THE LIVING WORLD
● The ecological conflict and cooperation among members of a population and among
populations of a community or even the molecular traffic inside a cell make us deeply
reflect on – what indeed is life?
● If you were to increase the area that you make observations in, the range and variety of
organisms that you see would increase. Ex: Dense forest.
● Growth, reproduction, ability to sense environment and mount a suitable response
come to our mind immediately as unique features of living organisms. More features
like metabolism, ability to self-replicate, self-organise, interact and emergence.
● Growth: All living organisms grow. Increase in mass and increase in number of
individuals are twin characteristics of growth.
❖ A multicellular organism grows by cell division, in plants, this growth occurs
t
continuously throughout their life span. In animals, this growth is seen only up
to a certain age. However, cell division occurs in certain tissues to replace lost
ul cells.
❖ Unicellular organisms grow by cell division. Ex: In vitro cultures by simply
counting the number of cells under the microscope.
In the majority of higher animals and plants, growth and reproduction are mutually
exclusive events.
va
Non-living objects also grow if we take increase in body mass as a criterion for growth.
Mountains, boulders and sand mounds do grow, by accumulation of material on the
surface. In living organisms, growth is from inside.
Growth, therefore, cannot be taken as a defining property of living organisms.
● Reproduction: a characteristic of living organisms.
❖ In multicellular organisms, reproduction is the production of progeny
possessing features more or less similar to those of parents. Invariably and
N
implicitly we refer to sexual reproduction.
❖ Organisms reproduce by asexual means also.
➢ Fungi multiply and spread easily due to the millions of asexual spores
they produce.
➢ In lower organisms like yeast and hydra, we observe budding.
➢ In Planaria (flat worms), we observe true regeneration, i.e., a
fragmented organism regenerates the lost part of its body and becomes
a new organism.
➢ The fungi, the filamentous algae, the protonema of mosses, all easily
multiply by fragmentation.
, ➢ When it comes to unicellular organisms like bacteria, unicellular algae
or Amoeba, by fission, growth and reproduction are Inclusive events.
❖ There are many organisms which do not reproduce (mules, sterile worker bees,
infertile human couples, etc).
❖ Hence, reproduction also cannot be an all-inclusive defining characteristic of
living organisms.No non-living object is capable of reproducing or replicating by
itself.
● Metabolism: All living organisms are made of chemicals constantly being made and
changed into some other biomolecules which are chemical reactions or metabolic
reactions.
The sum total of all the chemical reactions occurring in our body is metabolism. No
non-living object exhibits metabolism.
All plants, animals, fungi and microbes (unicellular and multicellular) exhibit
t
metabolism.
Metabolic reactions can be demonstrated outside the body in cell-free systems.
ulAn isolated metabolic reaction(s) outside the body of an organism, performed in a
test tube is neither living nor non-living.
Hence, while metabolism is a defining feature of all living organisms without
exception
Isolated metabolic reactions in vitro are not living things but surely living reactions.
va
Hence, cellular organisation of the body is the defining feature of life forms.
● The most obvious and technically complicated feature of all living organisms is this
ability to sense their surroundings or environment and respond to these
environmental stimuli which could be physical, chemical or biological. From
prokaryotes to complex eukaryotes.
❖ We sense our environment through our sense organs.
❖ Plants respond to external factors like light, water, temperature, other
N
organisms, pollutants, etc.
❖ Photoperiod affects reproduction in seasonal breeders, both plants and
animals.
❖ All organisms therefore, are ‘aware’ of their surroundings. A human being is the
only organism who is aware of himself, i.e., has self-consciousness.
● Consciousness therefore, becomes the defining property of living organisms.
● Patients lying in coma, virtually supported by machines which replace heart and lungs
are brain-dead. They have no self-consciousness but are living.
● All living phenomena are due to underlying interactions.
❖ Properties of tissues are not present in the constituent cells but arise as a result
of interactions among the constituent cells.
● The ecological conflict and cooperation among members of a population and among
populations of a community or even the molecular traffic inside a cell make us deeply
reflect on – what indeed is life?
● If you were to increase the area that you make observations in, the range and variety of
organisms that you see would increase. Ex: Dense forest.
● Growth, reproduction, ability to sense environment and mount a suitable response
come to our mind immediately as unique features of living organisms. More features
like metabolism, ability to self-replicate, self-organise, interact and emergence.
● Growth: All living organisms grow. Increase in mass and increase in number of
individuals are twin characteristics of growth.
❖ A multicellular organism grows by cell division, in plants, this growth occurs
t
continuously throughout their life span. In animals, this growth is seen only up
to a certain age. However, cell division occurs in certain tissues to replace lost
ul cells.
❖ Unicellular organisms grow by cell division. Ex: In vitro cultures by simply
counting the number of cells under the microscope.
In the majority of higher animals and plants, growth and reproduction are mutually
exclusive events.
va
Non-living objects also grow if we take increase in body mass as a criterion for growth.
Mountains, boulders and sand mounds do grow, by accumulation of material on the
surface. In living organisms, growth is from inside.
Growth, therefore, cannot be taken as a defining property of living organisms.
● Reproduction: a characteristic of living organisms.
❖ In multicellular organisms, reproduction is the production of progeny
possessing features more or less similar to those of parents. Invariably and
N
implicitly we refer to sexual reproduction.
❖ Organisms reproduce by asexual means also.
➢ Fungi multiply and spread easily due to the millions of asexual spores
they produce.
➢ In lower organisms like yeast and hydra, we observe budding.
➢ In Planaria (flat worms), we observe true regeneration, i.e., a
fragmented organism regenerates the lost part of its body and becomes
a new organism.
➢ The fungi, the filamentous algae, the protonema of mosses, all easily
multiply by fragmentation.
, ➢ When it comes to unicellular organisms like bacteria, unicellular algae
or Amoeba, by fission, growth and reproduction are Inclusive events.
❖ There are many organisms which do not reproduce (mules, sterile worker bees,
infertile human couples, etc).
❖ Hence, reproduction also cannot be an all-inclusive defining characteristic of
living organisms.No non-living object is capable of reproducing or replicating by
itself.
● Metabolism: All living organisms are made of chemicals constantly being made and
changed into some other biomolecules which are chemical reactions or metabolic
reactions.
The sum total of all the chemical reactions occurring in our body is metabolism. No
non-living object exhibits metabolism.
All plants, animals, fungi and microbes (unicellular and multicellular) exhibit
t
metabolism.
Metabolic reactions can be demonstrated outside the body in cell-free systems.
ulAn isolated metabolic reaction(s) outside the body of an organism, performed in a
test tube is neither living nor non-living.
Hence, while metabolism is a defining feature of all living organisms without
exception
Isolated metabolic reactions in vitro are not living things but surely living reactions.
va
Hence, cellular organisation of the body is the defining feature of life forms.
● The most obvious and technically complicated feature of all living organisms is this
ability to sense their surroundings or environment and respond to these
environmental stimuli which could be physical, chemical or biological. From
prokaryotes to complex eukaryotes.
❖ We sense our environment through our sense organs.
❖ Plants respond to external factors like light, water, temperature, other
N
organisms, pollutants, etc.
❖ Photoperiod affects reproduction in seasonal breeders, both plants and
animals.
❖ All organisms therefore, are ‘aware’ of their surroundings. A human being is the
only organism who is aware of himself, i.e., has self-consciousness.
● Consciousness therefore, becomes the defining property of living organisms.
● Patients lying in coma, virtually supported by machines which replace heart and lungs
are brain-dead. They have no self-consciousness but are living.
● All living phenomena are due to underlying interactions.
❖ Properties of tissues are not present in the constituent cells but arise as a result
of interactions among the constituent cells.
