NCERT Based Test: What is Living

• Increase in body mass (by cell division) and increase in number of individuals (by reproduction) are considered as twin characteristics of growth.
• As non-living organisms also grow and many living organisms are unable to reproduce, therefore, growth and reproduction are not considered as defining characteristics of living organisms.
• All organisms, from primitive prokaryotes to most advanced and complex eukaryotes, are able to sense and respond to environmental factors.
• The stimuli are perceived by sense organs in higher animals through sensory receptors e.g. eyes, ears, nose. Plants do not possess such sense organs. However, they do respond to external factors such as light, water, temperature, pollutants, other organisms, etc.
• Human beings have an additional facility of self consciousness (awareness of self).
• Consciousness and response to stimuli are said to be the defining properties of living organisms.
• The sum total of all the chemical reactions occurring in our body is called metabolism. Non-living objects do not exhibit metabolism. Metabolic reactions can be demonstrated outside the body in cell-free systems.
• An isolated metabolic reaction outside the body of an organism, performed in a test tube is neither living nor nonliving.
• Cellular structure is the defining property of living beings as each living being is a complex entity which is formed of one or more cells.

A multicellular organism increases its mass by cell division. In plants growth continues throughout life as they have meristematic areas where cell divisions occur continuously. In animals, growth occurs to a certain age after which cells divide only to replace worn out and lost cells.

• A mule is a hybrid of male donkey and female horse.
• It inherited size and intelligence from the horse and firm footedness, great tolerance and ability to live on rough food from the donkey. However, with all its hybrid vigour the mule is sexually sterile (i.e., unable to reproduce) and have to be produced every time a new.
• Honey bees are colonial, social and polymorphic inserts.
• Three types of individuals (castes) are found in the colony of honey bees: (i) Queen which is fertile female, (ii) Drones which are males, (iii) Workers are sterile females and perform various duties of the colony.
• A large number of couples are infertile It means they are unable to produce children inspite of unprotected sexual activities. Thus inability to conceive or produce children even after unprotected sexual cohabitation is called as infertility.

• In fungi, vegetative reproduction occurs by fragmentation, budding (in yeasts), sclerotia, rhizomorphs, etc.
• In algae, asexual reproduction occurs by means of various kinds of spores. However, in some filamentous algae, multiplication occurs by fragmentation.
• In Bryopsida (mosses), vegetative reproduction occurs through fragmentation, formation of secondary protonema, gemmae, tubers, etc

Reproduction is the formation of new individuals of the similar kind — Life arises promote-existing life. Reproduction is not essential for survival of the individuals It is required for perpetuation of a population.