NUTRITION
IN PLANTS
·
Nutrients are
essential components of food (like carbohydrates, proteins, fats, vitamins and
minerals) which are necessary for living body.
·
Nutrients are
important which enable living organisms to build their bodies, to grow, to
repair damaged parts of their bodies, provide energy and provide the energy to
carry out life processes.
·
Nutrition is the
mode of taking food by an organism and its utilization by the body. Nutrition
include nutrition requirement, taking of food by living organism and utilisation
of taken food by body of living organism.
MODE OF
NUTRITION IN PLANTS
·
Autotrophic (auto=self; trophos=nourishment) nutrition
is the mode of nutrition in which organisms make food themselves from simple
substances.
·
Only plants can
prepare their own food by using raw materials like water, carbon dioxide(CO2)
and minerals. Therefore, plants are autotrophs.
·
Animals and most
of other organisms are heterotrophs(heteros=others)
i.e. they take in ready made food prepared by the plants.
PHOTOSYNTHESIS
·
Leaves
are the food factories of plants i.e. photosynthesis(synthesis of food in
plants) occurs in leaves. Photosynthesis also takes place in other green parts
of plant like green stem and green branches-incase of desert plants whose
leaves are spine-like(scale leaves) to reduce loss of water by transpiration.
·
To
prepare food by plants in leaf, raw materials must reach leaf. Water and
minerals present in soil are absorbed by the roots and transported to the
leaves by continuous vessels (pipe like) which run throughout the root, stem,
branches and leaves. Carbon dioxide (CO2) from air is taken in
through tiny pores surrounded by guard cells (called stomata) present on the
leaf surface.
·
Chlorophyll
(green pigment) present in leaves helps in capturing energy of sunlight.
Absorbed/trapped energy is used to synthesise/prepare food using raw materials
like Carbon dioxide (CO2) and water(H2O) along with
release of Oxygen(O2). This process of synthesizing food in presence
of light is called photosynthesis (Photo: light, synthesis: to combine). Chlorophyll,
sunlight, Carbon dioxide and water are necessary to carry out photosynthesis.
·
Sun
is the ultimate source of energy for all living organisms.
·
In
the absence of photosynthesis, there would not be life on earth i.e. no plants,
least Oxygen, no food for herbivores and other animals.
·
During
photosynthesis, chlorophyll containing cells of leaves in presence of sunlight
use carbon dioxide and water to synthesise carbohydrates. The process can be
represented as an equation:
OxygenO2 is
released during the process. The carbohydrates are ultimately converted into
starch. Presence of starch in leaves indicates the occurrence of
photosynthesis. Starch is also a carbohydrate. Carbohydrates are made up of
Carbon(C), Hydrogen (H) and Oxygen (O)
·
Algae
can prepare their own food by photosynthesis. These are organisms seen as
slimy, green patches in ponds or in other stagnant water.
SYNTHESIS
OF PLANT FOOD OTHER THAN CARBOHYDRATES
·
Protein (Nitrogenous substance) and fats are
other essential food for plants.
·
Plants
can’t absorb abundant nitrogen from air. Certain soil bacteria convert gaseous
nitrogen into usable form and release it into soil. These soluble Nitrogen
forms are absorbed by the plants along with water and finally synthesise
proteins and fats.
OTHER
MODES OF NUTRITION IN PLANTS
·
Some
plants are heterotrophs i.e. can’t synthesise their own food. Example;
Cuscuta(Amerbel) doesn’t have chlorophyll and are yellowish tubular in
structure which climb on a host plant for nutrients. It is a parasite as it
deprives the host of valuable nutrients.
·
Insectivorous
plants are insect-eating plants. Example; Pitcher plant whose leaf is modified
in pitcher like structure and apex of leaf forms a lid which open and close the
mouth of the pitcher. There are hairs directed downwards inside the pitcher. The
lid closes and digest insect by the digestive juices secreted in the pitcher
after entangling the insect into the hair.
SAPROTROPHS
·
Fungi
secrete digestive juices on the dead and decaying matter and convert it into a
solution from which is nutrients are absorbed. This mode of nutrition in which
organisms take in nutrients in solution form from dead and decaying matter is
called saprotrophic nutrition. Fungi also grow on pickles, leather, clothes,
bread, etc left in hot and humid weather for long time.
·
Fungal
spores are generally present in the air. Once they land on wet and warm things,
they germinate and grow.
·
Plants
which use saprotrophic mode of nutrition are called saprotrophs.
·
In
symbiotic relationship, some organisms live together and share shelter and
nutrients. Example; Certain fungi live in the roots of trees where tree
provides nutrients to these fungi and plants in turn receives help in take up
of water and nutrients from soil.
·
In
organisms called lichens, a chlorophyll containing partner which is alga and a fungus
live together. Fungus provides shelter, water and minerals to alga and in
return alga provides food synthesised by photosynthesis.
HOW
NUTRIENTS ARE REPLENISHED IN THE SOIL
·
Plant
absorbs mineral nutrients from soil. Amount of these nutrients decline on
continuous plantation of crops. Fertilizers and manures containing plants
nutrients like nitrogen, potassium, phosphorous, etc are added from time to
time to enrich the soil.
·
Plants
need lots of nitrogen to make protein. Though nitrogen gas is available in
plenty in the air, plants can’t use it in the manner they can use carbon
dioxide. Plants can take only nitrogen in soluble form.
·
Rhizobium,
a bacterium can take atmospheric nitrogen and convert it into soluble form.
But, the bacterium can’t make its own food.
The bacterium gets shelter and food from leguminous plant root(gram,
peas, moong beans). This association of plant root and bacterium is symbiotic
relationship. This process helps farmers that they don’t need to add nitrogen
fertilizer to soil.
·
Most
plants are autotrophs. Only few plants adopt other modes of nutrition like
parasitic and saprotrophic.