CHAPTER – 1
Characteristics and Classification of Living Organisms
 Common characteristics of living organisms:
Living organisms including all types (unicellular or multicellular, plants, animal etc) have some common
characteristics as below. Remember MRS GREN
Movement:
Is an action by an organism or part of an organism causing a change of position or place
Respiration
The chemical reactions in cells that break down nutrient molecules and release energy
for metabolism
Sensitivity
The ability to detect and respond to changes in the internal or external environment
Growth
Is a permanent increase in size and dry mass
Reproduction Is the processes that make more of the same kind of organism.
Excretion
Is the removal of waste products of metabolism and substances in excess of requirements
Nutrition
Is the taking in of materials for energy, growth and development.
 Taxonomy:
It is the science of naming, describing and classifying organisms.
Kingdom: Highest taxonomic group used in classifying organisms.
Phylum: Grouping organisms based on general specialisation of characteristics.
Class: It consists of organisms that show a common attribute.
Order: Contains one or more families.
Family: A group of one or more genera, especially sharing a common attribute.
Genera: Closely related or similar species are placed together in a group called genus (plural: genera).
For example, there are 45 species of bronzeback snake, all in the same genus Dendrelaphis.
Species: Is a group of organisms that can reproduce naturally with one another (can interbreed) to
produce fertile offspring. They are the smallest natural group of organisms. Members of a species also
often look very similar to each other in appearance, almost identical in their anatomy, physiology and
behaviour. For example, all cats belong to same species, but there are wide variations in appearance
of different breeds.
 What is Binomial system:
It is the system of naming organisms is an internationally agreed system in which the scientific name of an
organism is made up of two parts i.e. genus and species.
1. Binomial means ‘two names’; the first name gives the genus and the second gives the species.
2. The name of the genus (the generic name) is always given a capital letter and the name of the species (the
specific name) always starts with a lowercase letter.
3. Often, the specific name is descriptive, for example, edulis means ‘edible’, aquatilis means ‘living in water’,
bulbosus means ‘having a bulb’, serratus means ‘having a jagged (serrated) edge’
Importance:
1. It is an internationally agreed system for naming organisms that is same throughout the world.
2. The use of the scientific name avoids any confusion between scientists of different countries.
3. If botanical name is used there is no chance of error.
4. Latin form of name allows it to be used in all countries of the world regardless of language barriers.
Example:
1. Egyptian mongoose and Indian grey mongoose are both in the genus Herpestes but they are different
species; the Egyptian mongoose is Herpestes ichneumon and the Indian grey mongoose is Herpestes
edwardsii.
2. People living in the Indian subcontinent are familiar with the appearance (color, design etc) of a robin.
Use of the scientific specie names Copsychus fulicatus (Indian robin) and Erithacus rubecula (British
robin) avoids any confusion.
 How are organisms classified?
There are many possible ways of classifying organisms.

Organisms should be classified in a way that it makes meaningful groups.

So, biologists look for a natural system of classification using important features that are shared by
as large a group as possible. It is not always easy to handle in all cases. As a result, biologists
change their ideas from time to time about how living things should be grouped. New groupings
are suggested and old ones abandoned.
 Dichotomous key:
It is the key used to identify unfamiliar organisms. It simplifies the process of identification and helps to
identify organism correctly.
How to make it:
Each key is made up of pairs of contrasting features (dichotomous means two branches), starting with quite
general characteristics and moving on to more specific ones.
The same technique may be used for assigning an organism to its class, genus or species. However, the
important features may not always be easy to see, so you must make use of less basic characteristics.
Example:
In first key, item 1 gives you a choice between two alternatives. If the animal is cold-blooded, you move to
item 2 and make a further choice. If it is warm-blooded, you move to item 4 for your next choice.
 How do classification systems reflect evolutionary relationships?
Evolution: It is the inheritance of characteristics of biological population over successive generations.
When we classify organisms, it is possible to understand evolutionary relationships. Studying the anatomy of
different groups helps us to learn about their evolution
Example:
Vertebrates
o
All have vertebral column, skull protecting a brain and a pair of jaws (usually with teeth).
o
Although skeletons of front limb of five types of vertebrates have different functions, such as holding on to
objects, flying, running and swimming, the arrangement and number of the bones is almost same in all five.
Basic pattern of bones is same in all these animals. There is a single top bone (the humerus), with a ball and
socket joint at one end and a hinge joint at the other. It makes a joint with two other bones (the radius and
ulna) that join to a group of small wrist bones. The limb skeleton ends with five groups of bones (the hand
and fingers), although some of these groups are missing in the bird.
o
If organisms share a common ancestor this will be reflected in how they are classified. However, if they are
found not to share a common ancestor, as is the case with the pangolin and armadillo, their classification will
be different. Although at first glance the pangolin and armadillo may appear to share a common ancestor, a
closer study of the two species reveals major differences. The two animals are both mammals but differences
between them mean that they are not classified in the same group.
Pangolin
Armadillo
body covered in scales made of keratin
Armoured body covering, made up of hard bony plates
It has no teeth but uses its long tongue to
Has small teeth, which are not covered in enamel, and
feed on ants and termites
feeds on grubs and insects. Has long claws which it
uses for digging and making a burrow.
Can roll into a tight ball for protection
Some armadillo species can roll up into a ball when
threatened by predators
 How is DNA used for classifying organisms?
What is DNA: Most organisms contain chromosomes made up of strings of genes. The chemical that forms
these genes is called DNA (deoxyribonucleic acid). DNA is made up of a sequence of bases, coding for amino
acids and proteins.
The use of DNA has revolutionised the process of classification.
Each species has a distinct number of chromosomes and a unique sequence of bases in its DNA, making it
identifiable and distinguishable from other species. This helps particularly when different species are very
similar morphologically (in appearance) and anatomically (in internal structure).
Example:
Human and primate evolution is a good example of how DNA has been used to make a process of evolution
clear.
 Traditional classification of primates:
Classifies them into groups of monkeys, apes and humans
This classification was based on their anatomy, particularly their bones and teeth.
This placed humans in a separate group, while placing the other apes together into one family called
Pongidae.
 Genetic classification:
However, genetic evidence using DNA provides a different understanding

humans are more closely related to chimpanzees (1.2% difference in the genome – the complete set of
genetic material of the organism) and gorillas (1.6% different) than to orangutans (3.1% different).

Chimpanzees are closer to humans than to gorillas. Bonobos and chimps are found in Zaire and were only
identified as different species in 1929. The two species share the same percentage difference in the genome
from humans.
 Features of organisms:
All living organisms have certain features in common
All have
(i)
cytoplasm
(ii)
cell membranes
(iii)
DNA as genetic material.
I. ANIMAL KINGDOM:
Features:
(i) Multicellular organisms
(ii) No cell wall
(iii) No chloroplast
(iv) Most ingest solid food.
(v) Digest food internally
1. Arthropods (Invertebrates)
The arthropods include the crustacea, insects, arachnids and myriapods.
What feature do all arthropods have in common?
1. They are invertebrate (without vertebral column)
2. The name arthropod means ‘jointed limbs’, and this is a feature common to them all.
3. They also have a hard, firm, external skeleton, called a cuticle, which encloses their bodies.
4. Their bodies are segmented (made up of several sections)
5. Between the segments (sections), there are flexible joints which allow movement.
6. In most arthropods, the segments are grouped together to form distinct regions, head, thorax (middle section
of body i.e. cephalothorax) and abdomen (part of body behind thorax).
Distinguish Features:
Features
Example
s
Legs
Crustacea
Insects
Arachnids
Myriapods
Marine: Crab, prawns,
Dragonfly, wasp,
Spider, mite, tick,
Centipede, millipede
lobsters, shrimps,
butterflies,
scorpions,
barnacles
mosquitos,
Freshwater: water
houseflies,
fleas, cyclpos, water
earwigs,
louse, shrimp
greenflies,
Land: woodlice (termite)
beetle, ladybird
5 or more pairs. One
3 pairs. No limb
4 pairs on
10 or more pairs (usually
pair in each segment,
in abdominal
cephalothorax
one pair in each segment)
those on head are
segment
but in millipede the
modified to form
abdominal segment are
antennae or specialised
merged and make it look
mouth part for feeding
tow pairs of legs on each
segment. As millipede
grow, extra segments are
formed
Body
Divided into
Divided into
Divided into
Have head and segmented
cephalothorax
head, thorax and
cephalothorax
body that is not clearly
(combined head and
abdomen
(combined head and
divided into thorax and
thorax) and abdomen
abdomen
None
1 pair
1 pair of compound eyes.
Several pairs of
Simple eyes
Compound eyes: They are made up of 10
simple eyes
thorax) and abdomen
Antennae
2 pairs. Sensitive to
1 pair
touch and chemicals
Eyes
or 100s of separate lenses with lightsensitive cells underneath. They can form
simple image and are very sensitive to
movement.
1 pair of compound eyes
Other
Exoskeleton often forms
•Usually have 2
Pair of pedipalps,
Centipede is carnivore
hard covering over most
pair of wings
one used for
(feeding on animal),
of body
•can withstand
reproduction, other is
millipede is herbivore
extreme hot
adapted for biting
feeding on plant)
because of
and poisoning
cuticle which
(secreted by gland at
prevent water
base) prey
loss
2. Vertebrates
What feature do all vertebrates have in common?
1. Have a vertebral column or spinal column, or just spine, and consists of a chain of cylindrical bones
(vertebrae) joined end to end. Each vertebra carries an arch of bone on its dorsal (upper) surface. This arch
protects the spinal cord (which runs most of the length of the vertebral column).
2. The front end of the spinal cord is expanded to form a brain, which is enclosed and protected by the skull.
3. The skull carries a pair of jaws which, in most vertebrates, contain rows of teeth.
Classes of vertebrates
There are five classes of vertebrates: fish, amphibia, reptiles, birds and mammals.
Cold blooded: There is no internal mechanism for temperature control.
Warm blooded: They have internal mechanism for temperature control which keep the temperature within
narrow limits. They have temperature higher than their surroundings. Their temperature is kept constant
despite any variation in external temperature-not dependant on external environment.
Advantage of being warm blooded: Animal activity is not dependant on surrounding temperature e.g. lizard
body movement may become slow if surround temperature fall. If it is chased by a predator who is cold
blooded it would be disadvantageous.
Why do you think cold-blooded animals are slowed down by low temperatures?
As all chemical reactions are slowed down at low temperature. So, at certain temperature below which
metabolism doesn’t not work properly. As we know enzymes work best at certain temperature.
Distinguish Features of Vertebrates:
Fish
Example Trout, rohu,
Amphibian
Reptiles
Birds
Mammals
Frog, toad, newt
Lizard, snake, turtles,
Sparrow,
Mouse, striped
tortoises, crocodiles
pigeon
hyena, humans
sharks
1. Body Temperature
Fish: Cold blooded
Amphibian: Cold blooded
Reptiles: Cold blooded but try to regulate their temperature. They do this by lying in the sun until their bodies
warm up. When reptiles warm up, they can move about rapidly to chase insects and other prey.
Birds: Warm blooded
Mammals: Warm blooded
2. Breathing
Fish: Filamentous gills for breathing which are protected by bony plate called operculum
Amphibian: Lungs, which can be inflated by the kind of swallowing action. They do not have diaphragm
or ribs. Skin, which has good blood supply of capillaries through which they exchange O2 and CO2 with air
and water
Reptiles: Lungs for breathing
Birds: Lungs for breathing
Mammals: Lungs for breathing, unlike the other vertebrates, they have a diaphragm which plays a part in
breathing
3. Body Covering
Fish: Overlapping scales
Amphibian: Moist Skin, No scale
Reptiles: Dry skin and outer layer of epidermis forms scales which helps reduce water loss
Birds: •Feathers: are of several kinds giving shape and colour
i. Fluffy down feathers form an insulating layer close to the skin ii. Contour feathers cover body and give
bird its shape and coloration iii. Large quill feathers on the wing are vital for flight
• Legs: have scales on it
Mammals: Fur (hair)
4. Sense Organ
Fish: - Eyes
- No Ear
Amphibian: -Eyes
Reptiles: -Eyes
Birds: -Eyes
-Lateral line along body for detecting vibrations in water
-Ear
-Ear
-Ear
Mammals: Eyes -Ear with pinna (external flap)
5. Movement
Fish: -Fins (also used for balance) •Have smooth, streamlined shape that allow easy flow in water
Amphibian: -4 limbs •Back feet are often webbed to make swimming more efficient (in frog and toads)
Reptiles: •4 legs (except snake) each with 5 toes
•Some species of snake still have the traces of limbs and girdle
Birds: • 4 limbs, but forelimbs are modified to form wings. The feet have 4 toes with claws, which help the
bird to perch, scratch for seeds or capture prey
Mammals: 4 limbs
6. Reproduction
Fish: Sexual reproduction, but fertilization usually external. In water, female lays jelly-covered eggs and male
sheds sperms on them
Amphibian: Sexual reproduction, Frogs and toads migrate to ponds where males and females pair up. The
male climbs on the female’s back and grips firmly with his front legs. When the female lays jelly covered eggs,
the male immediately releases sperms over them. Fertilisation, therefore, is external even though the frogs
are in close contact for the event.
Reptiles: • Sexual reproduction, Produce eggs with rubbery, waterproof paper like shell
•Laid on land
•Male and female reptiles mate, and sperms are passed into the female’s body. So, the eggs are fertilised
internally before being laid. In some species, the female keeps the eggs in the body until they are ready to
hatch
Birds: • Sexual reproduction, Produce eggs with hard shell in a nest where she incubates them (keeps
them warm and safe). •Laid on land •Fertilisation is internal
Mammals: Sexual reproduction, Produce live young. The eggs are fertilised internally and go through a
period of development in the uterus
7. Other Detail
Amphibian: •Amphibian means ‘double life’-they spend part of life in water and part on land.
•Carnivores
•Difference b/w Toad and Newt:
-Toad: skin drier than frog, has gland which release unpleasant-tasting chemical to put off predators
Newt: unlike frog and toad they have tails
Reptiles: Land Living, not limited to damp habitat. Don’t need water to reproduce
Birds: •Unlike other vertebrates, their vertebral column in neck is flexible. Rest of vertebrae are merged to
form rigid structure. It is an adaptation to flight as powerful wings need rigid framework.
•The upper and lower jaws are extended to form a beak, which is used for feeding in various ways
Mammals: •Females have mammary glands to produce milk to feed young for the first few weeks or months
•Four types of teeth •have 26 subgroups (order): 1. Insectivores
2. Carnivore
3. Rodents
4. Primates.
(only 4 mentioned)
II. PLANT KINGDOM:
Features:

Multicellular organisms

Has cell wall made up of cellulose

Most of leaves and stem contain chloroplast with photosynthetic pigment called chlorophyll

Make their own food by photosynthesis
1. Fern:
Features:
Ferns are land plants with well-developed structures. Their stems, leaves and roots are very similar to those
of flowering plants.
1. The stem is usually completely below ground. In bracken, the stem grows horizontally below ground, sending
up leaves at intervals.
2. Roots grow directly from the stem.
3. The stem and leaves have sieve tubes and water-conducting cells like those in the xylem and phloem of
a flowering plant.
4. The leaves of ferns vary from one species to another, but they are all several cells thick. Most of them have
an upper and lower epidermis, a layer of palisade cells and a spongy mesophyll, like the leaves of a flowering
plant.
5. Ferns produce gametes but no seeds. The zygote gives rise to the fern plant, which then produces singlecelled spores from many sporangia (spore capsules) on its leaves. The sporangia are formed on the lower
side of the leaf, but their position depends on the species of fern. The sporangia are usually arranged in
compact groups.
2. Flowering plants: (refer to chapter # 8 also).
Features:
1. Flowering plants reproduce by seeds that are formed in flowers. The seeds are enclosed in an ovary
2. Flowering plants are divided into two subclasses: monocotyledons and dicotyledons.
3. Cotyledon: The first leaf of a plant which is usually folded within a seed until germination and stores energy.
Features
Monocotyledons (monocots for short)
Dicotyledons (dicots for short)
Cotyledons
One in their seed
Two in their seed
Leaf shape
Most, but not all, have long, narrow leaves
Broad
Leaf veins
Parallel
Branching
Examples
Grass, daffodils, bluebell
Trees, shrubs, herbs
In multiple of threes
In multiple of fives
Number of
flower parts
are
(petals, sepals,
carpel)
Difference between flowering plant and fern
Fern
Flowering plant
 Don’t produce flower
 Reproduce by flower and seeds
 Leaves are called fronds
 Seeds are produced inside flower/ovary
 Reproduced by spores
 Are
 Have sporangia
in
2
different
categories,
monocotyledons, dicotyledons
III. FUNGI KINGDOM:
Examples: Mushrooms, Toadstools, Puffballs
Features:
1. Most fungi are made up of thread-like hyphae, rather than cells. Branching hyphae form mycelium
2. Reproduced by spores, don’t have chlorophyll, cell wall of Chitin.
3. There are many nuclei scattered throughout the cytoplasm in their hyphae

Bracket fungi that grow on tree trunks

Mould fungi that grow on stale bread, cheese, fruit or other food

Yeasts are single-celled fungi that have some features similar to moulds.

Some fungal species are parasites, as is the bracket fungus. A parasite is an organism living on another
organism (the host), gaining food and shelter from it. It is a very one-sided relationship. Fungal parasites
live in other organisms, particularly plants, where they cause diseases that can affect crop plants, such as
the mildew.
IV. PROKARYOTE KINGDOM:
Examples: Bacteria, Blue-green algae.
Features:
1. They consist of single cells (unicellular) and microscopic but are different from other single-celled organisms
because their chromosomes are not organised into a nucleus.
2. They lack membrane bounded organelles.
3. Bacteria has small ribosomes (30s and 50s subunit), The structure of bacterial cells is described in Chap 2.
4. Prokaryotes kingdom is called Monera according to five classification system
V. PROTOCTIST KINGDOM:
Features:

These are single-celled (unicellular) organisms.

Have their chromosomes enclosed in a nuclear membrane to form a nucleus.

Some have chloroplast e.g., euglena and Chlamydomonas.

Some eat solid food e.g., amoeba.
Some of Protoctista (e.g. Euglena) have chloroplasts and make their food by
photosynthesis. These Protoctista are often referred to as unicellular.
Organisms like Amoeba and Paramecium (protozoa) take in and digest solid food
and so are animal-like in their feeding. They may be called unicellular ‘animals’.
Amoeba:
o
is a protozoan (cannot make their own food and feed microorganisms or organic debri) that
moves by a flowing movement of its cytoplasm.
o
It feeds by picking up bacteria and other microscopic organisms as it moves.
Vorticella:
Protozoa which has a stalk that can contract and feeds by making a current of
water with its cilia (tiny hair-like organelles which project from the cell surface). The
current brings particles of food to the cell.
Euglena and Chlamydomonas have chloroplasts in their cells and feed, like
plants, by photosynthesis.
Viruses

Viruses are not included in any kingdom. They are small in size and have no cell.

All viruses have a central core of RNA or DNA surrounded by protein coat. So they do reproduce like living
organism, but this only happens inside the cells of living organisms, using materials provided by host cell.

They are not considered to be living organisms because:
1. They do not have cell membranes (made of protein and fat), cytoplasm and ribosomes though some forms
have membrane outside their protein coats.
2. They do not demonstrate characteristics of living things i.e. they do not feed, respire, excrete or grow. So,
virus particles are not cells.
Structure of virus:
The nucleoid acid core is coiled single strand surrounded by a protein coat. The protein coat is called a
capsid.
CLASSIFICATION SCHEMES
Many classifications scheme has been proposed by scientists and it changes with time.
The two-kingdom
The five-kingdom scheme
The three-domain scheme (proposed by
scheme (by Limmaeus):
(proposed by Whittaker)
Carl Woese in 1978)
1. Animal
1. Animal
This involves grouping organisms using
2. Plant
2. Plant
differences in ribosomal RNA structure. Under
3. Fungus
this system, organisms are classified into
4. Prokaryote
three domains and six kingdoms, rather
5. Protoctist
than five. The three domains are:
1. Archaea: containing ancient prokaryotic
Problem: This scheme
Problem: It is still not easy
organisms which do not have a nucleus
caused problem in trying
to fit all organisms into the
surrounded by a membrane. They have an
to classify fungi, bacteria
five-kingdom scheme. For
independent evolutionary history to other
and single organisms.
example, many Protoctista
bacteria and their biochemistry is very
with chlorophyll (the
different to other forms of life.
protophyta) show important
2. Eubacteria: prokaryotic organisms that do
similarities to some
not have a nucleus surrounded by a
members of the algae, but
membrane.
the algae are classified into
3.
the plant kingdom.
membrane-bound nucleus. This domain is
Eukarya:
organisms
that
have
a
subdivided into the kingdoms Protoctist,
Fungus, Plant and Animal.
The six-kingdom scheme: Splitting the
Prokaryote kingdom into two has created a
sixth kingdom.
1. Animal
2. Plant
3. Fungus
4. Eubacteria
5. Archaebacteria
6. Protoctist