Plant physiology transport in plants
Channel: ISHTA’s BIO ACADEMY
Date: 24/04/2023

Plants obtain a variety of inorganic elements (ions) and salts from their
surroundings especially from water and soil. The movement of these nutrients
from environment into the plant as well as from one plant cell to another plant cell
essentially involves movement across a cell membrane. Transport across cell
membrane can be through diffusion, facilitated transport or active transport. Water
and minerals absorbed by roots are transported by xylem and the organic material
synthesised in the leaves is transported to other parts of plant through phloem.
Passive transport (diffusion, osmosis) and active transport are the two modes
of nutrient transport across cell membranes in living organisms. In passive
transport, nutrients move across the membrane by diffusion, without any use of
energy as it is always down the concentration gradient and hence entropy driven.
This diffusion of substances depends on their size, solubility in water or organic
solvents. Osmosis is the special type of diffusion of water across a selectively
permeable membrane which depends on pressure gradient and concentration
gradient. In active transport, energy in the form of ATP is utilised to pump
molecules against a concentration gradient across membranes. Water potential is
the potential energy of water molecules which helps in the movement of water. It is
determined by solute potential and pressure potential. The osmotic behaviour of
cells depends on the surrounding solution. If the surrounding solution of the cell
is hypertonic, it gets plasmolysed. The absorption of water by seeds and drywood
takes place by a special type of diffusion called imbibition.
In higher plants, there is a vascular system comprising of xylem and phloem,
responsible for translocation. Water minerals and food cannot be moved within
the body of a plant by diffusion alone. They are therefore, transported by a mass
flow system – movement of substance in bulk from one point to another as a
result of pressure differences between the two points.
Water absorbed by root hairs moves into the root tissue by two distinct
pathways, i.e., apoplast and symplast. Various ions, and water from soil can be
transported upto a small height in stems by root pressure. Transpiration pull
model is the most acceptable to explain the transport of water. Transpiration is