Download NUTRITION ( Lesson ONE )

NUTRITION
(Lesson ONE)
Is the scientific study of food and
various modes of nutrition of living
organisms
IMPORTANCE of FOOD :
Source of energy
Needed for growth
Repair worn out tissues
TYPES of NUTRITION :
a) AUTOTROPHS
e.g Green Plants
can synthesize high energy organic
food from low energy inorganic
materials in the presence of sunlight
a process called PHOTOSYTHESIS
b) HETEROTROPHS
can obtain food from other living
organisms by feeding either green
plants or animals previously feeding
on plants.
Classified into:
1) Holozoic :
Carnivores, Herbivores , Omnivores
2) Parasites : Bilharzias
3) Saprophytes : Fungi and Bacteria
AUTOTROPHIC NUTRITION - NUTRITION
in GREEN PLANTS
includes 2 processes:
1) Absorption of water and salts
2) Photosynthesis
ABSORPTION of WATER and SALTS
it takes place through root hairs
until reaching ascending
vessels
Structure of Root hair :
A) Tubular outgrowth of an epidermal
cell
B) 4 mm
C) Thin layer of cytoplasm with
nucleus
D) Large cell vacuole
E) Exist only few days or weeks since
they are lost from time to time
F) Regenerated continuously from zone
of elongation
Adaptation:
a) Thin walls to permit passage of
water and salts
b) Large in number and protruded
outside to increase absorbing surface
c) Solution in its vacuole more
concentrated than in soil, so water
passes from soil to root hair
d) Secrete viscous substance to find
their ways and stick to soil particles
and fix the plant to the soil.
MECHANISM of WATER ABSORPTION
Depends on 4 phenomenon
1) Diffusion :
is the movement of molecules or ions
from highly concentrated medium to low
concentrated one due to their free
motion .
2) Permeability :
a) Permeable membranes e.g cell walls
covered by cellulose , they allow
water and mineral salts to pass
through
b) Impermeable membranes e.g cell
walls covered lignin , suberin , or
cutin , they are impermeable to water
and mineral salts
c) Semipermeable membranes i.e
Selectively permeable e.g Plasma
membranes , thin with tiny pores ,
they allow the passage of some
substances required by plants while
prevent others not required , allow
the passage of water , control passage
of salts , prevent passage of sugar
and amino acids as they have large
sized molecules
3) Osmosis :
is the diffusion of water from a
medium high water concentration to a
medium with low water concentration
though semipermeable membranes , its
pressure is called osmotic pressure
which increases by increasing
concentration of solutes in its
solution
4) Imbibition :
is the ability of colloidal substances
( cellulose , pectin , proteins of
protoplasm ) to absorb liquids , swell
and increase in volume e.g cell walls
absorb water by imbibition .
Explanation of absorption of water
by the root :
Root hairs covered by thin colloidal
layer which imbibe water from soil
solution , then water passes by 3
pathways to reach xylem vessels :
a) through cell sap by OSMOSIS , due
to high concentration of sugar
solution in cell sap and its low
concentration in soil solution until
reaching xylem vessels .
b) through PLASMODESMATA , cytoplasmic
strands connecting protoplasms
together .
c) through cell walls and small
intercellular spaces by IMBIBITION .
Role of Endodermal cells in
controlling passage of water and salts
to reach xylem vessels:
Walls of Endodermal cells facing Xylem
are completely thickened with Suberin
so water never passes by imbibition .
Walls of Endodermal cells facing
Phloem have CASPARIAN strip of
Suberin, water passes through
unthickened facing root hairs and
xylem vessels by osmosis and active
transport under the influence of
protoplasm .
G.R Some plants can grow in salty soil
while others wilt and die :
Root hairs of desert plants XEROPHYTES
and those grow in salty water
HALOPHYTES have high osmotic pressure
50 - 200 atmospheres to absorb as much
water as possible , while in ordinary
plants MESOPHYTES range from 5 - 20
atmospheres as the concentration of
salts in soil is higher than in cell
sap , so water move from root hair to
the soil , the plant wilt and die .