Chapter 11.2: Respiratory System

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Respiration occurs when gases are exchanged between the outside environment and the inside of an organism. This is what humans do when they inhale oxygen and exhale carbon dioxide.


A second type of respiration you might hear about in biology is called cellular respiration. Cellular respiration refers to the metabolic processes cells utilize to breakdown carbohydrates into ATP, the energy currency that allows organisms to function.

We have already discussed cellular respiration in Chapters 3 and 4. In this Chapter, we will focus on the first type of respiration (i.e., gas exchange). An organism’s respiratory system allows respiration to occur.


Respiration in Plants

Plants are autotrophs, meaning they make their own food through photosynthesis. In addition to making food, plants need to use food. This is why plants also respire.


As a brief refresher of photosynthesis, water is split apart so that electrons may be obtained by plants. Whenever water is split in this way, oxygen molecules are released into the environment, and the electrons from water become energized by light (photons) from the sun.

Once the electrons are energized, they are stored in ‘electron carriers’, namely ATP and NADPH. The Calvin cycle is where plants utilize the high energy electrons contained in ATP and NADPH to produce carbohydrates from atmospheric carbon dioxide.