Class IX Biology Book Notes

Biology Sindh Text Book Board, Jamshoro.

Book arranged by www.mynoteslibrary.com 1

SECONDARY STAGE BIOLOGY

BOOK ONE

FOR CLASS IX

For

Sindh Textbook Board, Jamshoro.



CONTENTS SECTION 1 LIFE AND ITS ORIGIN CHAPTER 1 INTRODUCTION TO BIOLOGY 3 SECTION 2 ORGANIZATION OF LIFE CHAPTER 2 STRUCTURAL ORGANIZATION OF LIFE 18 SECTION 3 BIODIVERSITY CHAPTER 3 CLASSIFICATION OF LIVING ORGANISMS 40 CHAPTER 4 VIRUSES, BACTERIA AND CYANOBACTERIA 45 CHAPTER 5 FUNGI AND ALGAE 53 CHAPTER 6 BRYOPHYTES AND TRACHEOPHYTES 58 CHAPTER 7 INVERTEBRATA 65 CHAPTER 8 CHORD ATA AND VERTEBRATA 71 SECTION 4 MAINTENANCE OF LIFE CHAPTER 9 FOOD AND NUTRITION 78 CHAPTER 10 RESPIRATION 102



Chapter 1 INTRODUCTION TO BIOLOGY

Biology, the study of life is the most vital and challenging branch of science. Why? Because it is concerned with and affects all the aspects of human life. This field is ever growing, as old questions are answered and new questions are raised. When and where living organisms originated? How do they grow? How did this diversity of organism come into being? Who created it? This is just a glimpse of questions, biologists are working upon right from the day one. They are using this acquired knowledge of the basic natural processes for the welfare of mankind. Learning objectives: Definitions of biology and other branches of biology. Relationship of biology with other sciences. Biological methods of study. Contribution of medieval are recent Muslim and other Biologists Islamic and other views about origin of life on earth. The word science is derived from a Latin word meaning "to know" Science is a way of knowing. It emerges from our curiosity about ourselves, the world and the universe. Science helps human beings to understand the natural world and is concerned solely with information gained by observing and testing that world. Natural world cannot be understood with out asking questions, like how did variety of living things evolve on earth? In what way they interact? What processes must occur in each organism? Why living things differ from non-living? Common questions like these form the basis of the science of biology. 1.1 WHAT IS BIOLOGY? On your way across school campus take a moment to look around you. You will notice a variety of organism around you, e.g. sparrows, squirrels trees, bushes, grasses etc. In addition to the countless tiny ones. These all living things are studied under the head of scientific discipline called Biology. The word biology is composed of two Greek words bios meaning life and logos meaning discourse, thought, and reasoning or in simply the study. It is a branch of natural science that deals with organisms and different phenomena of life. Biology is further divided into two main branches i.e. Botany and Zoology. Botany (Gr: Botane means plants) is a branch of biology which deals with scientific study of plants while Zoology (Gr: Zoo means animals) deals with the scientific study of animals. According to the revised classification system all the small, usually, microscopic organisms which were previously classified as plants or animals have now been separated into independent groups. Study of these micro-organisms is called Microbiology. The study of biology provides information about: 1) Various kinds of living organism existing on earth. 2) Relation of existing organisms with extinct organisms. 3) Identification and grouping of living organisms on the basis of similarities,

dissimilarities and relationship. 4) Structure, function of an organism. 5) Inheritance of characters from one generation to next generation. 6) Relationships of organisms to their environment. 7) Harmful and beneficial effects produced by different living organisms etc



1.2 QURANIC TEACHING ABOUT ANIMALS AND PLANTS LIFE Almighty Allah has conveyed a great knowledge about animals and plants through our Holy book the Quran. A few of the Ayah are quoted as under: It says about the origin of life that;

"We made every living thing of water. Will they not then believe?" (Surah Al-Anbiya, Ayah 30) "And Allah has created every animal of water. Of them is (a kind) that goes upon its belly and (a kind) that goes upon two legs and (a kind) that goes upon four. Allah creates what He will. Lo! Allah is able to do all things." (Surah Al-Nur, Ayah 45) An Egyptian mufassir, Allama Abdullah Yusuf Ali has symbolised water with the protoplasm and thus explains that the protoplasm is the basis of all living matter and "the vital power of protoplasm seems to depend on the constant presence of water." "He it is who sends down water from the sky and therewith we bring forth buds of every kind; We bring forth the green blade from which we bring forth the thick-clustered grain; and from the date-palm, from the pollen thereof, spring pendant bunches; and (we bring forth) gardens of grapes, and the olive and the pomegranate, alike and unlike. Look upon the fruit thereof, when they bear fruit, and upon its ripening. Lo! Herein verily are portents for a people who believe." (Surah Al-An'am, Ayah 100) Holy Quran has explained the significance of water for plants and animals at several places.

"Who has appointed the earth as a bed and has threaded roads for you therein and has sent down water from the sky and thereby We have brought forth divers kinds of vegetation." (Surah Ta-ha, Ayah S3) Glorious Quran has also revealed some facts about the growth and variety of plants. "And in the Earth are neighbouring tracts, vineyards and ploughed lands, and date-palms, like and unlike which are watered with one water. And We have made some of them to excel others in fruit. Lo! herein verily are portents for people who have sense." (Surah Al Ra'd, Ayah 4) "Lo! Allah (it is) who splitteth the grain of corn and the date-stone (for sprouting). He brings forth the living from the dead, and is the bringer-forth of the dead from the living. Such is Allah. How then are you pervented?" (Surah Al-An'am, Ayah 96) Above passage refers to the wonderful act of production and also interaction of living and dead. Allah has also indicated the usefulness of some of the plants and animals to the human welfare. The following Ayah can be quoted for reference.



"And Lo! In the cattle there is a lesson for you, We give you to drink of that which is in their bellies, from betwixt the refuse and the blood, pure milk palatable to the drinkers." (Surah An-Nahal, Ayah 66) "And the earth have We spread out and placed therein firm hills, and caused each seemly thing to grow there in." (Surah Al-Hijr, Ayah 19) The Holy Quran also informs us about the mechanism of reproduction. "Glory be to Him Who created all the sexual pairs, of that which the earth groweth, and of themselves, and of that which they know not!" (Surah Ya-sin, Ayah 36) "And thy Lord inspired the bee, saying: choose thou habitations in the hills and in the trees and in that which they hatch; then eat of all fruits, and follow the ways of thy lord made smooth (for thee). There cometh forth from their bellies a drink diverse of hues, wherein is healing for mankind Lo! Here is indeed a portent for people who reflect." (Surah Al-Nahal, Ayah 68-69) 1.3 BRANCHES OF BIOLOGY Nearly two million species (kinds-types) of plants and animals are known to the world. Modern biology does not concern only with the recognition and classification of these species but also deals with their structural and functional aspects. Extensive research during the 20 century has led to the division of biology into a large number of specialized branches. Some of the important branches of biology common to botany and zoology are: i) Morphology (Gr: Morphe = form): This branch deals with the study of

external structural characteristics of plants and animals.

ii) Anatomy (Gr: Ana = up, tome = to cut): It deals with the internal structures or organs of an organism. In plants it deals with the arrangement of different types of tissues in root, stem leaf etc.

iii) Histology: (Gr: Histos = web or tissues): It deals with the study of tissues of plants and animals under a microscope.

iv) Cytology or Cell-Biology (Gr: Kytos = hollow vessel or cell): The study of structure, function and composition of cell and cell organelles is called cytology or cell-biology.

v) Physiology (Gr: Phusis = nature): It is the study of functions of different parts of living organisms.

vi) Ecology (Gr: Oikos = home): It is the study of relationships of living organisms with each other and with their non-living environment. It is also called environmental biology.

vii) Embryology (Gr: Embryon = embryo) or developmental biology: It is the study of progressive developmental changes which occur after zygote formation upto an organism is formed.



viii) Taxonomy (Gr: Taxis = arrangement or grouping; Noms = laws related to naming): It deals with the description; identification, classification and scientific naming of living organisms, according to their similarities and dissimilarities.

ix) Genetics (Gr: Genesis = origin): It deals with the study of inheritance including transmission of hereditary characters from parents to their offspring.

x) Palaeontology (Gr: Palaios = ancient, ontos = being organisms): It is the study of animals and plants that lived in the remote past and are now found as fossils in the rocks. It can be further divided into two branches i.e. Palaeobotany; study of plant fossils, Palaeozoology, study of animal fossils.

In the ancient past large quantities of dead organisms were fossilized and formed coal, oil and other fossil fuel. xi) Biochemistry: It deals with the chemistry and chemical aspects of the

living system.

xii) Microbiology (Micro = very small): It deals with the study of microscopic organisms such as viruses, bacteria, etc.

xiii) Biotechnology: It is the manipulation of living things (animals, plants, micro-organism) for the welfare of mankind. Recently methods of genetic engineering have brought about a revolution in this field. By using these techniques not only yoghurt, cheese, bread, insulin, antibiotics etc. Are being produced but number of diseases are cured.

1.4 BIOLOGY AND OTHER SCIENCES Biology is a multi dimensional science. It is linked with the knowledge of chemistry, physics, mathematics, sociology, statistics etc. and these branches which are related to biology are biochemistry, biophysics, biometry, etc. Some of them are discussed below. 1. Biochemistry: A complete branch of chemistry which requires firm

knowledge of biology and chemistry to explain the synthesis of bio-molecules, their requirement and the effect caused by the deficiency and efficiency of different molecules on the organisms and their metabolism.

2. Biophysics: Branch of physics where we apply laws and techniques of physics to explain the metabolism of living organism, to find out the age of fossils etc. One of the sub-branch of biophysics is Radio-physics, where radioactive isotopes are used to trace the translocation of different material "in vivo", that is, within the living organism. Radio labeling and carbon dating also show some uses of radio active isotopes in determining the age of fossils. Use of sound waves as ultrasound and laser technology show some relationship of physics with biology.

3. Biometry: It is branch of mathematics where data and measurements related to living organisms are dealt with. Without knowledge of mathematics and statistics no biological research and data analysis is possible. All biologists conclude their results by using knowledge of



statistics and mathematics.

4. Behaviourial biology: Many of the facts of biology are reflected in the study of behaviour it is an intersection of biochemistry, genetics, physiology, evolutionary theory and ecology.

5. Biosociology: The study of behaviour, especially social behaviour, also associates biology to the social sciences and humanities. Through the study of life in general, we will learn more about ourselves.

Finally, we can say that biology is related with each branch of science. 1.5 BIOLOGICAL METHOD A biological method is a scientific approach used to resolve a biological problem related to or produced by a living organism. In order to resolve a specific biological problem a biological method is adopted, which consists of following steps. (i) Observation (ii) Hypothesis (iii) Deduction (iv) Experiment (v) Result (vi) Law or theory 1. Observation: Most of the biological investigations start with an observation. After selecting, specific biological problem, observations are made to collect relevant information. For example; take the case of malaria. Malaria is a the greatest killer disease of man for centuries. Malaria was the one among many other diseases for which a cure was needed. In 1878, a French physician, Laveran, studied the blood sample of malaria patient under microscope and observed tiny creatures in it. These creatures were later named Plasmodium. 2. Hypothesis: In the light of observed facts and previously collected information (data) biologists make 'intelligent guesses' as to what may be the possible answer to this particular question. This intelligent guess in a form of a statement is called hypothesis. So, the hypothesis is a statement made by scientists about a certain phenomenon, on the basis of available information. For example, an observation was made that Plasmodium is present in the blood of malaria patients. So a question was raised, is Plasmodium the cause of malaria? It would be a good guess to say 'yes' but it is only a guess which can be presented as a hypothesis that:

"Plasmodium is the cause of malaria. 3. Deduction: To test the hypothesis certain deductions that are logical prediction are made. In other words deduction is the logical explanation of a hypothesis. It does not require any type of experimentation. For example, to test the above hypothesis the following deductions were made. "If Plasmodium is the cause of malaria, then all the patient suffering from malaria should have malarial parasite in their blood while healthy people should not have". A number of deductions can be made to explain the hypothesis. These deductions can be tested and verified by experiments. 4. Experiment: The next step is to test each deduction (prediction) practically to find out whether or not the hypothesis is correct. In testing the deduction we are actually testing a hypothesis. This is where the scientist shows his skill as an experimenter. For this



purpose, scientist performs two types of test i.e. control and experimental groups. Control group means a group of healthy people and experimental group means group of malaria patients. Both groups were kept in identical conditions. In order to find out the real cause of malarial, scientists examined the blood of about 100 malaria patients and also examined the blood of 100 healthy persons. 5. Result: From above experiment it was found that all the malarial patients had Plasmodium in their blood, where as the blood of healthy persons were free from Plasmodium. These results verified the deduction and finally the hypothesis i.e. "Plasmodium is the cause of malaria". 6. Theory: It is not always possible to confirm a hypothesis immediately. The validity of a hypothesis rests on a gradual accumulation of indirect evidences. As more and more evidence come to hand, the hypothesis gain increasing acceptance and eventually is promoted to the rank of a theory: A theory is a set of scientific assumptions consistent with one another and supported by evidence, but not fully proved e.g. theory of evolution Thus a biologist studies a problem in a sequential manner through observations, questions, hypothesis, deduction, testing or experimentation. A set of data taken from experiment, proves or disproves the hypothesis. A cautious attitude expressed in the form of criticism and further tests are performed until a satisfactory answer is obtained. The results of observations and experiments are published in scientific journals or presented in conferences, where they can be examined by all. These results must be repeatable that is they should be obtained by any one doing the same procedure. 1.6 HISTORY OF BIOLOGY The history of biology goes back to the ancient and pre historic time. Very briefly, perhaps the first noticeable development in our knowledge of biology occurred during the Greek period. Individual like Aristotle (322-384 B.C) is remembered even today. He wrote a book "Historia Animalia". Carolus Linnaeus founder of biological classification, classified animals into two units i.e. genus and species. The Phrastus, discovered sex in plants and described about five hundred plants therefore, known as founder of Botany. Hardly any original addition to biological knowledge was made by the Romans, who followed the Greeks. It was not until the beginning of the Muslim period, nearly a thousand years later that revolutionary developments occurred not only in biology but in the science in general. From the 8th to the 15th century, Muslims studied Greek and other literature, translated books of Roman and Sanskrit into Arabic, wrote new books and opened numerous centers of learning which encouraged original research and exchange of ideas between different human societies. The most outstanding contribution of Muslim scientists had been the use of experiments for the first time in scientific study. This period was truly a period of progress in biology and medicine. The following is a modest list of contributions by the Muslim and other scientists between the 8th and 20th century. Muslim and other Biologists: Muslims have made important contributions in the field of biology in earlier ages. Jabir-Bin-Hayan (722-817 A.D), wrote books named "Al-Nabatat" and "Al-Haywan" on plants and animals respectively.



Abdul Malik Asmai (741 A.D), wrote books "Alkheil, Al-IbiL "Al-wahoosh", "As-Sha" and "khalaqul Insan", describing structure and function of body parts of horses, camels, sheep, wild animals and human being. "Khalaqul Insan" was popular among the western experts in Zoology. He was regarded a specialist of his time. Ali bin Rabban Tubri (775-870 A.D), wrote book "Firdus-ul-Hikma" having many illustrations and detailed articles on Philosophy, Zoology, Psychology and Astronomy. Abu-Usman Umer Aljahiz, wrote book "Al-Haywan" which described characteristics of 350 species of animals especially, about life of ants. Al-Farabi (870-950 A.D) and Abul-Qasim Al-Zahravi (936-1004 A.D). Both were the renowned hakim and surgeon of the Islamic World. Al Farabi is the author of two very well known books i.e. "Kitab-i-Nabatat" and "Kitab-ul-Haywanat" and Zahravi was famous for the removal of urinary bladder stone. Ibn-al Haitham (965-1039 A.D), wrote books like "Kitabul Manazir" and "Mizanul-Hikma", He explained the phenomenon of vision and corrected the Greek conception about vision. Bu-Ali Sina (980 A.D), wrote books "Al-Qanoon" and "Fil Tib Al-Shifa", about plants, animals and non-living things. He is considered as one of the founder of medicine, acknowledged by the greatest expert of his time in medicines in east and west. Ziauddin Ibn-Baitar (13th century A.D) specialized in the study of plants. He travelled to several countries, observed and studied many species of plants. Ibn-al Nafees (13th century A.D) described the process of blood circulation in human body. Kamal-ud-Din al-Damiri (14th century A.D) compiled a book "Hayat-al-Haywan" deals with the characteristics of 1000 kinds of animals. Ali bin Isa was a well known eye-specialist of his time and worked on structure, function and the diseases of the eye. He wrote three volumes on this subject in which he described 130 diseases of the eye. Abul Qasim Majreeti is especially known in Europe for his book on animal species. Other Biologists: After 15th century, European and other biologists made important contribution in the field of Biology. William Harvey (1578-1657 A.D), described circulation of blood. Galileo (1610) invented microscope to examine small organisms. Robbert Hook (1665) discovered "cell" the basic unit of living organism. Linnaeus (1707-1778 A.D), developed methods of classification for organisms and gave nomenclature and therefore, called father of taxonomy. Schleiden and Schawann (1839), worked on the detailed structures of plant and animal cell, finally formulated cell theory.



Louis Pasteur (1822-1895) discovered bacteria as causes of many diseases like Tuberculosis. J.Lister (1860), discovered antiseptics e.g. Iodine and carbolic acid. E. Jennar (1896), discovered method of vaccination against small pox. Charles Darwin (1859), wrote his famous book "origin of species" about evolution of different species through Natural selection. Gregor John Mendal (1822-1884) gave his famous laws of heredity and laid foundation of Genetics. Watson and Crick (1953) proposed double helix model of DNA to explain the function of DNA as heredity material. 1.7 IMPACT OP BIOLOGICAL STUDIES ON HUMAN WELFARE Biology has made an enormous impact on human welfare by improving quality of life. It also helped in increasing food production and to improve health. New discoveries in the field of biology are bringing revolution in medicine, public health, agriculture, dentistry, veterinary medicine, animal husbandry, land-scape, horticulture, pest control and other related fields. 1.7.1 Production of food: Production of various kind of food especially crops like wheat, maize, rice and barely is very active field of biology. Man grew different vegetables and fruits to supplement his diet. With the advancement of biological techniques man has not only improved the quality and yield of the existing varieties but also produced many new varieties of crops. These successes have been achieved due to biological researches in the fields of pest control, genetics and biotechnology. Man also improved the quality and quantity of food products by developing dairy farming, poultry farming, kettle farming etc, and wheat, rice, maize and other plants. This helped to overcome the problem of food shortage. Incidence of famine has declined and economic conditions for mankind have improved. 1.7.2 Improvement of health: In the field of health, the discovery and development of new medicines, vaccines and diagnostic medical equipment has been very helpful to man kind. This is only possible due to research in biology. The discovery and development of antibiotics by biologist has played a vital role in improving our general health conditions. Many fatal and epidemic diseases such as smallpox, tetanus, diphtheria etc. can be easily controlled because of" development of vaccines against these diseases. This has resulted in a great reduction in infant mortality. Every day new drugs are constantly being developed by biologists to fight against the pathogenic organism enabling to solve the health problems of mankind. 1.7.3 Improvement of environment: During the past few decades, rapid industrialization has resulted in pollution of surroundings including air, land and water sources. As a result of this pollution not only human beings but also animal and plant life is exposed to all kinds of harmful effects. It is through biological research that we are finding out ways and means to overcome and at last eliminate the pollutants, for providing and maintaining healthy environment. 1.7.4 Genetic engineering: A new methodology referred to as recombinant DNA technology or genetic engineering has been developed. It is technique in which alteration of gene, DNA of an organism is carried out to seek benefit for mankind. It provides a way by



which mammalian proteins can be produced in bacterial cells. Genes controlling the synthesis of important drugs and hormones can be taken from the organisms in which they occur naturally and placed in bacterium or other type of organism, from which the product can be recovered conveniently and in large quantities. Most noteworthy achievement is insulin production by adding human gene in bacterial DNA which is helping to produce human insulin (Humalin) from bacteria on commercial basis. This is very useful for treating diabetes. This is one example along with many others like cloning, tissue culture etc, where genetic engineering is being used. Many inheritable diseases can now be diagnosed in a developing child before birth. Recent research has led to the hope that cystic fibrosis (hereditary disease of human being in which affected individual secrete thick mucus that clogs the air ways of lungs / liver / pancreas) and other hereditary disease will soon be treatable. Although there are many side effects of these technologies yet no one of us wishes to go back to the days in which large number of people died of epidemic diseases. As science has conquered one disease after another, the world's death rate has fallen and the human population has exploded. Few of us are willing to give up technology's gift of private automobile, though we are concerned about the amount of air pollution that automobile generate. 1.8 ORIGIN OF LIFE 1.8.1 Islamic view about the Origin of life: The Holy Quran throws adequate light on the origin of life. The most important fact in the teachings of Quran is that Allah is the ultimate creator of every thing. Living and non-living are both created by Him. There are several verses of Quran in this regard. A few are quoted below: "He is the Creator of the heavens and the earth". (Surah Al'Ana'm, Ayah 102} "That is Allah your Lord. There is no god but Him, the Creator of all things. Therefore, serve Him. He is the Guardian of all things". (Surah Al-Ana'm, Ayah 103) The preceding verse explains that all living beings including insects and snakes (which crawl), monkeys and grazers (four legged creatures) and birds and humans (two legged creatures) were created ultimately from water. It is stated:

"We did create man from an essence of clay". (Surah Al-mominoon, Ayah 12) "He (Allah) who created all things in the best way. He first created man from clay, then bred his offspring from a drop of paltry fluid. He then moulded him and breathed into him of His spirit. He gave your eyes and ears, and hearts: yet you are seldom thankful". (Surah Al-Sajda, Ayah 7-9} Once the life had been created, Allah implemented the process of reproduction for the continuity of races of animals. The various stages of reproduction have been described in Holy Quran in following way. "Then fashioned we the drop a clot, then fashioned we the clot a little lump, then fashioned we the little lump bones, then clothed the bones with flesh".



(Surah Al-mominoon, Ayah 14) "Hath there come upon man (every) any period of time in which he was a thing unremembered?" (Surah Al-Dahar, Ayah 1) A close study of above sermons reveals that all animals had common origin but they gradually underwent changes afterwards and became different from each other i.e. some developed crawling, some started walking on two legs and some other had four. It seemed that animals of today are advanced forms of the past animals who achieved this form after passing through many changes. 1.8.2 Concepts of Abiogenesis and Biogenesis: Man had believed since ancient times that living organisms (both plants and animals) arise from clay, earth and other non-living matter not from pre-existing parents of their own kind. This was based on such observations as growth of fungus on pieces of bread and the appearance of maggots on dead bodies of animals. Aristotle believed that fishes, frogs and aquatic insects spontaneously developed from mud. This old belief that living beings can spontaneously develop from the non-living is termed as abiogenesis. The idea of production of living from the non-living was experimentally analyzed. The pioneer in such experiments was an Italian scientist named Redi. Through several experiments he showed that all living organisms arise from their parents and negated the idea of abiogenesis. The view that living beings can develop only from other living being is called biogenesis. The following are a few of the experiments which Redi performed and which led to the concept of biogenesis. Experiment No.1 Some dead snakes were placed in a box. It was noticed that flies gathered around the dead snakes. After three days maggots appeared in their bodies. After about eighteen days these maggots transformed into pupae. Some of these pupae were then transferred to separated glass containers covered with a sheet of paper. After eight days, a fly emerged from each pupa and all flies were similar to those which visited the body of the dead snakes. From this it was concluded that maggots were the offsprings of flies. The flies had laid eggs on the dead snakes. These eggs gave rise to maggots which formed pupae and ultimately flies emerged from them. Experiment No.2 In another experiment Redi took eight bottles. He put dead snakes in two; pieces of meat in other bottle and dead fishes in other bottle. He kept four bottles open and four covered. After a few days, maggots appeared in the open bottles only. No maggots appeared in the bottles kept covered. This showed that if the flies were prevented from entering the bottles, the maggots did not appear. Some workers, however, criticized this experiment and said that the maggots failed to appear in the covered bottles because air being so essential for abiogenesis could not enter these bottles. To test this, Redi performed another experiment. Experiment No.3 Some pieces of meat were put in a bottle whose mouth was covered with a gauze. Thus, air could enter the bottle while flies remained out. Again no maggots appeared on the piece of meat, even after many days inspite of the fact that entry of air was possible.



These experiments provide evidence supporting the idea that only living beings give rise to living beings. Thus, the concept of Biogenesis is correct and that of Abiogenesis is wrong. Needham's experiment: In 1748, an English Scientist Needham, boiled meat in water, poured this gravy in bottles and closed their mouth with cork. After a few days many micro-organisms were produced in these covered bottles. This once again excited the believers of Abiogenesis i.e. life from non-life (Fig: 1.3). Pasture's experiment: The argument on the issue of biogenesis and abiogenesis continued up to the middle of nineteenth century, till Louis Pasture, a renowned French scientist proved with experiments, that abiogenesis could not occur in the present environment of earth. In 1864, Pasture performed his experiment, in front of the commission formed of noted biologists, to resolve this issue. He took flasks which had long curved S-shaped necks (Fig. 1.4). He added fermentable infusion (yeast + sugar + water) in bottles and left their mouth open. The yeast infusions were boiled in the flasks and let steam released out of the neck of each flask. Then flasks were allowed to cool. No life was produced even after the lapse of several days; because micro-organisms entering along with incoming air got stuck up in on the curved walls of the glass neck. To prove this he broke up the curved necks, so that now contaminated air could reach directly to the infusion. It was observed that micro-organisms were produced within 48 hours. This proved that if care was taken and no micro-organisms or their spores were allowed to reach the infusion, no life could be produced. He rejected spontaneous generation. Commission decided in favour of bio-genesis. 1.8.3 Concept of chemical and organic evolutional The modern view of origin of life stresses upon the idea of chemical evolution and ties its origin to the history of the earth and the primitive atmosphere.

How did it happen and what evidence supports this idea? In the beginning, the universe was an intensely hot point where matter and energy were indistinguishable. About 15 billion year ago, there was a Big Bang (huge explosion). The universe started expanding and the temperature dropped drastically. In time, about 4.6 billion years ago our earth and other planets appeared as part of the solar system. The Primitive atmosphere of the earth was rich in Hydrogen. Soon gases from the very hot and liquid core of the earth added more elements to this atmosphere. It is believed that the earth's atmosphere at this stage consisted carbon monoxide, carbon dioxide, Hydrogen, Nitrogen, water vapours and was exposed to intense radiation and electric spark. It hardly had any free oxygen. With the passage of time, the atmospheric temperature gradually dropped. This allowed condensation and heavy rains which caused formation of oceans. Thunder and lightning sparks together with ultraviolet radiation caused reactions of the atmospheric gases. This led to formation of simple organic molecules. These molecules I came down with rain and accumulated in the oceans, lakes, rivers and the soil over a very long period of time. These molecules had enough chances to interact in this environment and produce amino acids and proteins which are the building blocks of life. This sequence of chemical evolution was demonstrated in the middle of the 20th century by some clever laboratory experiments. Scientists were able to produce amino acids and simple sugars from a mixture of methane, ammonia, hydrogen and water by exposing it to electric sparks. More recent experiments using electric sparks in laboratory chambers have successfully produced not only amino acids and sugar but also the basic ingredients of fatty substances and DNA, all of which are the constituents of life.



Life originated on earth more than 3.5 billion years ago. We do not know how life formed, although the evidence is consistent with the hypothesis that it evolved spontaneously from chemicals. There is considerable discussion among biologists about what the early stages of such an evolutionary process might have been like. What was the first life form like? The first life form, perhaps, was a sphere of naked protein or RNA and was capable of making its copies (reproduction). At some stage, a membrane assembled around the sphere giving rise to the first cell. There is now general agreement that this first life form respired anaerobically because the earth's atmosphere lacked free oxygen; it reproduced asexually. Our present day knowledge of viruses, bacteria and how DNA makes its copies provide enough hints in support of the above view. The first living organism may have been like viruses. The next step in this story was appearance of an autotrophic way of life, that is, an organism capable of photosynthesis, adding free oxygen into the atmosphere. This availability of free oxygen opened the way for an explosion of a variety of organisms in times to come. Further improvement became possible as some of the organisms achieved the capability, to reproduce sexually. For at least the first 2 billion years of life on earth, all organisms were bacteria. About 1.5 billion years ago, the first eukaryotes appeared. The story of origin of life highlights change in matter. First inorganic molecules interacted in a way that organic molecules came into existence. The latter formed aggregates capable of making their copies and existed as naked spheres of protein or nucleic acids (RNA or DNA). Ultimately there arose the first cell a unit with a membrane. This tells us that life eventually arose by a slow process of chemical changes or organic evolution. The basic underlying concept in this process is that over a period of time (a very long period) one form gave rise to another. The idea of organic evolution was supported by scientist like Lamarck and Charles Darwin. They argued that new forms of life must have arisen from older ones through variations and that it was something in the process of heredity which was responsible for variations.



SUMMARY Biology is the study of living things. It is further divided into three main

branches Botany, Zoology and Microbiology. Biology can be divided further into a large number of branches like

morphology, anatomy, histology, cytology, physiology ecology, embryology, taxonomy, genetics, paleontology, biochemistry, biotechnology, etc.

Biology and other natural and social sciences like chemistry, physics, mathematics, sociology and statistics are inter-related.

The systematic process used in resolving a biological problem is called a biological method.

Biological investigation starts with observations and collection of information about the biological problems.

Hypothesis is a guess made by scientist about the solution of a certain phenomenon.

Deduction is a logical explanation of hypothesis. Experiment is the practical testing of hypothesis and deduction. New discoveries in the field of biology are bringing revolution in the fields of

medicine, public health, agriculture, veterinary, landscape etc. The old discarded belief that the living beings can spontaneously develop

from the non-living is termed as abiogenesis, and the view that only living things can produce their own kind is called biogenesis.

Modern view of origin of life stresses upon the idea of chemical evolution and ties it with the origin of earth and the primitive atmosphere.

Living organisms had a common origin but, with the passage of time, they gradually changed and became different from one another.



EXERCISE 1. Fill in the blanks with appropriate terms:

i) Linnaeus developed method of _________ for organisms. ii) ________ was considered as one of the founder of

medicine. iii) Biology also provides information about relation of existing

organism with ______ organism. iv) Sound waves, laser technology and use of radio-active isotopes

shows relationship of biology with _______. v) ______ verify the deduction and finally the hypothesis.

2. Write whether the statements are true or false:

i) Galileo discovered the first microscope. ii) Origin of species is written by Charles Darwin. iii) Study of tiny organism like virus, bacteria, etc is called parasitology. iv) The living things spontaneously develop from mud and clay. v) Redi was the pioneer scientist who gave the idea of biogenesis.

3. Encircle the appropriate answer:

i) Biology is the study of (a) Life (b) Non-living things (c) Space (d) Earth

ii) Study of structure, function and composition of cell is called (a) Cell-Biology (b) Histology (c) Anatomy (d) Genetic Engineering

iii) Developmental biology deals with the (a) Growth of organism (b) Functions performed by an organism (c) Development of groups and classes (d) Changes occurring in zygote

iv) The intelligent guess of a scientist in the form of a statement is called. (a) Deduction (b) Theory (c) Hypothesis (d) Law

v) Alkheil, Al-Ibil, Al-wahoosh were written by (a) Jabir-Bin-Hayan (b) Abdul Malik Asmai (c) Ibn-al-Haitham (d) Zia-uddin Baitar

4. Write detailed answers of the following questions:

iv) Make a chart to show the steps of a scientific method.

ii) Write an essay on the contributions of various scientists in the field of biology.

iii) Name some branches of biology. Also describe the relationship of biology with other branches of science.

iv) What do you mean by biogenesis and abiogenesis? Also give some experiments which explain the concept of biogenesis.

v) Write an essay on origin of life. 5. Define the following terms:

i) Physiology ii) Biochemistry



iii) Observation iv) Deduction v) Genetic Engineering vi) Biogenesis

6. Distinguish between in tabulated form:

i) Biogenesis and abiogenesis ii) Hypothesis and theory.



Chapter 2 STRUCTURAL ORGANIZATION OF LIFE

The cell is the basic unit of life. It is the smallest entity in which the life can exist. All the things that living organism can do are done by its cells. In fact some living things are made up of only one cell. Each cell gets food for energy, obtains oxygen, produces energy, gets rid of wastes, maintains homeostasis and produces new cells. How are all these life activities carried out? The answer can be found by examining the composition and working of its parts. Learning objectives: Cell as a basic unit of living organism. Discovery of cell and cell theory. Concepts of light microscopy and electron microscopy. Microscopic and Ultramicroscopic structure of plant and animal cells. Structure and functions of different cell structures. Concept of Prokaryotic and Eukaryotic cells and their differences. Reproduction of cell, different methods. Mitosis and Meiosis and their significances. Three level of organization in living organism i.e. tissues, organs and system. Types of plant tissues, simple and compound tissues, their further

classification and function in different parts of plant body. Types of animal tissues, epithelial, connective, muscle and nervous tissues,

structure of these in relation to their function. Unicellular organization, Amoeba a unicellular organism. Multicellular organization. Brassica as multicellular organization, with root, stem, leaf, flower, fruit and

seed as their parts. Frog as multicellular organization with digestive, respiratory, circulatory,

excretory, nervous and reproductive organs and systems. Cell is as fundamental to biology as an atom is to chemistry. All organisms are made of cells, which behave as basic unit of their structure and function. The contraction of muscle cells moves your eyes as you read this book; when you decide to turn this page, nerve cells will transmit that decision from your brain to the muscle cells of your hand so every thing performed by organism is fundamentally occurring at the cellular level. 2.1 DISCOVERY OF CELL AND CELL THEORY In early classes we have studied that all living organisms are composed of cells. The question arises here how did biologist come to know that, obviously through observations. These observations started with the discovery of magnifying glasses and later on with the development of microscope. (Latin word micro = small; skopion = to see). In 1610 Galileo, an Italian astronomer and physicist developed microscope to observe small organisms. In 1665, Robert Hook made an improved microscope by combining lenses, called compound microscope and examined a slice of cork under it. He found small honey comb like chambers, which reminded him small rooms of monastery and are said cellula in Italian, so he also named these structures as cellulae or cell (small rooms). The cork was made from bark of oak, so he actually saw the cell-wall only. in 1842, Dutrochet, boiled plant material in nitric acid and then examined under microscope. It was found to consists of cells. In 1831, Robert Brown discovered a spherical body, the nucleus in the cells of orchids. Schleiden (1838) a German botanist, proposed that all plants are made up of cells. Next year another German Zoologist, Theoder Schwann stated that all animals are made up of cells. He



observed nuclei in all types of animal cells but failed to observe cell-wall in them. From here the difference between plant and animal cell started to establish. In 1858, Rudolf Virchow stated that new cells come only from other cells i.e animals cells come from animal cell and plant cells from plant cell. The combined efforts of Schleiden, Schwann and R.Virchow finally gave rise to cell theory. The salient features of the cell theory are as under: i) All living organisms are composed of one or more cells. ii) The cell is the smallest, basic structural and functional unit of all

organisms. iii) New cells are formed by the division of pre-existing cells. 2.2 LIGHT MICROSCOPY AND ELECTRON MICROSCOPY The evolution of biology as well as science often parallels the invention of instruments that extend human senses to new limits. The discovery and early study of cells progressed with the invention and improvement of visual instrument, like microscope. Microscopes of various types are still important tools for the study of cells.

Resolution Magnification Resolution is the capacity to

separate adjacent objects. Resolution is maintained upto

certain magnification. Resolution improves as the

wave length of illumination become shorter.

Magnification is a means of increasing size of the object.

By increasing magnification resolution is disturbed.

Magnification improves with the focal length of lens.

The microscopes first used by scientist, as well as the microscope you use in the biology laboratory are light microscopes. These microscope use visible light as the source of illumination and glass lenses for magnification. These lenses reflect the light in a way that the image of the specimen is magnified as it is projected into the human eye. The light microscope can magnify the object upto 1000 times but its resolving power is very limited, i.e just 0.2m (Resolving power is a measure of the clarity of the image). In 1935, a new type of power full microscope called Electron microscope was invented by scientist to improve the resolving power of microscope. It uses a beam of electron as a source of illumination. The electron beam increases its resolving power. Modern electron microscope can achieve a resolution of about 0.2 nm, a thousand times improvement over light microscope. The electron microscope uses electromagnet as lenses instead of glass lenses. This image cannot focus in human eye, therefore screen or photographic plates are used to review and focus these images.

Units of measurement 1 centimeter (cm) = 10-2 meter. 1 millimeter (mm) - 10-3 meter. 1 micrometer (m) =10-6 meter. 1 nanometer (nm) = 10-9 meter.

Electron microscopes reveals many organelles that are impossible to be seen with the light microscope. But the light microscope has many advantages especially for the study of live cells. In electron microscopy, chemicals and physical methods are used to prepare sample which kills cells.



2.3 BASIC STRUCTURE OF CELL Cells are of different shapes and size according to their functions. inspite of variation found in their shape, all cells basically share many structures in common like cell membrane, cytoplasm, nucleus, etc. In plant cell, cell-membrane is surrounded by a cell-wall. 2.3.1 Cell - Structural and Functional unit: Microscopic studies reveal that all living organisms are composed of cells. Therefore, cell is a unit of structure of living organisms. Cells are of different shapes and sizes, as they have to perform different functions. All basic functional activities, characteristic of living things, occur in the cell. Therefore, cell is also a unit of function of all living organisms. 1. Cell-wall: Cell-wall is the non living, outermost boundary of plant cells, bacterial cells and fungal cells. It is not found in animal cell. It is secreted by the protoplasm of the plant cell. In plant cell it is mainly composed of cellulose and pectin. Ultra microscopic structure of cell-wall shows that cellulose make the fibers which are arranged in criss cross manner. These fibers are kept in their position by a cementing material called calcium pectate (Pectin). Bacterial cell-wall is made up of protein and carbohydrate while fungal cell wall is made up of fungal cellulose and chitin. Thickness of cell-wall varies in different cells of plant. It is composed of three main layers: middle lamella, primary wall, secondary wall and some times tertiary wall. Middle lamella is formed between the primary walls of neighbouring cells. Primary wall, the first wall of plant cell is chemically composed of cellulose and pectin, some limes, lignin. Cell-wall provides protection and support to the cell. It gives a definite shape to the cell. It also performs the function of transport of material from outside to inside or vice versa, therefore, it is permeable in nature. 2. Cell- membrane: The cell-membrane or plasma membrane surrounds nucleus and cytoplasm in all types of cells. However in bacteria and plants, plasma membrane itself is surrounded by a cell-wall. It can repair itself to some extent. Different models have been presented to understand the structure of cell membrane. The most acceptable model among them is Fluid mosaic model presented by Singer and Nicholson (1972). According to it, cell membrane consists of lipid (Phospho-lipid) bilayer, in which protein molecules float like iceberg in the sea. This basic structure is found in all the membranes of mitochondria, chloroplast etc. Therefore, it is also called unit membrane. Cell membrane is a selectively permeable membrane because it regulates selective movement of molecules. In many animal cells the cell membrane infolds, taking in materials in the form of vacuoles. This process is called endocytosis. 3. Nucleus or Karyon: Nucleus (discovered by Robert Brown in 1831) is an important arid prominent structure present inside the cell. It controls all the activities of cell. It may be spherical or irregular in shape. In animal cell it is usually present in the center but in plant cell, due to presence of large vacuole it is pushed towards cell-membrane. Nucleus is enveloped by a double membrane called nuclear- membrane. This membrane possesses large number of nuclear pores. Nucleus is filled with a gel like substance called nucleoplasm. The nucleoplasm contains nucleoli and a network of thread like structures called chromatin network. The threads of chromatin become prominent during cell-division. Each thread is called chromosome. These structures of major importance. They are composed of Deoxyribo nucleic acid (DNA) and protein. DNA plays significant role in the



inheritance of characters as well as in controlling or regulating the cell activities. The number of chromosomes in the cells of all individual of the same species always remains constant.

Cells of organism No. of Chromosomes Man 46 Frog 26

Chimpanzee 48 Drosophila (fruit fly) 08

Onion 16 Potato 48

Garden pea 14 4. Cytoplasm: It is the translucent fluid portion of the cell lying in between plasma membrane and nucleus. It consists of an aqueous ground substance called cytosol and granular portion called cytoplasmic organelles. Chemically cytoplasm is about 90% water and forms a solution and serves as store house of vital chemicals. It is a site of metabolic reactions like protein synthesis, glycolysis etc. Many reactions can occur at the same time in different regions of the cytoplasm. Some important cytoplasmic organelles found in eukaryotic cells. 1. Endoplasmic reticulum 2. Golgi complex 3. Mitochondria 4. Plastids 5. Centrioles 6. Ribosomes 7. Vacuoles 1. Endoplasmic reticulum: (Endo= inside, plasma = protoplasm, reticulum=net work). It is a network of membranous channels or tubules extending throughout the cytoplasm. The channels seem to be in contact with plasma membrane as well as nuclear membrane. There are two types of endoplasmic reticulum. i) Rough endoplasmic reticulum having ribosomes at its outer surface which

are involved in protein synthesis. ii) Smooth endoplasmic reticulum without ribosome. Endoplasmic reticulum plays important role in the synthesis and transport of material within the cell. It also provides mechanical support to the cell so that its shape is maintained. It detoxifies the harmful effects of drugs. 2. Golgi complex: They were discovered by Camillo Golgi and thus called Golgi complex or bodies or apparatus". They are set of smooth membranes that are stacked into flattened, fluid filled sacs or vesicles containing carbohydrate, glycoproteins and enzymes. Golgi bodies are mainly concerned with the cell secretions. 3. Mitochondria (Sing; mitochondrion): They are generally rod-like or bean shaped organelles consisting of double membrane. The inner membrane is folded. These infoldings are called cristae while the fluid present inside is called matrix. Mitochondria contain enzymes which break the food for the production of energy. As producers of energy they are called Power house of the cell. The number of mitochondria in cell relates to its activities. 4. Plastids:



Plastids are found in the cells of all the higher plants. These are the organelles which contain different types of pigments. Plastids are of three types on the basis of their pigment or colour (Fig: 2.11) i) Chloroplasts have green pigment i.e. chlorophyll found in leaves and

other green parts of a plant. They manufacture carbohydrates by the process of photosynthesis.

ii) Chromoplast have coloured pigments other than green found in fruit, flower, petals and other coloured parts of plants .

iii) Leucoplast (leucos = white or colourless) are colourless, found in the cells of underground parts of plants. They store food in the form of starch.

5. Centrosome and Centrioles: A rounded structure, the centrosome is present near the nucleus in animal cells. A centrosome contains two centrioles (Fig: 2.12). Each centriole consists of a cylindrical array of 9 rows of microtubules. They form fibrous protein spindle which help in movement of chromosomes towards poles during animal cell division. 6. Ribosome: They are granules, rich in ribonucleic acid (RNA). They serve as sites where proteins are synthesized hence called protein factories of cell. They are found free in cytoplasm as well as attached on the surface of rough endoplasmic reticulum. 7. Vacuole: They are the fluid (other than cytoplasm) filled sacs surrounded by a membrane called tonoplast. In animal cell they are numerous, small but temporary structures while in plant cell they are permanent and very large in size, one or a few in number. They are concerned with storage of cell sap. 2.4 PROKARYOTIC AND EUKARYOTIC CELL There are two types of cells, Prokaryotic and eukaryotic cells. Prokaryotes have prokaryotic cell while eukaryotes have eukaryotic cells. Prokaryotic (pro: before; karyon: nucleus) cell does not possess true nucleus. It means its nuclear material is not enclosed in a proper nuclear membrane. These types of cells are found in bacteria and cyanobacteria (blue green algae). Such organisms are called prokaryotic organisms. Eukaryotic (eu: true, karyon: nucleus) cell possesses proper nucleus where nuclear material is enclosed in a proper nuclear membrane. Plants and animals are composed of this type of cells and are called eukaryotic organisms. Followings are the differences found between them.

Prokaryotic cell Eukaryotic cell 1. Nuclear membrane is absent

therefore prokaryotic cells do not possess distinct nucleus.

2. They do not have many of the membrane bound structures e.g. mitochondria E.R, Golgi apparatus etc.

3. Ribosomes are of small size and freely scattered in cytoplasm.

4. Nucleoplasm is absent. 5. Single chromosome is found. 6. Respiratory enzymes are located on

the inner surface of the cell

1. A double nuclear membrane is present. They have well defined nucleus.

2. They have membrane bounded structures (organelles).

3. Ribosomes are of large size and present either on endoplasmic reticulum or free in cytoplasm.

4. Nucleoplasm is present 5. Proper chromosomes in diploid

numbers are present. 6. Respiratory enzymes are



membrane. 7. These cells are simple and

comparatively smaller in size i.e. average 0.5 -l0nm in diameter.

8. Bacteria and cyanobacteria are examples of prokaryotes.

present in mitochondria. 7. These cells are complex and

comparatively larger in size i.e. 10- l00nm in diameter average.

8. Fungi, algae, animal and plants are examples of eukaryotes.

2.5 CELL DIVISION Cells reproduce and increase in number by division. After growing to a certain maximum size, a cell may undergo the process of cell division. During this process the nucleus divides first. This is followed by division of the cytoplasm. This nuclear division is called Karyokinesis (karyon=nucleus; kinesis = division) while the cytoplasmic division is called Cytokinesis. Thus two daughter cells arise from a single division of a cell. There are two main types of cell division found in living organisms. (1) Mitosis (2) Meiosis 1. Mitosis: In this type of cell division a parent cell divides into two daughter cells in a way that the number of chromosomes in the daughter cells remains the same as in the parent cell. Although mitosis is a continuous process, its karyokinesis can be divided for convenience into four phases which are Prophase, Metaphase, Anaphase and Telophase. Let us now study mitosis is an animal cell.

i) Prophase: During early prophase chromatin material condenses and becomes visible as thick coiled, thread like structures called chromosomes. Each chromosome at this stage is already double, i.e. consists of two chromatids. The chromatids are attached to each other at centromere. The nuclear membrane gradually disappears and at the same time centrosome divides to form two centrioles, each moves towards the opposite pole of the cell and forms the spindle fibres. The centrioles are absent in plant cells.

ii) Metaphase: During this phase each chromosome arranges itself on the equator of the spindle. Each chromosome is attached to separate spindle fibre by its centromere.

iii) Anaphase: In this phase the centromere of a chromosome divides and the chromatids of each chromosome separates from each other and begin to move towards opposite poles. In this way one set of the chromatids (each chromatid is now an independent chromosome) move towards one pole while the other set towards the other pole.

iv) Telophase: This is a stage when the chromatids (now called chromosomes) reach the poles and their movement ceases. Each pole receives the same number of chromosomes as were present in the parent cell. The nuclear membrane is reformed around each set of chromosomes. In this way two daughter nuclei are formed in each cell. Soon the cytoplasm of the cell also divides and two daughter cells arise. The nucleus of each daughter cell contains the same



chromosome number as in their parent cell. In this way the daughter cells are exact copies of their parent cell.

Significance of mitosis: Mitosis plays an important role in the life of an organism. It is responsible for development and growth of organisms by increasing exact copies of cells. With few exceptions all kinds of asexual reproduction and vegetative propagation take place by mitosis. The production of new somatic cells, such as blood cells depends on mitosis. The healing of wounds, repair of wear and tear within organism is also dependent upon the mitotic division. 2. Meiosis: Meiosis or reduction cell-division is a special type of cell-division S| which a parent cell finally divides into four daughter cells in a way that the number of chromosome in each daughter cell reduce to half of their parent cell. Thus it is the reduction of the diploid (2n) number of chromosomes to the haploid (n) number. In animals meiosis produces gametes (sperms and eggs) while in plants it gives rise to spores. The process of meiosis involves two consecutive divisions. (a) Meiosis I - First meiotic division or reduction phase (b) Meiosis II - Second meiotic division or meiotic mitotic phase (a) Meiosis I - First meiotic division or Reduction Phase: This division consists of the following phases.

i) Prophase I: Those chromosomes in the cell which 'are similar to each other in shape and size are called homologous chromosomes. Homologous chromosomes occur in pairs. The difference between mitosis and meiosis starts at this point. In mitosis individual chromosomes remain separate from each other while in meiosis the homologous chromosomes come together and form pairs. In each homologous pair, there are four chromatids, since each member (chromosome) of the pair has already doubled itself. Homologous chromosomes join to exchange their parts at certain places. This exchange is called crossing over. During crossing over exchange of genetic material takes place and new combination of genes result. The nuclear membrane disappears and at the same time spindle fibres are formed.

ii) Metaphase I: During this phase pairs of homologous chromosomes arrange themselves on the equator of the spindle. Unlike mitosis, it is the homologous pair and not the individual chromosomes which attach at separate fibre of the spindle.

iii) Anaphase I: The members of the homologous pairs now begin to separate and move towards the opposite poles.

iv) Telophase I: In this phase the chromosomes come to rest at the poles. The nuclear membranes are reformed around each set of chromosomes resulting in formation of two daughter nuclei. On completion of nuclear division, the cytoplasm also divides and two daughter cells are formed. Each daughter cell has half (haploid) the number of chromosomes present in the parent cell (compared with the cell in prophase) .Thus, the first meiotic division reduces the 2n (diploid-2 sets) chromosomes to n (haploid-half or one set).

(b) Meiosis II - Second meiotic division or Equational Division: During second meiotic division the details are almost similar to those seen in mitosis. During prophase, spindles are formed and the nuclear membrane



disappears. In metaphase, the chromosomes (each consisting of two chromatids) arrange themselves on the equator. Their chromatids separate from each other in anaphase and migrate to the opposite poles. In telophase, the nuclear membrane reappears around each set of chromatids (now called chromosomes) and the cytoplasm divides forming two daughter cells. So at the end of meiosis four daughter cells are produced in total, each possessing a haploid nucleus. Thus meiosis produces cells (gametes or spores) with a haploid number of chromosomes. Significance of meiosis: Meiosis plays very important role in keeping chromosome number constant in a species from generation to generation. When the haploid male gamete (sperm) fertilizes i.e. fuses with the haploid female gamete (ovum) to form a zygote, the diploid number of chromosomes is restored (n + n = 2n). Meiosis is responsible for genetic variability i.e. the individuals of a given species differ from one another. It is due to crossing over which takes place during prophase I. This genetic variability provides the basis of evolution by providing raw material for it. 2.6 ORGANIZATION OP CELLS TO FORM TISSUES, ORGANS AND ORGAN SYSTEM So far you have learnt about the cell as the basic structural and functional unit of life. The question now is how can a cell express itself as an independent living thing? You know that some small organisms (Amoeba) are made of only one cell These organisms are called unicellular organisms. They represent single cells capable of independent existence by making use of their organelles. Once capable of independent existence, the cell has become an organism. Such an organism represents the unicellular level of organization of life. In some cases, cells have come together to form loose assemblies and live together as a colony. In others, cell with similar structure and function have formed groups. Both have laid down the foundation of multicellular level of organization of life. 2.6.1 Tissues: A major step in the direction of multicellular organization of life has been the formation of tissues. A tissue consists of a group of cells which are similar in structure and function. Both plants and animals tissues have achieved increasing complexity by formation of organs and organ systems. 1. Plant tissues: In plants there are two basic types of tissues which are as follows.

i) Meristematic tissue: This tissue contains cells which have ability to divide, so that the number of cells increases and the organism can grow . Meristematic cells are smaller in size with comparatively thin walls and a nucleus in the center. This tissue is commonly present in root tips and shoot apex and helps to increase the length of the root and the shoot by adding primary tissue. ii) Permanent tissue: Permanent tissue is formed from meristematic cells. This tissue is different from meristematic tissue because its cells do not divide. The walls of these cells are thick enabling them to maintain their shape. Permanent tissue may be classified into two groups i.e. simple tissue and complex tissue. Simple tissue is made up of one type of cells forming a homogeneous or uniform mass and a complex tissue is made up of more than one type of cells working together as a unit.

a) Simple tissue: Simple tissues may further be divided into following type on the basis of their structure, i.e. Parenchyma, Collenchyma and Sclerenchyma.



i. Parenchyma: It consists of living cells which are more or less equally expanded on all sides. These cells have intercellular spaces. They are present in all the soft parts of plant. It is food storing tissue.

ii. Collenchyma: It consists of some what elongated cells with the corners filled with cellulose and pectin. Collenchyma occurs in a few layers under the epidermis of herbaceous dicotyledons.

iii. Sclerenchyma: Sclerenchyma (scleros =hard) consist of very long, narrow thick walled and lignified cells. They are dead cells. They become hard by deposition of chemical like lignin and thus provide support to the plants. They are found in xylem and hard fruit coats etc.

b) Complex or Compound tissues: Compound tissues are mainly of two types: (a) Xylem (b) Phloem. These will be discussed later under conducting tissues.

Types of permanent tissues on the basis of function:

i) Epidermal tissues: The cells of these tissues are rectangular in shape. These tissues form the outer layer of root, stem and leaf .The cells in it are very compactly arranged so that there is no space between them. However, in the stem and leaves, pores called stomata are present through which gases are exchanged. These tissues protect the inner parts of plant.

ii) Ground tissues: Ground tissues are composed of thin walled parenchymatous cells, which axe formed from meristematic tissue. These cells are basically meant for storing food. These tissues are present in all parts of the plant except the epidermal and the vascular tissues.

iii) Supporting tissues: When cells reach a maximum size their cell wails become thick due to deposition of special material and become dead. Such cells make up supporting tissue. This tissue is of various shapes and provides rigidity and support to the plant. Sclerenchyma (thick walled, lignified and elongated) and collenchyma (living cells with thick cellular walls with few small intercellular spaces) are examples of the supporting tissues.

iv) Conducting or Vascular tissues: These tissues consist of elongated cells with thick or thin walls. Xylem and Phloem are examples of this tissue. The xylem consists of sclerenchyma vessels and fibers, which conducts water and salts from the soil to the leaves and also provides support. The phloem is made up of living cells like sieve tubes, which conducts food from leaves to various parts of the plants. Xylem and phloem together form vascular bundle in the stem while they remain separate from each other in the roots.

2. Animal tissues: Like plants, animals have tissues which form organs and organ system. Some important types of animal tissues are: i) Epithelial tissue: The cells of this tissue occur in a single layer and are

closely packed together. This tissue forms surface layer under lines of the tubular organs of the body. Epithelial tissue occurs in glands where it is variously folded.

ii) Connective tissues: These tissues provide support to other tissues and organs and bind them together. They consist of a ground substance, cells and fibres. They range from soft to very hard tissues. Fatty tissues are examples of the soft type. Cartilage and bone are special types of these tissues and are hard. Blood is also a special connective tissue with cells suspended in a fluid medium. It transports materials in the body.



iii) Muscular tissues: This tissue is formed of muscle fibres. Each muscle fibre is an elongated cell, which has the ability to contract and relax. These tissues are responsible for movement of the body and body parts.

iv) Nervous tissues: These tissues are formed of cells called neurons or nerve cells. Nerve cells are specialized to conduct messages in the form of electrical currents. The nervous system (brain, spinal cord, nerves) is made up of this tissue. '

2.6.2 Organs: Your arm is an organ because it consists of various kinds of tissues such as epithelial tissue, muscular tissue, connective tissue and nervous tissue. All of these tissues have come together in the arm to make it an organ. Your heart, kidney, liver and many others structures are organs made in the same way. Similarly, in a plant the root, the stem and the leaves arc organs. The stem, for example, consists of several tissues such as epidermal tissue, ground tissue and conducting tissue. 2.6.3 Organ systems: Organs work together as a unit to perform a particular function to make an organ system. For example, the digestive system is made of organs such as mouth, gut, liver and pancreas are all working together to digest food. There are other systems in the animal body such as transport, respiratory, excretory, muscle, skeletal, nervous and reproductive systems. In plants also, the tissues and organs (root, stem, and leaves) are organized to form systems. However, the systems, here are not so clearly organized as in the animals. It is usual to study these in plants, as conduction, storage, supporting systems, or root and shoot systems. In this chapter you are studying life at various levels of organization from the simplest to the most complex. A simple diagram of this organization is given below: Cells Tissues Organs Systems Organism 2.7 UNICELLULAR ORGANISMS Those animals and plants, which are single-celled, are called unicellular organisms. Amoeba is one of the example. Amoeba: It is a unicellular aquatic organism found in stagnant water pools and ponds. It is microscopic in size measuring about 0.25 millimeter. It does not possess a permanent form and' keeps on changing its shape. The structure of Amoeba is very simple. The nucleus and cytoplasm are surrounded by a protective cell membrane. Cytoplasm is differentiated into two parts. Its outer portion, which is clear and transparent is called ectoplasm. The inner viscous, translucent and granular part is called endoplasm. The endoplasm contains many food vacuoles of different size, a contractile vacuole and other cells organelles. Nucleus is usually present in the centre but as the Amoeba moves, the nucleus changes its position. The contractile vacuole functions to remove excess water from the body. The food vacuoles contain food particles. The animal moves by producing temporary finger-like projections called pseudopodia (Pseudo = false, podia a feet). The pseudopodia are also used to capture food particles, which enter the body as food vacuoles. Amoeba respires by exchanging gases with the surrounding water through its surface. 2.8 MULTICELLULARORGANISMS



The majority of living organisms consist of many cells and are called multicellular organisms. Brassica and frog have been selected here as representative examples of multicellular plants and animals, respectively. 2.8.1 Brassica: Brassica campestris is the botanical name of mustard (sarsoun). You are very familiar with this plant since its oil (mustard oil) is used for cooking and its leaves are used as vegetable (saag). Structure of Brassica: This plant consists of roots, stem, leaves, flowers, fruit and seeds. These parts can be divided into two categories on functional basis i.e. vegetative parts and reproductive parts. The vegetative parts are those which do not directly take part in sexual reproduction. These parts are root, stem, branches and leaves. The reproductive parts consist of sex organs which are directly related to sexual reproduction. These are flowers. 1. Vegetative parts:

i) Root: The root is that part, which grows under the soil and develops from the radicle of the seed. The first part of the root to arise from the radicle is known as the primary root. During its growth it gives off secondary and tertiary roots. The primary roots are thicker than the secondary and tertiary roots. The tips of all the roots bear a cap, the root cap. The root bears fine, thin root hairs. The plant absorbs water and minerals from the soil through the root hairs only, the rest of the root fix the plant to the soil.

Internal structure: The outer part of a root is the epidermis (epi=above; derma=skin), which protects the root. Root hairs are outgrowths of epidermal cells. Next to epidermis is the cortex. Cortex is composed of parenchyma cells. Parenchyma cells store food material. Within the cortex is a central cylinder region called the stele. The stele of the root is surrounded on the outside by a layer of cells called endodermis. Next to the endodermis is a layer of cells called pericycle. Branch of the root originate from the pericycle. The central part of the stele is occupied by a star shaped xylem. In between the arms of the xylem is phloem. Rest of the stele is made of parenchyma cells.

ii) Stem: This part of plant develops from the plumule of the seed and grows away from the soil. It bears branches and flowers. The point, on the stem or on a branch, which gives rise to leaf, is known as the node. The part between two adjacent nodes is called the internode. The stem and the branches transport water and salts from the root to the leaves. It also transports prepared food from the leaves to all parts of the plant. In addition, the stem supports the leaves and the branches in the air, thus enabling the leaves to receive maximum amount of sun light for photosynthesis. The stem and its branches also bear flowers, which are the reproductive organs.

Internal structure: A cross section of Brassica stem shows that it is surrounded on the outside by a single layered epidermis. Next to the epidermis is cortex. The cortex is made up of parenchyma and collenchyma cells. Food material is stored in the cortex. Next to the cortex is a ring of vascular bundles. Each bundle consists of xylem and phloem. Xylem is located towards the inside and phloem towards the outside. In between xylem and phloem, there is a region consisting of meristematic cells



called cambium. The centre of the stem is occupied by pith. It is made up of parenchyma cells and stores food material.

iii) Leaf: Leaves grow out on the stem and its branches from the nodes. Generally, the leaf of Brassica consists of two parts. The lower stalk like part is the petiole and upper green expanded portion is the lamina. Young leaves are without petioles and their margins are entire or smooth but in mature leaves the margin is wavy. There is a swollen vein in the middle of the leaf which is known as midrib. The branch veins emerge and spread in the leaf like a net. These veins are actually vascular bundles consisting of xylem and phloem. This network of veins supports the leaf and keeps its lamina in an expanded position. New branches of the plant arise from buds present in the axil of the leaf. The function of the leaf is to prepare food. Therefore, all of its tissues are arranged in such a way that photosynthesis can take place easily.----------------------------------------- The leaves are arranged on the stem and branches in such a way that their upper surfaces remain directly exposed to sunlight while the lower surface does not get the same amount of light. Due to this difference the upper and lower surfaces are slightly different from each other. Leaves having different upper and lower surfaces are called bifacial leaves.

Internal structure: A leaf is composed of several distinct cell layers. The upper layer of a leaf is called the upper epidermis. The lower layer of the leaf is called the lower epidermis, which contains stomata (Sing: Stoma). Each stoma has a pore and two guard cells. The tissue between upper and lower epidermis is called the mesophyll. The mesophyll cells below the upper epidermis are longer than broad and are closely packed. It is called the palisade layer. The cells next to the palisade layer are irregular in shape and loosely arranged having spaces like sponge and is called the spongy layer. Photosynthesis takes place in palisade and spongy mesophylls. Running through the leaf are many vascular bundles or veins. The veins are composed of xylem and phloem. Xylem is located towards the upper side and the phloem towards the lower epidermis. 2. Reproductive parts Flower: With growing age, Brassica plant bears small, yellowish flowers. Flowers are the most beautiful and important parts of the plant. They are arranged on young branches in a special way. This special arrangement of the flowers on the stem is called inflorescence. Parts of the flower: The flower in Brassica is situated on a stalk known as pedicel. The tip of the pedicel bears thalamus. The floral leaves are arranged in four whorls on the thalamus. These whorls, starting from the outermost to the central one, are in the following order. i) Calyx: This is the outermost whorl and consists of four free sepals. The

sepals are light greenish in young flowers but as the flower matures, their colour also becomes yellowish like that of the petals. The most important function of the calyx is to cover the inner parts of the flower and to protect them from sunlight and rain.

ii) Corolla: This is the second whorl and is composed of four free yellow petals. Because of the petals, the flower becomes very conspicuous that honey bees, butterflies and other insects are easily attracted and thus help in pollination.



iii) Androecium: The androecium lies inside the petals. It makes the third whorl of the floral leaves. Its parts are not leaf-like. The androecium consists of six free stamens which are the male reproductive organs of the flower. In Brassica flower, the stamens are arranged in two circles. The outer circle has two small stamens. The inner circle has four long stamens. Each stamen has two well defined parts, a lower delicate stalk called the filament and an upper swollen part called the anther. Each anther contains numerous pollen grains. When the anther matures a longitudinal slit in its wall enables the pollen grains to escape. There are dark green nectaries of small size at the base of the androecium. These nectaries contain nectar (a honey-like substance). This nectar is the food of insects. When the insects are attracted towards the flowers to collect this nectar pollen grains get attached to their bodies and are transferred from one flower to another. This results in the pollination of flowers.

iv) Gynoecium: This is fourth whorl occupying the central position in the flower. The parts of the gynoecium are called carpels, who are the female reproductive organs of the plant. In Brassica, gynoecium is formed by the union of two carpels. Each carpel is divisible into three main parts. The lower swollen part is the ovary. Above the ovary carpel extends into a thin stalk, the style. The style has swollen tip, which is called stigma. In the ovary many ovules are present, which ripen into seeds. The ovary ripens and is converted into fruit. The fruit of Brassica is a long dry capsule with many seeds. The seeds are very small and light. They can be easily dispersed by air currents. When these seeds fall on a suitable place they germinate and produce new Brassica plants.

2.8.2 Frog: The frog lives both in water as well as on land. It swims in water and moves by jumping when on land. There is a membranous skin between its toes which helps in swimming. There are five toes in each foot but the hand has only four fingers because the thumb is rudimentary. In male frog the first finger is thicker than the others. Frog has neither a neck nor a tail. As the head is directly attached to the trunk frog cannot move it as we can. The conical head has two large bulging eyes. Behind each eye is a circular area called tympanic membrane. These membranes help in hearing. At the tip of the snout it has two openings called external nostrils by which frog breathes. The skin of the frog is loose and slippery. It is slippery due to secretions produced by glands present in it. Frogs are found in abundance in the rainy season during which they lay eggs. They hibernate during the winter season by burying themselves in the mud and stay there throughout the winter. This phenomenon is called hibernation or winter sleep. Internal organs: The internal organs are located in the body cavity, which is also called coelom. These organs make up various systems, which perform specific functions. These are as follows: 1. Digestive system: The organs involved in the breakdown of complex food

into simpler form (digestion) constitute the digestive system. This system is composed of a tube, the alimentary canal and special glands associated with it. The alimentary canal consists of buccal cavity, pharynx, oesophagus, stomach and intestine. i) Buccal cavity: Food enters into the buccal cavity through mouth.

The upper jaw has a row of weak but pointed teeth. They are not meant for chewing food but prevent it from slipping out of the mouth. The tongue of frog is unique in being attached in front to the floor of



the buccal cavity and being free behind. This allows the animal to throw it outward

Class IX Biology Book Notes

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