<P> Plants take up essential elements from the soil through their roots and from the air ( mainly consisting of nitrogen and oxygen ) through their leaves . Nutrient uptake in the soil is achieved by cation exchange , wherein root hairs pump hydrogen ions ( H ) into the soil through proton pumps . These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root . In the leaves , stomata open to take in carbon dioxide and expel oxygen . The carbon dioxide molecules are used as the carbon source in photosynthesis . </P>
where do plants obtain the chemicals that they need to sustain life
from the soil through their roots from the air ( mainly consisting of nitrogen and oxygen ) through their leaves