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ASVAB · Biology and Life Science

What gas do humans need to breathe in to survive, and what gas do they exhale?

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Correct answer

Inhale oxygen, exhale carbon dioxide

  1. A Inhale oxygen, exhale carbon dioxide
  2. B Inhale carbon dioxide, exhale oxygen
  3. C Inhale hydrogen, exhale oxygen
  4. D Inhale nitrogen, exhale helium

Why this is the answer

Humans INHALE OXYGEN (needed for cellular respiration to produce energy) and EXHALE CARBON DIOXIDE (a waste product of respiration). ASVAB General Science covers the respiratory system. In the lungs, oxygen from inhaled air passes into the blood, and carbon dioxide passes out of the blood to be exhaled (gas exchange in the alveoli). This is essentially the opposite of plant photosynthesis (which uses CO2 and releases O2). The oxygen-in, carbon-dioxide-out cycle is fundamental, commonly tested biology.
Source: ASVAB General Science — Respiratory System

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About this topic: Biology and Life Science

Biology questions cover cells and their organelles, genetics and heredity, classification, photosynthesis and respiration, and ecosystems. These are recall questions — know the vocabulary and the function of each structure. This is one of 15 General Science questions on biology and life science, each with a full explanation on a single study page.

New to this exam? Our ASVAB exam guide explains the format, scoring, and how to prepare.

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