Ecosystems: Interactions, Energy, and Dynamics — 7th Grade Science practice questions

Renewable resources INCLUDE:

1. Solar, wind, hydro, geothermal
2. Coal and oil
3. Natural gas
4. Uranium for fission

Answer: A — Solar, wind, hydro, geothermal

A) Replenished on human timescales. B/C/D) non-renewable on human timescales.

A food web differs from a food chain because:

1. A food web has fewer organisms
2. A food web shows multiple interconnected feeding relationships across many chains
3. Food webs apply only to plants
4. Food chains only describe oceans

Answer: B — A food web shows multiple interconnected feeding relationships across many chains

B) Webs interlink chains. A) Webs typically include more. C/D) Both apply universally.

An organism that makes its own food through photosynthesis is called a:

1. Consumer
2. Decomposer
3. Heterotroph
4. Producer (autotroph)

Answer: D — Producer (autotroph)

Producers (autotrophs) create their own food using sunlight. (A/C) consumers/heterotrophs eat other organisms; (B) decomposers break down dead matter.

A keystone species is removed from an ecosystem. The MOST likely outcome is:

1. No effect — the ecosystem stays the same
2. The ecosystem becomes more biodiverse
3. All species immediately die
4. The ecosystem may shift dramatically because the species had disproportionate impact relative to its abundance

Answer: D — The ecosystem may shift dramatically because the species had disproportionate impact relative to its abundance

D) Keystone removal cascades through food webs (e.g., sea otters → urchins → kelp). A/B/C) extremes.

A keystone species:

1. Has no impact on its ecosystem
2. Is always the smallest organism
3. Is always a plant
4. Has a disproportionately large effect on its ecosystem relative to its abundance

Answer: D — Has a disproportionately large effect on its ecosystem relative to its abundance

D) Definition of keystone species. A) Opposite. B/C) Overgeneralizations.

The process by which plants open and close tiny pores to control gas exchange is governed by:

1. Mitochondria
2. Stomata and guard cells
3. Root hairs
4. The cell wall

Answer: B — Stomata and guard cells

Stomata (pores on leaves) controlled by guard cells regulate CO₂ intake for photosynthesis and water loss (transpiration). (A) mitochondria produce ATP; (C) root hairs absorb water; (D) cell wall provides rigid structure.

What is the role of DECOMPOSERS in an ecosystem?

1. They produce food through photosynthesis
2. They break down dead organisms and recycle nutrients back into the soil
3. They are top predators
4. They only live in water ecosystems

Answer: B — They break down dead organisms and recycle nutrients back into the soil

Decomposers (bacteria, fungi) break down dead organisms, returning essential nutrients to the environment for producers to use. (A) producers photosynthesize; (C) decomposers are not predators; (D) they exist in all ecosystems.

Decomposers (fungi, bacteria) cycle MATTER through ecosystems. Which statement is MOST accurate about matter vs energy?

1. Matter and energy both cycle indefinitely
2. Neither matter nor energy is conserved
3. Energy cycles; matter flows one way
4. Matter cycles; energy flows one way and is lost as heat at each transfer

Answer: D — Matter cycles; energy flows one way and is lost as heat at each transfer

D) Foundational ecology principle. A) confuses matter with energy; C) reverses; B) violates conservation.

Cold fronts typically produce:

1. Slow, steady rain over many days
2. Brief but intense storms as cold air pushes warm air upward sharply
3. No precipitation
4. Snow only in summer

Answer: B — Brief but intense storms as cold air pushes warm air upward sharply

B) Steep slope of cold front lifts warm air rapidly → thunderstorms. A) warm fronts; C/D) wrong.

In the NITROGEN cycle, nitrogen-fixing bacteria do what?

1. Burn nitrogen
2. Have no role
3. Destroy nitrogen
4. Convert atmospheric N₂ into forms (like ammonia) that plants can use

Answer: D — Convert atmospheric N₂ into forms (like ammonia) that plants can use

D) Plants can't use N₂ directly; bacteria fix it into NH₃/NO₃⁻. A/B/C) wrong.

What is a 'food web'?

Multiple connected food chains showing all feeding relationships in an ecosystem.

What's a 'predator'?

An animal that hunts other animals.

What does it mean for ecosystems to be 'in balance'?

Populations of producers, consumers, and decomposers stay relatively stable over time.

What is 'parasitism'?

One species benefits, the other is harmed. Example: tapeworms inside an animal.