CLASS 9 Science
CHAPTER 7
Diversity In Living Organisms (NCERT Notes)
Different forms life occurs on earth. On one hand we have microscopic bacteria of a few micrometre in size. While on the other hand we have blue whale and red wood trees of california of approximate sizes of 30 metres and 100 metres repectively. Some pine trees live for thousands of years while insects like mosquitoes die within a few days. Life also ranges from colourless or even transparent worms to brightly coloured birds and flowers.
This bewildering variety of life around us has evolved on the earth over millions of years. However, we do not have more than a tiny fraction of this time to try and understand all these living organisms, so we cannot look at them one by one. Instead, we look for similarities among the organisms, which will allow us to put them into different classes and then study different classes or groups as a whole. In order to make relevant groups to study the variety of life forms, we need to decide which characteristics decide more fundamental differences among organisms. This would create the main broad groups of organisms. Within these groups, smaller sub- groups will be decided by less important
characteristics.
What is the Basis of Classification?
Greek thinker Aristotle classified animals according to whether they lived on land, in water or in the air. This is a very simple way of looking at life, but misleading too. For example, animals that live in the sea include corals, whales, octopuses, starfish and sharks. We can immediately see that these are very different from each other in numerous ways. In fact, their habitat is the only point they share in common. This is no good as a way of making groups of organisms to study and think about.
We therefore need to decide which characteristics to be used as the basis for making the broadest divisions. A characteristic is a quality or feature that is typical of someone or something.
Characteristics used for a hierarchical classification?
• A eukaryotic cell has membrane-bound organelles, including a nucleus, which allow cellular processes to be carried out efficiently in isolation from each other. Therefore, organisms which do not have a clearly demarcated nucleus and other organelles would need to have their biochemical pathways organised in very different ways. This would have an effect on every aspect of cell design. Further , nucleated cells would have the capacity to participate in making a multicellular organism because they can take up specialised functions. Therefore, this is a basic characteristic of classification.
• Do the cells occur singly or are they grouped together and do they live as an indivisible group? Cells that group together to form a single organism use the principle of division of labour. In such a body design, all cells would not be identical. Instead, groups of cells will carry out specialised functions. This makes a very basic distinction in the body designs of organisms. As a result, an Amoeba and a worm are very different in their body design.
• Do organisms produce their own food through the process of photosynthesis? Being able to produce one’s own food versus having to get food from outside would make very different body designs necessary.
• Of the organisms that perform photosynthesis (plants), what is the level of organisation of their body?
• Of the animals, how does the individual’s body develop and organise its different parts, and what are the specialised organs found for different functions?
Classification and Evolution
All living things are identified and categorised on the basis of their body design in form and function. A classification is a division or category in a system which devides things into groups or types. Charles Darwin first described this idea of evolution in 1859 in his book, The Origin of Species.
After classification two types of groups were created .Those in the first group are frequently referred to as ‘primitive’ or ‘lower’ organisms, while those in the second group are called ‘advanced’ or ‘higher’ organisms. In reality, these terms are not quite correct since they do not properly relate to the differences.
Evolution is change in the heritable characteristics of biological populations over successive generation.
The Hierarchy of Classification- Groups
Biologists, such as Ernst Haeckel (1894), Robert Whittaker (1959) and Carl Woese (1977) have tried to classify all living organisms into broad categories, called kingdoms. The classification Whittaker proposed has five kingdoms: Monera, Protista, Fungi, Plantae and Animalia, and is widely used. These groups are formed on the basis of their cell structure, mode and source of nutrition and body organisation. The modification Woese introduced by dividing the Monera into Archaebacteria (or Archaea) and Eubacteria (or Bacteria) is also in use.
Classification is done by naming the sub-groups at various levels as given in the following :
Kingdom
Phylum (for animals) / Division (for plants)
Class
Order
Family
Genus
Species
Thus, by separating organisms on the basis of a hierarchy of characteristics into smaller and smaller groups, we arrive at the basic unit of classification, which is a ‘species’. A species includes all organisms that are similar enough to breed and perpetuate.
The important characteristics of the five kingdoms of Whittaker are as follows:
MONERA
These organisms do not have a defined nucleus or organelles, nor do any of them show multi-cellular body designs. Some of them have cell walls while some do not. Having or not having a cell wall has very different effects on body design here from having or not having a cell wall in multi- cellular organisms. The mode of nutrition of organisms in this group can be either by synthesising their own food (autotrophic) or getting it from the environment (heterotrophic). This group includes bacteria, blue-green algae or cyanobacteria, and mycoplasma. Some examples are Bacteria and Anabaena .
PROTISTA
This group includes many kinds of unicellular eukaryotic organisms. Some of these organisms use appendages, such as hair-like cilia or whip-like flagella for moving around. Their mode of nutrition can be autotrophic or heterotrophic. Examples are unicellular algae, diatoms and protozoans .
FUNGI
These are heterotrophic eukaryotic organisms. They use decaying organic material as food and are therefore called saprophytes. Many of them have the capacity to become multicellular organisms at certain stages in their lives. They have cell-walls made of a tough complex sugar called chitin. Examples are yeast, Penicillium , Aspergillus, Agaricus and mushrooms . Some fungal species live in permanent mutually dependent relationships with blue- green algae (or cyanobacteria). Such relationships are called symbiotic. These symbiobic life forms are called lichens. We have all seen lichens as the slow-growing large coloured patches on the bark of trees.
PLANTAE
These are multicellular eukaryotes with cell walls. They are autotrophs and use chlorophyll for photosynthesis. Thus, all plants are included in this group.
ANIMALIA
These include all organisms which are multicellular eukaryotes without cell walls. They are heterotrophs.
Plantae
The first level of classification among plants depends on whether the plant body has well- differentiated, distinct components. The next level of classification is based on whether the differentiated plant body has special tissues for the transport of water and other substances within it. Further classification looks at the ability to bear seeds and whether the seeds are enclosed within fruits.
THALLOPHYTA
Plants that do not have well-differentiated body design fall in this group. The plants in this group are commonly called algae. These plants are predominantly aquatic. Examples are Spirogyra, Ulothrix, Cladophora and Chara.
BRYOPHYTA
These are called the amphibians of the plant kingdom. The plant body is commonly differentiated to form stem and leaf-like structures. However, there is no specialised tissue for the conduction of water and other substances from one part of the plant body to another. Examples are moss (Funaria) and
Marchantia .
PTERIDOPHYTA
In this group, the plant body is differentiated into roots, stem and leaves and has specialised tissue for the conduction of water and other substances from one part of the plant body to another. Some examples are Marsilea, ferns and horse-tails. The thallophytes, the bryophytes and the pteridophytes have naked embryos that are called spores. The reproductive organs of plants in all these three groups are very inconspicuous, and they are therefore called ‘cryptogamae’, or ‘those with hidden reproductive organs’. On the other hand, plants with well- differentiated reproductive tissues that ultimately make seeds are called phanerogams. Seeds are the result of the reproductive process. They consist of the embryo along with stored food, which serves for the initial growth of the embryo during
germination. This group is further classified, based on whether the seeds are naked or enclosed in fruits, giving us two groups: gymnosperms and angiosperms.
GYMNOSPERMS
This term is made from two Greek words: gymno– means naked and sperma– means seed. The plants of this group bear naked seeds and are usually perennial, evergreen and woody. Examples are pines, such as deodar.
ANGIOSPERMS
This word is made from two Greek words: angio means covered and sperma– means seed. The seeds develop inside an organ which is modified to become a fruit. These are also called flowering plants. Plant embryos in seeds have structures called cotyledons. Cotyledons are called ‘seed leaves’ because in many instances they emerge and become green when the seed germinates. Thus, cotyledons represent a bit of pre-designed plant in the seed. The angiosperms are divided into two groups on the basis of the number of cotyledons present in the seed. Plants with seeds having a single cotyledon are called monocotyledonous or monocots. Plants with seeds having two cotyledons are called dicots. For example Monocots – Paphiopedilum and Dicots – Ipomoea.
Animalia
These are organisms which are eukaryotic, multicellular and heterotrophic. Their cells do not have cell-walls. Most animals are mobile. They are further classified based on the extent and type of the body design differentiation found.
PORIFERA
The word means organisms with holes. These are non-motile animals attached to some solid support. There are holes or ‘pores’, all over the body. These lead to a canal system that helps in circulating water throughout the body to bring in food and oxygen. These animals are covered with a hard outside layer or skeleton. The body design involves very minimal differentiation and division into tissues. They are commonly called sponges, and are mainly found in marine habitats. Some examples are Euplectelia ,Sycon and Spongilla.
COELENTERATA
These are animals living in water. They show more body design differentiation. There is a cavity in the body. The body is made of two layers of cells: one makes up cells on the outside of the body, and the other makes the inner lining of the body. Some of these species live in colonies (corals), while others have a solitary like–span (Hydra). Jellyfish and sea anemones are common examples.
PLATYHELMINTHES
The body is bilaterally symmetrical, meaning that the left and the right halves of the body have the same design. There are three layers of cells from which differentiated tissues can be made, which is why such animals are called triploblastic. This allows outside and inside body linings as well as some organs to be made. There is thus some degree of tissue formation. However, there is no true internal body cavity or coelom, in which well- developed organs can be accommodated. The body is flattened dorsiventrally, meaning from top to bottom, which is why these animals are called flatworms. They are either free- living or parasitic. Some examples are free- living animals like planarians, or parasitic animals like liverflukes .For examples Planareia ,Liverfluke and Tape worm.
NEMATODA
The nematode body is also bilaterally symmetrical and triploblastic. However, the body is cylindrical rather than flattened. There are tissues, but no real organs, although a sort of body cavity or a pseudo- coelom, is present. These are very familiar as parasitic worms causing diseases, such as the worms causing elephantiasis (filarial worms) or the worms in the intestines (roundworm or pinworms). Some examples are Ascaris , Wuchereria .
ANNELIDA
Annelid animals are also bilaterally symmetrical and triploblastic, but in addition they have a true body cavity. This allows true organs to be packaged in the body structure. There is, thus, extensive organ differentiation. This differentiation occurs in a segmental fashion, with the segments lined up one after the other from head to tail. These animals are found in a variety of habitats– fresh water, marine water as well as land. Earthworms and leeches are familiar examples.
ARTHROPODA
This is probably the largest group of animals. These animals are bilaterally symmetrical and segmented. There is an open circulatory system, and so the blood does not flow in well- defined blood vessels. The coelomic cavity is blood-filled. They have jointed legs (the word ‘arthropod’ means ‘jointed legs’). Some familiar examples are prawns, butterflies, houseflies, spiders, scorpions and crabs. Examples are Palaemon (Prawn) ,Palamnaeus (Scorpion), Aranea(Spider) ,Pariplaneta (Cockroach) ,Butterfly ,Scolopendra (Centipede) and Musca (House fly).
MOLLUSCA
Animals of this group is bilateral symmetry. The coelomic cavity is reduced. There is little segmentation. They have an open circulatory system and kidney-like organs for excretion. There is a foot that is used for moving around. Examples are snails and mussels Chiton ,Octopus ,Pila and Unio.
ECHINODERMATA
In Greek, echinos means hedgehog, and derma means skin. Thus, these are spiny skinned organisms. These are exclusively free-living marine animals. They are triploblastic and have a coelomic cavity. They also have a peculiar water-driven tube system that they use for moving around. They have hard calcium carbonate structures that they use as a skeleton. Examples are starfish and sea urchins Antedon
(feather star) ,Holothuria (sea cucumber), Echinus (sea urchin) and Asterias (star fish).
PROTOCHORDATA
These animals are bilaterally symmetrical, triploblastic and have a coelom. In addition, they show a new feature of body design, namely a notochord, at least at some stages during their lives. The notochord is a long rod-like support structure (chord=string) that runs along the back of the animal separating the nervous tissue from the gut. It provides a place for muscles to attach for ease of movement. Protochordates may not have a proper notochord present at all stages in their lives or for the entire length of the animal. Protochordates are marine animals. Examples are Balanoglossus, Herdemania and Amphioxus.
VERTEBRATA
These animals have a true vertebral column and internal skeleton, allowing a completely different distribution of muscle attachment points to be used for movement. Vertebrates are bilaterally symmetrical, triploblastic, coelomic and segmented, with complex differentiation of body tissues and organs. All chordates possess the following features:
(i) have a notochord
(ii) have a dorsal nerve cord
(iii) are triploblastic
(iv) have paired gill pouches
(v) are coelomate.
Vertebrates are grouped into five classes.
(i) PISCES
These are fish. They are exclusively water- living animals. Their skin is covered with scales/plates. They obtain oxygen dissolved in water by using gills. The body is streamlined, and a muscular tail is used for movement. They are cold-blooded and their hearts have only two chambers, unlike the four that humans have. They lay eggs. Some with skeletons made entirely of cartilage, such as sharks, and some with a skeleton made of both bone and cartilage, such as tuna or rohu. For examples Synchiropus splendidus (Mandarin fish) , Caulophyryne jordani (Angler fish) ,Pterois volitans (Lion fish) ,Scoliodon (Dog fish) ,Electric ray (Torpedo).
(ii) AMPHIBIA
These animals differ from the fish in the lack of scales, in having mucus glands in the skin, and a three-chambered heart. Respiration is through either gills or lungs. They lay eggs. These animals are found both in water and on land. Frogs, toads and salamanders. For examples Rana tigrina (Common frog) ,Hyla (Tree frog) ,Salamander.
(iii) REPTILIA
These animals are cold-blooded, have scales and breathe through lungs. While most of them have a three-chambered heart, crocodiles have four heart chambers. They lay eggs with tough coverings and do not need to lay their eggs in water, unlike amphibians. Snakes, turtles, lizards and crocodiles fall in this category. For examples Turtle, Chameleon, King Cobra, House wall lizard (Hemidactylus) and Flying lizard (Draco).
(iv) AVES
These are warm-blooded animals and have a four-chambered heart. They lay eggs. There is an outside covering of feathers, and two forelimbs are modified for flight. They breathe through lungs. Are oviparous. All birds fall in this category. For examples White Stork (Ciconia ciconia), Ostrich (Struthio camelus) , Male Tufted Duck, (Aythya fuligula), Pigeon, Sparrow, Crow.
(V) MAMMALIA
Mammals are warm-blooded animals with four-chambered hearts. They have mammary glands for the production of milk to nourish their young. Their skin has hairs as well as sweat and oil glands. Most mammals familiar to us produce live young ones. However, a few of them, like the platypus and the echidna lay eggs, and some, like kangaroos give birth to very poorly developed young ones. For examples Whale, Human, Cat ,Rat, Bat.
Nomenclature
Nomenclature in biological classification , system of naming organisms. The system of scientific naming or nomenclature we use today was introduced by Carolus Linnaeus in the eighteenth century. The world it has been agreed that both these names will be used in Latin forms.
Certain conventions are followed while writing the scientific names:
1. The name of the genus begins with a capital letter.
2. The name of the species begins with a small letter.
3. When printed, the scientific name is given in italics.
4. When written by hand, the genus name and the species name have to be underlined separately.
( From NCERT Book )