CBSE NOTES CLASS 9 SCIENCE CHAPTER 7
Difference in characteristics of various organisms is called diversity.
Different kinds of life forms show great diversity among themselves in following ways,
Size: From microsercopic bacteria of a few micrometers to blue whale (30 metres) and red wood trees of California (100 metres).
Life Span: Insects (few days) to pine trees (thousands of years).
Colour: Colourless or even transparent worms to brightly coloured birds and flowers.
Habitat – The place of living. For example, Land, Water, Air, Cold climate to hot deserts
The variety in organism and the diversity is very vast and it is almost impossible to study them individually. To make the study of living things systematic and easier, we put them into different classes, groups and sub groups on the basis of similarities and differences in their body design in form and function.
What is the basis of classification of organism?
Characteristics - a characteristic is a particular form or a particular function.
A hierarchy of mutually related characteristics is used for classification.
Some characteristics are more basic than others. Important characteristics used for hierarchical classification are
(i) Cell Type – Prokaryotic or Eukaryotic.
(a) A eukaryotic cell has membrane-bound organelles, including a nucleus, which allow cellular processes to be carried out efficiently in isolation from each other.
On the other hand Prokaryotes, i.e., organisms which do not have a clearly demarcated nucleus and other organelles would need to have their biochemical pathways organised in very different ways.
(b) Nucleated cells can participate in making a multicellular organism because they can take up specialised functions.
Therefore, this is a basic characteristic of classification.
(ii) Uni-cellular or Multi-cellular –
Uni-cellular organisms perform all the life processes using the single cell.
On the other hand, multicellular organism use the principle of division of labour. In such a body design, all cells would not be identical. Groups of cells will carry out pecialized 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.
(iii) Autotrophic or Heterotrophic - Do organisms produce their own food through the process of photosynthesis?
Being able to produce own food versus having to get food from outside would make very different body designs, necessary. Hence plants and animals form different groups.
(iv) Level of organisation of body, how does the individual’s body develop and organises its different parts, and what are the specialized organs found for different functions?
The characteristics of body design used for classification of plants will be very different from those important for classifying animals.
This is because the basic designs are different, based on the need to make their own food (plants), or acquire it (animals). Therefore, these design features (having a skeleton, for example) are to be used to make sub-groups, sub groups among plants and animals.
Evolution & Classification
Evolution: The process by which different kinds of living organism are believed to have developed from earlier forms by accumulation of changes in body design that allow the organism to survive better, during the history of the earth.
Some characteristics are likely to make more wide-ranging changes in body design than others. Time also plays a big role. So, once a certain body design comes into existence, it will shape the effects of all other subsequent changes, because it already exists.
Characteristics that came into existence earlier are likely to be more basic and likely to be found in larger portion of the population than characteristics that have come into existence later.
Primitive and advanced body designs
A primitive organism is a lower organism which exhibits simple body structure and simple organization. They are said to have ancient body designs.
An advanced organism exhibits complexity in the body structure and organization. They are said to have advanced body designs. These organisms show high level of division of labour, by formation of organs and organ systems.
The changes in the body structure and design may result from adaptations developed by the organism to the environment.
In reality, these terms are not quite correct since they do not properly relate to the differences. Complexity of design does not mean efficiency or better adaptation to the environment.
We can only say that some are ‘older’ organisms, while some are ‘younger’ organisms. Complexity in design increases over evolutionary time. Hence older organisms are simpler, while younger organisms are more complex.
Biodiversity means the diversity of life forms and refers to the variety of life forms found in a particular region.
Diverse life forms share the environment, and are affected by each other.
The diversity in such communities is affected by particular characteristics of land, water, climate, and so on. Humans have changed the balance of such communities.
The warm and humid tropical regions of the earth, between the tropic of Cancer and the tropic of Capricorn, are rich in diversity of plant and animal life. This is called the region of megadiversity.
Hierarchy of Classification
The classification Whittaker proposed has five kingdoms. These 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 used.
Further classification is done by naming the sub-groups at various levels as follows,
Phylum (for animals)/Division (for plants)
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.
Classification of organisms into kingdoms
Based on the above criterion the organisms have been divided into 5 kingdoms.
- Prokaryotes - do not have a defined nucleus or organelles.
- Unicellular orgnism
- Some of them have cell walls (Archaebacteria or Archaea) while some do not (Eubacteria or Bacteria)
- Mode of nutrition of can be either by synthesising their own food (autotrophic) or getting it from the environment (heterotrophic).
- Examples - bacteria, blue-green algae or cyanobacteria, mycoplasma and anabaena.
- They are unicellular and eukaryotes.
- Some of them use appendages, hair-like cilia or whip-like flagella for moving around.
- Mode of nutrition can be autotrophic or heterotrophic.
- Examples are unicellular algae, diatoms and protozoans.
- These are eukaryotic, multicellular, heterotrophic organisms.
- They use decaying organic material as food hence they are 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 and mushrooms, Penicillium, Agaricus, Aspergillus
- Lichens - Some fungal species live in permanent mutually dependent relationships with blue green algae. Such relationships are called symbiotic relationships and the life forms are called lichens. Examples of lichens are slow-growing large coloured patches on the bark of trees.
- Multicellular eukaryotes with cell walls.
- Autotrophs and use chlorophyll for photosynthesis.
Basis of Further Classification of Plants
- Whether the plant body has well differentiated, distinct components or not,
- Whether the differentiated plant body has special tissues for transportation of water and other substances within it,
- Whether they have ability to bear seeds or not,
- Whether the seeds are enclosed within fruits or not.
- These plants that do not have well-differentiated body design.
- They are commonly called algae.
- These plants are predominantly aquatic.
- Examples are Spirogyra, Ulothrix, Cladophora and Chara, Ulva.
- These are amphibians of the plant kingdom.
- Plant body is commonly differentiated to form stem and leaf-like structures.
- There are no specialized tissues for the conduction of water and other substances (vascular bundle).
- Examples are moss (Funaria) and Marchantia, Riccica.
- The plant body is differentiated into roots, stem and leaves
- Have specialised tissues (vascular bundle) 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 plants,, in which the reproductive organs are hidden, are cllaed cryptogamae. They do not produce seeds. The thallophytes, the bryophytes and the pteridophytes have naked embryos that are called spores and do not produce seeds. The reproductive organs of plants in all these three groups are very inconspicuous (hidden), and they are therefore called ‘cryptogamae’, or ‘those with hidden reproductive organs’.
- Plants with well differentiated reproductive tissues that make seeds are called phanerogams.
- Seeds consist of the embryo along with stored food, which serves for the initial growth of the embryo during germination.
- Further classified, based on whether the seeds are naked (gymnosperms) or enclosed in fruits (angiosperms).
- Bear naked seeds and are usually perennial, evergreen and woody.
- Examples are pines, such as deodar, cycas etc.
- The seeds are covered, develop inside an organ which is modified to become a fruit.
- These are flowering plants.
- Plant embryos in seeds have structures called cotyledons, which are ‘seed leaves’ because they emerge and become green when the seed germinates. It represents 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
- Multicellular eukaryotes without cell walls.
- Most animals are mobile.
- They are further classified based on the extent and type of the body design differentiation found.
- Organisms with holes all over the body which lead to a canal system that helps in circulating water throughout the body to bring in food and oxygen.
- Non-motile animals attached to some solid support.
- Covered with a hard outside layer or skeleton.
- The body design involves very minimal differentiation and division into tissues.
- They are called commonly sponges, and are mainly found in marine habitats.
- More body design differentiation.
- There is a cavity in the body.
- The body is made of two layers of cells: one makes upper layer of the body, and the other makes the inner lining of the body.
- Some of these species live in colonies (corals), while others live solitary life (Hydra).
- Examples hydra, jellyfish and sea anemones.
- Complex body design compared to Porifera and Coelenterata.
Bilaterally Symmetrical: The body is bilaterally symmetrical if the left and the right halves of the body have the same design.
- Platyhelminthes arr bilaterally symmetrical.
- Platyhelminthes have three layers of cells from which differentiated tissues can be made. Hence they are triploblastic.
- They have some degree of tissue formation
Coelom – It is an internal body cavity, in which the well developed organs are accommodated.
- No true internal body cavity or coelom.
- The body is flattened dorsiventrally, meaning from top to bottom, so these animals are called flatworms.
- They are either freeliving or parasitic.
- Examples are free living animals like planaria, or parasitic animals like liver flukes, tape worm etc.
- Their body is bilaterally symmetrical
- They are triploblastic.
- Their body is cylindrical rather than flattened.
- There are tissues, but no real organs,
- Sort of body cavity or a pseudocoelom, is present.
- Examples - Parasitic worms causing diseases, such as the worms causing elephantiasis (filarial worms) or the worms in the intestines (roundworm or pinworms).
- Bilaterally symmetrical, Triploblastic
- Have a true body cavity and extensive organ differentiation.
- 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.
- Example – Earthworms and leeches.
- Largest group of animals
- Bilaterally symmetrical
- Segmented body
- Open circulatory system, 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’).
- Examples are prawns, butterflies, houseflies, spiders, scorpions and crabs.
- In the animals of this group, there 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.
- In Greek, echinos means hedgehog, and derma means skin.
- These are spiny skinned organisms.
- Exclusively free-living marine animals.
- Triploblastic and have a coelomic cavity.
- They 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
- Bilaterally symmetrical,
- They are triploblastic
- Have a coelom.
- 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.
- 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
- Complex differentiation of body tissues and organs.
- All chordates possess the following features:
(i) a notochord
(ii) a dorsal nerve cord
(iii) are triploblastic
(iv) have paired gill pouches
(v) are coelomate.
- Vertebrates are grouped into five classes.
- These are fish.
- Exclusively water living animals.
- Skin is covered with scales/plates.
- They obtain oxygen dissolved in water by using gills.
- 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 fish have skeletons made entirely of cartilage, such as sharks, and some with a skeleton made of both bone and cartilage, such as tuna or rohu.
- Lack scales on the body,
- Have mucus glands in the skin,
- Cold blooded and have three-chambered heart.
- Respiration is through either gills or lungs.
- They lay eggs in water.
- These animals are found both in water and on land.
- Examples- Frogs, toads and salamanders
- These animals are cold-blooded
- Have scales
- Breathe through lungs.
- While most of them have a three-chambered heart, crocodiles have four chambered heart.
- They lay eggs with tough coverings and do not need to lay their eggs in water.
- Examples- snakes, turtles, lizards and crocodiles.
- There is an outside covering of feathers on the body and two forelimbs are modified for flight.
- Warm-blooded animals and have a four-chambered heart.
- They lay eggs with hard covering.
- They breathe through lungs.
- All birds fall in this category.
- Warm-blooded animals with four-chambered hearts.
- Females of this category 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 produce live young ones (called viviparous), however, a few of them, like the platypus and the echidna lay eggs (called oviparous), and some, like kangaroos give birth to very poorly developed young ones.
- Examples - Cow, dog, whale, humans, bat, rat, lion etc.
Why is there a need for systematic naming of living organisms?
It is difficult for people speaking or writing in different languages to know when they are talking about the same organism. This problem is resolved by agreeing upon a ‘scientific’ name for organisms just like chemical symbols and formulae for various substances the world over.
The scientific name for an organism is unique and can be used to identify it anywhere in the world. Proposed by Carolus Linnaeus.
The scientific name of an organism is the result of the process of classification which puts it along with the organisms it is most related to.
It includes the name of the genus and species of that particular organism.
Both these names are to be used in Latin forms.
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 written in italics.
4. When written by hand, the genus name and the species name have to be underlined separately.
- Write the scientific names of following,
Tiger, Peacock, Ant, Neem, Lotus, Potatoe.