The carbon and oxygen for the plant are available from
the carbon-dioxide present in the atmosphere. The hydrogen for the plants is
obtained from the water and the mineral nutrients are obtained from the soil.
The plant roots cannot absorb mineral nutrients in a
passive manner from the soil unlike they take up water. Minerals cannot be
taken passively by the plants as they are present as ions or charged particles
in the soil. These charged particles cannot get transported across cell
membranes. The mineral concentration in the soil is found to be lower compared
to that of the root. Hence, the minerals have to enter into the epidermal cells
of the root through active absorption which means energy in the form of ATP is
essential for the entry of minerals into the plant. The gradient of water
potential in roots is caused by the active uptake of ions. Osmotic intake of
water is also done by the active process. The charged ions also move into the
epidermal cells in a passive manner.
The ions are absorbed from the soil through both
the active as
well as passive transport. The proteins present in the membrane of the root
hair cells pump the ions from the soil into the epidermal cell cytoplasm. The
endodermal plasma cell membrane consists of transport proteins that are usually
present in all other cells. Some of the solutes cross the membrane transport
proteins of the endodermal cells while some solutes are not transported. The
screening of solute types that enter into the xylem and the quantity of them is
monitored by the endodermal cells. The single direction active transport of
ions occurs due to the suberin layer of the root endodermis.
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