INTRODUCTION TO ZOOLOGY (properties of life) QnA (4,5)

Question: 4. What constitutes life? 

                         OR

    What are the properties of life?

Answer: 

Properties of life

Looking at the above picture, we can easily distinguish between a non-living and a living thing. The soil or the rocky base is non-living, while the leaves are of a plant and the millipede is an animal, and are both living. Identification of a living thing can be done based on some distinguishable fundamental characteristics or properties of life. They are:

Properties of life

ORGANISATION: 

All organisms, whether one-celled( unicellular) or many-celled( multicellular), are complex but highly organised with specialised co-coordinated parts.

In unicellular organisms, atoms make up molecules which form cell organelles. 

In multicellular organisms, similar cells form tissues which in turn form organs, having distinct functions and they form organ systems to propagate life.

REPRODUCTION: 

The process of producing new genetically identical organisms sexually ( recombination of genes from two interacting parents) or asexually ( single parent). 

While sexual reproduction requires the fusion of gametes from two parents, asexual reproduction involves a single parent. Single-celled organisms reproduce by first duplicating their DNA and then dividing it equally to form two new cells.

ADAPTATION:

 The process of changing to promote survival. This includes 

The adaptability of individual organisms in direct response to some specific challenge. 

For example, The changes occurring in the body between rest and exercise show the adaptability of the individual: the rapid heartbeat, increased frequency of breath, more blood to the muscles and skin instead of the digestive system and extra red blood cells entering the bloodstream from the spleen and so forth.

 These changes are temporary but with continuous training growth of muscle fibres, a slower stronger heartbeat, and other more lasting benefits accrue. Such adaptive changes are not genetically transmissible to the offspring. 

Mutability( Alteration) Of Genes And Chromosomes

This occurs at random and not in response to specific needs, thus producing a range of variability in offspring. 

Mutations are changes that occur in the hereditary material, especially when genes and chromosomes are reproducing themselves. 

They occur, spontaneously and can also be induced by mutagenic agents such as certain chemicals and forms of radiation. If these changes occur in the reproductive cells, then they are transmissible to the offspring. 

If this happens, the mutation will be carried by all the cells of the new individual. The recessive mutations never help nor harm the individual, although it can be seen that the next generation is affected. e.g albinism.

Example: The environment may define the survival rate of the mutant trait. The very restricted habitat of the White gypsum dunes of white sands National Monument, New Mexico, is successfully inhabited by whitish varieties of both mammals and reptiles, whose darker relatives inhabit the surrounding desert but lack protective colouration for the dunes. In this case, a minor genetic change affecting colouration has opened up an entirely new habitat for exploitation by the mutant organisms.

 RESPONSE TO STIMULUS(Irritability):

 Ability to sense and respond adaptively to external and internal stimuli. 

For example, 
(a)  Most common example exists of people, putting their hands off flame fast.

(b) an organism may migrate toward the source of nutrients or away from noxious chemicals.

(c) The plant Mimosa pudica shows a rapid response to stimuli, such as being touched, changes in heat or changes in light intensity. The reaction to the stimulus includes the folding in of the plant's leaves and the downward bending of the stem. 

ENDOGENOUS(self-generated) MOTILITY:

Not all organisms are capable of locomotion (mobility) during all stages of their lives, but no matter how stationary an organism itself may be, self-generated movement of body parts does occur. 

For example:

In plants, the foliage turns towards the light and roots turn towards gravity.

In animals, melatonin is secreted during darkness in 24 hr light-dark cycle. This means that the duration of melatonin secretion is greater on short days than on long days. An increased period of melatonin secretion in short days has a positive effect on reproductive function in short-day breeders ( e.g. Buffalo, deer, sheep). A decreased period of melatonin secretion on long days has a positive effect on reproductive function in long-day breeders ( hamster, horse).

NUTRITION: 

The process of obtaining and using substances ( nutrients) for growth maintenance, and reproduction.

Nutrition in plants: Plants synthesise nutrients for their nutrition from carbon dioxide(CO2) and water by trapping solar energy through the process of photosynthesis.

Plants need in total seventeen essential plant nutrients in which carbon, oxygen and hydrogen are absorbed from air and nitrogen from the soil.

The growing medium of the plant should have the following

Macronutrients: Nitrogen(N), phosphorus(P), potassium(K), calcium(Ca), sulfur(S), magnesium(Mg), carbon(C), oxygen(O), hydrogen(H).

Micronutrients (trace minerals): Iron(Fe), boron(B), chlorine(Cl), manganese(Mn), zinc(Zn), copper(Cu), molybdenum(Mo), nickel(Ni). 

All of these elements are there in the soil as salts. The plant absorbs them as ions.

Almost all soil conditions around the globe can provide plants with all these nutrients needed for their life cycle.

Nutrition in Animals: Plants are autotrophs and make their food but animals are heterotrophs and hence they depend on other organisms like plants or other animals for their food. The nutrients used by animals include carbohydrates, lipids, nucleic acids, proteins, minerals and vitamins.

There are processes which help get Nutrition. They're

Ingestion:The process of taking in food to get nutrients. The large nutrients in food cannot pass through the cell membrane. So food is first broken down into smaller particles so that the nutrients and organic molecules can be used. 

We ingest food through the mouth where the commencement of the breakdown of food begins for digestion.

 Digestion:Mechanical and chemical breakdown of nutrients.

Absorption:Uptake into tissues of products of digestion.

INTERNAL TRANSPORT: Distribution of foods, waste etc., through the body, often using the circulatory system.

METABOLISM:

Chemical conversion of nutrients within the cells includes 

(a) Catabolism, which is the breakdown of large molecules into smaller ones, with the liberation of energy, and, 

(b) anabolism, which is the synthesis of larger molecules from smaller ones, with the use of some of this energy.

EXCRETION: 

Removal of metabolic wastes, such as ammonia and urea, or any substance present to excess, as needed to maintain the body's state of dynamic chemical equilibrium( homeostasis). 

HOMEOSTASIS:

Homeostasis is the property of living organisms in which a stable internal environment is maintained even with changing external environment. Conditions like temperature, pH and concentrates of different chemicals are maintained by homeostasis.

In plants, the taking in of carbon dioxide and leaving out of oxygen is maintained by the presence of an organelle called stomata on the lower surface of the leaf. They are the openings which open and close to maintain the temperature and water level constant.

Example: In cold-blooded animals, homeostasis plays a vital role. 

In reptiles, amphibians and fishes, the body temperature is controlled by homeostasis. The African lungfish estivates. During summer, lungfish wrap themselves in mucus and mud and go to sleep ( estivation) till the environment is cooler.

Example: Just not the temperature, but in animals, from koalas to elephants, just to maintain the microbiome ( i.e., the bacteria and other beneficial organisms which grow inside the body and keep them healthy), the younger animals eat the faeces of their parents.

NUCLEIC ACIDS: 

DNA ( deoxyribonucleic acid) and RNA ( ribonucleic acid), are macromolecules synthesized by all living organisms and on which all biological reproduction depends.

So, these are the major factors which define life.

Question- 5. What is an animal?

Answer: The Latin word anima ( "breath", "soul") itself implies a being that is animated ( lively), mobile and sentient, a bit much to ask of a sponge! Yet sponges are animals. So more conservatively, let us say that an animal is an organism ( living thing) that as a rule, ingests organic materials (proteins, fats, carbohydrates, etc.) and digests them internally. 

Animals are multicellular Eukaryotic organisms in the biological kingdom Animalia, whose cells are bound together by collagen.

This kingdom of living things( earthworms, crabs, birds, humans) differs from plants typically in not being able to move about, not having cell walls made of cellulose and depending on plants and other animals for food.

Over 1.5 million living animal species have been described. It has been estimated that there are in total, over seven million animal species. 

Next: Difference between plants and animal.