7.1Chapter 7: The Health of the Environment

Ecosystems of the Earth — Alhussan Biology - Stage 8 Revision Notes & Topical Questions

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7.1 Ecosystems of the Earth — Biomes and Biodiversity — Alhussan International Academy — Biology (Stages 7–9) notes: Describe the main biomes, explain how climate shapes them and define biodiversity.Ecosystem — a community of living organisms together with the non-living parts of…

Abiotic factors
Deciding factors
Tropical rainforests
Temperate regions
Aquatic ecosystems
Desert plants

Part 1 of 6Ecosystems and the biosphere

Ecosystems and the biosphere

Ecosystem

Ecosystem a community of living organisms together with the non-living parts of their environment, such as soil, water and climate.
An ecosystem is an environment that supports life and may be as big as the Sahara or as small as a pond.

Biosphere

Biosphere the Earth itself is the biggest ecosystem, and each part of it is an ecosystem in its own right.

Abiotic factors

Abiotic factors they are non-living, such as soil, temperature and water supply.

Biotic factors

Biotic factors they are living, such as food supply, numbers of predators and prey, and diseases and parasites.

Part 2 of 6Biomes and what decides them

Biome

Biome a very large ecosystem covering a huge area with a characteristic climate and type of vegetation.

Deciding factors

Deciding factors temperature and rainfall decide which biome occurs in a place.
Temperature and rainfall depend on latitude, altitude and distance from the sea.

Part 3 of 6Major land biomes

Biome	Climate	Typical features
Tropical rainforest	Hot and wet all year	Tall evergreen trees, very high biodiversity
Savanna	Warm, distinct wet and dry seasons	Grassland with scattered trees, grazing animals
Desert	Very little rain	Cacti and succulents; animals active at night
Temperate forest	Moderate with four seasons	Deciduous trees that lose leaves in winter
Taiga (coniferous forest)	Long cold winters	Evergreen conifers with needle-like leaves
Tundra	Very cold, frozen soil	Mosses, lichens, low shrubs

Part 4 of 6Rainforest, desert, temperate and aquatic ecosystems

Rainforest, desert, temperate and aquatic ecosystems

Tropical rainforests

Tropical rainforests they grow where there is a lot of rain, sun and warmth all year.
These ideal conditions support many species, so biodiversity is high.

Deserts

Deserts they are very dry areas with little water.
Hot deserts and cold deserts (where water is frozen) are both tough for living organisms.

Temperate regions

Temperate regions temperature and light change a lot through the year.
Summer has plenty of sunlight, warmth and water.
Winter is cold with short days, so plants struggle to grow even when water is plentiful.
They have many more species than deserts but far fewer than tropical rainforests.

Aquatic ecosystems

Aquatic ecosystems about 71% of the Earth's surface is water, so there are more aquatic than land ecosystems.
Most water is salty (oceans and seas), and a small percentage is fresh water in rivers, streams, lakes and ponds.
Coral reefs are the tropical rainforests of the sea, found only in warm, clean, relatively shallow seas.

Part 5 of 6Adaptation to the biome

Desert plants

Desert plants they store water in thick stems and have spines instead of leaves, which cuts water loss.

Tundra animals

Tundra animals the Arctic fox has thick fur and a rounded body to reduce heat loss.

Rainforest trees

Rainforest trees they grow very tall to compete for light and have leaves with drip tips to shed heavy rain.

Part 6 of 6Biodiversity

Biodiversity

Biodiversity the variety of living organisms in an area, including the number of species and the genetic variation within each species.

Pattern

Pattern it is highest near the equator, where warmth and water allow plants to grow all year and support many food chains.
It is lower near the poles.

Stability

Stability a high-biodiversity ecosystem is generally more stable, because other species can fill the role of a lost species.

Human threats

Human threats deforestation, farming and pollution reduce biodiversity, which is why conservation matters.

Key terms

Term	Meaning
Ecosystem	A community of organisms together with the non-living parts of their environment.
Biome	A very large ecosystem with a characteristic climate and vegetation.
Biosphere	The whole Earth as one ecosystem.
Biodiversity	The variety of living organisms in an area.
Abiotic factor	A non-living part of the environment.
Biotic factor	A living part of the environment.