7th grade · Science · Unit 5 of 14
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.
New York State Learning Standards learning standard: MS-LS2-3; MS-LS2-4 · matter cycling in ecosystems and how ecosystems change after disturbances
How we explain it
Children can open this short lesson before they practice.
- Water, carbon and nitrogen are reused over and over as they cycle between living things, air, water and soil.
- Primary succession starts on bare rock with no soil, with pioneer species such as lichens.
- 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 New York
In the New York State Learning Standards, this is unit 5 of 14 in 7th grade Science, after Food Chains & Energy and before How Plants Work.
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.
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
How do decomposers help cycle matter?
- They remove nutrients from the ecosystem for good
- They turn nutrients into energy
- They make new nutrients from nothing
- They break down dead matter and return nutrients to the soil
They break down dead matter and return nutrients to the soil
Hint: Fungi and bacteria release nutrients so plants can use them again.
Question 2
Primary succession begins with…
- a mature forest
- soil full of seeds
- bare rock or new land with no soil
- a recently burned forest floor
bare rock or new land with no soil
Hint: Primary means first. No soil has formed yet.
Question 3
How do pioneer species such as lichens help build soil?
- They carry soil in from far away
- They turn rock into water
- They stop other plants from growing
- They slowly break down rock, and when they die they add organic matter
They slowly break down rock, and when they die they add organic matter
Hint: Rock bits plus dead plant matter make the first thin soil.
Question 4
Primary or secondary succession? Sort each situation.
Sort into: 🪨 primary succession · 🌱 secondary succession
- 🌋a new island formed by a volcano
- 🧊bare rock exposed by a melting glacier
- 🪨cooled lava with no soil
- 🪵a logged forest left to regrow
- 🌾an abandoned farm field
- 🏖️a new sand dune
- 🔥a forest regrowing after a wildfire
- 🌪️woodland growing back after a storm
🪨 primary succession: a new island formed by a volcano, bare rock exposed by a melting glacier, cooled lava with no soil, a new sand dune · 🌱 secondary succession: a logged forest left to regrow, an abandoned farm field, a forest regrowing after a wildfire, woodland growing back after a storm
Hint: Primary succession starts on bare rock or new land with no soil. Secondary succession starts where soil and seeds are still there, such as after a fire or when a field is left alone.
Question 5
A wildfire burns a forest. The next spring, fireweed is already growing. Why so soon?
- Fireweed seeds fall from clouds
- The fire created new soil from rock
- Succession cannot happen after a fire
- Roots, seeds and soil survived the fire
Roots, seeds and soil survived the fire
Hint: This is secondary succession, which starts with soil and seeds already in place.
Question 6
Why does cycling matter help keep an ecosystem sustainable?
- New nutrients fall from space each day
- Cycling removes all waste from Earth
- Producers create extra matter as they grow
- Nutrients are reused, so the supply does not run out
Nutrients are reused, so the supply does not run out
Hint: Atoms of carbon, nitrogen and water are used again and again.