Living World For Neet

INTRODUCTION

Biology is, the science of life forms and living processes

The living world comprises an amazing diversity of living organisms.

Early man could easily recognise the difference between non-living matter and living organisms.

Early man worshiped some non living matter like wind,sea, fire etc.,., and some living organisms like animals and plants out of fear they created.

Living organisms share similarities among themselves both horizontally and vertically. That allpresent day living organisms are related to each other and also to all organisms that ever lived on this earth, was a revelation which humbled man and led to cultural movements of conservation of biodiversity.

Ernst Mayy the Harvard University Evolutionary Biologist is knownas " The Darwin of 20th Century' and was one ofthe hundred greatest scientists of all times.

Ernst Mayr almost single handedly made the origin of species diversity the central question of Evolutionary Biology that it is today.

What is Living

The organisms which exhibit growth, reproduction response, metabolism, self-replication, selforganization, interactions and emergence are the unique features of the living organisms.

Growth:

Alliving organisms show growth.

The twin characteristics of growth are increase in mass and increase in number of individuals.

A multicellular organism grows by cell division

In plants growth occurs continuously throughout their life span.

In animals, growth is seen only upto a certain age.

Unicellular Organisms also grow in size until they divide by cell division

In living organisms growth is (from inside

Non-living objects also exhibit growth by accumulation of material on the surface. Hence growth cannot be taken of defining property of living organisms.

Eg: Moutains, Boulders, Sand mounds

[ ] Growth is a permanent and irreversible increase in the size of a living organism generally accompanied by the change dry weight.

[ ] A dead organismdoes not grow.

[ ] in vitro: Outsidea living organism and in an artificial envronment.

Reproduction:

In multicellular organisms reproduction refers to the production ofprogeny possessing features more or

less similar to those of parents.

Organisms reproduce by sexual and asexual methods.

Spore : It is anasexualunicellular reproductive unity which directly develops in to a new plant. In higher plants, spores develop following meiosis in spore

mother cell and they are called meiospores. In Thallophytes, they maybe formed following mitosis when they are called mitospores.

Fungi multiply and spread easily due to the millions of asexual spores produced by them.

Lower organisms like yeast and Hydra exhibit budding.

Budding is a method of asexual reproduction in unicellular organisms where new individuals develop

from parent as an out growth of mature organism.

The Fungi, filamentous algae, the protonema of mosses easily multiply by fragmentation.

Fragmentation is a method of vegetative

reproduction commonly found in flamenteus forms where the plant body breaks up into smaller pieces

or fragments and each fragment develops into a new plant.

In unicellular organisms like Bacteria, unicellular algae and Amoeba, reproduction is egual to growth

i.e., increase in number of cells.

In unicellular organisms we are not clear about the usage of growth and r reproduction.

Fission is a method of asexual reproduction in unicellular organisms involving the division of nucleus

and cytoplasm into two or more parts to form new individuals.

Mules, sterile worker bees, Infertile human

couples etc, do not show reproduction. Hence reproduction cannot be taken as defining property of living organısms.

Growth