Unit 2: Classification

➔ Classification means arranging the organisms in groups and sub-groups based

on their similarities and differences
➔ Species are the group of closely related organisms that can reproduce fertile
offspring freely in nature
➔ Dichotomous key is a commonly used tool for classification, which helps in
identifying unknown organisms (Mostly MCQs will be related to this) Used to:
↳ Identify unfamiliar organisms
↳ Simplify the process of identification
↳ Separating species by contrasting features

System of Classification
➔ All the living organisms are classified into domains; the two domains are Domain
Prokaryotes and Domain Eukaryotes
➔ Living organisms are then divided according to the Kingdom
➔ Examples: Kingdom Animalia, Kingdom Plantae; we have 5 major kingdoms which are
included in our syllabus.
➔ Viruses are at the boundary of living and nonliving organisms and hence, aren't a part
of the 5 kingdoms
➔ Within each kingdom, the organisms are further divided into several phyla (Singular:
Phylum); this is equivalent to division, which we use in the case of plants
➔ Each phylum consists of organisms which differentiate them with other kingdoms. The
organisms of one phyla share similar characteristics, but they might not be obvious,
forming one of the main categories in biological classification that ranks above the
class and below the kingdom
➔ The phylum is made up of classes; organisms of a class further share more common
attributes
➔ Class ranks below the phylum and above the order
➔ Classes are divided into orders; the orders further divide organisms into more
specialised groups which have more qualities in common. Order ranks above family
and below class
➔ Within each order are the families. In the family, the name suggests the species'
resemblance is fairly close
➔ For animals, the family usually ends with idae; meanwhile, in plants it ends with
aceae. Family ranks below order and above genus
➔ Each family consists of a varying number of genera (Singular: Genus). Each genera
divides species into having similar structural characteristics, but the species are not as
closely related

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 ➔ Lastly, genera divides into species; each genus has several species
➔ Binomial nomenclature means ‘two-term naming system’; it comprises of genus and
species and is often written in italics
E.g. Canis (Genus) familiaris (specie)

Modes of nutrition
➔ There are 2 modes of nutrition, and they are:
↳ Autotrophic nutrition: In which organisms make their own food; such
organisms are called autotrophs, which includes Plants and some bacteria
↳ Heterotrophic nutrition: In which the organisms feed on readily available food
materials; such organisms are called heterotrophs

- Animals and their kingdoms

➔ There are further two types in the animal kingdom:
↳ Vertebrates: animals with a backbone
↳ Invertebrates: animals without a backbone

Invertebrate Groups

- Arthropods
➔ Arthropods are invertebrate animals that have an exoskeleton, a segmented body and
jointed appendages as their main features
➔ The "Phylum" arthropoda is subdivided into 4 classes:
↳ Insects
↳ Arachnids
↳ Myriapods
↳ Crustaceans

➔ Characteristics of all arthropods:

↳ Exoskeletons made of chitin
↳ Highly developed sense organs
↳ Jointed limbs
↳ Segmented bodies
↳ Ventral nervous system
↳ Bilateral symmetry, which is the same externally and internally

Key terms:
➔ Appendages : refer to any of the homologous body parts that may extend from a body
segment, including antennae,wings etc.

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 ➔ Ventral : Underside; along the stomach

Insecta ➔ 3 pairs of legs (Total 6) ➔ Have compound eyes which ➔ Examples:

➔ 3 segments of the body (Head, produce several images on Ants, Wasps, Butterflies
thorax and abdomen) the retinula cells
➔ 1 pair of antennae ➔ This forms a complex image,
➔ Usually have 2 pairs of wings due to which the insects are
able to detect even the
slightest of movements

Arachnida ➔ 4 pairs of legs and have 2 ➔ Mostly carnivorous and feed ➔ Examples:
pairs of appendages near the on insects and other small Spiders, Scorpions
mouth: Chelicerae and animals
Pedipalps(Total 10 ➔ Some arachnids are
appendages). venomous, who inject venom
➔ 2 segments of the body, which in their prey to paralyse it
are the cephalothorax (head ➔ Arachnids usually lay eggs,
and thorax fused together) and which hatch into immature
abdomen arachnids that are similar to
➔ No antennae or wings adults. Scorpions, however,
➔ Several pairs of simple eyes give birth to live young
➔ Chelicerae are tipped with
fangs for feeding ,while
pedipalps are sensing or
mating.

Myriapoda ➔ Many joined limbs ➔ Breath through series of ➔ Examples:

➔ They have a head and the small openings known as Centipedes, Millipedes
body is elongated with spiracles
numerous segments, ➔ Most abundant and diverse
in tropical and temperate
therefore, it does not divide
forests
into a thorax or abdomen
➔ There is at least 1 pair of legs
on each segment
➔ Simple eyes
➔ They have a pair of antennae

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Crustaceans ➔ 2 pairs of antennae ➔ Exclusively aquatic ➔ Examples:
➔ The head is fused with the ➔ Gills for breathing Crabs, Lobsters,
thorax region to form a ➔ Front limbs are modified into Shrimps
cephalothorax, and an chelipeds, which help in
abdomen is also present holding and biting, as well as
Therefore, it has two segments catching the prey
of the body ➔ Hard covering of the
➔ Compound eyes exoskeleton
➔ 5 or more pairs of limbs

Phylum Cordata/Vertebrates
➔ The "Phylum" Cordata is sub-divided into 5 classes:
↳ Fishes
↳ Amphibians
↳ Reptiles
↳ Birds
↳ Mammals

➔ Common features of Phylum Cordata animals:

↳ All the animals except tunicates are vertebrates
↳ They have separate openings for the mouth and the anus
↳ Vertebrates do not have an exoskeleton, but they have an internal skeleton
↳ Animals are heterotrophs (Feed on other organisms for nutrition

Features Fishes Amphibians Reptiles Mammals Birds

Skin ➔Scally, lose ➔ Thin, moist ➔ Dry, hard and ➔ Hair/fur on ➔ Scales on legs,
wet scales and slimy scaly their body and body covered
with feathers

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Reproduction ➔ External ➔ External ➔ Eggs are ➔ Sexual ➔ Internal
Fertilisation fertilisation takes internally Reproduction fertilisation, when
takes places place, when fertilised, when between male and birds mate
when male male the reptiles mate. female
shed sperm on amphibians Females can lay ➔ Sexual
the eggs laid shed sperm on the eggs, or keep reproduction
by females eggs it until the time for
hatching
➔ Sexual ➔ Sexual
reproduction reproduction ➔ Sexual
as two parents reproduction
involves

Eggs ➔ Soft ➔ Do not have a ➔Thick, leathery ➔ Sperm ➔ Hard,

jelly-like shell soft skin, not a or rubbery shells, and calcareous shells
in water hard shell which are Ovum fertilised
waterproof together to make ➔ Laid on
➔Laid on land embryo land, in the nests,
where mother will
➔ Embryo incubate them
turns into foetus
and then a baby
(Pregnancy)

Sensitivity ➔ Lateral lines ➔ Sensory ➔ Eyes and ➔ Eyes and ears

➔ Sense organs
along their organs such as ears to sense present
such as eyes,
body to detect eyes and ears
ears and nose are
and respond to are present ➔ Do not ➔ Pinna is absent
present
vibrations have a
➔ Do not pinna
➔External flap of
have a

pinna ear known as pinna

is also present

Have ears with 3

bones: Malleus,
incus and stapes

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Locomotion / ➔Fins ➔Some ➔4 limbs, which ➔4 limbs are ➔2 Wings and 2
Mobility ➔Stream-line amphibians such each having 5 present Feet
body as frogs and toes
toads have 4
➔Helps to limbs ➔Snakes don’t
swim have any limbs
underwater, ➔Their hind feet
while have webbed
maintaining toes, which
balance provides a large
surface area for
efficient
swimming

Breathing ➔Use gills ➔They can live ➔Lungs ➔Lungs ➔Lungs

on land and
water both,
hence may have
lungs and gills
both; however,
diaphragm is
absent

➔Amphibians
perform gas
exchange
through their
skin, which is
thin, most and
has good supply
of blood

Blood Temp. Cold-Blooded Cold-Blooded Cold-Blooded Warm-Blooded Warm-Blooded

Food ➔ Adults ➔ Mostly ➔ Omnivores

➔ Diet consist ➔ Carnivores,
amphibians are carnivores
of eggs, algae, Herbivores or ➔ Have beak to
carnivores
plants, Omnivores feed on variety of
which feed on ➔ Feed on
crustaceans, insects, things
insects
worms, ➔ Have 4
amphibians and
mollusks, types of
➔ Young can feed on other
insects, insect teeth: incisors,
ones, such as, reptiles
larvae, canines, premolars
tadpoles, are
amphibians, and molars to chew
herbivores and
and plankton the food
feed on algae

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 ➔ Have
Other ➔ Transparent ➔ Nictitating ➔ Have special ➔ Have
nictitating

features eyelids to membrane to membrane, to mammary glands lightweight

prevent water protect the eyes protect the eyes to breastfeed their bones,
entering and young ones which help in
allowing focus flying

➔Wings also
help
in flying

Examples Shark, Tuna, Snakes, lizards Humans, cats and Chicken,

Frogs, Toads,
Rahu, Trout and crocodiles bears hummingbird
Newts,
Salamanders

Plants
➔ Kingdom Plantae plants are the multicellular organisms which belong to the Domain
Eukaryote; therefore, they have a nucleus and membrane bound organelles
↳ Plants are the organisms that use chlorophyll to carry out photosynthesis
↳ There are two main divisions of plants: ferns and flowering
plants ↳ Flowering plants have further two types: monocots
and dicots

- Ferns:
➔ Ferns, also known as filicinophytes are the plants that do not have flowers;
therefore, they do not reproduce by pollination. Ferns do not produce:
↳ Flowers
↳ Fruits
↳ Seeds
↳ Ovules (female gamete)
↳ Pollen (male gamete) Cambium tissue is also absent in ferns
➔ Flowering plants reproduce sexually by pollination, (which we will study in a later
Unit) while ferns reproduce in a way similar to fungi
➔ This asexual way of reproduction is known as spore formation. The leaves of ferns
are known as fronds. At the underside of fronds, sporangia can be found
➔ When sporangia are mature, they burst and the spores are released; they are
carried by the wind and rain to far away areas. The spores find moist soil,
germinate and then grow.

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- Flowering plants:
➔ Also known as angiospermophytes can be classified into:
↳ Dicotyledons
↳ Monocotyledons
➔ In flowering plants, roots, stems, and leaves are present
➔ Cambium tissue is also present
- Reproduction in flowering plants/angiospermophytes:
➔ Flowering plants reproduce by pollination
➔ This process of sexual reproduction involves two gametes: pollen and ovule
➔ The pollen is released from the anthers of flowers, and is carried by the wind or
insects to the stigma of the flower
➔ The pollen grains secrete special hydrolysis enzymes on the stigma and digest its
wall to make its way to the ovary
➔ The male nucleus from the pollen then travels through this pollen tube and enters
the ovary through the microphile. The male nucleus will fuse with the ovule (female
nucleus), and fertilisation will occur
➔ After fertilisation, the ovule develops into a seed and the ovary develops into a fruit
The dispersal of seeds by wind/water/animals will allow the seeds to find a place for
germination and grow into a plant

Dicotyledons and Monocotyledons

Dicots Monocots

Two cotyledons present in their seeds One cotyledon present in their seeds

Broad leaves, with network a of veins Elongated leaves, with parallel veins

Petals in multiples of 4 or 5 Petals in multiples of 3

Tap roots Fibrous roots

Ringed vascular bundle Scattered vascular bundle

Viruses
➔ They are at the boundary of living and non-living things ➔ Viruses have the
following characteristics:
↳ Live as parasites in the hosts’ body
↳ Strictly parasitic

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 ↳ Take food and shelter in the hosts’ body, and give diseases in
return ↳ Have no organelles, cytoplasm, etc.
↳ Acellular
↳ Reproduce inside the hosts’ body
↳ Cannot survive outside (die outside)
↳ Crystallise outside hosts
↳ Different shapes

➔ Viruses are made up of:

↳ A nucleic acid (Either RNA or DNA)
↳ Protein coat, known as capsid
↳ No protoplasm and, therefore, are non-cellular

➔ Viruses are made up of a nucleic acid, which can be RNA or DNA (genetic
material), which is surrounded by a protein coat known as a capsid
➔ In cellular cells, DNA is always double strand, and RNA is single strand. Since
viruses are not cellular structures, they can have single strand DNA and double
strand RNA as well; therefore, viruses can have 4 types of nucleic acids
1. Single strand DNA
2. Double strand DNA 3. Single strand RNA
4. Double strand RNA

➔ Viruses cause various diseases such as:

↳ AIDS (Acquired Immunodeficiency Syndrome)
↳ Ebola
↳ Influenza
↳ SARS (Severe Acute Respiratory Syndrome)
↳ Smallpox
↳ Chicken Pox
↳ Herpes

➔ Antibiotics cannot be used to treat viral infections, and viruses can only be
destroyed by antibodies produced by white blood cells. However, doctors might
prescribe antibiotics when you have a viral infection as a precautionary/deterrent
measure.
➔ This protects your body from acquiring a possible bacterial infection which it
would normally be able to fight against, but not currently, as your resistance is
very low during this time.

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