Linnaeus (the father of taxonomy system) divided all the living organisms into
two kingdoms in 1758.
Features of Kingdom—Plantae
The features of this kingdom are
(i) Cell wall is present.
(ii) A big central vacuole is present.
(iii) Absorb inorganic nutrients from outside.
(iv) Unlimited growth and well-defined growing
points.
(v) Autotrophic mode of nutrition, reserve food is
starch.
(vi) No locomotion (except in some lower algae).
(vii) Absence of excretory organs, nervous system, sense
organs and muscular system.
(viii) Slow response 😮 external stimuli.
Features of Kingdom—Animalia
The features of this kingdom are
(i) Absence of cell wall.
(ii) Inorganic crystals are not present in their cells.
(iii) Central vacuole is not present.
(iv) Heterotrophic mode of nutrition.
(v) Growth is limited and well-defined growing points
are not present.
(vi ) Reserve food as glycogen.
(vii) Excretory organs, nervous system and sense organs
are present.
(viii) Locomotion is present.
(ix ) Muscular system is present.
(x) Show quick response to external stimuli.
Shortcomings Of Two Kingdom
Classification System
The two kingdom system of classification was accepted
for a long time. However, some difficulties arised from
this classification as several new living organisms have
been discovered.
Some of these difficulties are mentioned below
(i) The first formed organisms (bacteria) were neither
plants nor animals. These were not given proper place
in the two kingdom classification system.
(ii ) Prokaryotes do not have an organised nucleus. They
have single envelope organisation, absence of spindle
, meiosis and sexual reproduction.
apparatus
Eukaryotes have a well-defined nucleus, a double
envelope organisation, spindle apparatus, meiosis and
sexual reproduction.
On the other hand, viruses have no protoplasm and
metabolic machinery of their own. Therefore, all of
these cannot be kept in a single group.
(iii) It is not easy to recognise the lower organisms as plants
or animals. For example, Euglena has chloroplast and
follows mixotrophic (dual) mode of nutrition, while
sponges are fixed, branched and irregular creatures like
plants that have holozoic mode of nutrition and
excrete nitrogenous waste like animals.
(iv) Fungi do not show structural, physiological and
reproductive similarity with other plants under
kingdom—Plantae. Fungi have heterotrophic mode of
nutrition with chitin in their walls while, other plants
are mostly autotrophic in nature with a cellulosic cell
wall.
(v) Slime moulds, a group of fungi, are wall-less in
vegetative phase. They develop cell wall in the
reproductive phase. Slime moulds can neither be
placed in animals, nor in plants.
(vi ) Lichens are formed by the symbiotic association of an
alga and a fungus. They neither resemble plants nor
animals.
(vii) This system does not distinguish multicellular and
unicellular organisms. For example, Chlamydomonas
and Spirogyra are placed together.
(viii) Unicellular algae like diatoms, euglenoids,
dinoflagellates and protozoans resemble each other.
But they are placed in different kingdoms.