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Extinction and Biodiversity — Reading Comprehension

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MS-LS4-1
MS-LS4-4

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This comprehensive middle school science passage explores the concepts of extinction and biodiversity, aligned to NGSS standards MS-LS4-1 and MS-LS4-4. Students will learn what extinction means, the difference between background extinction and mass extinction, and the mechanisms driving these events. The passage emphasizes the importance of biodiversity at genetic, species, and ecosystem levels, explaining how biodiversity supports ecosystem stability, medicine, food supply, and aesthetics. It discusses current human-driven threats leading to a possible sixth mass extinction and highlights conservation efforts to protect species. Key vocabulary is highlighted and defined to support comprehension. The passage is accessible for grades 6-8, includes a simplified version, and is available in Spanish. Interactive activities include a quiz, writing prompts, and graphic organizers to deepen understanding. Audio integration and visual prompts are provided for diverse learning needs.

CONTENT PREVIEW

IUCN Red List 2007 — Percentage of species listed on the IUCN Red List, by group. Vectorization by B. Jankuloski
Wikimedia Commons (Public domain).

Extinction occurs when a species disappears completely from Earth. Throughout history, many species have become extinct, changing the planet’s biodiversity. Biodiversity is the variety of life at all levels, from genes to species to entire ecosystems. Scientists study extinction and biodiversity to understand how life on Earth changes over time and why protecting this diversity is important for all living things.

Mechanisms of Extinction: Background and Mass Events
Earth’s history shows two main types of extinction: background extinction and mass extinction. Background extinction happens at a slow, steady rate as species fail to adapt to environmental changes, competition, or disease. For example, about 0.1-1 species per million go extinct each year under normal conditions. In contrast, mass extinctions are rare events when a large number of species—sometimes over 75%—vanish in a short period. The Permian mass extinction, about 252 million years ago, wiped out around 90% of marine species. The Cretaceous mass extinction, about 66 million years ago, led to the end of the dinosaurs. Scientists use fossil records to identify these events and study their causes, such as volcanic eruptions, asteroid impacts, or rapid climate changes.

Causes and Interactions: Human Impact and Biodiversity Crisis
Today, scientists warn of a possible "sixth mass extinction," mainly driven by human activity. Human actions like habitat destruction, pollution, overhunting, and introducing invasive species are causing species to disappear at rates 100 to 1,000 times faster than normal background extinction. This rapid loss reduces biodiversity, which affects ecosystem stability and the ability of nature to recover from disturbances. For example, the extinction of pollinating insects can disrupt food production for both wildlife and humans. Biodiversity loss also limits sources for new medicines and food, and decreases the natural beauty and inspiration that ecosystems provide.

Conservation and the Importance of Biodiversity
Conservation efforts aim to protect biodiversity and prevent further extinctions. Scientists and conservationists create protected areas, restore damaged habitats, and work to save endangered species. Biodiversity increases resilience in ecosystems, helping them withstand environmental changes. It also supports ecosystem services—like clean water, fertile soil, and climate regulation—that humans depend on. By understanding the causes of extinction and the value of biodiversity, society can make choices that protect life on Earth for future generations.

Interesting Fact:
Over 99% of all species that have ever lived on Earth are now extinct, but new species continue to evolve, keeping our planet full of life.

What is extinction?

The complete disappearance of a species from Earth.The process of a species adapting to new environments.When a species moves to a new area.The increase in the number of species.

What does biodiversity include?

Only animals and plantsOnly genesGenes, species, and entire ecosystemsOnly rare species

Which is an example of a mass extinction?

Background extinction of a few species each yearThe Permian extinction that wiped out 90% of marine speciesA single species disappearingA new species evolving

What evidence do scientists use to study past extinctions?

DNA onlyWeather patternsFossil recordsSatellite images

What is the main cause of the current biodiversity crisis?

Volcanic eruptionsHuman activitiesAsteroid impactsNatural climate cycles

What is meant by 'ecosystem stability'?

How many animals live in an areaThe ability of an ecosystem to remain healthy and balancedThe number of plants in a forestThe age of an ecosystem

How can biodiversity loss affect humans?

It can limit sources for medicine and food.It makes the planet warmer.It increases the number of species.It causes more mass extinctions.

Which of the following is TRUE based on the passage?

All extinctions are caused by humans.Mass extinctions have only happened once.

Conservation efforts can help prevent extinction. True or False?

TrueFalse