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9th grade · Science · Unit 13 of 14

Populations & Stability

Limiting factors, carrying capacity, succession and how ecosystems recover.

What your child practices

Your child explains how density-dependent and density-independent factors affect population growth and why some ecosystems recover well after a disturbance.

Alabama Course of Study content standard: BIO.6; BIO.8 · interactions among organisms, populations and communities, and factors that limit population growth

How we explain it

Children can open this short lesson before they practice.

  1. Density-dependent factors, like disease and food, matter more in crowded populations.
  2. Density-independent factors, like hurricanes, affect a population whatever its size.
  3. Primary succession begins on bare rock; secondary succession begins where soil remains.

Example: A hurricane destroys part of a forest no matter how many animals live there. Which kind of factor is it? Its effect doesn’t depend on crowding. Answer: density-independent

Populations & Stability in Alabama

In the Alabama Course of Study, this is unit 13 of 14 in 9th grade Science, after Alabama's Biodiversity and before Ecosystem Stability.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Alabama State Department of Education (ALSDE)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Which is a density-dependent limiting factor?

    • Disease spreading in a crowded population
    • A sudden freeze
    • A volcanic eruption
    • A wildfire

  2. Question 2

    A logistic growth curve levels off at…

    • the starting population
    • zero
    • infinity
    • carrying capacity

  3. Question 3

    Why does a disturbance that removes a keystone species change an ecosystem a lot?

    • Keystone species are the biggest
    • Many other species depend on its role
    • Nothing depends on it
    • It adds energy

  4. Question 4

    Overfishing can cause…

    • populations to collapse
    • colder water
    • fish populations to grow
    • more biodiversity

  5. Question 5

    Competition for food gets stronger as a population grows. Competition is a…

    • density-independent factor
    • producer
    • density-dependent factor
    • type of weather

  6. Question 6

    A hurricane destroys part of a coastal forest whatever the number of animals living there. The hurricane is a…

    • density-independent factor
    • decomposer
    • keystone species
    • density-dependent factor

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