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01 THE LIVING WORLD
THE LIVING WORLD 9 SCAN CODE The Living World Chapter 01 The Living World 1. What is “Living”? Fig 1.1: The living world  The Earth is a beautiful place filled with wonder, adventure, and more. The living world is wonderful.  The wide range of living organisms makes it amazing.  The extraordinary habitats in which we find living organisms, be it cold mountains, deciduous forests, oceans, freshwater lakes, deserts, or hot springs, leave us speechless.  The beauty of a galloping horse, of the migrating birds, the valley of flowers, or the attacking shark evokes awe and a deep sense of wonder.  The ecological conflict and cooperation among members of a population of a community or even the molecular traffic inside a cell make us deeply reflect on what indeed is life? 1.1 Characteristics of Living Things  Growth, reproduction, ability to sense the environment and mount a suitable response are unique features of living organisms.  A few more features are metabolism, ability to self-replicate, self-organize, interact, and emergence. Fig 1.2: Characteristics of living organisms Growth Consciousness Cellular organisation Metabolism Reproduction
10 THE LIVING WORLD SCAN CODE The Living World 1.1.1 Growth  All living organisms grow.  An increase in mass and increase in the number of individuals are twin characteristics of growth. Fig 1.3: Twin characteristics of growth Increase in cell number  A multicellular organism grows by cell division. Fig 1.4: Growth by cell division  However, cell division occurs in certain tissues to replace lost cells.  Unicellular organisms also grow by cell division. It can be easily observed in 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. Cell Division Plants Growth by cell division occurs continuously throughout their life span. Animals Growth is seen only up to a certain age. Growth Increase in cell number Increase in body mass
THE LIVING WORLD 11 SCAN CODE The Living World Increase in Body Mass  An increase in body mass is considered as growth. So, non-living objects also grow if we take an increase in body mass as a criterion for growth.  Mountains, boulders, and sand mounds do grow. However, this kind of growth exhibited by non-living objects is by the accumulation of material on the surface whereas, in living organisms, growth is from the inside.  A dead organism does not grow. Fig 1.5: Increase in body mass of non-living things Growth, therefore, cannot be taken as a defining property of living organisms. Conditions under which it can be observed in all living organisms have to be explained and then we understand that it is a characteristic of living systems. 1.1.2 Reproduction  Reproduction, likewise, is a characteristic of living organisms.  In multicellular organisms, reproduction refers to the production of progeny possessing features more or less similar to those of parents.  Organisms reproduce by asexual means also. Mode of Asexual Reproduction Organism Asexual spores Fungi Budding Yeast and Hydra Regeneration Planaria (flatworms) Fragmentation Fungi, filamentous algae, and protonema of mosses  Planaria (flatworms) show true regeneration i.e. if a fragmented organism regenerates the lost part of its body and becomes a new organism.  Asexual reproduction has no significant role in evolution because there are no variations (no meiosis).