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100

These are ecosystems that are situated on land and are surrounded by air.

Terrestrial ecosystems

100

These are types of ecosystems that are situated in water environments.

Aquatic ecosystems

100

These are bodies of flowing water and are home to plants and algae, turtles, otters, and salmon.

Rivers

100

It's a type of relationship when organisms benefit each other. For example, bees obtain nectar from flowers and flowers are pollinated by bees. 

Mutualism

100
It is when trees in forests are cut down to make space to grow crops or to build houses.

Deforestation

200

These are flat areas with grass and a few trees. They have hot summers and cold winters and are home to grazing animals like buffaloes, coyotes, and foxes.

Grasslands

200

They are the driest regions in the world. There is little rain and they have very hot days and very cold nights.

Deserts

200

These two are the biggest aquatic ecosystems. They contain salt water in constant motion due to waves and currents.

Oceans and seas

200

It's a type of relationship when it benefits one organism and harms the other. For example, fleas bite dogs and feed on their blood and the dog gets infected skin.

Parasitism

200

When toxic waste by-products from human activities contaminate the environment, it causes air, water, and soil ___________.

Pollution

300
These are typical of humid regions with cool summers. There many types of trees, usually ones that turn red/orange in autumn.

Deciduous forests

300

It is the coldest terrestrial ecosystem. It is so cold that the top layer of soil is almost always frozen.

Tundra

300

It's a type of relationship when organisms compete with each other to survive. It happens when some animals share the same territory and compete with each other for the same food.

Competitive relationships

300

This happens when two or more organisms need the same resources (water, food, light, space, or shelter).

Competition

300

It is the term used for when there are very few organisms of a species left.

Endangered species

400

They have a hot, humid climate with abundant rain all year round. They are the most biodiverse ecosystems on Earth.

Rainforests

400

These are small freshwater cosystems that can be natural or man-made. 

Ponds

400

It's a type of relationship when organisms depend on each other to survive. For example, some animals eat fruits. In turn, they help to disperse the seeds.

Symbiotic relationships
400

It happens when one animal hunts and eats the other animal.

Predation

400

These are aquatic ecosystems like rivers, lakes, and ponds.

Freshwater ecosystems

500

They grow in dry regions with warm summers. Most of the trees are evergreen.

Mediterranean forests

500

These are large bodies of still water. Some plants like reeds grow here.

Lakes

500

It's a type of relationship when only one organism gets the benefit and the other is unaffected. For example, spiders build webs on plants but the webs do not benefit or harm the plant.

Commensalism

500

It is when we, humans, use up more natural resources than are replaced.

Overexploitation

500

These are saltwater ecosystems like oceans and seas.

Saltwater ecosystems