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why do plants need nitrogen and magnesium

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 в 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. 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 в 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. Now try a. Plants need to take in a number of elements to stay alive. The most important are: Plants get hydrogen and oxygen from water in the soil, and carbon and oxygen from carbon dioxide and oxygen in the atmosphere. Water and carbon dioxide are used to synthesise food during photosynthesis.

Oxygen is used to release energy from food during respiration. In addition to these three elements, plants need a number of minerals for healthy growth. These are absorbed through the roots as mineral ions dissolved in the soil water. Two important mineral ions needed by plants are: nitrate - for making amino acids, which are needed to make proteins magnesium If a plant does not get enough minerals, its growth will be poor. It will suffer from deficiency symptoms: Now try a

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