Individuals & Societies · Topic 5.2
Physical Geography
Physical geography studies the natural features of the Earth: its landforms, climates, biomes, and the processes that shape them. Understanding these physical systems helps explain where people live, how they use resources, and how environments are changing.
What You'll Learn
- Describe the characteristics and locations of major world biomes
- Distinguish between weathering and erosion and explain their effects
- Explain plate tectonics and its connection to earthquakes and volcanoes
- Describe the features and processes of a river system (drainage basin)
- Distinguish between weather and climate
- Explain how physical geography affects human settlement and activity
IB Assessment Focus
Criterion A: Recall biome characteristics, tectonic processes, and river features accurately.
Criterion B: Identify patterns in data about climate, landforms, or natural disasters.
Criterion C: Use geographical vocabulary correctly; support explanations with specific examples.
Criterion D: Apply knowledge to real-world issues (e.g., deforestation, climate change impacts on biomes).
I&S · Topic 5.2
World Biomes
A biome is a large geographic area characterised by its climate, characteristic plants, and animals. Biomes are determined primarily by temperature and precipitation.
Major World Biomes
| Biome | Location | Climate | Key Features |
|---|---|---|---|
| Tropical rainforest | Near Equator (Amazon, Congo, SE Asia) | Hot and wet year-round; >2000mm rain/yr | Highest biodiversity; dense canopy; thin, nutrient-poor soil |
| Desert | Subtropical zones (~30°N/S) | Very low rainfall (<250mm/yr); extreme temperature swings | Sparse vegetation; specialist adaptations; mostly bare rock/sand |
| Temperate grassland | Mid-latitudes (Great Plains, Pampas, Steppe) | Seasonal rainfall; hot summers, cold winters | Few trees; rich, deep soils; important for agriculture |
| Tundra | Near poles and high altitudes | Very cold; permafrost; short summer | Low-growing plants (mosses, lichens); few trees; permafrost limits roots |
| Temperate forest | Mid-latitudes (Europe, eastern USA, China) | Moderate rainfall; four distinct seasons | Deciduous trees (lose leaves in autumn); high biodiversity |
| Boreal/Taiga | Northern Canada, Russia, Scandinavia | Long cold winters; short summers; moderate rainfall | Coniferous (evergreen) trees; less biodiversity than temperate forest |
Weather vs Climate
- Weather: The short-term atmospheric conditions at a specific place (temperature, rainfall, wind on a particular day)
- Climate: The long-term average weather patterns in a region (typically averaged over 30 years)
I&S · Topic 5.2
Landforms and Processes
The Earth's surface is constantly being shaped by internal forces (tectonic) and external forces (weathering and erosion).
Weathering vs Erosion
| Process | Definition | Types | Example |
|---|---|---|---|
| Weathering | Breakdown of rock in place (no movement) | Physical (freeze-thaw), Chemical (acid rain dissolving limestone), Biological (plant roots cracking rock) | Rock cracking due to repeated freezing and thawing of water in cracks |
| Erosion | Wearing away AND transport of material | Water erosion, wind erosion, glacial erosion | River carrying sediment downstream |
Critical Difference: Weathering breaks rock down in place; erosion moves and transports material away. Weathering often prepares material for erosion by breaking it into smaller pieces.
Types of Weathering in Detail
- Physical/Mechanical weathering: Breaks rock into smaller pieces without changing its chemical composition. E.g., freeze-thaw action (water expands 9% when it freezes, cracking rock)
- Chemical weathering: Changes the chemical composition of rock. E.g., acid rain dissolves limestone, forming caves and sink holes (carbonation)
- Biological weathering: Living organisms break down rock. E.g., plant roots growing into cracks; lichens releasing acids
I&S · Topic 5.2
Plate Tectonics
Plate tectonics is the theory that the Earth's crust is divided into large moving plates. The movement of these plates causes earthquakes, volcanoes, and the formation of mountain ranges.
Structure of the Earth
| Layer | Composition | State |
|---|---|---|
| Crust | Thin outer layer; continental (thicker, less dense) and oceanic (thinner, more dense) | Solid |
| Mantle | Mostly solid rock; upper mantle is semi-molten (asthenosphere) | Mostly solid, semi-molten upper layer |
| Outer core | Iron and nickel | Liquid |
| Inner core | Iron and nickel | Solid (extreme pressure) |
Types of Plate Boundaries
| Boundary Type | Movement | Landform Created | Example |
|---|---|---|---|
| Convergent | Plates move toward each other | Mountains, trenches, volcanoes | Himalayas (India-Eurasia collision); Andes |
| Divergent | Plates move apart | Rift valleys, mid-ocean ridges, volcanoes | Mid-Atlantic Ridge; East African Rift |
| Transform | Plates slide past each other | Fault lines; earthquakes (no new rock created) | San Andreas Fault (California) |
Why do plates move? Convection currents in the semi-molten asthenosphere (upper mantle) carry plates like a conveyor belt. Hot mantle material rises, spreads, and cools, pulling plates apart at divergent boundaries and forcing them together at convergent boundaries.
I&S · Topic 5.2
Rivers and Drainage
Rivers are among the most powerful agents of erosion and deposition on Earth's surface. They shape landscapes over millions of years.
Key River Vocabulary
| Term | Definition |
|---|---|
| Drainage basin | The area of land drained by a river and all its tributaries |
| Watershed/Divide | The boundary between two drainage basins (high ground) |
| Tributary | A smaller stream or river that flows into a larger one |
| Source | Where the river begins (usually in mountains or hills) |
| Mouth | Where the river ends (usually meets the sea) |
| Confluence | Where two rivers join |
| Meander | A curve in a river formed by erosion on the outside and deposition on the inside of the bend |
| Delta | Triangular deposit of sediment at a river's mouth where it enters the sea |
Long Profile of a River
- Upper course (near source): Steep gradient; fast flow; vertical erosion; V-shaped valleys; waterfalls
- Middle course: Moderate gradient; lateral (sideways) erosion; meanders begin to form
- Lower course (near mouth): Gentle gradient; slow flow; deposition; floodplains; oxbow lakes; deltas
I&S · Topic 5.2
Worked Examples
These examples demonstrate the depth of geographical reasoning expected at Grade 7.
EXAMPLE 1Explain the difference between weathering and erosion. Give one example of each.
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Full Solution
Weathering is the breakdown of rock in place without transport. Example: freeze-thaw action — water enters cracks in rock, freezes and expands, widening the crack until the rock splits.
Erosion involves the wearing away AND transport of broken material. Example: a river carrying sediment — the force of flowing water picks up rock fragments and moves them downstream, cutting a deeper channel.
Erosion involves the wearing away AND transport of broken material. Example: a river carrying sediment — the force of flowing water picks up rock fragments and moves them downstream, cutting a deeper channel.
EXAMPLE 2Why does a tropical rainforest have greater biodiversity than a tundra?
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Full Solution
A tropical rainforest has greater biodiversity because it has more favourable abiotic conditions: high rainfall (often >2000mm/year), consistently warm temperatures, and abundant year-round sunlight. These conditions support rapid plant growth — creating a complex, multi-layered habitat (emergent layer, canopy, understory, forest floor) with abundant food and shelter for thousands of species.
Tundra has extreme cold, permafrost, and a very short growing season. Only organisms adapted to these harsh conditions can survive, limiting biodiversity to mosses, lichens, and a few hardy mammals and birds.
Tundra has extreme cold, permafrost, and a very short growing season. Only organisms adapted to these harsh conditions can survive, limiting biodiversity to mosses, lichens, and a few hardy mammals and birds.
EXAMPLE 3Explain why earthquakes and volcanoes are concentrated near tectonic plate boundaries.
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Full Solution
Earthquakes and volcanoes occur where tectonic plates interact, because this is where the most stress and heat accumulate:
• Convergent boundaries: Oceanic plates are forced under continental plates (subduction), creating intense heat and melting rock that erupts as volcanoes. The pressure and friction also cause earthquakes.
• Divergent boundaries: Plates pull apart, allowing magma from the mantle to rise and create new crust — forming volcanoes (e.g., along mid-ocean ridges).
• Transform boundaries: Plates grinding past each other build up stress that is periodically released as earthquakes (e.g., San Andreas Fault).
• Convergent boundaries: Oceanic plates are forced under continental plates (subduction), creating intense heat and melting rock that erupts as volcanoes. The pressure and friction also cause earthquakes.
• Divergent boundaries: Plates pull apart, allowing magma from the mantle to rise and create new crust — forming volcanoes (e.g., along mid-ocean ridges).
• Transform boundaries: Plates grinding past each other build up stress that is periodically released as earthquakes (e.g., San Andreas Fault).
EXAMPLE 4Describe the characteristics of a desert biome and explain why it has low biodiversity.
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Full Solution
Deserts are characterised by very low rainfall (<250mm per year), extreme temperature variations (very hot days, cold nights), sparse or no vegetation, and sandy or rocky terrain.
Biodiversity is low because most organisms cannot survive with so little water. The few species that do live there (cacti, camels, scorpions) have developed remarkable adaptations: water storage, nocturnal activity, and reduced water loss. The lack of vegetation means little food or shelter is available for most species.
Biodiversity is low because most organisms cannot survive with so little water. The few species that do live there (cacti, camels, scorpions) have developed remarkable adaptations: water storage, nocturnal activity, and reduced water loss. The lack of vegetation means little food or shelter is available for most species.
EXAMPLE 5Explain the difference between weather and climate, using an example.
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Full Solution
Weather is the short-term atmospheric conditions at a specific place and time. For example, "It is 28°C and sunny in London today" describes weather.
Climate is the long-term average of weather patterns in a region, typically measured over 30+ years. For example, "London has a temperate maritime climate with mild, wet winters and warm, sometimes dry summers" describes climate.
A useful distinction: a single cold winter day in a normally hot desert is a weather event; if those cold days become more frequent over decades, it signals a change in climate.
Climate is the long-term average of weather patterns in a region, typically measured over 30+ years. For example, "London has a temperate maritime climate with mild, wet winters and warm, sometimes dry summers" describes climate.
A useful distinction: a single cold winter day in a normally hot desert is a weather event; if those cold days become more frequent over decades, it signals a change in climate.
EXAMPLE 6Explain why meanders form in a river's middle course.
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Full Solution
In the middle course, rivers flow over flatter land at a more moderate speed. Small irregularities in the river channel cause water to flow faster on the outside of any slight curve — this erodes the outer bank (lateral erosion), making the curve wider. On the inside of the curve, water flows slower and deposits sediment, building up a gentle slope. Over time, the contrast between erosion on the outside and deposition on the inside causes the curve to become more exaggerated, forming a meander.
EXAMPLE 7How might deforestation of the Amazon rainforest affect its climate?
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Full Solution
The Amazon rainforest creates its own rainfall through a process called the water cycle: trees release water vapour through transpiration, which condenses to form clouds and rainfall. If large areas are deforested:
1. Less transpiration → less rainfall in the region
2. Exposed soil absorbs more heat → higher temperatures
3. Without tree roots, soil is more easily eroded by rain → increased erosion
4. Less CO&sub2; is absorbed → contributes to global climate change
This can create a feedback loop: less rain means trees struggle to survive, leading to further forest loss.
1. Less transpiration → less rainfall in the region
2. Exposed soil absorbs more heat → higher temperatures
3. Without tree roots, soil is more easily eroded by rain → increased erosion
4. Less CO&sub2; is absorbed → contributes to global climate change
This can create a feedback loop: less rain means trees struggle to survive, leading to further forest loss.
I&S · Topic 5.2
Practice Q&A
Attempt each question before revealing the model answer.
DEFINEWhat is a biome?
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Model Answer
A biome is a large geographic region characterised by its climate, characteristic plants, and animals. Biomes are primarily determined by temperature and precipitation patterns.
COMPARECompare a tundra and a tropical rainforest biome in terms of temperature, rainfall, and biodiversity.
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Model Answer
Tropical rainforest: High temperature (25–30°C year-round), very high rainfall (>2000mm/yr), extremely high biodiversity. Tundra: Very cold (often below −20°C in winter), low precipitation (<250mm/yr, often as snow), very low biodiversity. The contrasting conditions explain the dramatic difference in biodiversity.
DESCRIBEDescribe what happens at a convergent plate boundary.
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Model Answer
At a convergent boundary, two plates move toward each other. If an oceanic plate meets a continental plate, the denser oceanic plate is forced under the continental plate (subduction). This creates deep ocean trenches, volcanic mountain ranges (as melted rock rises through the continental plate), and frequent earthquakes. Example: the subduction of the Nazca Plate under South America created the Andes mountains.
EXPLAINExplain what permafrost is and why it limits the biodiversity of tundra.
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Model Answer
Permafrost is permanently frozen ground (soil and rock that stays below 0°C year-round, even in summer). It limits biodiversity because: (1) most trees cannot grow — their roots cannot penetrate the frozen ground; (2) the thin active layer above permafrost thaws in summer, making the ground waterlogged and unstable; (3) few species can adapt to these harsh conditions, so only mosses, lichens, and low shrubs survive.
IDENTIFYWhat is the difference between a river's source and its mouth?
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Model Answer
The source is where the river begins — usually in hills or mountains where water collects from rainfall or melting snow. The mouth is where the river ends, flowing into the sea, a lake, or another river. Rivers flow from source (high elevation) to mouth (low elevation), following gravity.
APPLYWhy is temperate grassland (prairie/steppe) particularly important for agriculture?
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Model Answer
Temperate grasslands have very rich, deep soils (called chernozem or "black earth") because centuries of decomposed grass has created highly fertile topsoil. The flat terrain is ideal for machinery. The seasonal rainfall (enough to grow crops but not enough for dense forest) suits cereal farming. Regions like the US Great Plains, Ukrainian steppe, and Argentine pampas are among the world's most productive agricultural areas.
DESCRIBEDescribe the process of freeze-thaw weathering.
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Model Answer
Freeze-thaw weathering occurs when water enters cracks in rock. When temperature drops below 0°C, the water freezes and expands by approximately 9%, exerting pressure on the crack walls. When temperatures rise, the ice melts. Repeated cycles of freezing and thawing gradually widen the crack until pieces of rock break off. This is common in mountain environments and high latitudes where temperatures frequently cross the freezing point.
EXPLAINWhy do the driest deserts tend to occur around 30° North and South of the equator?
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Model Answer
At the equator, intense solar heating causes moist air to rise (bringing heavy rainfall to tropical rainforests). As this air rises, it cools and loses its moisture. The dry air then spreads toward the tropics (~30°N and S) where it descends. Descending air warms, increases in pressure, and absorbs moisture from the land below rather than releasing it. This creates the dry, high-pressure conditions that produce the world's great deserts (Sahara, Arabian, Australian, Atacama).
I&S · Review
Flashcard Review
Tap each card to reveal the answer. Try to answer from memory first.
What is a biome?
A large geographic region characterised by its climate, characteristic plants, and animals. Primarily determined by temperature and rainfall.
Tap to reveal
What is the difference between climate and weather?
Weather = short-term atmospheric conditions at a specific time/place. Climate = long-term average weather patterns in a region (30+ years).
Tap to reveal
What is the difference between weathering and erosion?
Weathering = breakdown of rock in place (no movement). Erosion = wearing away AND transport of material from its original location.
Tap to reveal
What is plate tectonics?
The theory that Earth's crust is divided into large, moving tectonic plates. Their movement causes earthquakes, volcanoes, and mountain formation.
Tap to reveal
What is a convergent plate boundary?
Where two tectonic plates move toward each other. Creates mountains, trenches, and volcanoes. Example: Himalayas (India meeting Eurasia).
Tap to reveal
What is a divergent plate boundary?
Where two plates move apart. Creates rift valleys and mid-ocean ridges as new crust forms. Example: Mid-Atlantic Ridge.
Tap to reveal
What is a drainage basin?
The area of land drained by a river and all its tributaries. Water falling within the drainage basin eventually flows to the same river's mouth.
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What is permafrost?
Ground (soil and rock) that remains frozen year-round, found in tundra and subarctic regions. Limits plant root growth and biodiversity.
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Name the biome near the equator with the highest biodiversity.
Tropical rainforest. High year-round temperatures and rainfall (>2000mm/yr) support the greatest diversity of plants and animals on Earth.
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What is a tributary?
A smaller stream or river that flows into a larger one. Multiple tributaries feed into the main river of a drainage basin.
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What is freeze-thaw weathering?
Water enters rock cracks, freezes (expands ~9%), widens the crack, then melts. Repeated cycles eventually break off rock fragments.
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What is a meander?
A curve in a river formed by erosion on the outer bank and deposition on the inner bank, causing the bend to grow more exaggerated over time.
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Why do deserts have low biodiversity?
Very low rainfall (<250mm/yr) and extreme temperatures limit available water and food. Only highly specialised organisms can survive these conditions.
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What is a transform plate boundary?
Where two plates slide horizontally past each other, building stress that is released as earthquakes. No new crust is created or destroyed. Example: San Andreas Fault.
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Where do rivers begin and end?
Rivers begin at their source (usually in hills/mountains) and end at their mouth (where they meet the sea, a lake, or another river).
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I&S · Practice Test
Practice Test — 20 Questions
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