162 |
A Handbook of Biology
Plants do not have interstitial fluid and circulatory system. But they need
to move various substances (water, minerals, organic nutrients, growth
regulators etc. over long distances.
Over small distances substances move by diffusion & by cytoplasmic
streaming supplemented by active transport.
Transport over long distances proceeds through the vascular system
(xylem and phloem) which is called translocation.
DÏRËÇTÏØÑ ØF TRÅÑSPØRT
Unidirectional transport: E.g. Transport of water and minerals in xylem
(from roots to the stems, leaves etc.).
Multidirectional transport/bidirectional transport E.g.- Transport of
photosynthates (organic compounds) through phloem.
Transport of mineral nutrients.
(NEET 2019)
Sometimes, plant hormones and other chemical stimuli are transported
in a polarised or unidirectional manner from where they are synthesised
to other parts.
MËÅÑS ØF TRÅÑSPØRT
DÏFFÜSÏØÑ
It is the slow movement of gases, liquids and solutes from higher
concentrated region to lower concentrated region without the
energy expenditure. Movement by diffusion is passive.
It may be from one part of the cell to the other or from cell to cell,
or over short distances.
Diffusion is a slow process.
It is not dependent on a ‘living system’.
It is the only means for gaseous movement in a plant body.
Diffusion is obvious in gases and liquids.
FÅÇTØRS ÅFFËÇTÏÑG DÏFFÜSÏØÑ RÅTËS:
Concentration gradient
Permeability of the membrane