What is the primary difference between a biome and an ecosystem?

A biome is a large-scale geographic area defined by its climate and dominant vegetation, whereas an ecosystem refers to the specific interactions between biotic and abiotic factors in a localized area. Biomes can contain many different ecosystems within them.

How do Tropical Rainforests and Savannas differ in terms of precipitation patterns?

Tropical Rainforests receive high rainfall consistently throughout the year with no significant dry season. Savannas, while also warm, experience distinct wet and dry seasons, which limits the growth of continuous forest cover.

Compare the limiting factors of NPP in terrestrial vs. aquatic biomes.

In terrestrial biomes, NPP is primarily limited by temperature and moisture availability. In aquatic biomes, especially the open ocean, NPP is limited by light penetration (depth) and the availability of inorganic nutrients like nitrogen and phosphorus.

Why is it a misconception to define deserts only by high temperatures?

Deserts are defined by aridity (low precipitation, typically less than 25 cm per year), not temperature. Cold deserts, such as those in the Antarctic or parts of Central Asia, experience freezing temperatures while maintaining desert-like precipitation levels.

What error is made when confusing Gross Primary Productivity (GPP) with Net Primary Productivity (NPP)?

GPP is the total energy captured by photosynthesis, while NPP is the energy remaining after plants have used some for their own respiration. Confusing them leads to an overestimation of the energy available to the rest of the food web.

Why is it incorrect to assume that high biomass always indicates high current NPP?

Biomass is the 'standing crop' or total accumulated organic matter, while NPP is the 'rate' of new production. An old-growth forest may have massive biomass but relatively low NPP because its respiration rate nearly equals its photosynthetic rate.

Define 'Net Primary Productivity' (NPP) in the context of carbon cycling.

NPP is the net amount of carbon fixed by plants per unit area and time. It represents the actual biomass gain available for consumption by heterotrophs after accounting for plant respiratory losses.

What is an 'Estuary' and why is it ecologically significant?

An estuary is a coastal body of water where freshwater from rivers mixes with saltwater from the ocean. It is significant because it is one of the most productive biomes on Earth, serving as a nutrient-rich nursery for many marine species.

What is 'Permafrost' and which biome is it associated with?

Permafrost is a layer of soil that remains frozen year-round, preventing deep root growth and water drainage. It is a defining characteristic of the Arctic Tundra biome.

How does vertical stratification affect biodiversity in a forest biome?

Vertical stratification creates multiple layers (canopy, understory, forest floor), each with unique light, moisture, and temperature conditions. This variety of microhabitats allows different species to coexist by specializing in specific layers, thereby increasing overall biodiversity.

Key Terms: Biomes | AQA A-Level Geography

Ecosystems Under Stress

Key Terms: Biomes

Summary

Biomes represent the largest scale of biological organization, categorized by distinct climate patterns, vegetation structures, and animal adaptations. Understanding biomes requires analyzing the interplay between abiotic factors like temperature and precipitation and biotic metrics such as Net Primary Productivity (NPP).

1. Definition & Core Concepts

Biomes are large-scale terrestrial or aquatic communities characterized by specific climate conditions and dominant plant types. They serve as a framework for understanding how environmental variables dictate the distribution of life across the planet.
Abiotic factors, including temperature, precipitation, sunlight, and soil nutrients, are the primary determinants of a biome's characteristics. These non-living components create the selective pressures that drive the evolution of specialized biological adaptations.
Biotic factors refer to the living components, such as vegetation structure and animal diversity, that define the community's internal dynamics. In terrestrial biomes, the dominant plant growth forms (e.g., broadleaf trees vs. grasses) are often used as the primary identifier for the biome type.

A conceptual Whittaker diagram showing the distribution of biomes based on the relationship between annual mean temperature and annual precipitation.

2. Terrestrial Biome Classification

Tropical Rainforests are characterized by high constant temperatures and significant rainfall, leading to high biodiversity and complex vertical stratification. The lack of seasonal temperature variation allows for year-round plant growth, though soil nutrients are often depleted due to rapid leaching.
Savannas and Temperate Grasslands are dominated by grasses and are maintained by periodic fires and grazing. Savannas exist in warmer climates with distinct wet and dry seasons, while temperate grasslands experience significant seasonal temperature fluctuations.
Deserts are defined primarily by extremely low precipitation rather than temperature; they can be hot or cold. Vegetation is sparse and highly adapted to water conservation, often featuring deep root systems or succulent tissues.
Boreal Forests (Taiga) and Arctic Tundra represent high-latitude biomes with short growing seasons. The Taiga is dominated by cold-tolerant coniferous trees, whereas the Tundra is characterized by permafrost and low-growing vegetation like mosses and lichens.

3. Aquatic Biome Dynamics

4. Biological Productivity: NPP and Biomass

5. Key Distinctions

6. Exam Strategy & Tips