticket). W9 transfer task and W10 mastery quiz close the chapter in one or two further periods.

Materials overview: No chemicals beyond diluted liquid houseplant fertilizer, which the teacher dilutes. Lab 1 needs about 70 beads or dried beans (plus 15 of a second color for the two-species trial) and one deck of playing cards per group. Lab 2 needs four clear cups per group, common duckweed (an aquarium shop or online supplier; about 70 fronds per group), aged tap water, the diluted fertilizer, a box for the dark cup and a bright window or a grow light. Lab 3 needs only the printed case file, graph paper and calculators. The frog phenomenon is described, not demonstrated; no live animals are used.

Common misconceptions (5)
“A population keeps growing as long as nothing eats it.”
Why it happens: Students picture predators as the only thing that kills, and they rarely see a population run out of food, water or space in everyday life.
Correction: Every population needs resources, and every area holds only so much of each. When the limiting resource runs short, fewer individuals survive and reproduce, so growth stops near a carrying capacity even with no predators at all. The bead meadow has no predators and still levels off.
“Temperature and rainfall are resources, just like food.”
Why it happens: The textbook itself calls a biome's temperature range and rainfall amount 'limited resources', and both clearly limit where organisms live.
Correction: Rainfall delivers water, which is a resource because organisms take it in and use it up. Temperature is a condition: it affects organisms, but no organism consumes it or competes for it. Keeping the two apart matters because competition only happens over resources.
“If two things rise together on a graph, one must cause the other.”
Why it happens: The pattern looks convincing, and the textbook presents rainfall-grass and rainfall-zebra scatter graphs as cause-and-effect relationships.
Correction: A pattern is evidence, but a cause-and-effect claim also needs a mechanism (grass needs water to grow; zebras eat grass) and a check that nothing else changed at the same time. Predictions should also stay inside the range of rainfall that was actually measured.
“Competition means animals fighting, and the strongest animal wins.”
Why it happens: The everyday word means a contest, and nature programs show rams butting heads.
Correction: Most competition is quiet: a yak that eats a mouthful of grass has removed it from every horse. Plants compete for light, water and nutrients without moving. The 'winner' is whichever individual gets enough of the resource to survive and leave offspring, which may be the plant with the deepest roots, not the biggest animal.
“Animals make their poisons, colors and other traits from nothing; captivity makes frogs 'tame' so they stop being poisonous.”
Why it happens: Students think of traits as fixed by the kind of animal and do not connect a trait to what the animal eats.
Correction: Poison dart frogs cannot make their skin alkaloids themselves. They collect them from alkaloid-carrying prey such as certain ants, mites, beetles and millipedes and store them in skin glands. Captive frogs fed fruit flies and crickets never take in those chemicals, so they never become poisonous, and wild-caught frogs slowly run down the supply they stored.
Differentiation suggestions (5)
  • Multilingual learners: Pre-teach resource, competition, population and limit with a picture card set that shows a horse, grass, water and a thermometer; sort the thermometer separately and say why. Let students label the levels-of-organization diagram in their home language first. Pair the Lab 1 recorder role with a partner who calls out each count aloud.
  • Students who need more support: Give the Lab 1 table with round 1 completed and the check 'deer at end = deer at start + fawns (red cards) − starved (deer with no card)' printed at the top. In Lab 3, give the forage-per-rainfall column already computed and highlight the dry years. Offer a sentence frame for the CER: 'When ___ was scarce, ___ fell from ___ to ___, because ___.'
  • Students ready for extension: Ask them to change one rule in the Lab 1 model (two fawns per lush card, or a second grazer species) and predict the new carrying capacity before running it. In Lab 2, have them design a fifth cup that tests space alone (same nutrients, half the surface area). Challenge them to find out which arthropods supply dart-frog alkaloids and how researchers tested it.
  • Students who need movement or alternative output: Run the first two rounds of Lab 1 as a whole-class floor game with students as deer and card stations as patches of meadow, then switch to beads. Accept a recorded spoken recommendation for Lab 3 and a labeled photo series instead of a drawing for Lab 2.
  • Students with low vision or limited fine-motor control: Use large wooden beads or dried lima beans and jumbo playing cards in Lab 1. In Lab 2 let a partner count fronds with a toothpick while the student records and interprets; a phone photo of the cup can be enlarged on a screen for counting.
Accuracy notes: where the textbook simplifies (13)
  • Resources versus conditions: the Introduction (p. 263) and Section 4 (pp. 268-269) call temperature and rainfall 'limited resources'. Rainfall supplies water, a true resource. Temperature is a condition: it limits where organisms live but is not consumed. The chapter teaches the distinction explicitly and never asks a student to classify temperature as a resource.
  • Carrying capacity and limiting resource are not named in the lesson, but the brief and the performance expectation call for them. They are taught here as the ceiling an area's resources put on a population and the resource that runs short first. Say that real populations fluctuate around the carrying capacity rather than sitting on it, and that it changes when resources change.
  • The graph page (p. 267) labels grass in kilograms per hectare. That measures the mass of grass per area (biomass), not a count of plants. The chapter calls it 'grass grown (kg per hectare)' and uses deer counts, not biomass, for the animal side.
  • The two scatter graphs on p. 267 show correlations and cover different rainfall ranges, so they cannot be chained numerically. The chapter treats them as patterns that need a mechanism before they become cause-and-effect claims, and warns against predicting outside the measured range. All quantitative tasks use clearly labeled simulated data.
  • Yak and horse feeding (p. 266): the claim that yaks pull grass out by the roots while horses clip only the tops is not supported by the feeding descriptions we found; cattle-like grazers wrap grass with the tongue and horses, with incisors in both jaws, can crop grass very short. The chapter keeps the big idea (species that use a shared resource in different ways compete less) and describes the difference as tongue-wrapping of taller grass versus close cropping, with the premise stated.
  • Grasslands and latitude: the Figure 4 caption (p. 268) places grasslands at middle latitudes but lists savannas, which are tropical. Teach that prairies, steppes and pampas are temperate (middle-latitude) grasslands and savannas are warm tropical grasslands with a long dry season.
  • Species definition: the book says only members of one species can reproduce together. Some different species can produce hybrids (horse and donkey make a mule), but the hybrids are usually infertile. The chapter's definition adds 'offspring that can also reproduce'. Dandelions, the book's example, mostly set seed without fertilization, so avoid using them to illustrate mating.
  • Levels of organization: Section 5 (p. 270) uses organism, population, ecosystem and biosphere. Most biology references put a community level (all the interacting populations) between population and ecosystem. The chapter includes it and tells students the book skips it.
  • Boreal forests (p. 269): the book says the trees are evergreen with needles that shed snow. Say 'mostly evergreen conifers' (larches drop their needles and dominate much of Siberia's boreal forest) and do not teach snow-shedding as the single reason for needle leaves.
  • 'Wild horses' in Mongolia: the opener photos show herded, free-ranging horses with riders. Mongolia's true wild horse, Przewalski's horse, disappeared from the wild in the 1960s and survives today at reintroduction sites. The chapter uses horses only as model grazers and makes no claim about wild-horse numbers.
  • Poison dart frogs (the curriculum's phenomenon; it does not appear in the lesson text): the frogs sequester alkaloids from arthropod prey, mainly certain ants, mites, beetles and millipedes, and store them in skin glands; a few species chemically modify some of the alkaloids they take in, but none is known to build them from scratch. Frogs born in captivity and fed fruit flies or crickets are not poisonous, and wild-caught frogs lose alkaloids slowly over long periods. Only a few species, such as the golden poison frog, are dangerous to touch; most are mildly toxic. 'Poison' (harmful when eaten or absorbed) is the right word, not 'venom' (injected).
  • Tule elk connection: National Park Service counts of the fenced Tomales Point herd at Point Reyes fell from about 540 to about 280 between 2012 and 2015. The Park Service attributed the decline to too many elk for the poor dry-year forage, reported that the elk had water throughout the drought and found no evidence that they died of thirst; some advocacy groups argued that water was short as well. Teach forage as the documented limit and the water claim as a rival explanation that was tested. In December 2024 the Park Service decided to remove the fence and a lawsuit paused the work, so check the current status before teaching. Do not generalize to all tule elk, whose statewide numbers grew to about 5,700 by 2020.
  • Oxygen for plants: the book lists oxygen as a resource for horses and carbon dioxide for grass. Plants also take in oxygen for cellular respiration (especially roots and at night), so the compare diagram places oxygen in the shared set. This is accurate and connects to Lesson 5.

Review status: reviewed · 2026-10-19 · Re-solved every numeric, multiple-choice, true/false, fill and table item in W1-W10 and Labs 1-3, including the Lab 3 index and planning tables (averages 35.0 and 27.0; 230/196, 201/174 and 172/151 deer; plan E with 50 cattle 216/185 deer at $9,000; feasible plan E keeps about 34 to 71 cattle), the W9 capacities (600, 360, 120; corridor 303; plans at $57,000 and $37,400) and the W3, W4, W5, W6, W7 and W10 arithmetic; all keys agree. Lab 1 re-simulated (100,000 runs): the levels 36, 26 and 20 are exact; Meadow A first reaches 36 in round 4 (89 percent) or 5; Meadow B misses 26 by round 10 in about 1 run in 60, not 1 in 25 (corrected); the two-species deer median is 18. Lab 1 cost floor raised to $12, since eight decks of cards alone are about $10. Tule elk: the Park Service attributes the Tomales Point decline (about 540 to about 280, 2012-2015) to too many elk for poor dry-year forage, reports that water was available and found no evidence of death by thirst; the drafts said it linked the deaths to scarce water. Corrected in the accuracy notes, slide 18 (body, notes, links), W9 (case text, q2 key, teacher notes) and Lab 3 q8 (prompt and key now ask how the water question was settled); the fence is described in the past tense with the December 2024 removal decision and lawsuit flagged; the NPS FAQ page was added to externalReferences. Other science fixes: slide 24 no longer gives bees and rattlesnakes (venomous) as animals that make their own poison, and its bullet now says captive-bred; slides 19-20 no longer say water removes light within a few meters everywhere; exit item 1 asks about a horse because a grass plant has no clean biotic resource; slide 13 says less grass, not fewer grass plants (biomass); W1 frogs soak up water through the skin instead of drinking; W3 puts St. Matthew over 300 km from the mainland and drops an unsupported 'few thousand' carrying-capacity figure; W5 extension uses six pronghorn per cow (about 10 kg of forage a day, in line with Lab 3's six mule deer), so the key is now 24 percent; W8 card 7 uses Connell's 'crushing' and card 9 no longer says Gause's winning species 'kept growing'; W4 duckweed is smaller than a grain of rice. Ambiguity: the slide 9 year-3 count is now 37 instead of 38 so slide 11's 'grew the most' has one answer (years 3 to 4, a gain of 15). Vocabulary trimmed from 13 to 12 by removing biosphere, which L10 defines; the term is still taught on slide 22 and in W2 and W10. The population example sentence no longer states an untested Lab 2 result as fact. Standards: MS-ETS1-2 added to chapter.json and Lab 3 as practice, matching W9 (the drought plan) and the Lab 3 plan check, where the options, criteria and checking steps are supplied, as in L21; W9's note now agrees with its practice role. caGrade checked everywhere (7 for the LS2 codes, 6 for MS-LS1-5 with the Grade 6 note, 6-8 for ETS1). Consistency: the sequence's slides 15-16 (pattern versus cause), W7 (Sam's packet, statements 3 and 5) and W8 (the twelve-card jigsaw) match the files as written, and period 6 now names what W7 covers. Pacing now says the seven periods cover the deck and the labs while the ten worksheets (about 395 minutes) need homework or extra periods. The W6 evidence-of-learning item describes the Daphnia CER. Four slide links corrected (slides 9 and 11 point to W4, slide 12 to W8 cards 7-9, slide 20 to W8 card 4 and W10 q11). Checked and kept: the dart-frog explanation (alkaloids sequestered from ants, mites, beetles and millipedes; captive-bred frogs not toxic; feeding experiments; accuracy note now adds that some species modify alkaloids but none is known to build them), the St. Matthew facts (Klein 1968: 29 released in 1944, about 1,350 in 1957, about 6,000 in 1963, 42 with 41 females in 1966, gone by the 1980s) and the W8 card facts. Originality: no 6-word runs shared with the lesson text. Flagged, not changed: W9 and the Lab 3 decision both choose a plan against criteria and a budget, and W5 and Lab 3 both compute forage per millimeter of rain; they differ in data and purpose but repeat a move. The labs have not been physically tested.

Source references

Verified against the student edition of Bring Science Alive! 7th Grade Integrated (Student Edition). Printed page numbers appear in the book; PDF pages are the physical pages of the 524-page scan (printed + 36). The textbook is not reproduced on this site.

SectionPrinted pagesPDF pagesUsed for
Introduction: grazers on the Mongolian steppe; lesson vocabulary; publisher's standards box262, 263298, 299Lesson question, the idea that nonliving conditions limit where organisms live, the vocabulary list that the chapter redefines.
1. Living Things Need Resources264300Definition of resource, living and nonliving resources, the different resource lists of a horse and a grass plant, organism and species.
2. Competition for Resources Affects Populations265301Competition within a species, population defined, abundant versus sparse grass and population size, the cause-and-effect framing the chapter refines.
3. Competition for Resources Affects Ecosystems266302Competition between species (yaks and horses), reduced competition when species use a resource differently, the ecosystem definition, rainfall to grass to grazers.
Key Science Concept: Limited Resources Affect Populations (graph page)267303The rainfall-grass and rainfall-zebra relationships that the pattern-versus-cause slides and Lab 3 build on with original simulated data.
4. Biomes are Shaped by Limited Resources; terrestrial and aquatic biomes268, 269304, 305Biome definition, grassland types, water and temperature on land, light and nutrients in water, the lake-light layers diagram.
5. Organization of Earth's Biosphere; humans in the biosphere; Lesson Summary270, 271306, 307Levels of organization, the biosphere's extent, human use of resources and its effect on other populations and on ecosystems.

External references used for accuracy checks

  • Biology 2e, 45.3 Environmental Limits to Population Growth (OpenStax, Rice University): Carrying capacity, density-dependent limits and the leveling-off growth curve used in the deck and Lab 1.
  • Biology 2e, 44.2 Biogeography (OpenStax, Rice University): Temperature, water, light and nutrients as the factors that limit where organisms live; light decreasing with water depth.
  • Biology 2e, 44.3 Terrestrial Biomes (OpenStax, Rice University): Savannas as tropical grasslands, temperate grasslands at middle latitudes, boreal forests dominated by conifers.
  • Tule Elk at Point Reyes National Seashore (National Park Service): Tomales Point herd history, the 2015 low count and the statewide tule elk total used in the California connection slide and W9.
  • Tule Elk at Tomales Point FAQ (National Park Service): The 540-to-283 decline of 2013-2015, the Park Service's finding of no evidence that elk died from lack of water, and its forage and overpopulation explanation (slide 18, W9, Lab 3 q8).

Related chapters

Ch. 6: Food Webs and Trophic PyramidsCh. 21: Interactions Among OrganismsCh. 22: Changing EcosystemsCh. 27: Biodiversity
← Previous chapterChapter 19: Earth's Natural Resources Next chapter →Chapter 21: Interactions Among Organisms