Diversity-1
DIVERSITY-1
CLASSIFICATION
Biodiversity: The variety of living beings found in geographical area is called biodiversity of that area. Amazon rainforests is the largest biodiversity hotspot in the world.
Need for Classification: Classification is necessary for easier study of living beings. Without proper classification, it would be impossible to study millions of organisms which exist on this earth.
Basis of Classification:
Ancient Greek thinker Aristotle classified living beings on the basis of their habitat. He classified them into two groups, i.e. those living in water and those living on land. But his classification was too simple to justify inclusion of a particular organism into a particular group.
Some examples of scientific bases of classification are as follows:
Organization of nucleus: Nucleus may or may not be organized in an organism. On this basis, organisms can be divided into two groups, viz. prokaryotes and eukaryotes.
(a) Prokaryotes: When nucleus is not organized, i.e. nuclear materials are not membrane bound; the organism is called prokaryote.
(b) Eukaryotes: When nucleus is organized, i.e. nuclear materials are membrane bound; the organism is called eukaryote.
Number of cells: An organism can be composed of a single cell or many cells. An organism with a single cell is called unicellular organism. On the other hand, an organism with more than one cell is called multicellular organism.
Mode of Nutrition: On this basis, organisms can be divided into two broad groups, i.e. autotrophs and heterotrophs. An autotroph makes its own food, while a heterotroph depends on other organisms for food.
Level of Organisation: Even in case of multicellular organisms, there can be different levels of organization. When a cell is responsible for all the life processes, it is called cellular level or organization. When some cells group together to perform specific function, it is called tissue level of organization. When tissues group together to form some organs, it is called organ level of organization. Similarly organ system level of organization is seen in complex organisms.
Classification and Evolution: It is a well established fact that all the life forms have evolved from a common ancestor. Scientists have proved that the life begun on the earth in the form of simple life forms. During the course of time, complex organism evolved from them. So, classification is also based on evolution. A simple organism is considered to be primitive while a complex organism is considered to be advanced.
Five Kingdom Classification by Robert Whittaker (1959)
This is the most accepted system of classification. The five kingdoms and their key characteristics are given below:
1. Monera: These are prokaryotes; which means nuclear materials are not membrane bound in them. They may or may not have cell wall. They can be autotrophic or heterotrophic. All organisms of this kingdom are unicellular. Examples: bacteria, blue green algae (cyanobacteria) and mycoplasma.
2. Protista: These are eukaryotes and unicellular. Some organisms use cilia or flagella for locomotion. They can be autotrophic or heterotrophic. Examples: unicellular algae, diatoms and protozoans.
3. Fungi: These are heterotrohic and have cell wall. The cell wall is made of chitin. Most of the fungi are unicellular. Many of them have the capacity to become multicellular at certain stage in life. They feed on decaying organic materials. Such a mode of nutrition is called saprophytic. Some fungi live in symbiotic relationship with other organisms, while some are parasites as well. Examples: yeast, penicillum, aspergillus, mucor, etc.
4. Plantae: These are multicellular and autotrophs. Presence of chlorophyll is a distinct characteristic of plants, because of which they are capable of doing photosynthesis. Cell wall is present.
5. Animalia: These are multicellular and heterotophs. Cell wall is absent.
Kingdom Plantae:
The Plant Kingdom can be further classified into five divisions. Their key characteristics are given below:
1. Thallophyta:- The plant body is simple thallus type. The plant body is not differentiated into root, stem and leaves. They are commonly known as algae. Examples: Spirogyra, chara, volvox, ulothtrix, etc.
2. Bryophyta:- Plant body is differentiated into stem and leaf like structure. Vascular system is absent, which means there is no specialized tissue for transportation of water, minerals and food. Bryophytes are also known as the amphibians of the plant kingdom, because they need water to complete a part of their life cycle. Examples: Moss, marchantia.
3. Pteridophyta:- Plant body is differentiated into root, stem and leaf. Vascular system is present. They do not bear seeds and hence are called cryptogams. Plants of rest of the divisions bear seeds and hence are called phanerogams. Examples: Marsilear, ferns, horse tails, etc.
4. Gymnosperms:- They bear seeds. Seeds are naked, i.e. are not covered. The word ‘gymnos’ means naked and ‘sperma’ means seed. They are perennial plants. Examples: Pine, cycas, deodar, etc.
5. Angiosperms:- The seeds are covered. The word ‘angios’ means covered. There is great diversity in species of angiosperm. Angiosperms are also known as flowering plants, because flower is a specialized organ meant for reproduction. Angiosperms are further divided into two groups, viz. monocotyledonous and dicotyledonous.
(a) Monocotyledonous: There is single seed leaf in a seed. A seed leaf is a baby plant. Examples: wheat, rice, maize, etc.
(b) Dicotyledonous: There are two cotyledons in a seed. Examples: Mustard, gram, mango, etc.
Kingdom Animalia:-
The animal kingdom is classified into different phyla. Their detail is given below:
1. Porifera: These animals have pores all over their body. The pores lead into the canal system. Water flows through the canal system and facilitates entry of food and exchange of other materials. The animal is not differentiated into tissues. The body is covered with a hard outer skeleton. These are commonly known as sponges. They are marine animals. Examples: Sycon, spongilla, euplectelea, etc.
2. Coelenterata: The body is made up of a coelom (cavity) with a single opening. The body wall is made up of two layers of cells (diploblastic). Some of the species live a solitary life while others live in colonies. Examples: Hydra, Jelly fish, Sea anemone, etc.
3. Platyhelminthes: The body is flattened from top to bottom and hence the name platyhelminthes. These are commonly known as flatworms. The body wall is composed of three layers of cells (triploblastic). Because of three layers, it is possible to form some organs as well. But a proper ceolom is absent in platyhelminthes and hence proper organs are absent. They are free-living or parasitic animals. Examples: Planaria, liver fluke, tapeworm, etc.
4. Nematohelminthes: The body is bilaterally symmetric and there are three layers in the body wall. Animals are cylindrical in shape. A pseudocoelom is present and hence organs are absent. Examples: Roundworms, pinworms, filarial parasite (Wuchereria), etc.
5. Annelida: True body cavity is present in these animals. The body is divided into segments and hence the name annelida. Each segment is lined one after another and contains a set of organs. Examples: Earthworm, leech, etc.
6. Arthropoda: Animals have jointed appendages which gives the name arthropoda. Exoskeleton is present which is made of chitin. This is the largest group of animals; in terms of number of species. Circulatory system is open, which means blood flows in the coelomic cavity. Examples: cockroach, housefly, spider, prawn, scorpion, etc.
7. Mollusca: The animal has soft body; which is enclosed in a hard shell. The shell is made of calcium carbonate. Circulatory system is open and kidney like organ is present for excretion. The body has well developed muscular feet for locomotion. Examples: Snail, mussels, octopus, etc.
8. Echinodermata: The body is covered with spines, which gives the name echinodermata. Body is radially symmetrical. The animals have well developed water canal system, which is used for locomotion. Skeleton is made of calcium carbonate. Examples: Starfish, sea urchins, etc.
9. Protochordata: Animals are bilaterally symmetrical, triploblastic and ceolomate. Notochord is present at least at some stages of life. Notochord is a long rod-like structure which runs along the back of the animal. This provides attachment points for muscles. It also separates the nervous tissues from the gut. Examples: Balanoglossus, herdmania, amphioxus, etc.
10. Chordata: Animals have notochord, pharyngeal gill slits and post anal tail; for at least some stages of life. Phylum chordata is divided into many sub-phyla; out of which we shall focus on vertebrata.
Vertebrata:
The notochord is replaced by a spinal column during embryonic stage. Following are the main characteristics of vertebrates.
- Notochord present; which is replaced by spinal column.
- Dorsal nerve chord is present.
- Animals are triploblastic and coelomate.
- Animals have paired gill pouches.
Vertebrates are divided into two super classes, viz. pisces and tetrapoda.
A. Pisces: They are commonly known as fish. The body is streamlined. Muscular tail is present which assists in locomotion. Body is covered with scales. Paired gills are present; which can breathe oxygen dissolved in water. They are cold-blooded animals. The heart has only two chambers. They lay eggs. Fishes can be bony or cartilaginous. Shark is an example of cartilaginous fish. Rohu and katla are examples of bony fish.
B. Tetrapoda: Animals have four limbs for locomotion and hence the name tetrapoda. Tetrapoda is divided into four classes, viz. amphibia, reptilia, aves and mammalia.
(1) Amphibia: These animals are adapted to live both in water and land. Mucus glands on skin keep the skin moist. The animals breathe through skin when in water and through lungs when on land. The heart has three chambers. These are cold blooded animals. Examples: Frog, toad, salamander, etc.
(2) Reptilia: These animals show crawling movement for locomotion. Skin is hardened to form scales. Most of the reptilians have three chambered heart but crocodile has four-chambered heart. They don’t need water to lay eggs, rather eggs are covered with hard shells and laid on land. Examples: snakes, lizards, crocodile, turtle, etc.
(3) Aves: The body is covered with feathers. Forelimbs are modified into wings. These are warm-blooded animals. The heart has four chambers. Bones are hollow (pneumatic); which assists in flying. All the birds belong to this class.
(4) Mammalia: The body is covered with hairs. Skin has seat glands and sebaceous glands. Mammary glands are present in females and are used for nourishing the young ones. Most of the mammalians give birth to young ones and are called viviparous. Some of the mammals lay eggs and are called oviparous. Examples: human, chimpanzee, lion, platypus, horse, etc.
Binomial Nomenclature of Organisms:
The system of binomial nomenclature was proposed by Carolus Linneaus (1707 – 1778). Conventions of writing biological name are as follows:
- The biological name is composed of two terms. The first term is called genetic name and the second term is called species name.
- The genus name starts with a capital letter, while the species name starts with a small letter.
- In print, the scientific name is written in italics.
- When handwritten, the genus name and species name need to be underlined separately.
Key Learnings
1) Every living organism is unique and this uniqueness is the basis of the vast diversity
displayed by the organisms in our world.
2) This huge diversity is the result of evolution, which has occurred over millions of years.
3) The massive biological diversity can only be studied by classification i.e. arranging
organisms into groups based on their similarities and differences.
4) Different characteristics are used to determine the hierarchy of classification.
5) The primary characteristics that determine the broadest divisions in classification are
independent of any other characteristics. The secondary characteristics depend on the
primary ones.
6) Prokaryotic or eukaryotic cell organization is the primary characteristic of classification,
since this feature influences every detail of cell design and capacity to undertake
specialized functions.
7) Being a unicellular or multicellular organism forms the next basic feature of classification
and causes huge differences in the body design of organisms.
8) The next level of classification depends on whether the organism is autotrophic or
heterotrophic. Further classification depends on the various levels of organization of the
bodies of these organisms.
9) The evolution of organisms greatly determines their classification.
10) The organisms who evolved much earlier have simple and ancient body designs whereas
the recently evolved younger organisms have complex body designs.
11) Older organisms are also referred to as primitive or lower organisms whereas the younger
organisms are also referred to as advanced or higher organisms.
12) The diversity of life forms found in a region is biodiversity.
13) The region of mega-diversity is found in the warm and humid tropical regions of the Earth.
14) Aristotle classified organisms depending on their habitat.
15) Robert Whittaker proposed the five-kingdom scheme of classification, based on the cell
structure, nutrition and body organization of the organisms.
16) The main characteristics considered in the five-kingdom scheme of classification are:
i) Presence of prokaryotic or eukaryotic cells.
ii) If eukaryote, whether the organism is unicellular or multicellular.
iii) Whether the cells possess or lack cell wall and whether they can prepare their own
food.
17) The categories or taxa used in the classification of
organisms are kingdom,
phylum/division, class, order, family, genus and species. The smallest unit of classification
is species whereas the highest unit is kingdom.
18) The 5 kingdoms proposed by Whittaker are Monera, Protista, Fungi, Plantae and Animalia.
Carl Woese further divided Monera into Archaebacteria and Eubacteria.
19) Prokaryotic one-celled organisms such as bacteria, cyanobacteria and mycoplasma are
included in Monera.
20) Monerans show either autotrophic or heterotrophic nutrition. Cell wall may be present or
absent.
21) Unicellular eukaryotic organisms such as protozoans, unicellular algae and diatoms are
grouped under Protista. They may be autotrophic or heterotrophic and may use
appendages for locomotion.
22) Fungi, such as yeast and mushrooms, include heterotrophic, eukaryotic organisms, which
are normally saprophytes. Their cell walls are composed of chitin.
23) Lichens are symbiotic associations of certain fungi with blue green algae.
24) Multicellular, autotrophic eukaryotes possessing cell wall are included under kingdom
Plantae.
25) Classification of plants is done at three levels on the basis of
i) Presence or absence of well-differentiated body
ii) Presence or absence of vascular tissue
iii) Ability to bear seeds, which could be naked or enclosed in fruits.
26) The important divisions of Plantae
are
Thallophyta,
Bryophyta,
Pteridophyta,
Gymnospermae and Angiospermae.
27) Thallophytes, Bryophytes and Pteridophytes possess inconspicuous reproductive organs
and are called Cryptogams. Gymnosperms and Angiosperms are grouped under
Phanerogamae, since they possess well-differentiated, seed producing reproductive
tissues.
28) Thallophytes (or algae) are the simplest plants lacking well-differentiated body design.
E.g. – Spirogyra.
29) Bryophytes, such as moss and Riccia, show differentiated plant body lacking vascular
tissue.
30) Plants grouped under Pteridophyta show well-differentiated plant body with vascular
tissues for conduction. E.g. Ferns.
31) Gymnosperms, for e.g. pines and deodar, are phanerogams bearing naked seeds.
32) In Angiosperms/flowering plants, the seeds are enclosed in fruits.
33) Cotyledons are present in the embryos of seeds.
34) Monocot plants possess seeds with single cotyledons whereas dicots are plants with 2
cotyledons in seeds.
35) Monocots show fibrous root system, parallel venation of leaves and flowers with three (or
multiple of three) petals.
36) Tap root system, reticulate venation of leaves and flowers with five (or multiple of five)
petals are features of dicots.
37) Organisms grouped under Animalia are eukaryotic, multicellular, heterotrophic and lacking
cell walls.
38) Animals are further divided into ten groups – Porifera, Coelenterata, Platyhelminthes,
Nematoda, Annelida, Arthropoda, Mollusca, Echinodermata, Protochordata and Vertebrata.
39) In Porifera, also called sponges, the body is perforated by numerous pores and shows
cellular level of organization. In addition, a hard exoskeleton and canal system are
present. Sponges are non-motile. E.g. – Sycon.
40) Coelenterates are radially symmetrical and show a cavity called coelenteron between
epidermis and gastrodermis. Some like Hydra are solitary forms whereas others like corals
live in colonies.
41) Platyhelminthes includes the flat worms which are bilaterally symmetrical, dorsoventrally
flattened, triploblastic and acoelomate. They may be free-living (e.g. Planaria) or parasitic
(e.g. tape worm).
42) The body of nematode worms is cylindrical, bilaterally symmetrical, triploblastic and
pseudocoelomate. They are usually parasitic. E.g. Ascaris.
43) Annelids are triploblastic, bilaterally symmetrical with true coelom and found in diverse
habitats. Segmentation and extensive organ differentiation is seen. E.g. Earthworm and
Nereis.
44) The largest phylum of animal kingdom, Arthropoda, contains triploblastic, bilaterally
symmetrical and segmented animals. These animals possess jointed legs and open
circulatory system. E.g. Butterfly, centipede, crab, spider.
45) In phylum Mollusca, (e.g. snail and Octopus) organisms show bilateral symmetry, soft
body, open circulatory system and reduced coelom.
46) Echinodermata includes spiny skinned organisms with calcareous skeleton. They are
triploblastic, coelomate, marine and free-living. Water vascular system is an important
feature. Starfish and Holothuria are examples of this phylum.
47) All chordates have a notochord, dorsal nerve cord and
paired pharyngeal gill
slits/pouches. Also they are triploblastic, coelomic and bilaterally symmetrical.
48) Vertebrates and Protochordates are grouped under Chordata.
49) The Protochordates possess notochord at some or the other stage of their life, e.g.
Balanoglossus, Amphioxus.
50) Vertebrates show true vertebral column and endoskeleton. Complex body organization
and differentiation is seen.
51) The five classes of vertebrates are Pisces, Amphibia, Reptilia, Aves and Mammalia.
52) The endoskeleton in fish may be cartilaginous or bony.
53) Mammary glands produce milk in mammals to nourish the young ones.
54) Binomial nomenclature, developed by Carolus Linnaeus, uses two names to identify an
organism. The first name is the generic name beginning with a capital letter whereas the
second name is the species name which begins with a small letter.
55) Binomial nomenclature makes it possible to identify every species of organisms in the
astounding diversity of life present in our planet.
|