The number of species in a region reflects a balance between extinction and speciation, the process by which new species form.
Missing Word
speciation
Speciation is the formation of new species. When it outpaces extinction the number of species rises, and when extinction outpaces it the number falls.
Category: Extinction Through Time
Question 2
The most recent of the five major mass extinctions, which ended the non-avian dinosaurs, came at the end of the Cretaceous period.
Missing Word
Cretaceous
The Cretaceous period ended about 65 to 66 million years ago with a mass extinction widely attributed to an asteroid impact. It is the youngest of the five major mass extinctions.
Category: Extinction Through Time
Question 3
The earliest of the five major mass extinctions in the fossil record came at the end of the Ordovician period.
Missing Word
Ordovician
The end-Ordovician extinction, more than 440 million years ago, is the oldest of the five major mass extinctions, each of which wiped out more than half of the species alive at the time.
Category: Extinction Through Time
Question 4
The flightless dodo, which went extinct in the late 1600s, lived only on the Indian Ocean island of Mauritius.
Missing Word
Mauritius
Mauritius is the island where the dodo lived. Hunting by sailors and predation by introduced pigs, rats and dogs drove the bird extinct within decades of human arrival.
Category: Extinction Through Time
Question 5
Methane, a greenhouse gas made of one carbon atom bonded to four hydrogen atoms, is released by livestock, landfills and leaking natural gas wells.
Missing Word
Methane
Methane is CH4, the simplest hydrocarbon. Along with carbon dioxide it is a major greenhouse gas that traps heat Earth would otherwise radiate to space.
Category: Major Threats
Question 6
Wild orangutans survive only on the islands of Sumatra and Borneo, where rainforest is being cleared for timber and palm oil plantations.
Missing Word
Borneo
Borneo and Sumatra are the only places where orangutans live in the wild. Forest clearing on both islands is a clear example of habitat loss threatening many species.
Category: Major Threats
Question 7
Polar bears hunt from Arctic sea ice to catch seals, their main source of food, so shrinking ice threatens their survival.
Missing Word
seals
Seals are the main prey of polar bears, which catch them from the sea ice. As warming reduces the ice, polar bears lose access to their food supply.
Category: Major Threats
Question 8
Wangari Maathai founded the Green Belt Movement, which planted tens of millions of trees across her home country of Kenya, and she later won the Nobel Peace Prize.
Missing Word
Kenya
Kenya is Wangari Maathai's home country, where she started the Green Belt Movement in 1977 to replant trees, reduce soil erosion and restore land degraded by deforestation.
Category: Major Threats
Question 9
Yellowstone, set aside in 1872, was the first national park established in the United States.
Missing Word
Yellowstone
Yellowstone was the first U.S. national park preserved as wilderness. It later became the site of the 1995 wolf reintroduction that restored much of its ecosystem.
Category: Conservation Strategies
Question 10
Strips of protected habitat called corridors connect separate preserves so animals can move and breed between them.
Missing Word
corridors
Corridors are connecting strips of habitat, often along rivers, that link isolated preserves. They let animals move between populations, which helps maintain genetic diversity.
Category: Conservation Strategies
Question 11
Plant communities growing along the banks of rivers and streams are described as riparian.
Missing Word
riparian
Riparian describes the zone along the banks of rivers and streams. Riparian vegetation recovered in Yellowstone after wolves reduced browsing by elk.
Category: Conservation Strategies
Question 12
When salmon swim upstream from the ocean to spawn, they carry marine nutrients far inland, so dam removal in the Pacific Northwest is expected to help these fish recover.
Missing Word
salmon
Salmon are migratory fish that hatch in rivers, grow in the ocean and return upstream to spawn. Their bodies deliver ocean nutrients to inland ecosystems, which is why they are considered keystone species.
Category: Conservation Strategies
Question 13
Potatoes were first domesticated thousands of years ago in the Andes Mountains of South America, where many varieties suited to different elevations and soils still grow.
Missing Word
Andes
The Andes are the mountain range of western South America where potatoes were domesticated. The many local potato varieties there are a reservoir of crop genetic diversity.
Category: Value to Humans
Question 14
The pain reliever aspirin was developed from salicylic compounds found in willow bark.
Missing Word
aspirin
Aspirin is a medicine developed from a natural plant compound found in willow. It is one of many drugs whose origins trace back to plant chemicals.
Category: Value to Humans
Question 15
The scientific study of where species live today and where they lived in the past is called biogeography.
Missing Word
biogeography
Biogeography studies the distribution of species across Earth, both present and past. Its branches include ecological, historical and conservation biogeography.
Category: Types and Patterns