7th grade · Science · Unit 9 of 16
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.
Alabama Course of Study content standard: 7.5; 7.7 · the carbon, nitrogen and water cycles, and changes in ecosystems over time
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 Alabama
In the Alabama Course of Study, this is unit 9 of 16 in 7th grade Science, after Food Chains & Energy and before Ecosystems.
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
A wildfire burns a forest. The next spring, fireweed is already growing. Why so soon?
- The fire created new soil from rock
- Succession cannot happen after a fire
- Roots, seeds and soil survived the fire
- Fireweed seeds fall from clouds
Roots, seeds and soil survived the fire
Hint: This is secondary succession, which starts with soil and seeds already in place.
Question 2
Why is secondary succession usually faster than primary succession?
- There is more bare rock
- Fewer plants are needed
- Animals plant all the seeds first
- Soil, roots and seeds are already present
Soil, roots and seeds are already present
Hint: Primary succession must build soil from rock first.
Question 3
Burning coal and oil mainly moves carbon from…
- the Sun into the Earth
- the atmosphere into the ocean floor
- underground deposits into the atmosphere
- plants into the soil
underground deposits into the atmosphere
Hint: Fossil fuels hold carbon from ancient living things. Burning releases it as carbon dioxide.
Question 4
Plants release water vapor through their leaves. This process is called…
- transpiration
- runoff
- condensation
- precipitation
transpiration
Hint: Trans means across or through. Water moves up the plant and out of the leaves.
Question 5
Put the steps of the water cycle in order.
- 🌊Water runs off or soaks in and collects in lakes and oceans
- ♨️Water evaporates from lakes and oceans
- 🌧️Rain or snow falls
- ☁️Water vapor cools and condenses into clouds
Water evaporates from lakes and oceans → Water vapor cools and condenses into clouds → Rain or snow falls → Water runs off or soaks in and collects in lakes and oceans
Hint: Water evaporates, condenses into clouds, falls as precipitation and then collects, ready to evaporate again.
Question 6
Primary or secondary succession? Sort each situation.
Sort into: 🪨 primary succession · 🌱 secondary succession
- 🪨cooled lava with no soil
- 🔥a forest regrowing after a wildfire
- 🌪️woodland growing back after a storm
- 🌋a new island formed by a volcano
- 🪵a logged forest left to regrow
- 🧊bare rock exposed by a melting glacier
- 🏖️a new sand dune
- 🌾an abandoned farm field
🪨 primary succession: cooled lava with no soil, a new island formed by a volcano, bare rock exposed by a melting glacier, a new sand dune · 🌱 secondary succession: a forest regrowing after a wildfire, woodland growing back after a storm, a logged forest left to regrow, an abandoned farm field
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.