Biomes & Aquatic Systems — Practice · Grade 12 Science

Chapter: Ecology, Populations & Biodiversity

What this practice covers

By the end of Biomes & Aquatic Systems you should be able to:

9 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: biome, climate, estuary, photic zone, wetland, salinity.

Problem 1

The two climate factors that most determine which terrestrial biome forms in a region are
  1. altitude and soil color
  2. temperature and precipitation
  3. wind speed and day length
  4. latitude and longitude
Answer and explanation

temperature and precipitation

Average temperature and annual precipitation are the master controls that define terrestrial biomes.

Problem 2

A biome with very cold temperatures, a short growing season, and a layer of permanently frozen soil (permafrost) is the
  1. tropical rainforest
  2. hot desert
  3. tundra
  4. temperate grassland
Answer and explanation

tundra

Permafrost and a short, cold growing season are defining features of the tundra.

Problem 3

A tropical rainforest has an NPP of about 2,000 g/m²/yr; a hot desert about 80 g/m²/yr. About how many times greater is the rainforest's productivity?
Answer and explanation

25 times

2,000 ÷ 80 = 25 times greater, driven mainly by abundant water and warmth.

Problem 4

Estuaries, where rivers meet the sea, are among the most productive ecosystems on Earth mainly because
  1. they are extremely deep and dark
  2. they have very high salinity that excludes most life
  3. they never exchange water with the open ocean
  4. they receive abundant nutrients from the river and plenty of sunlight in shallow water
Answer and explanation

they receive abundant nutrients from the river and plenty of sunlight in shallow water

River-borne nutrients plus sunlit shallow water fuel very high productivity, making estuaries rich nurseries.

Problem 5

Explain how a warming climate could shift the location of a biome, and why some species may struggle to keep up.
Answer and explanation

Because biomes are defined by temperature and precipitation, warming shifts those conditions toward the poles and higher elevations, so a biome's suitable zone moves. Species must migrate to track their climate, but many cannot move fast enough, are blocked by cities or mountains, or run out of cooler ground, so their populations decline or the community reorganizes into a new ecosystem.

Problem 6

Why can deep water limit photosynthetic production even when nutrients are available? Show the reasoning, not just the conclusion.
Hints

Use multiple variables at relevant spatial scales.

Answer and explanation

Light availability declines with depth; energy input can become limiting.

Problem 7

How can seasonal rainfall matter despite equal annual totals?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Long dry intervals and timing relative to growth affect water availability and survival.

Problem 8

Link a trait to a constraint without inventing a purposeLink a trait to a constraint without inventing a purposeEnvironmentalconditionWater limitationTrait / processReduced leaf area /water lossPerformancetradeoffPossible growth costAn adaptation explanation needs a mechanism and context.A useful trait is not evidence of conscious evolutionary intent.
Original trait–constraint example; no claim that every dryland plant uses the same strategy.
Interpret the supplied visual. Why might a water-saving trait be less favorable in a shaded, wet setting?
Answer and explanation

Its reduced light capture or other costs can outweigh water savings under different constraints.

An adaptation is a heritable feature shaped by evolutionary processes that can improve performance in a relevant environment. Reduced leaf area can reduce water loss but also limit light capture; traits have tradeoffs and depend on context. Acclimation within an individual’s life is different from inherited evolutionary change across generations. Explain how a trait affects exchange, survival or reproduction and what comparison could test that mechanism, rather than saying organisms simply decided what they needed.

Its reduced light capture or other costs can outweigh water savings under different constraints.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 9

A well-mixed 1000 L tank gains 600 mg oxygen/day and loses 900 mg/day with no water-volume change. Find mass and concentration changes per day; state a model limit.
Answer and explanation

Mass change=−300 mg/day; concentration change=−0.30 mg/L/day. The result assumes the stated constant volume, uniform mixing and continuing fluxes; real fluxes can respond to changing conditions.

Mass change=−300 mg/day; concentration change=−0.30 mg/L/day.

The result assumes the stated constant volume, uniform mixing and continuing fluxes; real fluxes can respond to changing conditions.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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