Transport in living organisms
Concept of transport living organisms
- Primitive Plants e.g Algae :
CO2 , water , mineral salts , and products
of photosynthesis move from one cell to
another by diffusion or active transport ,
there is no need for specialized transport
system .
- Higher Plants :
Gases move by diffusion , but water , salts
, products of photosynthesis transported
by special vascular tissues .
- Small Animals e.g Protozoa and Hydra :
Both gases and food move by diffusion
- Bigger and more complicated Animals :
Diffusion is not sufficient for transport ,
so there must be specialized transport
system .
TRANSPORT in HIGHER PLANTS
- Xylem vessels of the root transport water
and salts from the root to Xylem of the
stem , then to the leaves to carry out
photosynthesis .
- Sieve tubes of leaves , stem and root
transfer organic high energy food from the
leaves to all parts of the plant .
T.S in Dicot stem
Epidermis :
one row , adjacent , barrel shaped ,
parenchyma cells , outer walls covered by
cutin ( cuticle)
Cortex :
. Collenchyma : rows , they are parenchyma
but their corner thickened by cellulose .
It is mechanical tissue to support the stem
+ some contain chloroplasts for
photosynthesis .
. Parenchyma : rows , with intercellular
spaces for Aeration
. Starch sheath , innermost row , store
starch grains .
Vascular Cylinder :
consists of :
a. Pericycle : group of parenchyma
alternate with group of fibers , it makes
the stem strong and elastic .
b. Vascular Bundles : cylindrical ,
triangular with its base directed outward
, consist of :
1. Phloem , outer tissue , consists of
sieve tubes , companion cells and phloem
parenchyma , it transports organic food
from leaves to all parts of the plant .
2. Cambium , one row or more of
meristematic cells between phloem and
xylem , it
divides externally forming secondary
phloem and internally forming secondary
Xylem , so it increases the thickness of
the stem .
3. Xylem : the internal part ,
translocates water and solutes from the
root to the leaf + supporting the stem ,
consists of : Vessels and Tracheids :
Vessels : tubes ,vertical rows ,
elongated , cylindrical , joined end to
end , transverse walls dissolved ,
protoplasmic content died leaving one
hollow tube .
the cellulose walls thickened by lignin
impermeable to water and solutes
( annular , spiral , scalariform , ,
reticulate ) , it supports the vessel +
prevent the collapse of its wall .
Pits : numerous , the primary wall is
left unthickining , these pits permit
water to pass from inside outward .
Tracheids : more or less similar to
vessels , but pentagonal or hexagonal ,
pitted , their ends pointed and closed .
Xylem Parenchma : several rows
between xylem vessels .
c. Pith , in the center , parenchma ,
for storage of food .
d. Medullary Rays : parenchma cells
extend between vascular
bundles , join the cortex
with the pith , its function
is storage food .