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7th grade · Science · Unit 8 of 10

Cycles & Succession

Matter cycles; land regrows

What your child practices

How water, carbon and nitrogen are cycled through ecosystems, why cycling supports sustainability, and the difference between primary and secondary succession.

Minnesota K-12 Academic Standards benchmark: 7L.4.1.2.1; 7L.4.1.2.2 · how ecosystems change over time, and ways to protect biodiversity

How we explain it

Children can open this short lesson before they practice.

  1. Water, carbon and nitrogen are reused over and over as they cycle between living things, air, water and soil.
  2. Primary succession starts on bare rock with no soil, with pioneer species such as lichens.
  3. Secondary succession happens where soil is left, such as after a fire or on an old field.

Example: A forest grows back after a wildfire. Primary or secondary succession? The fire left the soil behind. Life returns on existing soil. Answer: secondary succession

Cycles & Succession in Minnesota

In the Minnesota K-12 Academic Standards, this is unit 8 of 10 in 7th grade Science, after Food Chains & Energy and before Genes & Heredity.

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: Minnesota Department of Education (MDE)

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

    Burning coal and oil mainly moves carbon from…

    • underground deposits into the atmosphere
    • the Sun into the Earth
    • plants into the soil
    • the atmosphere into the ocean floor

  2. Question 2

    Why do pioneer species usually come first?

    • They can survive harsh conditions with little soil and few nutrients
    • They need rich soil
    • Animals plant them on purpose
    • They are the largest plants

  3. Question 3

    Put the steps of the water cycle in order.

    • ♨️Water evaporates from lakes and oceans
    • 🌧️Rain or snow falls
    • 🌊Water runs off or soaks in and collects in lakes and oceans
    • ☁️Water vapor cools and condenses into clouds

  4. Question 4

    Primary or secondary succession? Sort each situation.

    Sort into: 🪨 primary succession · 🌱 secondary succession

    • 🏖️a new sand dune
    • 🧊bare rock exposed by a melting glacier
    • 🪵a logged forest left to regrow
    • 🌋a new island formed by a volcano
    • 🔥a forest regrowing after a wildfire
    • 🌪️woodland growing back after a storm
    • 🌾an abandoned farm field
    • 🪨cooled lava with no soil

  5. Question 5

    How do decomposers help cycle matter?

    • They make new nutrients from nothing
    • They turn nutrients into energy
    • They break down dead matter and return nutrients to the soil
    • They remove nutrients from the ecosystem for good

  6. Question 6

    A wildfire burns a forest. The next spring, fireweed is already growing. Why so soon?

    • The fire created new soil from rock
    • Fireweed seeds fall from clouds
    • Succession cannot happen after a fire
    • Roots, seeds and soil survived the fire

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