IB Biology Topic B4.1.8 Adaptations to Life in Hot Deserts and Tropical Rainforest Revision Notes (SL/HL)

IB Biology Topic B4.1.8 Adaptations to Life in Hot Deserts and Tropical Rainforest Revision Notes (SL/HL) | RevisionDojo

Written by official IB examiners

Desert and Rainforest Species Carry Traits Built by Natural Selection

The adaptations below are inherited traits of whole populations, not choices made by individual organisms.
Each one spread because organisms carrying it survived and reproduced more successfully through natural selection.

Hot Desert Species Survive by Conserving Water and Beating Heat

Hot deserts combine extreme daytime heat with very scarce water.
Selection therefore favours traits for water conservation and temperature regulation.

Example

The Saguaro Cactus (Carnegiea gigantea)

Water storage and uptake
- A thick, fleshy stem stores large volumes of water from rare rains.
- A wide, shallow root system captures brief rainfall over a large area.
- A deep taproot reaches water stored below the surface.
Reduced water loss
- A thick waxy cuticle cuts transpiration from the epidermis.
- Leaves are reduced to spines, lowering surface area for water loss and deterring herbivores.
Temperature regulation
- A vertical stem reduces the surface exposed to the fierce midday sun.
- CAM photosynthesis opens the stomata only at night, so far less water is lost while gases are exchanged.
- A pleated stem swells to store water and shrinks in drought without splitting.

Desert Animals Avoid Heat by Timing and Body Shape

Example

The Fennec Fox (Vulpes zerda)

Avoiding heat
- Nocturnal habits keep it in cool underground dens by day and active in the cooler night.
- Very large ears carry a rich blood supply that radiates excess body heat.
Insulation and protection
- Thick fur insulates against daytime heat and the cold desert night.
- A pale coat reflects sunlight rather than absorbing it.
- Hair-covered footpads shield the feet from scorching sand.
Water conservation
- It obtains most of its water from food, so it rarely needs to drink.

A Shared Desert Pattern: Shed Heat, Hoard Water

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Desert and Rainforest Species Carry Traits Built by Natural Selection

The adaptations below are inherited traits of whole populations, not choices made by individual organisms.
Each one spread because organisms carrying it survived and reproduced more successfully through natural selection.

Hot Desert Species Survive by Conserving Water and Beating Heat

Hot deserts combine extreme daytime heat with very scarce water.
Selection therefore favours traits for water conservation and temperature regulation.

Example

The Saguaro Cactus (Carnegiea gigantea)

Water storage and uptake
- A thick, fleshy stem stores large volumes of water from rare rains.
- A wide, shallow root system captures brief rainfall over a large area.
- A deep taproot reaches water stored below the surface.
Reduced water loss
- A thick waxy cuticle cuts transpiration from the epidermis.
- Leaves are reduced to spines, lowering surface area for water loss and deterring herbivores.
Temperature regulation
- A vertical stem reduces the surface exposed to the fierce midday sun.
- CAM photosynthesis opens the stomata only at night, so far less water is lost while gases are exchanged.
- A pleated stem swells to store water and shrinks in drought without splitting.

Desert Animals Avoid Heat by Timing and Body Shape

Example

The Fennec Fox (Vulpes zerda)

Avoiding heat
- Nocturnal habits keep it in cool underground dens by day and active in the cooler night.
- Very large ears carry a rich blood supply that radiates excess body heat.
Insulation and protection
- Thick fur insulates against daytime heat and the cold desert night.
- A pale coat reflects sunlight rather than absorbing it.
- Hair-covered footpads shield the feet from scorching sand.
Water conservation
- It obtains most of its water from food, so it rarely needs to drink.

A Shared Desert Pattern: Shed Heat, Hoard Water

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Tip

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A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic B4.1.8: Adaptations to Life in Hot Deserts and Tropical Rainforest Notes

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

Desert and Rainforest Species Carry Traits Built by Natural Selection

Hot Desert Species Survive by Conserving Water and Beating Heat

The Saguaro Cactus (Carnegiea gigantea)

Desert Animals Avoid Heat by Timing and Body Shape

The Fennec Fox (Vulpes zerda)

A Shared Desert Pattern: Shed Heat, Hoard Water

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Desert and Rainforest Species Carry Traits Built by Natural Selection

Hot Desert Species Survive by Conserving Water and Beating Heat

The Saguaro Cactus (Carnegiea gigantea)

Desert Animals Avoid Heat by Timing and Body Shape

The Fennec Fox (Vulpes zerda)

A Shared Desert Pattern: Shed Heat, Hoard Water

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account