6th grade · Science · Unit 9 of 9
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.
Arizona Academic Standards learning standard: 6.L2U1.14; 6.L2U3.11 · matter cycling in ecosystems, and how ecosystems change
How we explain it
Children can open this short lesson before they practice.
- Matter cycles: nutrients like carbon and nitrogen are reused again and again.
- Primary succession starts on bare rock with no soil, like a new volcanic island.
- Secondary succession happens where soil remains, like after a fire. It is faster.
- Burning coal and oil moves carbon from underground into the atmosphere.
Example: A forest regrows after a wildfire. Primary or secondary succession? The fire left soil, roots and seeds behind. Starting with soil is secondary succession. Answer: secondary
Cycles & Succession in Arizona
In the Arizona Academic Standards, this is unit 9 of 9 in 6th grade Science, after Food Chains & Energy.
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: Arizona Department of Education
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
Why does cycling matter help keep an ecosystem sustainable?
- Cycling removes all waste from Earth
- Nutrients are reused, so the supply does not run out
- Producers create extra matter as they grow
- New nutrients fall from space each day
Nutrients are reused, so the supply does not run out
Hint: Atoms of carbon, nitrogen and water are used again and again.
Question 2
Which are usually the first living things to grow on bare rock?
- lichens
- deer
- tall shrubs
- oak trees
lichens
Hint: Lichens and mosses are pioneer species that can live where there is almost no soil.
Question 3
How do pioneer species such as lichens help build soil?
- They stop other plants from growing
- They slowly break down rock, and when they die they add organic matter
- They turn rock into water
- They carry soil in from far away
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
A farmer plants a different crop in a field each year. How can this keep the soil healthy?
- It removes all decomposers
- Different crops use and return different nutrients
- It stops the water cycle
- It adds new matter to Earth
Different crops use and return different nutrients
Hint: Crop rotation helps keep nutrients in balance.
Question 5
Primary or secondary succession? Sort each situation.
Sort into: 🪨 primary succession · 🌱 secondary succession
- 🪵a logged forest left to regrow
- 🪨cooled lava with no soil
- 🌾an abandoned farm field
- 🔥a forest regrowing after a wildfire
- 🧊bare rock exposed by a melting glacier
- 🏖️a new sand dune
- 🌪️woodland growing back after a storm
- 🌋a new island formed by a volcano
🪨 primary succession: cooled lava with no soil, bare rock exposed by a melting glacier, a new sand dune, a new island formed by a volcano · 🌱 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 6
Which would take longer to turn into a forest?
- an abandoned farm field
- a bare rock surface
- a burned forest with soil left behind
a bare rock surface
Hint: Soil has to be built on rock. In the other two, soil is already there.