7th grade · Science · Unit 4 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.
Alaska content 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 Alaska
In the Alaska content standards, this is unit 4 of 10 in 7th grade Science, after Food Chains & Energy and before Particles & Mixtures.
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: Alaska Department of Education and Early Development
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
Primary or secondary succession? Sort each situation.
Sort into: 🪨 primary succession · 🌱 secondary succession
- 🌾an abandoned farm field
- 🏖️a new sand dune
- 🪨cooled lava with no soil
- 🧊bare rock exposed by a melting glacier
- 🔥a forest regrowing after a wildfire
- 🌪️woodland growing back after a storm
- 🪵a logged forest left to regrow
- 🌋a new island formed by a volcano
🪨 primary succession: a new sand dune, cooled lava with no soil, bare rock exposed by a melting glacier, a new island formed by a volcano · 🌱 secondary succession: an abandoned farm field, a forest regrowing after a wildfire, woodland growing back after a storm, a logged forest left to regrow
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 2
A wildfire burns a forest. The next spring, fireweed is already growing. Why so soon?
- Succession cannot happen after a fire
- Fireweed seeds fall from clouds
- The fire created new soil from rock
- 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 3
Which are usually the first living things to grow on bare rock?
- deer
- lichens
- tall shrubs
- oak trees
lichens
Hint: Lichens and mosses are pioneer species that can live where there is almost no soil.
Question 4
Why do pioneer species usually come first?
- They are the largest plants
- Animals plant them on purpose
- They can survive harsh conditions with little soil and few nutrients
- They need rich soil
They can survive harsh conditions with little soil and few nutrients
Hint: Tough, small species are able to start where others cannot.
Question 5
How do pioneer species such as lichens help build soil?
- They carry soil in from far away
- They slowly break down rock, and when they die they add organic matter
- They stop other plants from growing
- They turn rock into water
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 6
Plants release water vapor through their leaves. This process is called…
- condensation
- runoff
- transpiration
- precipitation
transpiration
Hint: Trans means across or through. Water moves up the plant and out of the leaves.