DEFINING FEATURES OF LIVING ORGANISMS [ CLASS XI LIVING WORLD ]

CLICK ON THE BELOW LINK FOR A VIDEO EXPLANATION OF THIS TOPIC IN MARATHI -DEFINING PROPERTIES OF LIVING ORGANISM                                                                                                                             

We find living organism in variety of habitats like  deserts, cold mountains, oceans, grasslands, forests, lakes, hot springs etc. When we try to define living, we look into characteristics like growth, reproduction, metabolism, ability to sense and respond. But what differentiates living from non- living or define living is called DEFINING FEATURE of living organisms.

Let us try to understand which is the defining feature of living organisms.

1. GROWTH- All living organisms show growth. An increase in mass or increase in number of individuals can be considered as growth. In plants, growth occurs throughout their life. In animals growth is seen only up to certain age. Unicellular organisms grow by cell division like a single bacterial cell divides to form two new cells. 

Growth is also exhibited by non-living objects like sand mounds, when air currents bring sand and deposit it over sand mounds it shows growth. However this growth of non living objects is from outside.

Growth shown by living beings is from inside. But as growth is shown by living and non living, GROWTH CANT BE CONSIDERED AS DEFINING PROPERTY of living beings.

2. REPRODUCTION: Living organisms can form progeny like themselves this property is reproduction. Types of reproduction are sexual and asexual. Sexual reproduction involves formation of gametes and fertilization  to form zygote and offspring. 

Asexual reproduction involves only one parent and progeny formed is the clone of their parents. Eg. Plants can reproduce using their vegetative parts like root, stem, leaf this is vegetative reproduction, Amoeba, Paramoecium and Bacteria can divide by binary fission, Planaria exhibits true regeneration, Hydra shows budding. Yeast also reproduces by budding, Fungi like Penicillium, Mucor produces spores, Algae like spirogyra reproduces by fragmentation of filaments.

Their are certain examples of living organisms who cannot show reproduction like Infertile human couple who cannot have offsprings,

Sterile worker bees in honeybees are female who are engaged in the protection of honeycomb and collection of honey. but these worker bees cant lay eggs.

Mules produced by the artificial crossing of horse and donkey also cant reproduce. From these examples, we can conclude that REPRODUCTION ALSO CANT BE CONSIDERED AS DEFINING PROPERTY of living organisms.

3. METABOLISM: Cells of living organisms have enzymes and biomolecules. These substances in cytoplasm exhibits reactions. The sum total of all reactions occurring inside the cell is called metabolism. Metabolic reactions are catabolic plus anabolic. Catabolic reactions are degradative and anabolic are synthetic.

METABOLISM IS DEFINING FEATURE of living organism but reactions can also be performed outside the cell in vitro ( inside the test tube) such reactions are living reactions but as it is occurring outside the cell so, cant be considered as living thing.

So if metabolic reactions are occurring inside the cell then we can consider it as defining feature.

hence, cellular organization showing reactions is defining feature of  living organisms

4. CONSCIOUSNESS- All living organisms respond to their surroundings. Plant show response to light, water, temperature, pollutant, etc. Animals sense their surrounding through their sense organs. Organisms from prokaryotes like bacteria to eukaryotes show ABILITY TO SENSE AND RESPOND. This property is also called IRRITABILITY.

So, We can say that all living organisms are aware of their surroundings and show CONSCIOUSNESS.

Human beings are the only organisms who are aware of themselves, so they are the only SELF CONSCIOUS beings.

This property is exclusive feature of living organisms, no non living objects exhibits it. So, CONSCIOUSNESS IS DEFINING FEATURE of living organisms.

Growth and Reproduction are feature of living organisms but not a defining feature while Metabolism with Cellular organization and Consciousness are defining feature of living organism

RELATED LINKS- 

PRACTICE MCQS ONLINE- CLASS XI- LIVING WORLD

PRACTICE MCQS ONLINE- CLASS XI- CELL CYCLE AND CELL DIVISION

SOLVE MCQS ONLINE- CLASS-XI- ANATOMY OF FLOWERING PLANTS