Question 1:
Why do we classify organisms? Answer:
There are a wide range of life forms (about 10 million −13 million species) around
us.
These life forms have existed and evolved on the Earth over millions of years ago. The huge range of these life forms makes it very difficult to study them one by one. Therefore, we look for similarities among them and classify them into different
classes to study these different classes as a whole. Thus, classification
makes our
study easier.
Question 2:
Give three examples of the range of variations that you see in life-forms around you.
Answer:
Examples of range of variations observed in daily life are:
(i) Variety of living organisms in terms of size ranges from microscopic bacteria to
tall
trees of 100 metres.
(ii) The colour, shape, and size of snakes are completely different from those of
lizards.
(iii) The life span of different organisms is also quite varied. For example, a crow
lives for only 15 years, whereas a parrot lives for about 140 years.
Question 1:
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?
Answer:
The kind of cells that living organisms are made up of is a more basic characteristic
for
classifying organisms, than on the basis of their habitat. This is because on the
basis of the kind of cells, we can classify all living organisms into eukaryotes
and prokaryotes. On the other hand, a habitat or the place where an organism lives is a very broad characteristic to be used as the basis for classifying organisms. For
example, animals that live on land include earthworms, mosquitoes,
butterfly, rats,
elephants,
tigers, etc. These animals
do
not resemble each other except for the fact that they share a common habitat. Therefore, the
nature or kind of
a cell is considered to be a fundamental characteristic for the classification of living organisms.
Question 2:
What is the primary characteristic on which the first division of organisms is made? Answer:
The primary characteristic
on
which the first division of organisms is made is the nature of the cell. It is considered to be the fundamental characteristic for classifying
all
living organisms.
Nature of the cell includes the presence or absence of membrane-bound organelles. Therefore, on the basis of this fundamental characteristic, we can classify all living organisms into two broad categories of eukaryotes and prokaryotes. Then, further classification is made on the basis of cellularity or modes of nutrition.
Question 3:
On what basis are plants and animals put into different categories? Answer:
Plants and animals differ in many features such as the absence of chloroplasts,
presence of cell wall, etc. But, locomotion is considered as the characteristic feature
that separates animals
from plants. This is because the absence of locomotion in
plants gave rise to many structural changes such as the presence of a cell wall (for
protection), the presence of chloroplasts (for photosynthesis) etc. Hence, locomotion is considered to be the basic characteristic as further differences arose because of
this characteristic feature.
Question 1:
Which organisms
are called primitive and how are they different from the so-called advanced organisms?
Answer:
A primitive organism or lower organism is the one which has
a simple body structure
and
ancient body design or features
that
have not changed much over a period of
time. An advanced
organism or higher organism has a complex body structure
and organization. For example, an Amoeba is more primitive as compared to a starfish. Amoeba has a
simple body structure and primitive features as compared to a starfish. Hence, an Amoeba is considered more primitive than a starfish.
Question 2:
Will advanced organisms be the same as
complex organisms? Why?
Answer:
It is not always true that an advanced organism
will have a complex body structure.
But,
there is a possibility that over the evolutionary time, complexity
in
body design will increase. Therefore, at times, advanced organisms can be the same as complex
organisms.
Question 1:
What is the criterion for classification of organisms as belonging to kingdom Monera
or
Protista?
Answer:
The criterion for the classification of organisms belonging to kingdom Monera or
Protista is the presence or absence of a well-defined nucleus or membrane-bound organelles. Kingdom Monera includes organisms that do not have a well-defined nucleus or
membrane-bound organelles
and these are known as
prokaryotes.
Kingdom Protista, on the other hand, includes organisms with a well-defined nucleus and membrane-bound organelles and these organisms are called eukaryotes.
Question 2:
In which kingdom will you place an organism which is single-celled, eukaryotic and
photosynthetic?
Answer:
Kingdom Protista includes single celled, eukaryotic, and photosynthetic organisms.
Question 3:
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?
Answer:
In the
hierarchy
of classification,a species will
have the
smallest number of
organisms with a maximum of characteristics
in common, whereas the kingdom will
have
the largest number of organisms.
Question 1:
Which division among plants has the simplest organisms? Answer:
Thallophyta is the division of plants that has the simplest organisms. This group includes plants, which do not contain a well differentiated plant body. Their body is not differentiated into roots, stems, and leaves. They are commonly known as algae. Question 2:
How are pteridophytes different from the phanerogams?
Answer:
Pteridophyta
|
Phanerogams
|
They
have
inconspicuous
or less
differentiated reproductive organs.
|
They
have well developed
reproductive organs.
|
They produce naked embryos called spores.
|
They produce seeds.
|
Ferns,
Marsilea,
Equisetum, etc.
are examples of pteridophyta.
|
Pinus, Cycas, fir, etc. are examples of phanerogams.
|
Question 3:
|
Porifera
|
Coelenterate
|
They are mostly marine,
non- motile, and
found
attached to
rocks.
|
They are exclusively marine animals that
either live in colonies
or have a solitary life-
span.
|
They
show
cellular level of
organisation.
|
They show tissue level of
organisation.
|
Spongilla,
Euplectella,
etc.
are poriferans.
|
Hydra, sea anemone,
corals,
etc. are coelenterates.
|
Question 2:
How do annelid animals differ from arthropods? Answer:
Annelids
|
Arthropods
|
The
circulatory
system of
annelids is
closed.
|
Arthropods have an
open circulatory system.
|
The body is divided into several identical
segments.
|
The body is divided into few specialized
segments.
|
Question 3:
What are the differences between amphibians and reptiles?
Answer:
Amphibian Reptiles
They have a dual mode of life. They are completely terrestrial.
|
Question 4:
What are the differences between animals belonging to the Aves group and those in the mammalia group?
Answer:
Aves
|
Mammals
|
Most
birds
have feathers and they possess a beak.
|
They do
not
have
feathers and
the beak
is also absent.
|
They lay eggs. Hence, they are oviparous.
|
Some of them lay eggs and some give birth to young
ones. Hence, they are both oviparous and viviparous.
|
There are a wide range of life forms (about 10 million-13 million species) around us. These life forms have existed and evolved on the Earth over millions of years ago. The huge range of these life forms makes it very difficult to study them one by one.
Therefore, we look for similarities among them and classify them into different
classes so that we can study these different classes as a whole. This makes our study easier.
Therefore, classification serves the following advantages:
(i) It determines the methods of
organising the diversity of life on Earth. (ii) It helps in understanding millions of life forms in detail.
(iii) It also helps in predicting the line of
evolution.
Question 2:
How would you choose between two characteristics
to
be used for developing a hierarchy in classification?
Answer:
For developing a hierarchy of classification, we choose the fundamental characteristic among several other characteristics.
For example, plants differ from animals in the
absence of locomotion, chloroplasts, cell wall, etc. But, only
locomotion is considered
as the basic or fundamental feature that is used to distinguish
between plants and
animals. This is because the absence of locomotion
in plants gave rise to many
structural changes such as the presence of a cell wall for protection, and the
presence of chloroplast for photosynthesis (as they cannot move around in search of
food like animals). Thus, all these features are a result of locomotion.
Therefore,
locomotion is
considered to be a fundamental characteristic. By choosing the basic or fundamental characteristic,
we can make broad divisions in living organisms as the next level of characteristic is dependent on these. This goes on to form a hierarchy of
characteristics.
Question 3:
Explain the basis for grouping organisms into five kingdoms.
Answer:
R.H. Whittaker proposed a five kingdom classification of living organisms on the basis of Linnaeus’ system of classification. The five kingdoms proposed by Whittaker
are Monera, Protista, Fungi, Plantae, and Animalia.
The basis for grouping organisms into five kingdoms is as follows:
(i) On the basis of the presence or absence of membrane-bound organelles, all living
organisms are divided into two broad categories of eukaryotes and prokaryotes. This division lead to the formation of kingdom Monera, which includes all prokaryotes.
(ii) Then, eukaryotes are divided as unicellular and multicellular, on the basis of
cellularity. Unicellular eukaryotes
form kingdom Protista, and multicellular
eukaryotes form kingdom Fungi, Plantae, and Animalia.
(iii) Animals are then separated on the basis of the absence of a cell wall.
(iv) Since fungi and plants both contain a cell wall, they are separated into different
kingdoms on the basis of their modes of nutrition. Fungi have saprophytic mode of
nutrition, whereas plants have autotrophic
mode of nutrition. This results in the formation of the five kingdoms.
Question 4:
What are the major divisions in the Plantae? What is the basis for these divisions?
Answer:
The kingdom Plantae is divided into five main divisions: Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms.
The classification depends on the following criteria:
• Differentiated/ Undifferentiated plant body
• Presence /absence of vascular tissues
• With/without seeds
• Naked seeds/ seeds inside fruits
(i) The first level of classification depends on whether a plant body is well differentiated
or
not. A group of plants that do not have a well differentiated plant
body are known as Thallophyta.
(ii) Plants that have well differentiated body parts are further divided on the basis of
the
presence or absence of vascular tissues. Plants without specialised vascular
tissues are included in division Bryophyta, whereas plants with vascular tissues are known as Tracheophyta.
(iii) Tracheophyta is again sub-divided into division Pteridophyta, on the basis of the absence of seed formation.
(iv) The other group of plants having well developed reproductive organs that finally
develop seeds are called Phanerogams. This group is further sub- divided on the
basis of whether the seeds are naked or enclosed in fruits. This classifies
them into gymnosperms and angiosperms. Gymnosperms are seed bearing, non-flowering plants, whereas angiosperms
are flowering plants in which the seeds are enclosed
inside the fruit.
Question 5:
How are the criteria for deciding divisions in plants different from the criteria for
deciding the subgroups among animals?
Answer:
Criteria for deciding divisions in plants are:
(i) Differentiated/ Undifferentiated plant body
(ii) Presence/ absence of vascular tissues
(iii) With/without seeds
(iv) Naked seeds/ seeds inside fruits
Criteria for deciding subgroups among
animals are:
Kingdom Animalia is divided into two major groups on the basis of the presence or
absence of a notochord.
Non-chordates do
not
possess a notochord,
while
all
members of the
phylum chordates possess a notochord.
Non-chordate is further divided into subgroups on the basis of the following features:
On the basis of the above features, non-chordates are divided into the following subgroups: Porifera, Coelenterate, Platyhelminthes,
Nematodes, Annelids, Molluscs,
Arthropoda, and Echinodermata.
All members of the phylum chordate possess a notochord.
However, some animals such as Balanoglossus, Amphioxus, Herdmania, etc. have a notochord, which is
either absent or does not run the entire length of the animal’s body. Therefore, these animals are kept in a separate sub-phylum called Protochordata, and the rest of the
chordates are included in the sub-phylum
vertebrata. The members of the sub-
phylum vertebrata are advanced chordates. They are divided into five classes:
Pisces, Amphibian, Reptilia, Aves, and Mammalia.
Question 6:
Explain how animals in Vertebrata are classified into further subgroups. Answer:
Animals in Vertebrata are classified into five classes:
(i) Class
Pisces: This class includes fish such as Scoliodon, tuna, rohu, shark, etc.
These animals mostly live in water. Hence, they have special adaptive features such
as
a streamlined body, presence of
a tail for movement, gills, etc. to live in water.
(ii) Class Amphibia: It includes frogs, toads, and salamanders. These animals have
a dual mode of life. In the larval stage, the respiratory
organs are gills, but in the
adult stage, respiration occurs through the lungs or skin. They lay eggs in water.
(iii) Class Reptilia: It includes reptiles such as lizards, snakes, turtles, etc. They usually creep or crawl
on land. The body of
a reptile is
covered with dry and cornified
skin
to prevent water loss. They lay eggs on land.
(iv) Class
Aves: It includes all birds such as sparrow, pigeon, crow, etc. Most of them have feathers. Their forelimbs
are modified into wings for flight, while hind
limbs are modified for walking and clasping. They lay eggs.
(v) Class Mammalia: It includes a variety of animals which have milk producing
glands to nourish their young ones. Some
lay eggs and some
give birth to young ones. Their skin has hair as well as sweat glands to regulate their body temperature.
No comments:
Post a Comment