Rajasthan Board RBSE Class 9 Science Notes Chapter 7 Bio-Diversity
Meaning and Significance of Biodiversity:
The 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 its knowledge, to try and understand all the living organisms. So, we classify the living organisms into groups or classes, and then study different classes or groups, as a whole.
Major characteristics considered for classification are:
- Whether they are made of prokaryotic or eukaryotic cells.
- Whether the cells are living single or organised into multicellular complex organisms.
- The cells have a cell wall or not.
- Whether they prepare their own food.
- Various types of organisms in the world differ in shape, structure and physiology. Division of organisms in groups, on the basis of similarities and dissimilarities is called classification. The science of studying classification is called Taxonomy. The different types of organisms with variations in structure constitutes the bio-diversity.
Need of classification:
The main purpose of classification is to inform us about the inter-relationship between different groups of plants & animals and a natural evolutionary relationship, is based on natural affinity among organisms and their evolution.
Major groups of animals and plants
Carolus linnaeus classified the living organisms into two kingdoms:
- Plant kingdom
- Animal Kingdom
German Zoologist, E.H Haeckel raised third kingdom for unicellular organisms called protista, Later on, an American ecologist. Robert. H. Whittaker proposed a fourth kingdom, Monera for bacteria and fifth kingdom, fungi.
To arrange organisms into these kingdoms, three criteria were considered:
- Complexity of cell structure,
- Complexity of the organisms body, and
- Method of obtaining nutrition.
The five kingdoms are:
- Monera: In it, are included all prokaryotic cell organisms. Examples: Bacteria, Blue green algae, mycoplasma etc.
- Protista: In it, all unicellular organisms with nucleus and nuclear membrane are included. Example: Protozoans.
- Fungi: They are unicellular or multicellular. Nucleus is present, but chlorophyll is absent. They can not perform photosynthesis.
- Plant Kingdom (Plantae): They are multicellular plants. They have chlorophyll, so they can synthesise their own food. Examples: Members of Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.
- Animal kingdom(Animalia): They are multicellular animals. They do not have chlorophyll. Examples: Sponge, hydra, earthworm, frog, snake, man, etc.
- Kingdom plantae is a large group of organisms include all the coloured multicellular, simple and complex plants. On the basis of Phylogeny and evolution, Oswald Tippo in 1942, classified this kingdom into two subkingdoms
- Thallophyta plants do not form embryos. Embryophyta plants form embryo. Based on certain common trails, such as whether they produce seeds or not and whether the seeds are contained in fruits or are exposed, this kingdom is grouped into four phyla.
- Thallophyta: e.g. (bacteria, fungi, lichens, and algae)
- Bryophyta: (Liver worths, Hornworts and mosses)
- Pteridophyta: (lycopodium, pteridium and ferns)
- Spermatophyta: (a) Gymnosperms e.g., pinus, cycas, etc (b) Angiosperms, e.g., Wheat, Rice, etc.
- Thallophyta: Plant body is not differentiated into root, stem and leaves. Body is called thallus. Reproductive organ is unicellular. It has three sub-divisions.
- Algaes are unicellular or multicellular. They have chlorophyll, so they can manufacture their own food, by photosynthesis. They are aquatic.
Example: Spirogyra,Chlamydomonas, Chlorella, etc.
- Fungi plants do not have chlorophyll. They are saprophytes or parasites. Example: Yeast, Mucor.
- Bacteria are unicellular, prokaryotic organisms. Nuclear membrane and membrane bound cell organelles are absent.
- In Bryophyta, body is more developed in comparison to thallophyta. They have rhizoids, instead of root, which absorb water and salts from soil. Mostly the plants are found in moist and shady places. Their body is made of parenchyma tissue. Sex organs are multicellular. Examples: Funaria, Riccia etc.
- In Pteridophyta, the body of plants is differentiated into root, stem and leaves. Xylem and phloem are found in the conducting tissues of the plants. Reproducive organs are multicellular. Male sex organ is called antheridia and female sex organ is called archegonia.
Examples: Lycopodium, Pteridium and other ferns.
- In Gymnosperms, body is differentiated into root, stem and leaves. The seeds of the plants are naked (exposed), because fruit is not formed in these plants. The reproductive organs are cone shaped. Examples: Pinus,Cycas etc.
- In Angiosperms body is differentiated into root, stem and leaves Flowers, Fruits and Seeds are formed. Seeds are formed inside the fruits. Example: Wheat, Rice, Mustard, Neem, Pea, Gram, etc.
- The two major group of animals are non chordates and chordates. In non chordates, animals do not have notochord, dorsal solid nerve chord and pharengeal gill clefts.
They are further divided into following phylums:
- Protozoa: They are unicellular, microscopic, simple and primitive animals. Example: Amoeba, Paramecium.
- Porifera: They are multi cellular with minute pores on their body and found in sea water. Example: Sycon, Euspongia.
- Coelentrata: They are radially symmetrical, diploblastic. Gastro vascular cavity is found and mouth is surrounded by hollow tentacles. Example: Hydra, Obelia.
- Platyhelminthes: They are parasites of vertebrates. Animals are bilaterally symmetrical, triploblastic and organisation is of organ system level. Example: Fasciola, Taenia.
- Aschelminthes: They are long, cylindrical, worm like triplobastic, bilaterally symmetrical. Alimentary canal is found completely. Example: Ascaris, Bucheria.
- Annelida: They are long, cylindrical, segmented, bilaterally symmetrical and triploblastic
Example: Nereis, Leech, Earthworm.
- Arthropods: They are multicellular, triploblastic, bilaterally symmetrical. Their body is divided into head, thorax and abdomen. Jointed appendages are found, which are modified for different functions. Example: Scorpion, Cancer, etc.
- Mollusca: They are aquatic, bilaterally symmetrical. In most of the animals shell is found. Example: Unio, Pila.
- Echinodermata: They are found in sea, skin is spiny, True body cavity is entrocoel type. Tube feet is found for locomotion. Example: Starfish, Sealily, etc.
- In chordata, animals have notochord in some stage of their life. Heart is present on ventral surface and blood circulatory system is of closed type.
They are divided into five classes:
- Pisces: It includes fishes and other aquatic animals. They are cold blooded, body is spindle shaped, divided into head, thorax and tail and covered with scales. Heart is two chambered and respiration takes place through gills. Example: Dog fish, Rohu, Seahorse, etc.
- Amphibia: It include frogs. They can live both on land and water. Their body is divided into head, thorax and abdomen. Respiration takes place through skin and lungs. Heart possess two auricles and one ventricle. Example: Frog, Toad, Tree frog, etc.
- Reptilia: It includes snakes. They crawl on the ground and respire through lungs. Their body is divided into head, neck, thorax and tail, covered with endodermal scales. Their heart has two auricles and one incompletely divided ventricle. They lay eggs. Example: Tortoise, Lizard, etc.
- Aves: It include aerial animals, like birds. Their body is boat shaped, stream-lined, divided into head, thorax, neck and tail, covered with feathers, horny beak is found, teeth are not found and bones are hollow. Example: Pigeon, Crow, etc.
- Mammalia: It includes big animals. Developed mammary glands are found in females. Their body is divided into head, thorax, neck and tail. They are warm blooded, respire through lungs, and heart is four chambered. Example: Bat, Man, Rat, etc.
Adaptation of Animals and Plants on the basis of habitat:
- Habitat is a place where an organism lives. The special characteristics which help the plants and animals to live successfully in a particular environment are called adaptations. Owing to the basis of availability of water in the environment, different plants are classified into following categories:
- Hydrophytes are the plants which live in abundance of water or grow in wet habitat, aquatic plants.
Adaptation in Hydrophytes:
- Roots: The root system is poorly developed, which do not play any significant important role in water absorption due to availability of plenty of water. Roots of these plants do not have root caps and root hairs. The roots of these plants contain air cavity.
- Stems: The stems are long, slender, soft and spongy, due to large air cavity. The conducting tissues, xylem and phloem are poorly developed.
- Leaves:The leaves of submerged plants are thin, long, ribbon shaped or linear. Floating leaves are large and flat and are often coated with wax or covered with hairs. Leaves of emergent and rooted plants below water, are long, narrow and dissected, while those which lie outside the water, are broad and non-dissected.
- Reproduction: In hydrophytes, reproduction is mostly asexual and where flowers develop, seeds are rarely formed. In some plants and vegetables, cuticle is absent.
- Reproduction is also found.
- Mucilage is secreted from all parts of the plants, thus plants is not palatable.
- Osmotic pressure is less, in hydrophytes plants.
General characters of Xerophytes:
Xerophytes are the plants which grow in deserts. Deserts are a typical example of dry habitat. The places which receives little rainfall and where there is no water for irrigation are Xerophytic habitats. The main feature of this habitat are bright light, lack of moisture, high temperature and fast blowing dry winds.
- Non-succulent Xerophytes have long tap root, while in succulent xerophytes, roots are on the upper surface of soil. Root hair and root cap are poorly developed.
- Stems are short, irregular, woody and hard. The stem is modified into under-ground rhizome.
- In Asparagus, axial branches are modified into needle like structures, called cladode.
- In Xerophytes, there is cover of wax and silica on the surface of stem and in some xerophytes, the stem surface is covered with hairs, e.g., Argemone.
- Leaves of majority of xerophytes are smaller in size and very less in number, e.g., Acacia, Opuntia.
- Leaves and stems are provided with thick cuticle.
- The conducting tissues are highly developed and vessels are in large number in xylem tissue.
- The cells of epidermis of xerophytes are smaller in size and outer walls are thick.
- Chloroplast and columnar tissues are found in the outer cortex of stem, of xerophytes.
General characters of Halophytes:
- Halophytes are special type of xerophytes, which grow in saline soils. The soil has high concentrations of sodium chloride, magnesium sulphate and magnesium chloride. The plants that grow in saline and marshy soil are called halophytes.
- Halophytes of sub-tropical places are herbs, while those in tropical zone are shrubs and trees.
- The roots do not penetrate much deeper.
- Adventitious roots that develop from the main stems of halophytes, support these plants, after entering into the soil.
- Special type of roots develop from Mangrove are called respiratory roots or pneumetophores. These are negatively geotrophic roots. Each root is provided with numerous pores, towards the upper end for the exchange of 02 and C02.
- Stem of some plants are fleshy and covered with hairs.
- Leaves of halophytes are absent or little developed and fleshy.
- Thick cuticle is found on the epidermis of stems and leaves.
- The rate of evaporation is very less in these plants.
- Carbonic acid is formed during respiration, due to special metabolic activities.
- Mangrove plants show a special type of germination of their seeds, known as, vivipary. The seeds germinate inside the fruit, which is still attached to the parent tree. When germinated, seeds fall on the soil, and begines to development soon., e.g., Rhizophora and Sonneratia.
- There are diverse group of animals that are found in different habitats. There are favourable characteristics (structural and functional) which the organism develops over a period of time, which enables them to survive, breed and prosper. Adaptations may be in the form of modifications in shape, structure of organs, colour, size, behaviour and food habits.
Adaptations in animals are of the following three main types:
Aquatic adaptations is one of the most important habitat, where large number of animals live. The aquatic habitat include, both fresh water and salt water habitats.
The adaptive features of aquatic animals are:
- Body shape: Body is streamlined and it offers least resistance to motion, as swimming.
- Swimming organs: Body is covered by waterproof scales and a slippery substance, for reducing surface tension. The flippers of whale, fins and tail of a fish helps in increasing speed and changing the direction.
- Air bladders: They are present in some fishes. It communicates with pharynx and filled with air.
- Respiratory organs are gills, in fishes. Gills have large surface area, to extract oxygen dissolved in water.
- In amphibious adaptation, frog is adapted for both aquatic and terrestrial life.
- limbs, through webbed feet, are adopted for swimming.
- Hind limbs are longer than fore limbs.
- Skin is always moist, which helps in breathing, when the animal is on land.
Fertilisation is external.
Animals living on land, differs in their habits of living. The walkers and runners have cursorial adaptations, the burrowers have fossorial adaptations, climbers and fliers have arboreal adaptations. Animal living in deserts have desert adaptations.
Some adaptations found in Mesic habitat animals are:
- All fast moving animals, have streamlined body and strong limbs for running.
- Certain animals have protective coloration mechanism, such as the ability to change the body color to deceive the predator or prey, e.g., green lizard.
- Insects and certain worms have modified mouth parts for feeding, e.g., wall lizard, which catches insects using its long, sticky tongue.
Xeric adaptations of Desert animals:
Animals such as camels, desert rats, rabbits, foxes, etc., have to adapt in order to overcome, the xeric conditions.
Some xeric adaptations are as follows:
- Moloch absorbs water, like blotting paper. Its surface is covered by thorn like scales.
- Water cells are developed in the walls of camel. It uses its entire foot, while walking.
- The desert animals do not perspire and conserve water.
- The nostril of camel can be closed like eyelids. The eyelids are modified into window, like structure which covers the eye.
- The ear openings are either small or protected by scales.
- Sense of light, hearing and smell are highly developed.
- The animals who live and flourish, mainly on land, but come to the trees or branches for safety and shelter are called arboreal animals, e.g., monkey, flying lizard, flying squirrel, bats, birds, etc.
The bird and bats are adapted for aerial mode of life. Some adaptation of birds
are as follows:
- The body of birds is streamlined, i.e., spindle shaped, for the easy and swift passage through air.
- Forelimbs are modified into wings, for flying.
- The entire body of birds are covered by light, elastic and water-proof feathers. They also help in maintaining the body temperature.
- Birds have hollow bones, strong flight muscles, light body covering, sharp eyesight, modified beaks and tails. Birds do not have teeth and urinary bladder.
- Ovary and oviduct is single, lungs are provided with air sacs, which are air filled and make the body light.
- The feet of birds are modified for climbing and perching.
Classification give a scientific name:
- A name is used for every living organism throughout the world. Common name does not serve the purpose, because a particular animal is known by different names in different parts of the world. On the other hand, scientific name is universally accepted and used for a particular group of animals.
- As the binomial name indicates, the naming is done by two words. The first word is generic and the second is specific. The generic word starts from capital letter and specific starts from small letter.
- In some species, some special type of dissimilarities are found, which are called subspecies. So, first name is of genus, second one is species and then another name is added, that is of subspecies