Submitted By:

Name: Jannatun Nasa Ritu

Submitted to:
Name: Farzana Sultana Bari
Assistant Professor
Dept. of Public Health &Nutrition, PAU
 What is life?

Life is a characteristic shared by ‘objects’ with self-sustaining biological processes. the condition

that distinguishes animals and plants from inorganic matter, including the capacity for growth,

reproduction, functional activity, and continual change preceding death. Life is defined as any

system capable of performing functions such as eating, metabolizing, excreting, breathing,

moving, growing, reproducing, and responding to external stimuli. An example of life is a person

who is breathing, walking and talking . An example of life is all the plants living in a pond.

Theories of Origin of Life

The origin of life means the emergence of heritable and evolvable self-reproduction. “Origin of

Life” may be a very complex subject, and oftentimes controversial. Two opposing scientific

theories that existed on this complex subject for an extended time were the socalled intelligent

design and creationism. the large bang theory of the origin of the Universe gave new ideas about

the subject of biological evolution. it's been hypothesized that complex life-forms on Earth,

including humans, arose over a period of your time from simple bacterialike tiny cells by a

process of self-organization like the evolution of the Universe by self-organization of

straightforward material structures (i.e, fundamental particles produced by the large bang)

toward more and more complex structures. There are several theories about the origin of life. it's

a really difficult task to seek out the idea involves behind the origin of life. Some important

theories are discussed here:

1. Special creation: Life formation on the world may are taken place thanks to supernatural or

divine forces. There are different sorts of accreditations by different religions. •HINDU
CONCEPT: the entire world, plants, oceans, rivers, humans, animals are created by Lord

Brahma. •CHRISTIAN & ISLAM CONCEPT: God created the universe, citizenry, plants,

oceans and rivers in six days. All the plants and animals were created directly. All the living

organisms were created within the same form as they exist today. Electric Spark Community

Clay Deep-Sea Vents Chilly Start RNA world Simple beginning Theory of biochemical

evolution Spontaneous Origin Extraterrestrial Origin (Panespermia) Special Creation Origin of

life the idea of special creation also suggests that Diversity of body won't change in future. This

theory of origin of life has no scientific explanations. 2. Extraterrestrial origin: This theory is

given by Richer in 1865 and also referred to as cosmozoic theory. Panspermia means "seeds

everywhere". This hypothesis states that the "seeds" of life exist everywhere the Universe and

may be propagated through space from one location to a different. Some believe that life on

Earth may have originated through these "seeds" i.e. Life formation didn't happen on earth. It

happened elsewhere within the space or on the other planet and carried to the world. Mechanisms

for panspermia include the deflection of interstellar dust by radiation pressure and extremophile

microorganisms traveling through space within an asteroid, meteorite or comet. for instance,

rocks regularly get blasted off Mars by cosmic impacts, and variety of Martian meteorites are

found on earth that it's controversially stated that microbes brought up here, potentially making

us all Martians originally. it's also suggested that life may need carried from comets. Three

popular variations of the panspermia hypothesis are: Litho panspermia (interstellar panspermia) -

impact-expelled rocks from a planet's surface function transfer vehicles for spreading biological

material from one system to a different. Ballistic panspermia (interplanetary panspermia) -

impact-expelled rocks from a planet's surface function transfer vehicles for spreading biological

material from one planet to a different within an equivalent system Directed Panspermia - the
intentional spreading of the seeds of life to other planets by a complicated extraterrestrial

civilization, or the intentional spreading of the seeds of life from Earth to other planets by

humans. Panspermia doesn't provide an evidence for evolution or attempt pinpoint the origin of

life within the Universe. The panspermia hypothesis gives no explanation for a way life that

arrived on Earth came to be. albeit we are ready to show that life on Earth was a results of

panspermia, the question of where and the way life originated are going to be tons harder to

answer. 3. Spontaneous origin: Life may have evolved from non-living matter as association

with prebiotic molecules under primitive earth conditions, became more and more complex. This

theory suggests that life could come from nonliving things, decaying and rotting matter like

straw, mud, etc. Several experiments are conducted to disprove abiogenesis. In 1668, Francesco

Redi a scientific experiment to check the spontaneous creation of maggots by placing fresh meat

in three different jars. He found the maggots in open jar and on the outside surface of the

material that covered the jar. No maggots were found within the sealed jar. Redi successfully

demonstrated that the maggots came from fly eggs and thereby helped to disprove abiogenesis.

Pasteur rejected the idea of abiogenesis and demonstrated that life came from pre-existing life. In

his experiment, he kept killed yeast cells in pre-sterilised flask and another flask open into air.

The life didn't evolved within the former but new animate thing evolved within the later flask.

Several other experiments like Needham’s experiment, Spallanzani's Experiment etc. are

performed which disprove the idea of spontaneous origin. abiogenesis is that the incorrect

hypothesis that nonliving things are capable of manufacturing life. 4. Theory of Biochemical

Evolution: Several models for the origin of life are suggested. the primary 'modern' model for the

origin of life was presented within the 1923 independently by the Russian biochemist A. I.

Oparin and later supported by British evolutionary biologist J. B. S. Haldane in 1928. The
Oparin and Haldane theory is understood as biochemical theory for the origin of life. consistent

with the Oparin-Haldane model, life could have arisen through a series of organic chemical

reactions that produced ever more complex biochemical structures. They proposed that common

gases within the early Earth atmosphere combined to make simple organic chemicals, which

these successively combined to make more complex molecules. Then, the complex molecules

became separated from the encompassing medium, and purchased a number of the characters of

living organisms. They became ready to absorb nutrients, to grow, to divide (reproduce), and so

on. The biochemical origin of life are often studied in three catogeries: A) Chemical Evolution of

life: 1. Formation of straightforward inorganic compounds The atmosphere of primitive earth

had various elements like hydrogen, oxygen, carbon, sulphur, phosphorous, nitrogen etc. These

free atoms combine to make molecules and straightforward inorganic compounds like ammonia,

water vapor, HCN etc. 2. Formation of straightforward organic molecules the straightforward

inorganic compounds formed in atmosphere interacted and combined to supply simple

compounds like simple sugars, purines, pyrimidines, amino acids, etc. The source of energy for

reaction could be solar radiations like UV rays, lightening, radiations from radioactive rocks and

warmth of earth. the straightforward organic compounds forms reached the ocean with rainwater.

3. Formation of complex organic molecules the straightforward organic molecules have

undergone polymerization to make complex organic molecules like protiens, nucleic acids,

amino acids etc in oceanic water. Formation of those molecules plays a key role within the

chemical evolution of life. The oceanic water rich in mixture of organic compounds. B)

Biological evolution of life Formation of life initiated from the ocean containing organic

compounds. 1. Formation of Coacervate The complex organic molecules of primordial soup in

ocean aggregated together through the colloidal system and bounded by water layer were called
coacervates. they will grow by absorbing nutrients. they need the facility of self growing and

dividing by budding like bacteria. they're intermediate between molecule and organism. a

number of the proteins within coacervates acted as enzymes and commenced metabolic

activities. 2. Formation of primary living organism The coacervates presumably obtained energy

by fermentation from the oceanic soup. They were anaerobes. They trusted the prevailing

organic molecules for his or her nutrition. 3. Origin of Autotrophs When supply of existing

organic compounds was exhausted, a number of the heterotrophs may need evolved into

autotrophs. These organisms were capable of synthesizing their own organic compounds by

chemosynthesis. They were therefore chemoautotrophs. They develop the chlorophyll through

which the autotrophs can prepare the food. Oxygen evolved during the photosynthesis and began

to accumulate in atmosphere. C) Cognogeny With gradual increase within the number of

heterotrophs as they consumed nutrients of the ocean, there became a declination in organic

nutrients. in order that they began to look other alternatives for obtaining food. During

photosynthesis, solar power was trapped by light trapping pigment called chlorophyll. during this

way several other organisms evolved (prokaryotic, anaerobic etc.). With the rise meant in

number of photoautotrophs O2 released in great extent in ocean and came into atmosphere. Now

an oxidising type atmosphere has been formed. Then prokaryotes gradually modified to be

adapted to the aerobic mode of respiration. Gradually many sorts of algae, fungi, protozoa and

other organic living organisms developed.

5. Simple Beginnings: rather than originating from complex molecules like RNA, DNA, life may

need begun with small and straightforward molecules interacting with one another in cycles of

reactions. These reactions may need been change an easy capsule to cell membranes and over

time more complex molecules or cells. this is often the foremost simple of the standing theories,
and is difficult to dismiss. 6. RNA world: within the formation of life DNA, RNA and proteins

play important role. DNA can store genetic information and proteins can catalyze the reactions.

But RNA can do both the roles. RNA has the self-replicating properties. The RNA world theory

suggests that life on Earth began with simple RNA molecule that would copy itself without help

from the other molecule. The compelling feature of RNA World is that a primordial molecule

provided both catalytic power and therefore the ability to propagate its chemical identity over

generations. Pieces of RNA are made which will copy RNA strands longer than themselves,

supporting the thought that the primary life was supported self-replicating RNA, not DNA. 7.

Chilly start: Ice may need covered the oceans 3 billion years ago, because the sun was 3 times

less luminous than it now. This layer of ice, possibly many feet thick, may need protected fragile,

organic compounds within the water below from ultraviolet and destruction from cosmic

impacts. The cold may need also helped these molecules to survive longer, allowing reactions to

happen. The enzyme doesn't yet copy itself. the most barrier seems to be the folded structure that

permits it to repeat other RNA. The RNA enzyme’s effectiveness at cold temperatures suggests

ice was crucial to the primary life. When a mixture of RNA and metal ions freezes, growing ice

crystals suck up the water, leaving tiny pockets of RNA. At cold temperatures, RNA strands

often stay together, making it tricky to separate them after the RNA has been copied. Ice freezes

and melts all the time, so you'll easily see how an RNA replicator might be enclosed, released

and allowed to spread. 8. Deep-Sea Vents: This theory suggests that life arose deep within the

ocean within warm, rocky structures called hydrothermal vents. This theory suggests that life

may have begun at submarine hydrothermal vents and ejecting hydrogen rich molecules. Their

rocky nooks could then have concentrated these molecules together and provided mineral

catalysts for critical reactions. These vents are rich in chemical and thermal energy. Deep-sea
hydrothermal vents are porous geological structures produced by chemical reactions between

solid rock and water. Alkaline fluids from the Earth’s crust flow up the vent towards the more

acidic ocean water, creating natural proton concentration differences remarkably almost like

those powering all living cells. 9. Community Clay: the primary molecule of life, hydrocarbon,

may need met on the clay. These surfaces won't only have concentrated these organic

compounds together but also helped organize them into patterns very similar to our genes.

Mineral crystals in clay could have arranged organic molecules into organized patterns. Clay

minerals played a key role in chemical evolution and therefore the origins of life due to their

ability to require up, protect (from UV radiations), concentrate, and catalyse the polymerization

of organic molecules. Clay minerals also can store and replicate structural defects and ionic

substitutions and act as ‘genetic candidates’. therefore the minerals and organic molecules within

the layers of clay would favour the formation and replication of biological molecules (e.g.

enzymes, polynucleotides) and favour the likelihood of origin of life through this theory.

10.Electric Spark: Lightning may have provided the spark needed for all times to start. There are

two distinct versions of the spark of life theory. the primary of those versions holds that the

primary sort of life came into existence following “one spark” or on one particular "spark day."

the opposite version argues that life came into existence, or rather emerged, following prolonged

sparking rather one specific spark. Electric sparks can generate amino acids and sugars from an

environment loaded with water, methane, ammonia and hydrogen, as described in Miller Urey

experiment. this means that lightning may need helped create the key building blocks of life on

Earth in its youth. Over time larger molecules could form as a results of this.