Organisms exchange substances

Insects utilize an internal network of air-filled tubes called tracheae, which open to the outside through pores called spiracles, delivering oxygen directly to tissues. Lungs and gills are incorrect because they are specialized respiratory structures found in vertebrates and aquatic organisms, rather than terrestrial insects.

Oxygen diffuses passively down its partial-pressure gradient from the high concentration in the alveoli to the lower concentration in the blood, facilitated by a very thin respiratory membrane. Active transport is incorrect because gas exchange is entirely passive and does not require ATP to move molecules against a gradient.

Oxygen diffuses passively down its partial-pressure gradient from the high concentration in the alveoli to the lower concentration in the blood, facilitated by a very thin respiratory membrane. A diagram for this topic isn't available yet — the worked example below walks the same reasoning step by step.

• !Active transport is incorrect because gas exchange is entirely passive and does not require ATP to move molecules against a gradient.
• !Lungs and gills are incorrect because they are specialized respiratory structures found in vertebrates and aquatic organisms, rather than terrestrial insects.
• !Active transport in the roots is incorrect because, while it helps absorb minerals, it does not generate the physical force required for bulk upward water movement.

Answer each from memory — you'll see instantly whether you're right and why.

Run a focused 10-question mini-mock on Organisms exchange substances and see it stick.