Diversity in living organisms Class 9 Notes
Classification
The method of arranging organisms into groups or sets on the basis of their similarities and differences is called classification.
Advantages of classification are:
• It gives information regarding the existing diversity of plants and animals.
• It makes the study of a wide variety of organisms convenient.
• It helps us to understand the pattern of evolution.
• It forms the basis for the development of other biological sciences like Ecology, Biogeography, Biochemistry and other disciplines of Biology.
Characteristics used for classification
Some of the characteristics used for hierarchical classification are given below:
The complexity of cell structure
The complexity of cell structure matters at first, i.e. whether the cell is prokaryotic or eukaryotic.
The body structure
The organisms can be found as a single cell (unicellular) or a group of cells (multicellular).
Mode of nutrition
According to this characteristic, organisms are of two types, i.e. autotrophic and heterotrophic.
Levels of organisation of the body
The level of body organisation is different in different organisms.
Functional organisation
As the structure and the body design vary, the function of living organisms also shows changes.
Classification and evolution
Evolution is a process by which early organisms on the earth diversified into various forms through a slow and continuous process.
Hierarchy of classification
Classification is done by naming the sub-groups at various levels as given in the scheme that follows:
Kingdom
Phylum (for animals) Division (for plants)
Class
Order
Family
Genus
Species
Species: It is the basic unit of classification. It is a group of individuals, capable of interbreeding along themselves to give birth to fertile offsprings, e.g. horse (Equus cabalus) and ass (E. asinus) are different species.
Genus: Consists of closely related species ranked higher than species, e.g. dog and wolf belong to the same genus, i.e. Canis.
Family: Group of related genera having several common characters to form a family, e.g. cat and lion belong to the same family-Felidae.
Order: Assemblage of a number of families having few common characters, e.g. tiger and wolf belong to the same order-Carnivora.
Class: Organisms of related order or orders having similarity are placed together in a class, e.g. rats, camels, monkeys are all included in the same class-Mammalia.
Phylum: The different classes having some specific characters, which are common in them, are placed under the same phylum, e.g. phylum-Chordata with all animals having a notochord.
Five Kingdom classification
Whittaker classified organisms into five kingdoms on the basis of following three levels of organisation:
(i) Cell structure (prokaryotic or eukaryotic)
(ii) Modes and source of nutrition (autotrophic or heterotrophic)
(iii) Body organisation (unicellular or multicellular)
(i) Monera (Gk. Moneres single)
The characteristics of Kingdom-Monera are as follows:
• These organisms are unicellular prokaryotes.
• They do not have well-defined nucleus and membrane-bound cell organelles like mitochondria, Golgi apparatus, plastids, lysosomes, etc., as found in eukaryotes.
• Mode of nutrition can either be autotrophic or heterotrophic.
(ii) Protista (Gk. Protistos-primitive or the very first)
• This group consists of unicellular eukaryotes.
• The true nucleus is present in them and membrane-bound cell organelles like mitochondria, plastids and sap vacuoles are also present.
• Some protists use appendages, such as hair-like cilia, (Paramecium), pseudopodia (Amoeba) or whip-like flagella (Euglena) for locomotion.
(iii) Fungi (Lt. fungus-mushroom)
• These are heterotrophic and eukaryotic organisms.
• They may be unicellular (yeast) or filamentous (most fungi). Many of them have the capacity to become multicellular organism at certain stages of their lives.
• Some are parasitic (depends on the host for their food) such as Puccinia, Albugo and Ustilago, while some are saprophytes (use decaying organic material as food), such as Mucor and Agaricus.
(iv) Plantae
• These are multicellular eukaryotes with cell walls made up of cellulose.
• Growth is unlimited and continuous until death.
• They are always fixed at one site and cannot move like animals.
(v) Animalia
• These are multicellular eukaryotes without cell walls.
• They have definite shape and size.
• Most of them can move easily from one place to another.
Kingdom-Plantae
Cryptogame
The thallophytes, bryophytes and pteridophytes do not have external flower or seeds and have naked embryos called spores. These plants are thus also called cryptogamic (meaning with hidden reproductive organs) because their reproductive organs are inconspicuous.
Thallophyta (Gk. thallos-undifferentiated; phyton-plant)
• They do not have well-differentiated body design.
• Plants in this group are commonly known as algae.
• These are predominantly aquatic.
Bryophyta (Gk. Bryon-moss; phyton-plant)
• These are called as the amphibians of the plant kingdom because they can live in soil, but are dependent on water for sexual reproduction.
• In bryophytes, true vascular system is absent, i.e. they do not have specialised tissues for the conduction of water and food materials from one part of the body to another.
• The body is commonly differentiated into stem and leaf-like structures. They lack real roots, stem, leaves, etc., and do not bear flower.
Pteridophyta (Gk. pteris-fern; phyton-plant)
• These are first land plants having vascular tissues.
• The body of these plants is differentiated into roots, stems and leaves and has specialised tissue for the conduction of water and food (well-developed vascular system, xylem and phloem). Thus, are called vascular cryptogams.
• They do not bear flowers and do not produce seeds.
Phanerogamae
Some plants, which make seeds and have well-differentiated reproductive tissues are called phanerogams.
On the basis of the presence or absence of naked seeds, these are divided into two groups:
(i) Gymnosperms
(ii) Angiosperms
Gymnosperms(Gk. gymnos-naked; sperma-seed)
• These plants are most primitive and bear seeds.
• The seeds produced are naked and are not enclosed within fruits.
• Plants are usually perennial, evergreen and woody.
Angiosperms (Gk. angion-covered; sperma-seed)
• These are also called flowering plants. Their seeds develop inside an organ, which modifies to become a fruit.
• Plant embryos in seeds have structures, called cotyledons. Cotyledons are also called seed leaves because in many cases they emerge and become green when germinates.
The angiosperms are divided into two groups on the basis of number of cytoledons present in the seed.
The groups are:
(i) Dicotyledonous plants or Dicots
(ii) Monocotyledonous plants or Monocots
| Monocots | Dicots |
| They contain one cotyledon. | They contain two cotyledons. |
| Leaves have parallel venation. | Leaves have reticulate venation. |
| Fibrous root system is present. | Tap root system is present. |
Kingdom-Animalia
Porifera (Gk. porus-pore; ferre-to bear)
• Animals that belong to this phylum are commonly called sponges.
• These have minimal differentiation and division into tissues.
• These organisms are acoelomate (body cavity absent) with cellular level of body organisation.
Coelenterata (Cnidaria) (Gk. koilos-hollow; entron-gut)
• These animals show more body design differentiation.
• These organisms are multicellular and acoelomate having tissue level of organisation with a distinct division of labour.
• They live in water and have tentacles (appendages) for locomotion.
Platyhelminthes (Gk. Platys-flat; helmin-worm)
• These are triploblastic (body make up of three layer of cells), dorsoventrally flattened, (flattened from back through to the abdomen) leaf-like animals with tissue level of organisation. So, these are also called flatworms.
• They have bilateral symmetry i.e. the left and right halves of the body has the same design.
• They are mostly parasitic animals (living in the bodies of other animals) like liver flukes and some are free-living like Planaria. e.g. Taenia solium (pork tapeworm, Dugesia (Planaria), Fasciola (liver fluke), etc.
Nematoda (Nemathelminthes or Aschelminthes) (Gk. nema-thread; helmin-worm)
• These are triploblastic, cylindrical works with pseudocoelom (no true body cavity coelom).
• Their body is biliterally symmetrical.
• They are parasitic worms causing diseases such as Elephantiasis (filarial worms) or the worms in the intestines (roundworms or pinworms).
Annelida (Lt. annulus-little ring; lidos-form)
• These are triploblastic animals having bilaterally symmetrical, elongated, vermiform, cylindrical or dorsoventrally flattened body.
• These animals are found in a variety of habitats i.e. freshwater, marine water as well as on land.
• Annelids are the first animals to develop true body cavity or coelom, i.e. coelomates.
Arthropoda (Gk. arthron-jointed; podos-foot)
• Arthropoda is the largest group of animals. These are found everywhere on the Earth.
• These are triploblastic, bilaterally symmetrical and segmented animals.
• Body is segmented and is grouped into three regions, i.e. head, thorax and abdomen.
Mollusa (Lt. molluscus-soft or thin-shelled)
• The coelomic cavity is reduced. Oysters and clans of this group produce pearls.
• Open circulatory system is present. Kidney-like structures or a pair of metanephridia is present for excretion.
• The body is divided into an anterior head, a ventral muscular foot and a dorsal visceral mass.
Echinodermata (Gk. echinos-spines or hedgehog; derma-skin)
• These are simple spiny skinned animals with star-like, spherical or elongated body.
• These are triploblastic, coelomate, unsegmented and their body has radial symmetry in adults, but bilateral in larvae.
• These are exclusively free-living marine animals.
Chordata (Lt. chorda-string)
• Body of these animals is triploblastic, coelomate with bilateral symmetry.
• All of them have a notochord (a new feature of body design). Notochord is a long rod-like support structure that runs along the back of the animal separating the nervous tissue from the gut. It provides site for muscle attachment.
• They have dorsal nerve cord and paired gill pouches.
Protochordata (Gk. proto-first; chordata-notochord)
• They are triploblastic, have bilaterally symmetrical body and a coelom.
• They show notochord in some stages of life, i.e. tail of young larvae.
• These are mostly marine animals.
Vertebrata
• They have a true vertebral column and internal skeleton which allows completely different distribution of muscle attachment points that help in movement.
• Their body is bilaterally symmetrical, triploblastic, coelomic and segmented.
• In these animals, complex differentiation of body tissues and organs is present.
Thus, vertebrates are considered the most advanced group of animals. These are further grouped into five classes:
(i) Class-Pisces (Fishes) (Lt. piscis-fish)
• These are exclusively aquatic animals.
• They have streamlined body covered with scales that end in a muscular tail (which help inmovement).
• Respiration occurs by gills by taking oxygen dissolved in water.
(ii) Class-Amphibia (Gk. amphi-double; bios-life)
• In evolutionary terms, these are the first group among the chordates to live on land.
• They are amphibious in nature, viz can live on land as well as in water.
• They lack scales and have mucous glands in their skin which secrete mucous that keep the skin moist.
(iii) Class-Reptilia (Lt. repere-to crawl)
• These animals possess dry skin, with scales and mostly live in warmer regions. They are cold-blooded.
• These are the first class of terrestrial animals.
• They lay eggs with tough covering on land unlike amphibians that lay eggs in water.
(iv) Class-Aves (Lt. avis-bird)
• These are warm-blooded animals having four-chambered heart.
• Their body is divisible into head, neck, trunk and tail.
• These are flying animals, having exoskeleton (outside covering) of feathers.
(v) Class-Mammalia (Lt. mamma-breast)
• These are warm-blooded animals which have four-chambered heart.
• Females have mammary glands for the production of milk to nourish the young ones. Thus, called mammals.
• These are known to be the advanced group of animals with a very well-developed brain.
Answer these Questions:
Q1. Five Kingdom of classification?
Q2. Advantages of classification are?
Q3. Difference between Monocotyledonous plants or Monocots?