Diversity in Living Organisms
Why do we classify organisms?
There is vast number of living organisms in this biosphere and they have a great diversity ,in shape, size and forms. It is practically not possible to examine and study every organism separately at individual level. It is, therefore, advisable to study the diversity of organisms by classifying them in orderly manner.
Give three examples of the range of variations that you see in life-forms around you.
The three examples are :
- The living organisms vary in size from a few micrometers (e.g., microscopic bacteria) to more than 30 metres long (e.g., blue whale) and more than 100 metres tall (e.g., red wood trees of California).
- The living organisms vary in longevity from a few days (like mosquitoes) to several thousand years (pine trees).
- The living organisms range from colourless or transparent to brightly coloured birds and flowers.
Which do you think is a more basic characteristic for classifying organisms?
(a) the place where they live.
(b) the kind of cells they are made of. Why?
The kind of cells organisms are made of is a more basic characteristic for classifying organisms because it is the cell and its components which perform the specialized functions to help organisms survive and multiply.
We cannot classify organisms on the basis of place where they live because many different kinds of organisms may live in the same habitat but they do not belong to the same group.
What is the primary characteristic on which the first division of organisms is made?
The primary characteristic used for making the broadest division of organisms is “whether the organisms are prokaryotic or eukaryotic?”
On what bases are plants and animals put into different categories?
Plants and animals are put into different categories on the basis of their mode of nutrition as well as their body designs. Plants are autotrophic and perform photosynthesis whereas animals are heterotrophic and get food from outside.
The basic difference between their cell designs is that plant cells have cell wall whereas animal cells lack cell wall.
Which organisms are called primitive and how are they different from the so-called advanced organisms?
Primitive organisms are those which retain their ancient body designs and basic characteristic and have not changed much during the course of evolution.
They differ from so called advanced organisms as the advanced organisms have acquired new body designs and have developed specialised characteristics in accordance with the demand of the changing environment through the process of organic evolution.
Will advanced organisms be the same as complex organisms? Why?
No, it is not so. Evolutionary advanced organisms can be simple in structure. For example, monocots which are simpler in structure than dicots are more advanced in terms of evolution. However, generally advancement is related with complexity in body design.
What is the criterion for classification of organisms as belonging to Kingdom Monera or Protista?
It is “the presence or absence of a well defined nucleus. Monerans have no nuclear membrane, while Protistans show well defined nucleus.
In which kingdom will you place an organism which is single-celled, eukaryotic and photosynthetic?
The members of Kingdom Protista are single-celled (unicellular), eukaryotic (bearing well defined nucleus and membrane- bound cell organelles) and many of them are photosynthetic (like protistan algae and Euglena)- Hence organism which is single- celled, eukaryotic and photosynthetic should be placed in Kingdom Protista.
In the hierarchy of classification, which grouping will have the smallest number of organisms with a maximum of characteristics in common and which will have the largest number of organisms?
Taxon species which lies at the bottom of the classification ladder contains the smallest number of organisms and since the members of a species can interbreed among themselves, they possess maximum characteristics in common.
In the hierarchy of classification, kingdom is at the top. It bears the largest number of organisms because a kingdom is split into several phyla, classes, orders, families, genera and species, each having their specific characteristics.
Which division among plants has the simplest organisms?
Thallophyta or algae.
How are pteridophytes different from the phanerogams?
Pteridophytes are different from phanerogams in the following characteristics:
|1.||They are seedless plants.||They are seedbearing plants.|
|2.||Gametophytes are independent.||Gametophytes are dependent upon sporophytes for nutrition.|
|3.||Water is required for fertilisation.||Fertilisation does not require water.|
How do gymnosperms and angiosperms differ from each other?
The gymnosperms bear naked seeds (ix., the seeds are not enclosed within the fruits) whereas the angiosperms bear seeds inside the fruits.
How do poriferan animals differ from coelenterate animals?
Poriferan animals differ from coelenterate animals in following aspects :
- Animals from Porifera show cellular level of organisation, while those from Coelenierata show tissue level of organisation.
- Poriferans have no digestive or gastrovascular cavity while coelenterates have such cavity.
- Poriferans have central cavity called spongocoel has many opening viz. ostia and osculum while coelenterates have central cavity called coelenteron has one opening.”
Write the differences between annelids and arthropods.
The differences between annelids and arthropods are given below :
|1.||Animals are segmented both externally as well as internally||Animals are segmented externally, but not internally.|
|3.||True coelom is well-developed.||Blood-filled pseudocoelomic body cavity called haemocoel is present.|
|4.||Exoskeleton is absent.||Exoskeleton made up of chitin present.|
|5.||Nephridia act as excretory organs.||Green glands act as excretory organs.|
|6.||Closed type of circulatory system is present.||Open type of circulatory system is present.|
|7.||Blood flows in closed blood vessels.||Blood flows through large sinuses.|
What are the differences between amphibians and reptiles?
Amphibians differ from reptiles in following aspects:
|1.||They have slimy skin without scales.||They have exoskeleton of scales.|
|2.||They mostly lay eggs inside water.||They lay eggs outside water.|
|3.||Larvae have gills.||They do not have gills.|
What are the differences between animals belonging to the aves group and those in the mammalian group?
The differences between animals belonging to the Aves group and in the mammalian group:
|1.||Body is covered with feathers.||Body is covered with hairs.|
|2.||They are oviparous i.e., lay eggs.||They are mostly viviparous i.e., give birth to young ones.|
|3.||No mammary glands.||They possess mammary glands for production of milk to nourish their young.|
|4.||They possess hollow bones for flying.||No hollow bones.|
What are the advantages of classifying organisms?
The advantages of classifying organisms are as follows:
- Classification facilitates the identification of organisms.
- It helps to establish the relationship among various groups of organisms.
- It helps to study the phylogeny and evolutionary history of organisms.
- By studying a few animals, the characteristics of the whole group can be known.
How would you choose between two characteristics to be used for developing a hierarchy in classification?
Before developing a hierarchy in classification, we need to decide which characteristics should be used as the basis for making the broadest divisions. Then we should pick up next set of characteristics for making sub-groups. This process must continue and each time new characteristics should be used.
The characteristics that decide the broadest divisions among living organisms should be independent of any other characteristics. For example, nature of cell and form of the body is considered to classify organisms into broad divisions.
The characteristics in the next level should be dependent on the previous one that will decide the subsequent divisions of the groups. ^
Explain the basis for grouping organisms into the five kingdoms.
Robert H. Whittaker proposed his five- kingdom classification on the following basis :
- Phylogenetic relationship between organisms.
- Complexity of cell structure and body design.
- Mode of nutrition among organisms.
What are the major divisions in the plantae? What is the basis for these divisions?
The major divisions of the kingdom Plantae are: Thallophyta, Bryophyta, Pteridophyta Gymnosperms and Angiosperms.
The first level of classification of plants is based on the presence and absence of well- differentiated distinct components in the body. Algae are separated from the rest in having simple and less differentiated thalloid plant body.
The next level of classification is based on the presence and absence of vascular tissues (i.e., xylem and phloem). This character separates bryophyta from the rest. Further classification is based on the ability to bear seeds. Pteridophyta do not bear seeds.
Finally, the groups are made on the basis of seeds naked or enclosed within fruits. The gymnosperms have naked seeds whereas angiosperms bear seeds enclosed within the fruits.
How are the criteria for deciding divisions in plants different from the criteria for deciding the subgroups among animals?
The criteria for deciding divisions in plants are the presence or absence of seeds and flowers, differentiation of body parts, presence or absence of specialised vascular tissues and nature of the seed.
The criteria for subdivisions among animals are the presence or absence of notochord and coelom, position of nerve cord, gill slits, body segmentation, habitat and oviparity or viviparity.
How are animals in Vertebrata further classified into sub-groups? Explain.
The Subphylum Vertebrata has been classified into two superclasses, namely, Agnatha and Gnathostomata, on the basis of presence or absence of jaws and paired appendages. Agnatha members do not have jaws and paired appendages while Gnathostomata members bear jaws and paired appendages.
Superclasses have further been classified into Classes Pisces, Amphibia, Reptilia, Aves and Mammalia. The major characteristics used to classify are :
- The kind of exoskeleton or endoskeleton,
- The kind of respiratory organs
- The method of reproduction and giving birth to young ones.
It can be summarized as follows:
- Exoskeleton of scales; Endoskeleton of cartilage’ or bones; Breathing through gills – Pisces (fishes).
- Breathing through gills only in larva; Skin slimy – Amphibia.
- Exoskeleton of scales; Laying eggs outside the water-Reptilia.
- Exoskeleton of feathers; Lay eggs; Flight possible – Aves (Birds).
- Exoskeleton of hairs; External ears ; Give birth to young ones -Mammalia.