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First exams 2025

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Biomes (HL IB Biology)

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Naomi H

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Naomi H

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Biomes

Biomes

  • The term biome can be defined as follows:

A large community of plants and animals that has developed as a result of environmental factors

  • Abiotic environmental factors, such as rainfall and temperature patterns determine which biome develops in a particular location
  • Regions of the world that experience similar abiotic factors will contain the same biome, e.g. desert occurs in parts of Africa, North and South America, and Australia

Biomes map

Map showing the location of different biomes

Regions of the world that experience similar abiotic factors will contain the same biome

  • Biomes contain many ecosystems
  • The ecosystems found in equivalent biomes in different parts of the world contain similar communities, even if the species are not exactly the same
    • E.g. the ecosystems in the deserts of South America will contain similar communities to those in the deserts of Africa
  • These similarities exist due to shared abiotic factors and resultant convergent evolution
    • Species face similar selection pressures, so similar features provide a survival advantage
    • These advantageous features become more common in the population due to natural selection
  • This means that these communities are similar not because they have all evolved from a recent common ancestor, but because they have independently adapted to have similar features
    • Species that are adapted to survive in the deserts of South America will not be close genetic relatives of those found in the deserts of Africa, though they may have similar morphology
cactus-photograph

CC BY-SA 3.0, via Wikimedia Commons

euphorbia-photograph

CC BY-SA 3.0, via Wikimedia Commons

The cacti of the South American deserts (left) and the euphorbias of the African deserts (right) share spines and succulent stems as adaptations to their desert biome environments, but the two plant groups are not closely related

Climate conditions of major biomes table

Biome Climate conditions Community features
Tropical forest

Annual rainfall 2000 - 10 000 mm

Temperatures consistently between 20 - 25 °C

Nutrient poor soil due to lack of seasonal leaf fall

Layers of vegetation, e.g. canopy and undercanopy

Highly productive, i.e. high levels of photosynthesis

Very high levels of biodiversity
Temperate forest

Annual rainfall 750 - 1500 mm

Seasonal, but no extremes temperatures

Fertile soil due to leaf fall each autumn

Dominant deciduous trees

Productive during part of the year

High levels of biodiversity
Taiga (conifer forest)

Annual rainfall 300 - 900 mm but high snow fall

Very short summer growing period

Temperatures between -40 - 20 °C

Dominant coniferous (evergreen) trees

Low productivity

A small number of well-adapted species
Grassland

Annual rainfall 500-950 mm

Dry and wet seasons

Temperatures between -20 - 30 °C (differs depending on region)

Dominant grasses

Not enough water for significant tree growth; low productivity

Grazing animals and a small number of top predators
Tundra

Annual rainfall 150-250 mm

Dark winter periods and frozen soil

Temperatures between -50 - 18 °C

Not enough water, light, or warmth for tree growth; low productivity

Hibernating or migrating animal species
Hot desert

Annual rainfall less than 250 mm

Hot days (up to 49 °C) and cold nights (down to 0 °C)

Productivity very low due to lack of water

A small number of well-adapted species
tropical-rainforest-photo

 CC BY-SA 4.0, via Wikimedia Commons

temperate-forest-photo

CC BY 2.0, via Wikimedia Commons

taiga-boreal-forest-photo

Public domain, via Pix4free

savanna-photo

CC BY-SA 3.0, via Wikimedia Commons

tundra-photo

CC BY-SA 2.5, via Wikimedia Commons

K49oJZCL_desrt-habitat-sahara-photograph

CC BY-SA 2.5, via Wikimedia Commons

Tropical forest (top left), temperate forest (top right), taiga (middle left), grassland (middle right), tundra (bottom left) and hot desert (bottom right) are all examples of biomes

Adaptations to biomes

Adaptations

  • Adaptations are traits, or characteristics, that increase survival chances in a specific environment
  • Adaptations come about by the process of natural selection
  • Species are adapted to the abiotic and biotic features of the biome in which they live, e.g.
    • Species living in hot desert biomes have adaptations to hot, dry conditions
    • Species living in tropic rainforests are adapted to deal with competition and predation

Hot desert adaptations

Saguaro cactus

  • The saguaro cactus (Carnegia gigantea) is native to the hot deserts of North America, and is adapted for survival in dry conditions
    • Its stem has a thick waxy cuticle to reduce water loss by evaporation
    • It has spines instead of leaves; this reduces the surface area from which water can be lost by adaptation, and reduces grazing
    • Cells in the stem can expand to take on and store water
    • A deep tap root enables access to water deep under the ground, and shallow surface roots allow fast absorption of any water from rainfall
cactus-photograph

CC BY-SA 3.0, via Wikimedia Commons

Kangaroo rat

  • Kangaroo rats (Dipodomys sp.) are small rodents found in the hot deserts of North America
  • They spend daylight hours in underground burrows, a behavioural adaptation that allows them to avoid the high daytime temperatures
  • Kangaroo rats are able to extract enough water to survive from their diet, and can produce highly concentrated urine, so can go without drinking water for extended periods
kangaroo-rat-photo

CC BY-SA 2.0, via Wikimedia Commons

Tropical rainforest adaptations

Kapok tree

  • Kapok trees (Ceiba pentandra) form parts of the upper canopy in the tropical rainforests of Central and South America
  • Rapid growth allows Kapok trees to outcompete other species by growing tall very quickly; this height allows them to absorb enough sunlight in a densely forested habitat
  • Wide buttress roots provide a sturdy base to support the trees during their rapid growth
kapok-tree-photo

CC BY-SA 4.0, via Wikimedia Commons

Kapok trees have wide buttress roots to provide stability

Orchid mantis

  • The orchid mantis (Hymenopus coronatus) is an insect found in the tropical rainforests of southeast Asia
  • The adult female mantis looks very similar to an orchid flower, enabling it to attract insect pollinators which then become its prey; this is an example of mimicry
    • Scientists believe that orchid mantis are 'aggressive mimics', meaning that they are more attractive to insects than the surrounding orchid flowers
  • The male orchid mantis is much smaller and plainer in appearance, allowing it to camouflage in amongst the stems and branches of plants
orchid-mantis-photo

CC BY-SA 3.0, via Wikimedia Commons

The orchid mantis is camouflaged on the surface of the orchid

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Naomi H

Author: Naomi H

Expertise: Biology

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.