Minerals in plants
Plants use minerals from the soil to build the complex molecules they need to survive and grow. Poor plant growth may be due to a deficiency of one or more minerals. Tests can be done to establish which mineral is deficient or a general purpose NPK fertiliser added.
Plants need to build the complex molecules they need from minerals (elements and simple compounds), which they get from the soil. Animals on the other hand get their complex molecules ready made from their food – they need very few minerals to supplement their diet.
If a plant shows poor growth it may be due to a lack of one or more minerals in the soil. It's possible to do chemical tests to find out which minerals are deficient, but it's often more convenient to add a general fertiliser. This is sometimes called NPK fertiliser because it contains the elements nitrogen (N), phosphorus (P) and potassium (K). These elements, plus magnesium (Mg), are the minerals that plants need in the greatest quantities.
|Nitrate ions (NO3)||Building proteins and growth||Poor growth and yellow leaves||All amino acids contain nitrogen. Amino acids are the building blocks of protein.|
|Phosphate ions (PO4)||Respiration and growth||Poor root growth and discoloured leaves||A component of DNA molecules and cell membranes|
|Potassium ions (K+)||Respiration and photosynthesis||Poor flower and fruit growth, discoloured leaves||Must be present for photosynthesis and respiration enzymes to work|
|Magnesium ions (Mg2+)||Photosynthesis||Yellow leaves||Chlorophyll molecules contain magnesium ions. It's the magnesium that makes chlorophyll green.|
The concentration of minerals in the soil is very low. They dissolve in water and move around the soil in solution. Root hair cells are adapted to absorb the water out of soil by osmosis – they have a large surface area, thin walls and are close to the xylem cells used for transporting water up the plant. Minerals cannot be absorbed by osmosis (which is the movement of water only) or diffusion (because the minerals are in very low concentration). The root hair cells have carrier molecules on their surface that pick up the minerals and move them into the cell against the concentration gradient. This requires energy, and is called active transport.
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