Mineral elements, which are required by plants, can be classified into two groups: macronutrients and micronutrients.
The major micronutrients, needed by plants are iron, chlorine, manganese, boron, zinc, copper and molybdenum.
The mineral elements required by higher plants come from the soil or the water in which the plants grow.
The role of individual elements has been largely determined by growing plants with their roots immersed in nutrient solution without soil. This technique is known as hydroponics.
Nitrogen is the mineral element required by plants in greatest amount.
Phosphorus is found in plants as a constituent of nucleic acids, phospholipids, coenzymes NAD and NADP and most important, as a constituent of ATP.
Phosphorus deficiency may cause premature leaf fall, and purple of red anthocyanin pigmentation.
The vitamins biotin, thiamine and coenzyme A contain sulphur.
Calcium deficiency affects the meristematic regions of stems, leaf and root tips which eventually die resulting in termination of growth in these regions.
Iron is also found in the iron porphyrins, such as cytochrome. The most easily observed symptom of iron deficiency in plants is extensive chlorosis in the leaves.
Magnesium is a constituent of the chlorophyll molecule without which photosynthesis would not occur.
Chlorine influences the process of photosynthesis and also helps in the maintenance of ionic balance.
Absorption of salts takes place through the root system which is in intimate contact with the soil colloids or soil solution.
Mineral nutrients absorbed by the root are carried to the xylem. This takes place by two pathways called apoplast and symplast.
Nitrate is either available to the plant or converted into nitrogen gas in the process of denitrification by other microorganisms, e.g. Pseudomonas.
The two most important amides found in plants are asparagines and glutamine.
The nodules of the leguminous plants represent an excellent example of symbiosis, a relationship in which two different organisms live in close association, in intimate physical contact, with mutual benefit.
The parasitic fungi may be of two types: facultative and obligate parasites.
Some plants adopt a carnivorous mode of nutrition to supplement their photosynthetic diet. These plants capture and digest flies and other insects.
There are two types of vascular tissues in plants: the xylem and the phloem.
Phloem tubes translocate the food manufactured in the leaves to all other parts of the plant body.
Water enters the plant through roots hairs. As a result of higher concentration of solutes in these cells than in the soil solution, water enters osmotically.
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