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What is the Most Abundant Gas in the Atmosphere — Reading Comprehension

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This NGSS-aligned reading passage for middle school students explores nitrogen, the most abundant gas in Earth's atmosphere. It details nitrogen's role in sustaining life and explains the critical process of nitrogen fixation and the nitrogen cycle. The passage is designed to build a deep understanding of atmospheric composition and its connection to biological systems, aligning with core concepts in physical and life sciences. The content highlights how nitrogen, despite its abundance, must be converted into usable forms and the significant roles played by bacteria and lightning in this process. The reading is suitable for grades 6-8 and supports inquiry-based learning about Earth's systems.

CONTENT PREVIEW

The composition of Earth's atmosphere, with a large section for nitrogen (78%) and a smaller one for oxygen (21%). The image also depicts the nitrogen cycle, with lightning and bacteria converting atmospheric nitrogen into the soil. — The composition of Earth's atmosphere, highlighting nitrogen as the most abundant gas, and depicts the nitrogen cycle where atmospheric nitrogen is converted into a usable form for life.

The Earth's atmosphere is a crucial, protective blanket of gases surrounding our planet. It provides the air we breathe and shields us from harmful solar radiation. While we often think of oxygen as the most important gas, it is actually nitrogen that is the most abundant, making up about 78% of the atmosphere. Oxygen is the second most common, comprising approximately 21%, with the remaining 1% consisting of other gases like argon, carbon dioxide, and neon.

Nitrogen's abundance is vital for life, but its atmospheric form, N2, is not directly usable by most organisms. The strong triple bond holding the two nitrogen atoms together makes the gas largely unreactive. To become useful, nitrogen must undergo a process called nitrogen fixation, which converts it into compounds like ammonia (NH3) that plants can absorb. This process is primarily carried out by specialized bacteria found in the soil and on the roots of certain plants, such as legumes. Lightning strikes can also provide enough energy to fix a small amount of nitrogen.

Once nitrogen is fixed, it becomes a key building block for life. It is an essential component of amino acids, which form proteins, and nucleic acids, which make up our DNA and RNA. Animals get the nitrogen they need by consuming plants or other animals that have incorporated fixed nitrogen into their tissues. The cycling of nitrogen through the atmosphere, soil, and living organisms is known as the nitrogen cycle, a fundamental process that sustains ecosystems. Without this cycle, the abundant nitrogen in the atmosphere would remain unavailable, and life as we know it would not exist.

Fun Fact: Nitrogen is also a key ingredient in many industrial products. Liquid nitrogen, with its extremely low temperature of -196°C (-321°F), is used in cryogenics for preserving biological samples and even in some forms of cooking to create instant freezing effects.

What is the most abundant gas in Earth's atmosphere?

OxygenNitrogenCarbon dioxideArgon

Approximately what percentage of the atmosphere is made up of nitrogen?

21%50%78%99%

What process converts atmospheric nitrogen into a usable form for plants?

RespirationPhotosynthesisNitrogen fixationCombustion

Which of the following is an example of an organism that performs nitrogen fixation?

AnimalsSpecialized bacteriaHumansFungi

What is the primary reason atmospheric nitrogen is not directly usable by most living things?

It is a noble gas.It is a liquid at room temperature.The nitrogen atoms are bonded very strongly.It is too heavy for organisms to absorb.

According to the passage, what would be the result if the nitrogen cycle did not exist?

The amount of oxygen would increase.Animals would get nitrogen directly from the atmosphere.Life as we know it would not be sustained.Plants would use atmospheric nitrogen directly.

What is the main idea of this reading passage?

The importance of oxygen in the atmosphere.How nitrogen is the most abundant and essential gas.The process of lightning strikes in the atmosphere.The composition of all gases in the atmosphere.

A scientist discovers a new type of plant that can directly absorb and use atmospheric nitrogen. This new plant would most likely:

need a lot more sunlight to grow.not rely on nitrogen-fixing bacteria.be unable to produce proteins or DNA.release oxygen into the atmosphere.