The Living World : Class 11th Biology Notes Ch - 1 (Part 1)

The Living World : Class 11th Biology Notes Chapter – 1 (Part 1) – It is the first part of class eleventh ncert biology chapter 1 ‘the living world’. It is important notes for the students preparing for NEET. It (the living world chapter) is also very important notes for 11th class students preparing for cbse and state level board examination.

What is Life ?

Life is a unique, complex organisation of ions and molecules which perform certain chemical reactions in order to bring about life activities.

Life is not the property of any single part of an organism. It is the property of the organism as a whole.

For example, we know that the exact chemical composition of the protoplasm but we can not create it by simply puttin together all the elements in a mixture in the right proportion and supplying it with energy.

The Living World : Class 11th Biology Notes Chapter - 1 (Part 1) in english ncert cbse

What is Living ?

In order to have an understanding of ‘living’, we conventionally look for the characteristic features exhibited by the living organsims which distinguish them for non-living matter.

All living organisms and non-living matter have one thing in common that they are made up of some basic elements (about 99 % of the living matter is composed of C, H, O and N probably because these elements were abundant when life first began).

The living and non-living things are also subjected to the same physical laws such as, gravitation, magnetism, radition, action and reaction, etc.

Still, the living organisms are different from non-living matter on the basis of some fundamental characteristics such as, presence of protoplasm, cellular organisation, nutrition, metabolism, growth, reproduction, responses to environment, etc.

Presence of protoplasm is the most important characteristic feature of living organisms which acts as the site of all vital activities. Therefore, Huxley (1863) called it “physical basis of life”.

The Living World : Class 11th Biology Notes Chapter – 1 (Part 1)

Characteristics of Living Being –

Growth
Reproduction
Metabolism
Consciousness

1. Growth :

Overall increase in mass or size of tissue or organism or its parts is called growth.
Growth is a fundamental characteristic of all living organisms.
It is regarded as an intrinsic property of living organisms through which they can increase both in mass and in number of cells, in their body.
Increase in mass and increase in number of individuals are twin characteristics of growth.
Intrinsic growth : Growth from inside of the body of living organism.
All living organisms whether unicellular or multicellular grows by cell division.
In plants, this growth by cell division occurs continuously throughout life span.
In animals, this growth is seen only up to a certain age.
The pattern and duration of growth is distinct in different organisms.
In unicellular organisms like bacteria, amoeba growth occurs by cell division also leads to the growth of their population.
Growth and reproduction are mutually inclusive events, in unicellular organisms.
In higher animals and plants, growth and reproduction are linked but are mutually exclusive events.
Also during maintenance to replace lost cells due to some injury, etc. from the body.
To maintain original size shape and structure of a body, new cells are formed by division in various living beings.
Growth involves both increase in mass and number of cells which takes place from inside the body of living organisms and is irreversible.
On the other hand non-living objects can also be seen growing like snow mountain grow by addition of snow on them, crystal increase in size by addition of molecule.
Non-living objects growth is extrinsic as compared to intrinsic growth in living organism.
Non-living objects can increase their mass by accumulation of maternal on surface by any external agency which can be reversed.

Growth, therefore cannot be taken as defining property of living organisms, though it takes place in all living organisms and is absent in dead organisms.

2. Reproduction :

Reproduction is one of the fundamental characteristics of living organisms.
It can be defined as the production of new individuals of same kind by the grown up individuals.
It is the characteristic exhibits the living organisms which can produce new young ones of their own kind.
In asexual mode, new individuals are produced from specialised or any unspecialised part of single parent (i.e. with or without the involvement of gamete formation).
Bacteria, protozoa and other unicellular organisms mostly reproduce by splitting of their cells. It is a kind of asexual reproduction.
The lower organisms reproduce asexually by budding and fission.

By Asexual spores : In algae and fungi.
By Budding : In Yeast and Hydra.
By Fragmentation : In filamentous Algae, Fungi and Protonema of moss plants.
By True Regeneration : In Planaria.
By Fission : In bacteria, unicelluar algae and protozoans (amoeba)

For instance, unicellular organism like bacteria, unicellular algae (chalmydomonas, Chlorella) or protozoans (Amoeba) divide by fission to produce new individuals.
In such processes parent body undergoes division to form two or more individuals, i.e. number of cells increases.
Unicellular organisms reproduction is synonymous with growth, i.e., increase in number of cells.
In lower organism like yeasts and hydra budding takes place in which new individuals are produced by the formation of an outgrowth known as “bud”.
These buds first grows on parent’s body and then separates from it, to give rise new individual.
Fragmentation is also an another mode of asexual reproduction, in this body of an organism (parent body) breaks up into two or more parts (known as fragments) each of which grows into a new individual.
It is also quite common in filamentous algae, fungus, bryophytes (at protonema stage which occurs during life cycle in mosses).
Planaria (flatworm) exhibits an extraordinary ability to regenerate its lost body parts completely (which is known as true regeneration).
This is a method of reproduction as new planarians develop by splitting of parent planarian body either lengthwise or transversely.
In higher organisms like plant, animals sexual mode of reproduction is quite common which involves formation of gametes (i.e. sex cells) from two parents of opposite sexes but same species.
These gametes that fuse to form zygote (2n) which develops to form a new organism of same kind.
Male Sperm + Female Egg — Zygote — Embryo — Baby
Reproduction is shown by all living organisms except a few which are either sterile or infertile, like mule, worker-bees, infertile human couples, etc do not reproduce at all.

Reproduction can be regarded as characteristic of living organisms but it is not their exclusive defining characteristic.

3. Metabolism :

The sum total of all the chemical reactions occuring in the body of living organisms is known as metabolism.

Anabolism

These are the biochemical reactions concerned with ‘building up’ or ‘synthesis‘ of complex substances from simple ones.
During this process, the free energy is stored in the form of potential energy.
Example – synthesis of carbohydrates from CO2 and H2O in presence of light and chlorophyll during photosynthesis – 6CO₂ + 12 H₂O —- C₆H₁₂O₆ (glucose) + 6O₂ + 6H₂O
Other examples of anabolism are synthesis of proteins from amino acid, synthesis of starch from glucose, synthesis of lipids from fatty acids and alchols etc.
Anabolic reaction : energy + smaller molecules — larger molecule

Catabolism

Large molecules are broken down into smaller are known as catabolism.
During breakdown, the potential energy is converted into kinetic energy.
E.g. Sugar broken down into molecules of water and carbon dioxide, to liberate energy, i.e. ATP.
Catabolic Reaction : larger molecule — energy + smaller molecules

On the other hand, non-living objects do not show metabolism. So, metabolism can be regarded as defining feature of all living organisms.

An isolated metabolic reaction 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. Hence, cellular organisation of the body is the defining feature of life forms

4. Consciousness :

Most obvious and technically complicated feature of all living organism.

All living organisms are able to detect changes, i.e., sense their surroundings and can also respond to them.

Sensitivity –

The ability to detect changes in the environment and to give response towards it accordingly.

Stimulus –

Any change that can be detected by an organism is called stimulus.

This can be physical (like intensity, duration, direction of light, sound, change in temperature, duration of day length, i.e. photoperiod, etc), chemical (like acids, pollutants, etc) or biological (like other organisms).

We sense and feel stimuli through our sense organs.
Similarly, plants also respond to their external factors like light, water, temperature, other organisms, pollutants etc.
For example, phototropic curvature (i.e., bending towards or away from light) in plants occur due to external stimulus of light.
Some plants like soyabean, raddish, etc or animal like sheep, goat, horse, etc breed or produce at specific seasons only, like in winter, summers and autumn.
They are known as seasonal breeders as their reproductive behaviour changes with length of day, i.e. photoperiod.

Self-Consciousness –

Human being is the only organism, who is aware of himself.
He has self-consciousness too with awareness of surroundings.
He can relate his mind to the changes taking place in the world.
He is an intelligent animal with thoughts, feelings and self-hood

Sensitivity or awareness is refining as defining property of living organisms.

Consciousness therefore, becomes the defining property of living organisms.

Interaction :

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.
Similar properties of organelles are not present in the molecular constituents of the organelle but arise as a result of interaction among the molecular components comprising the organelle.
These interactions result in emergent properties at a higher level of organization.
This phenomenon is true in the hierarchy of organizational complexity at all levels.

All living organisms – present, past and future are linked to one another by the sharing of the common genetic material, but to varying degrees.

Therefore, we can say that living organisms are self-replicating, evolving and self regulating interactive systems capable of responding to external stimuli.

Biology is the story of life on earth. Biology is the stoy of evolution of living organisms on earth. All living organisms — present, past and future, are living one another by the sharing of the common genetic material, but to varying degrees.

Cells — Tissues — Organ — Organ System — Organism

The Living World : Class 11th Biology Notes Chapter – 1 (Part 2) [coming soon…]

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