The topic of our presentation is The Living World
which is the first chapter of Class 11 from NCERT book
 
 
This chapter includes the very basics and concepts of Biology
which every Biology student must understand
We will start with the characteristic features of living organisms
first of which is Growth
There are two aspects of growth - either increase in cell mass
if we're talking at the cellular level then growth of cytoplasm
or increase in the number of cells through cell division.
When both these events occur in a a living organism
then that organism is said to grow.
here is a brief discussion of the topic
In plants, the growth is continuous
Growth occurs throughout life in plants.
But in animals, growth occurs only up to a certain age.
Growth will stop but cell division will continue.
Therefore growth stops but cell division never stops.
Now, why does the cell division occur?
Cell division will occur either for healing
of the wound
or to replace the old cells of the body
For example
in the lining of our digestive track
the cells are continuously replaced
the old ones get destroyed
and new cells arise
These new cells are formed through cell division.
Similarly in RBCs
the life span of the cell is 120 days
So after 120 days, the old RBCs get destroyed
and new RBCs will replace them
So in this way, in animals
growth stops after a certain age
but cell division continues to occur in some parts of the body
During growth, an organism takes in material from the environment and
organises the material into its structure or
basically convert it into its cellular organisation
So in this way, the living organisms grow from the inside
Body grows from inside
there is no deposition of material on top of the body
Even in the case of non living organisms,
we can see growth
because growth means accumulation of substances
therefore we can see growth in non living organisms as well
but in this case
there will be accumulation of material
on the surface of the body
Thus, non living organisms grow from the outside
For example even a rock undergoes growth
but in this case there is
deposition of material on the surface of the rock
which is resulting in growth
So this difference can be seen in living and non living world
Living organisms grow from the inside
while non living organisms grow from the outside.
Therefore, growth cannot be considered as defining property of living organisms.
because growth can be see in non living organisms as well.
The second aspect is Reproduction which is
Production of progeny possessing features more or less similar to those of parents
In unicellular organisms
reproduction and growth are considered synonym
in a biological definition
In the previous slide we discussed
that growth has two aspects
either number of cells should increase
or there is accumulation of cytoplasm
which is increase in cell mass
In unicellular organisms,
we are not clear about the usage of these two terms
During cell division in a unicellular organism,
the number of cells are increasing
so should this be considered growth or reproduction
as the organism is also producing progeny similar to itself?
Therefore, there isn't much clarity about the usage of these two terms
for unicellular organisms
There are many other organisms which are
sterile like mule,
sterile worker bees, infertile human couples
All these organisms cannot reproduce
but they are still living organisms
Therefore, reproduction cannot be a defining characteristic of living organisms.
Reproduction is not the defining feature of living organisms
because reproduction is not required to live
All these organisms are sterile
but these are living organisms
The third aspect is Metabolism
In any living organism, there are a number of
chemical reactions taking place
and all those chemical reactions are collectively called metabolism
Hence, metabolism is a defining feature of all living organisms without exception.
As in the case of reproduction,
some living organisms could not reproduce
but metabolism is a feature that has no exception
it can be seen in every living organism
No organism can survive without metabolism.
We can demonstrate metabolism outside the body
in a laboratory
but these reactions are not called metabolic reactions
but instead are called biological reactions
We can call a reaction Metabolism only if it takes place inside a living organism
But if the same reaction takes place in a laboratory,
in a cell free system, it is termed as Biological Reaction
because these reactions involve bio chemicals
Bio chemicals are the chemicals found in a living organism
There are two types of Biochemical Pathways
one is Anabolism
in which smaller molecules utilize energy
make a bigger molecule
for example in Photosynthesis
plants use CO2 and H20
and utilize solar energy
to make a bigger molecule of glucose
Therefore, photosynthesis is an example of anabolism
Such metabolic reactions are called anabolic reactions.
catabolism is just the opposite of anabolism
in catabolism, a bigger molecule breaks its bonds
and gets transformed into smaller molecules
and releases the energy trapped in those bonds
Cellular Respiration is an example of catabolism
in this the bonds of glucose are broken
the smaller molecules of H2O and CO2 are released
along with a lot of energy
Such a metabolic reaction is called a catabolic reaction.
The forth aspect is Cellular Organisation
A living being has an organisation which
consists of several components which interact with one another
for proper functioning of whole organism.
For example in human beings
our body has several kinds of system
which are well coordinated with each other
without these interactions and coordination
life and survival would not be possible
Therefore these interactions are very important
between different components
and this interaction is called organization
Properties of tissues are not present in the constituent cells
but arise as a result of interactions among constituent cells
Now visualize a tissue
a tissue has various types of cells
the property of that tissue may not be found in the constituent cell
so if we place the constituent cells separately,
we may not be able to see the properties
which the tissue possesses
because when these constituent cells interact
and work in coordination,
then we observe the properties of that particular tissue
So for the tissue to perform properly, the
interactions between the constituent cells is crucial
So this type of interaction and coordination is called cellular organisation
Same can be seen in the case of cell organelles
these organelles have to coordinate well with each other
when these coordinate then we can see the
organisation in a cell
If we place these organelles separately,
we won't be able to observe the properties of that cell
Properties of cellular organelles are not present
in the molecular constituents of the organelles
but arise as a result of interactions among the molecular components comprising the organelle.
Hence, cellular organisation of the body is the defining feature of life forms.
The fifth feature is consciousness
Every living organism has consciousness
and can sense their surroundings
and respond according to their surroundings.
Consciousness therefore, becomes the defining property of living organisms
for example, Photoperiod affects reproduction in seasonal breeders both plants and animals.
so some plants show seasonal flowering
this means they are aware when their season has arrived
and the plant undergoes flowering
Similarly, some animals are seasonal breeders
and bread only in that particular season
Therefore, animals also sense their surroundings
and respond accordingly
Consciousness therefore, becomes the defining property of living organisms
Therefore, we can say that living organisms are self- replicating
evolve on their own
self regulating and have an interactive system
and they respond to external stimuli
So these were some features of living organisms
Now we will discuss how many species are in the world
and also in India
According to IUNC, we have discovered 1.5 million species
both plant and animal
and this data is of 2004
Robert May estimated global species diversity at about 7 million.
so a lot of species are yet to be discovered
So why is it that several species have not yet been discovered?
This is because these species are either in dense forests
where we cannot reach
or because they live at the bottom of the ocean
where we are unable to reach
That is why out of the estimated 7 million,
we have been able to discover only 1.5 million.
More than 70% of all species recorded are animals
Why are animals more in number than plants?
This is mainly because animals can move
and can change their location on this planet
As soon as they change their location, evolution starts and thus a new species is formed
so the rate of speciation is very high in animals
and due to this animal species is more in number as compared to plants.
Among animals, insects are the most species rich
taxonomic group comprising more than 70% of the total animal species
In invertebrates, starting from porifera to echinodermes
insects are the most abundant group
In vertebrates, almost 50% of the population is of fishes
and the rest are other vertebrates as seen in the pie chart
In plants, the most successful group is of Angiosperm
and the next one is Fungi
The types of organisms present on earth reflect the Biodiverity
Millions of species are found on Earth
for the systematic study of these organisms,
to make their study easy,
it is important to classify these organisms
The process of classification of an organism is called taxonomy
Morphology refers to the external features
Anatomy refers to the internal features
Cytology is the study of features of cell
Embryology is the study of embryos
and the ecological information regarding the ecological behavior of the organism
All this information is used for taxonomic studies
or  to classify an organism
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
