The cell theory

The cell Theory
   
The German botanist, M.J. Schleiden and the Zoologist Theoder Schwann first propounded the cell theory in 1839. Biologists corrected and modified the cell theory given by Schleiden and Schwann and summarized it as follows.
Statement of cell theory:
1. All living organisms are composed of small living unit called 'cells'.
2. All the cells are fundamentally similar in chemical compositions and metabolic activities.
3. The functions of an organism as a whole are the outcome of the activities and        interactions of the cells consisting the body of that organism.
4. All cells arise from pre-existing cells.
5. The cells are structural and functional unit of life.
6. The growth of organism occurs by the cell division and cellular growth in multicellular organisms while by cellular growth in unicellular organisms.

Short-comings of cell theory
   
The cell theory is more generalized and corrected. However, it does not apply for all organisms. There are some exceptions. These are:
1. Bacteria and Cyanobacteria lack true nucleus. Their nuclear material (DNA) is not enclosed by nuclear membrane but lies directly in the cytoplasm.
2. The coenocytic bodies of some lower plants like Vaucheria (an alga) and Mucor, Rhizopus (fungi) are explainable according to the cell theory because their bodies are made up of the undivided mass of protoplasm in which many nuclei remain scattered i.e. coenocytic.
3. Viruses are also not expected to be covered by the cell theory. They consist of core of nucleic acid (DNA or RNA) surrounded by a protein sheath. They are as non-living outside the living tissue.
4. The tissues like connective tissues possess the non living materials, Matrix. About matrix like material, nothing is mentioned in cell theory.
Levels of Organization

Biosphere: The sum of all living things taken in conjunction with their environment. In essence, where life occurs, from the upper reaches of the atmosphere to the top few meters of soil, to the bottoms of the oceans. We divide the earth into atmosphere (air), lithosphere (earth), hydrosphere (water), and biosphere (life).

Ecosystem: The relationships of a smaller groups of organisms with each other and their environment. Scientists often speak of the interrelatedness of living things. Since, according to Darwin's theory, organisms adapt to their environment, they must also adapt to other organisms in that environment. We can discuss the flow of energy through an ecosystem from photosynthetic autotrophs to herbivores to carnivores.

Community: The relationships between groups of different species. For example, the desert communities consist of rabbits, coyotes, snakes, birds, mice and such plants as sahuaro cactus (Carnegia gigantea), Ocotillo, creosote bush, etc. Community structure can be disturbed by such things as fire, human activity, and over-population.

Species: Groups of similar individuals who tend to mate and produce viable, fertile offspring. We often find species described not by their reproduction (a biological species) but rather by their form (anatomical or form species).

Populations: Groups of similar individuals who tend to mate with each other in a limited geographic area. This can be as simple as a field of flowers, which is separated from another field by a hill or other area where none of these flowers occur.

Individuals: One or more cells characterized by a unique arrangement of DNA "information". These can be unicellular or multicellular. The multicellular individual exhibits specialization of cell types and division of labor into tissues, organs, and organ systems.

Organ System: (in multicellular organisms). A group of cells, tissues, and organs that perform a specific major function. For example: the cardiovascular system functions in circulation of blood.

Organ: (in multicellular organisms). A group of cells or tissues performing an overall function. For example: the heart is an organ that pumps blood within the cardiovascular system.

Tissue: (in multicellular organisms). A group of cells performing a specific function. For example heart muscle tissue is found in the heart and its unique contraction properties aid the heart's functioning as a pump. .

Cell: The fundamental unit of living things. Each cell has some sort of hereditary material (either DNA or more rarely RNA), energy acquiring chemicals, structures, etc. Living things, by definition, must have the metabolic chemicals plus a nucleic acid hereditary information molecule.

Organelle: A subunit of a cell, an organelle is involved in a specific subcellular function, for example the ribosome (the site of protein synthesis) or mitochondrion (the site of ATP generation in eukaryotes).

Molecules, atoms, and subatomic particles: The fundamental functional levels of biochemistry.

The cell

The cell
    Cell is the basic structural land functional unit of life. The cell is the simplest and smallest unit capable of carrying all the life activities. The cell may be defined as a "unit of biological activity delimited by a selectivity premeable membrane and capable of self- reproduction in a medium free of other living systems."
    Each cell is capable of performing the basic functions of life such as respiration, reproduction, excretion, growth and so on. All the life activities exhibited by the living organism are the result of combined action of these cells. In the unicellur organism a single cell performs all the life activities. Hence cell is considered as the structural and functional unit of life.

Discovery of cell
   
The science of cells began to develop only after the discovery of compound microscope by Jansens in 1590. The term "cell" was introduced by an English Scientist Robert Hooke in his book Micrographia published in London in 1665. He observed plant cells for the first time in 1665 using the compound microscope. He observed a thin section of cork and found that the bottle cork was not a homogeneous compact material but consisted many empty small cavities bounded by definite walls.
Anton Van Leeuwenhoek, the famous Dutch microscopist observed for the first time green colored bodies in the cells of plants. These bodies are now called chloroplasts. He also observed and described the bacteria and uncellur organisms.
In 1831, Robert Brown, an English Botanist described nucleus as a spherical body in plant cells. German biologists Schleiden (Botanist) and Theodar Schwann (Zoologist) formulated their well known "cell theory" in 1839, out of their parallel and independent studies of the tissues or plants and animals.
    Purkinje, the Bohemian physiologist in 1839 introduced the term protoplasm for the living content of the cell. In 1855, Rudolf Virchow stated the fact that all the cells in the body arise from pre-existing cells by cell division.

The Five Kingdoms.

Kingdom Methods of Nutrition Organization Environmental Significance Examples
Monera

(in the broadest sense, including organisms usually placed in the Domain Archaea).
 Photosynthesis, chemosynthesis, decomposer, parasitic.
 Single-celled, filament, or colony of cells; all prokaryotic.
 Monerans play various roles in almost all food chains, including producer, consumer, and decomposer.

Cyanobacteria are important oxygen producers.

Many Monerans also produce nitrogen, vitamins, antibiotics, and are important components in human and animal intestines.
 Bacteria (E. coli), cyanobacteria (Oscillatoria), methanogens, and thermacidophiles.

Protista
 Photosynthesis, absorbs food from environment, or trap/engulf smaller organisms.
 Single-celled, filamentous, colonial, and multicelled; all eukaryotic.
 Important producers in ocean/pond food chain.

Source of food in some human cultures.

Phytoplankton component that is one of the major producers of oxygen
 Plankton (both phytoplankton and zooplankton), algae (kelp, diatoms, dinoflagellates), and Protozoa (Amoeba, Paramecium).

Fungi
 Absorb food from a host or from their environment.

All heterotrophic.
 Single-celled, filamentous, to multicelled; all eukaryotic.
 Decomposer, parasite, and consumer.

Produce antibiotics, help make bread and alcohol.

Crop parasites (Dutch elm disease, Karnal Bunt, Corn Smut, etc.).
  Mushrooms (Agarics campestris, the commercial mushroom), molds, mildews, rusts and smuts (plant parasites), yeasts (Saccharomyces cerevisae, the brewer's yeast).

Plantae
 Almost all photosynthetic, although a few parasitic plants are known.
 All multicelled, photosynthetic, autotrophs...
 Food source, medicines and drugs, dyes, building material, fuel.
Producer in most food chains. Angiosperms (oaks, tulips, cacti), gymnosperms (pines, spuce, fir), mosses, ferns, liverworts, horsetails (Equisetum, the scouring rush)

Animalia
 All heterotrophic.
 Multicelled heterotrophs capable of movement at some stage during their life history (even couch potatoes).
 Consumer level in most food chains (herbivores, carnivores, omnivores).
Food source, beasts of burden and transportation, recreation, and companionship.
 Sponges, worms, molluscs, insects, starfish, mammals, amphibians, fish, birds, reptiles, and dinosaurs, and people.

Monera, the most primitive kingdom, contain living organisms remarkably similar to ancient fossils. Organisms in this group lack membrane-bound organelles associated with higher forms of life. Such organisms are known as prokaryotes. Bacteria (technically the Eubacteria) and blue-green bacteria (sometimes called blue-green algae, or cyanobacteria) are the major forms of life in this kingdom. The most primitive group, the archaebacteria, are today restricted to marginal habitats such as hot springs or areas of low oxygen concentration.
Protista were the first of the eukaryotic kingdoms, these organisms and all others have membrane-bound organelles, which allow for compartmentalization and dedication of specific areas for specific functions. The chief importance of Protista is their role as a stem group for the remaining Kingdoms: Plants, Animals, and Fungi. Major groups within the Protista include the algae, euglenoids, ciliates, protozoa, and flagellates.
Fungi are almost entirely multicellular (with yeast, Saccharomyces cerviseae, being a prominent unicellular fungus), heterotrophic (deriving their energy from another organism, whether alive or dead), and usually having some cells with two nuclei (multinucleate, as opposed to the more common one, or uninucleate) per cell. Ecologically this kingdom is important (along with certain bacteria) as decomposers and recyclers of nutrients. Economically, the Fungi provide us with food (mushrooms; Bleu cheese/Roquefort cheese; baking and brewing), antibiotics (the first of the wonder drugs, penicillin, was isolated from a fungus Penicillium), and crop parasites (doing several billion dollars per year of damage).
Plantae include multicelled organisms that are all autotrophic (capable of making their own food by the process of photosynthesis, the conversion of sunlight energy into chemical energy). Ecologically, this kingdom is generally (along with photosynthetic organisms in Monera and Protista) termed the producers, and rest at the base of all food webs. A food web is an ecological concept to trace energy flow through an ecosystem. Economically, this kingdom is unparalleled, with agriculture providing billions of dollars to the economy (as well as the foundation of "civilization"). Food, building materials, paper, drugs (both legal and illegal), and roses, are plants or plant-derived products.
Animalia consists entirely of multicellular heterotrophs that are all capable (at some point during their life history) of mobility. Ecologically, this kingdom occupies the level of consumers, which can be subdivided into herbivore (eaters of plants) and carnivores (eaters of other animals). Humans, along with some other organisms, are omnivores (capable of functioning as herbivores or carnivores). Economically, animals provide meat, hides, beasts of burden, pleasure (pets), transportation, and scents (as used in some perfumes).

Darwinian evolution

Charles Darwin, former divinity student and former medical student, secured (through the intercession of his geology professor) an unpaid position as ship's naturalist on the British exploratory vessel H.M.S. Beagle. The voyage would provide Darwin a unique opportunity to study adaptation and gather a great deal of proof he would later incorporate into his theory of evolution. On his return to England in 1836, Darwin began (with the assistance of numerous specialists) to catalog his collections and ponder the seeming "fit" of organisms to their mode of existence. He eventually settled on four main points of a radical new hypothesis:

Adaptation: all organisms adapt to their environments.
Variation: all organisms are variable in their traits.
Over-reproduction: all organisms tend to reproduce beyond their environment's capacity to support them (this is based on the work of Thomas Malthus, who studied how populations of organisms tended to grow geometrically until they encountered a limit on their population size).
Since not all organisms are equally well adapted to their environment, some will survive and reproduce better than others this is known as natural selection. Sometimes this is also referred to as "survival of the fittest". In reality this merely deals with the reproductive success of the organisms, not solely their relative strength or speed.

Unlike the upper-class Darwin, Alfred Russel Wallace (1823-1913) came from a different social class. Wallace spent many years in South America, publishing salvaged notes in Travels on the Amazon and Rio Negro in 1853. In 1854, Wallace left England to study the natural history of Indonesia, where he contracted malaria. During a fever Wallace managed to write down his ideas on natural selection.

In 1858, Darwin received a letter from Wallace, in which Darwin's as-yet-unpublished theory of evolution and adaptation was precisely detailed. Darwin arranged for Wallace's letter to be read at a scientific meeting, along with a synopsis of his own ideas. To be correct, we need to mention that both Darwin and Wallace developed the theory, although Darwin's major work was not published until 1859 (the book On the Origin of Species by Means of Natural Selection, considered by many as one of the most influential books written [follow the hyperlink to view an online version]). While there have been some changes to the theory since 1859, most notably the incorporation of genetics and DNA into what is termed the "Modern Synthesis" during the 1940's, most scientists today acknowledge evolution as the guiding theory for modern biology.

Recent revisions of biology curricula stressed the need for underlying themes. Evolution serves as such a universal theme. An excellent site devoted to Darwin's thoughts and work is available by clicking here. At that same site is a timeline showing many of the events mentioned above in their historical contexts.

Science and the Scientific Method

Science is an objective, logical, and repeatable attempt to understand the principles and forces operating in the natural universe. Science is from the Latin word, scientia, to know. Good science is not dogmatic, but should be viewed as an ongoing process of testing and evaluation. One of the hoped-for benefits of students taking a biology course is that they will become more familiar with the process of science.

Humans seem innately interested in the world we live in. Young children drive their parents batty with constant "why" questions. Science is a means to get some of those whys answered. When we shop for groceries, we are conducting a kind of scientific experiment. If you like Brand X of soup, and Brand Y is on sale, perhaps you try Brand Y. If you like it you may buy it again, even when it is not on sale. If you did not like Brand Y, then no sale will get you to try it again.

In order to conduct science, one must know the rules of the game (imagine playing Monopoly and having to discover the rules as you play! Which is precisely what one does with some computer or videogames (before buying the cheatbook). The scientific method is to be used as a guide that can be modified. In some sciences, such as taxonomy and certain types of geology, laboratory experiments are not necessarily performed. Instead, after formulating a hypothesis, additional observations and/or collections are made from different localities.

Steps in the scientific method commonly include:

Observation: defining the problem you wish to explain.
Hypothesis: one or more falsifiable explanations for the observation.
Experimentation: Controlled attempts to test one or more hypotheses.
Conclusion: was the hypothesis supported or not? After this step the hypothesis is either modified or rejected, which causes a repeat of the steps above.
After a hypothesis has been repeatedly tested, a hierarchy of scientific thought develops. Hypothesis is the most common, with the lowest level of certainty. A theory is a hypothesis that has been repeatedly tested with little modification, e.g. The Theory of Evolution. A Law is one of the fundamental underlying principles of how the Universe is organized, e.g. The Laws of Thermodynamics, Newton's Law of Gravity. Science uses the word theory differently than it is used in the general population. Theory to most people, in general nonscientific use, is an untested idea. Scientists call this a hypothesis.

Scientific experiments are also concerned with isolating the variables. A good science experiment does not simultaneously test several variables, but rather a single variable that can be measured against a control. Scientific controlled experiments are situations where all factors are the same between two test subjects, except for the single experimental variable.

Consider a commonly conducted science fair experiment. Sandy wants to test the effect of gangsta rap music on pea plant growth. She plays loud rap music 24 hours a day to a series of pea plants grown under light, and watered every day. At the end of her experiment she concludes gangsta rap is conducive to plant growth. Her teacher grades her project very low, citing the lack of a control group for the experiment. Sandy returns to her experiment, but this time she has a separate group of plants under the same conditions as the rapping plants, but with soothing Led Zeppelin songs playing. She comes to the same conclusion as before, but now has a basis for comparison. Her teacher gives her project a better grade.

Theories Contributing to Modern Biology
Modern biology is based on several great ideas, or theories:
The Cell Theory
 The Theory of Evolution by Natural Selection
Gene Theory
Homeostasis
Robert Hooke (1635-1703), one of the first scientists to use a microscope to examine pond water, cork and other things, referred to the cavities he saw in cork as "cells", Latin for chambers. Mattias Schleiden (in 1838) concluded all plant tissues consisted of cells. In 1839, Theodore Schwann came to a similar conclusion for animal tissues. Rudolf Virchow, in 1858, combined the two ideas and added that all cells come from pre-existing cells, formulating the Cell Theory. Thus there is a chain-of-existence extending from your cells back to the earliest cells, over 3.5 billion years ago. The cell theory states that all organisms are composed of one or more cells, and that those cells have arisen from pre-existing cells.James Watson (L) and Francis Crick (R), and the model they built of the structure of deoxyribonucleic acid, DNA. While a model may seem a small thing, their development of the DNA model fostered increased understanding of how genes work. Image from the Internet.

 In 1953, American scientist James Watson and British scientist Francis Crick developed the model for deoxyribonucleic acid (DNA), a chemical that had (then) recently been deduced to be the physical carrier of inheritance. Crick hypothesized the mechanism for DNA replication and further linked DNA to proteins, an idea since referred to as the central dogma. Information from DNA "language" is converted into RNA (ribonucleic acid) "language" and then to the "language" of proteins. The central dogma explains the influence of heredity (DNA) on the organism (proteins).

Homeostasis is the maintenance of a dynamic range of conditions within which the organism can function. Temperature, pH, and energy are major components of this concept. Thermodynamics is a field of study that covers the laws governing energy transfers, and thus the basis for life on earth. Two major laws are known: the conservation of matter and energy, and entropy. These will be discussed in more detail in a later chapter. The universe is composed of two things: matter (atoms, etc.) and energy.

These first three theories are very accepted by scientists and the general public. The theory of evolution is well accepted by scientists and most of the general public. However, it remains a lightening rod for school boards, politicians, and television preachers. Much of this confusion results from what the theory says and what it does not say.

Development of the Theory of Evolution | Back to Top
Modern biology is based on several unifying themes, such as the cell theory, genetics and inheritance, Francis Crick's central dogma of information flow, and Darwin and Wallace's theory of evolution by natural selection. In this first unit we will examine these themes and the nature of science.

The Ancient Greek philosopher Anaxiamander (611-547 B.C.) and the Roman philosopher Lucretius (99-55 B.C.) coined the concept that all living things were related and that they had changed over time. The classical science of their time was observational rather than experimental. Another ancient Greek philosopher, Aristotle developed his Scala Naturae, or Ladder of Life, to explain his concept of the advancement of living things from inanimate matter to plants, then animals and finally man. This concept of man as the "crown of creation" still plagues modern evolutionary biologists

Post-Aristotlean "scientists" were constrained by the prevailing thought patterns of the Middle Ages -- the inerrancy of the biblical book of Genesis and the special creation of the world in a literal six days of the 24-hour variety. Archbishop James Ussher of Ireland, in the late 1600's calculated the age of the earth based on the geneologies from Adam and Eve listed in the biblical book of Genesis. According to Ussher's calculations, the earth was formed on October 22, 4004 B.C. These calculations were part of Ussher's book, History of the World. The chronology he developed was taken as factual, and was even printed in the front pages of bibles. Ussher's ideas were readily accepted, in part because they posed no threat to the social order of the times; comfortable ideas that would not upset the linked applecarts of church and state.
 Often new ideas must "come out of left field", appearing as wild notions, but in many cases prompting investigation which may later reveal the "truth". Ussher's ideas were comfortable, the Bible was viewed as correct, and therefore the earth must be only 5000 years old.
Geologists had for some time doubted the "truth" of a 5,000 year old earth. Leonardo da Vinci (painter of the Last Supper, and the Mona Lisa, architect and engineer) calculated the sedimentation rates in the Po River of Italy. Da Vinci concluded it took 200,000 years to form some nearby rock deposits. Galileo, convicted heretic for his contention that the Earth was not the center of the Universe, studied fossils (evidence of past life) and concluded that they were real and not inanimate artifacts. James Hutton, regarded as the Father of modern geology, developed the Theory of Uniformitarianism, the basis of modern geology and paleontology. According to Hutton's work, certain geological processes operated in the past in much the same fashion as they do today, with minor exceptions of rates, etc. Thus many geological structures and processes cannot be explained if the earth was only a mere 5000 years old.

Responsibilities of Modern Biologists

Man occupies the special position in the living world. Man is trying to understand nature and has been making efforts to control according to the needs. Man has solved a few of the problems, but there are still a number of problems like
Hazards of radiation, hunger, incurable diseases and steady of population increase and deterioration of environment. In some parts of the world due to nuclear explosion the environment becomes dangerously polluted. This has area effects on the
Plants and animals of that area and there are many appear some sudden changes in the characters if plants and animals. Modern zoologist is engaged in the solution of these problems.
In some underdeveloped countries people face malnutrition. This problem can be solved from our knowledge of biological sciences. The increasing population of a country is barrier to its progress and development. The available resources
For human life like food and houses are limited. Therefore, if population of a country goes on increasing it will be a problem for the country. All though the biologist have been able to find out the medicines for some medicines for some
Diseases, still there are some incurable diseases like cancer, heart diseases, allergy, etc for which no medicines have been yet discovered.
In addition to the above problems biologists of the world are serious in solving the problems like gene-synthesis, actual steps in some biological processes, origin of life, etc. One of the fastest growing fields of biological research is
Genetic engineering which involves synthesis and combination of different gene pools to produce desirable genotypes. Thus it is felt that the study of biology is not necessary but it is essential for human welfare.

Human Responsibilities for the Protection of the Earth

Nature is the source of supporting life. It must be kept balanced for which human being must try to follow and understand their responsibilities. Some of responsibilities are-
1. Natural resources must be properly utilized, recycled and conserved. We must find out the alternatives of natural resources.
2. Wild life especially endangered species must kept preserved by protecting habitant of wildlife.
3. Indiscriminate cutting of forest trees should be checked and hunting should be stopped. Afforestration programs should be encouraged.
4. Air, land, water or noise pollution must be avoided and make the environment free of pollution. Use of insecticides and pesticides should be discouraged.
5. Ecological imbalances such as green house effect, acid rain and depletion ozone layer are major concern with the human. These ecological imbalances can be minimized.
6. Must aware the people to follow the family planning strategies and make better hygienic conditions.

Characteristics of living things

 Living organisms have their own characteristics. On the basis of certain characteristics, living organisms can be distinguished from non-living like stone, car, pencil, table, etc. The living organisms have
The following characteristics which are not found in non living organisms.
1. Definite shape and size
2. Cellular structure and protoplasm
3. Movement and locomotion
4. Nutrition
5. Respiration
6. Metabolism
7. Excretion
8. Irritability
9. Reproduction
10. Growth
11. Life-cycle
12. Repair of injured part
13. Ageing and death

1. Definite shape and size: All living organisms have definite shape and size. Due to this shape and size, we can distinguish them from one to another. Non-living has
No definite shape or size. For example, stone, sand, water, and a piece of wood have no definite shape and size.

2. Cellular structure and protoplasm: All living beings are made up of small unit called cell. Each cell is the structural and fictional unit of the body containing protoplasm which performs all the functions of the
Body. Hence, protoplasm is called the physical basis of life.

3. Movement and locomotion: Movement is the process in which the entire body moves from one place to another. Generally locomotion is commonly seen in animals. Animals generally move from one place to another by locomotory
Organs. Amoeba moves by pseudopodium, paramecium by cilia, insects by wings and man by legs.
Movement of plants is generally due to external stimuli and shows slow movement. Plants are fixed to the soil so they cannot move.
The bending of plants towards light is also a kind of movement.

4. Nutrition: Every living organism requires food for energy to perform various body functions. Nutrition is a process of taking food. Plants are autotrophs as they can synthesize food their own photosynthesis. Animals are
Heterotrophs as they are dependent on others for foods. Non-living has not such type or nutrition.

5. Respiration: All living things (plants and animals) perform respiration. In this process oxygen is taken in to oxidize the foods in order to release energy. Carbon dioxide and oxygen are released as by products. To carry out
This process, various respiratory organs are found in living organisms. A non-living cannot perform respiration

6. Metabolism: Various physiological activities are going inside the body of living organisms. All these physiological activities together called as metabolism. It can be divided in two parts
(I) Anabolism
(ii) Catabolism
Anabolism is a constructive process. One of such processes is photosynthesis. In this process, glucose in synthesized.
Catabolism is a destructive process. In this process substances are broken down. One of such processes is glucose is broken down into water, carbon dioxide and energy.

7. Excretion: Excretion means discharge of metabolic wastes. Due to metabolic processes inside the body, many excretory products like carbon dioxide, water, inorganic salts, urea, uric acid, creatinine, etc. are formed. As these
Substances are very toxic, therefore, they are urgently required to expel out from the body. The removal of these waste substances is called excretion.

8. Irritability: It is the ability of organism to respond to the stimuli. Any change in the environment is called the stimulus and the response of the organism though the stimulus is due to irritability. The movement of plant towards
Light, contraction and expansion of pupil due to change in the intensity of light, etc. are the examples of sensitivity or irritability.

9. Reproduction: Living organisms have the ability to produce young ones. The process of giving birth to the young ones of its own kind is called reproduction. Lower organisms reproduce asexually whereas the higher organisms reproduce
Sexually. Reproduction is essential (I) to increase the number of its own kind and (ii) for continuation of race of the organism. But non living things like stone or a chair cannot reproduce its own kind.

10. Growth: Growth is increase in size followed by permanent change in its form. Living organisms as a result of building up of protoplasm within the cells and this is due to intrinsic (internal) growth of organism. In non-living increase
In size may take place but this is due to deposition of materials on its outer surface (extrinsic).

11. Life-cycle: During development an animal or a plant passes through different stages before attaining an adult individual. In any living organism these stages are passed in a cycle and so the different stages of the developing individual
From the formation of zygote up to the adult stage is called is life-cycle. This is characteristic of higher living organisms and is absent in non-living.

12. Repair of injured part: living body can repair an injured part but non living cannot do so. For example, if small part of a stone is broken it cannot repair the broken end.

13. Ageing and death: Every living organism has a definite life span. At the end, it dies. This is applicable to both plants and animals. But a piece of stone can stay on the earth for a definite time. It has no definite age when it dies.