BIOLOGY
Characteristics and classification of living organisms
Lesson objectives:
• list and describe the characteristics of living organisms
• define the terms:
 nutrition as obtaining the organic substances and mineral ions from which organisms gain their energy and the raw materials for
growth and tissue repair
 excretion as the removal of toxic materials and the waste products of metabolism from organisms.
 respiration as the release of energy from food substances in all living cells
 sensitivity as the ability to sense and respond to changes in the surroundings
 reproduction as producing offspring, preventing extinction of the species
 growth as an increase in size, mass and complexity of an organism
 movement as a change in position of the whole body or any part of the organism
• List the seven levels of classification of organisms in hierarchical order (taxa) as: kingdom, phylum, class, order,
family, genus and species
• describe the binomial system as the system of naming organisms using two names, genus and species
• describe the main characteristics of the five kingdoms of organisms as: plantae, animalia, fungi, prokaryotae
and protoctista
• state that animals are classified into vertebrates and invertebrates
• classify, using visible, external characteristic features:
 vertebrates into the classes: fishes, amphibians, reptiles, birds and mammals
 invertebrates into arthropods, annelids, nematodes and molluscs
 arthropods into the classes: insects, crustaceans, arachnids and myriapods
 flowering plants into monocotyledons and dicotyledons (Local examples to be studied as appropriate)
• list the main features used in the classification of the following groups: viruses, bacteria and fungi, and their
adaptation to the environment, as appropriate
• construct and use simple dichotomous keys based on easily identifiable features
Biology
• The earth consists of living and non living things
• Biology is the branch of Science that deals with
living things (living organisms)
Careers in Biology
People that have studied biology can be:
1. Academic researchers
2. Biotechnologists
3. Marine biologists
4. Microbiologists
12. Dental technicians
5. Nature conservation officers
13. Dental therapists
6. Pharmacologists
14. Dentists
7. Soil scientists
15. Genetic counsellors
8. Animal physiotherapists
16. Neuroscientists
9. Anatomical Pathology technologists
17. Zoologists
10. Clinical scientists, cardiac sciences
18. Veterinary nurses
11. Dental hygienists
19. Prosthetist science writers
Characteristics of living things
• Biology is the study of living things, which are often called organisms. Living organisms have seven
characteristics which make them different from objects that are not alive. The characteristics of living
things include movement, reproduction, sensitivity, growth, respiration, excretion and nutrition.
Describing and defining characteristics of living things
• Movement – All organisms are able to move to some extent. Most animals can move their whole
body from place to place, and plants can slowly move parts of themselves.
 Definition: Movement is the change in position of the whole body or any part of the organism
• Reproduction – Organisms are able to make new organisms of the same species as themselves. This
ensures that organisms do not go extinct.
 Definition: Reproduction is producing offspring of the same kind, preventing extinction of the species
• Sensitivity – All organisms pick up information about changes in their environment and react to the
changes.
 Definition: Sensitivity is the ability to sense and respond to changes in the surroundings
• Growth – All organisms begin small and get larger, by the growth of their cells and by adding new
cells to their bodies.
 Definition: Growth is a permanent increase in size, mass and complexity of an organism
• Respiration – All organisms break down glucose and other substances inside their cells, to release
energy that they can use.
 Definition: Respiration is the release of energy from food substances in all living cells
• Excretion – All organisms produce unwanted or toxic waste products as a result of their metabolic
reactions, and these must be removed from the body.
 Definition: Excretion is the removal of toxic materials and the waste products of metabolism from organisms
• Nutrition – Organisms take substances from their environment and use them to provide energy or
materials to make new cells.
 Definition: Nutrition is obtaining the organic substances and mineral ions from which organisms gain their energy and
the raw materials for growth and tissue repair
NB: Use this mnemonic to help you remember these processes:
‘MRS GREN’
 Movement
 Respiration
 Sensitivity
 Growth
 Reproduction
 Excretion
 Nutrition
Classification
How Organisms are Classified
• There are millions of species of organisms on Earth
• A species is defined as a group of organisms that can breed to produce fertile offspring
• These species can be classified into groups by the features that they share e.g. all mammals have
bodies covered in hair, feed young from mammary glands and have external ears (pinnas)
The Binomial System
• Organisms were first classified by a Swedish naturalist
called Linnaeus in a way that allows the subdivision of
living organisms into smaller and more specialized groups
• The species in these groups have more and more
features in common the more subdivided they get
• He named organisms in Latin using the binomial
system where the scientific name of an organism is
made up of two parts starting with the genus (always
begins with a capital letter) and followed by the
species (starting with a lower case letter)
• When typed, binomial names are always written in italics
(which indicates they are Latin) e.g. Homo sapiens
• When written by hand, binomial names are underlined
using separate lines e.g.
• The sequence of classification is: Kingdom, Phylum,
Class, Order, Family, Genus, Species
NB: The order of classification can be remembered by using
mnemonic like:
KING PHILIP CAME OVER FOR GRAN’S SPAGHETTI
a
Linnaeus’s system of classification
Classification examples
Domestic cat
Leopard
Wolf
Dog
Lion
Kingdom
Animalia
Animalia
Animalia
Animalia
Animalia
Phylum
Chordata
Chordata
Chordata
Chordata
Chordata
Class
Mammalia
Mammalia
Mammalia
Mammalia
Mammalia
Order
Carnivora
Carnivora
Carnivora
Carnivora
Carnivora
Family
Felidae
Felidae
Canidae
Canidae
Felidae
Genus
Felis
Panthera
Canis
Canis
Panthera
Species
catus
pardus
lupus
familiaris
leo
How Organisms are Classified
• Organisms share features because they originally descend from a common ancestor
• Example: all mammals have bodies covered in hair, feed young from mammary glands and have
external ears (pinnas)
• Originally, organisms were classified using morphology (the overall form and shape of the organism,
e.g. whether it had wings or legs) and anatomy (the detailed body structure as determined by
dissection)
• As technology advanced, microscopes, knowledge of biochemistry and eventually DNA sequencing
allowed us to classify organisms using a more scientific approach
• Studies of DNA sequences of different species show that the more similar the base sequences in the
DNA of two species, the more closely related those two species are (and the more recent in time
their common ancestor is)
• This means that the base sequences in a mammal’s DNA are more closely related to all other
mammals than to any other vertebrate groups
DNA sequences can show how closely related different species are
• The sequences above show that Brachinus armiger and Brachinus hirsutus are more closely related
than any other species in the list as their DNA sequences are identical except for the last but one
base (B. armiger has a T in that position whereas B. hirsutus has an A)
• As DNA base sequences are used to code for amino acid sequences in proteins, the similarities in
amino acid sequences can also be used to determine how closely related organisms are
Features of Organisms
Common Cell Structures
• The cells of all living organisms contain the following:
 Cytoplasm
 Cell membrane
 DNA as genetic material (either found in the nucleus or free in the cytoplasm)
General cell features
A typical animal cell and plant cell
A typical prokaryotic cell
Cell Composition & Structure
• When viewed under an electron microscope (at a much higher magnification), all cells also contain
the following:
 Ribosomes for protein synthesis
 Enzymes for respiration (in many, but not all types of cells, found in mitochondria
The Five Kingdoms
• The first division of living things in the classification system is to
put them into one of five kingdoms. They are:
 Animals
 Plants
 Fungi
 Protoctists
 Prokaryotes
Main features of all animals:
• They are multicellular (their bodies have many cells)
• Their cells contain a nucleus but no cell walls
or chloroplasts
• They feed on organic substances made by
other living things (heterotrophic)
A typical animal cell
Main features of all plants:
• They are multicellular
• Their cells contain a nucleus, chloroplasts and cellulose cell walls
• They all feed by photosynthesis (phototrophic)
• May have roots, stems and leaves
A typical plant cell
Fungi, Protoctists & Prokaryotes
Main features of all fungi (e.g. moulds, mushrooms, yeast)
• Usually multicellular
• Cells have nuclei and cell walls not made from cellulose usually made of a mixture of substances including chitin
• Do not photosynthesize but feed by saprophytic (on dead or decaying material) or parasitic (on live material)
nutrition
A basic fungal cell
Example of fungi (bread mould)
• Most fungi are made up of thread-like hyphae rather than
cells
• Have many nuclei distributed throughout the cytoplasm in
their hyphae
• The branching hyphae forms a mycelium
• Vertical hyphae bears some structures called sporangia
• Spores usually formed inside the sporangia
• When ripe, the sporangium bursts open allowing the
spores to be dispersed
• In suitable conditions the spores germinate and grow to
form new individuals
• Spores land and develop into hyphae which grow into
mycelium
• Single-celled yeast reproduces by binary fission, all other
fungi produce via spores
Main features of all Prokaryotes (bacteria, blue-green algae)
• Include mainly bacteria
• Often unicellular (single-celled)
• All have a nucleus, some may have cell walls and
chloroplasts
• Their cell walls do not contain cellulose or chitin but
are made of a complex mixture of proteins, sugars
and lipids (peptidoglycan/murein)
• Some protoctists photosynthesise and some feed on
organic substances made by other living things
• Some bacteria have a slime capsule outside their cell
wall
• They may have one or more flagella to aid movement
• Have circular DNA fragments called plasmids
• Their cytoplasm or cell membrane may contain
granules of glycogen
• May be parasites feeding off living organisms, or saprotrophs feeding off dead organisms
• Photosynthetic bacteria contain chlorophyll
Main features of all Protoctists (e.g. Amoeba, Paramecium, Plasmodium)
• Most are unicellular but some are multicellular
• Cells have a nucleus
• Cell may or may not have a cell wall or chloroplast
• Have cytoplasm but no nucleus or mitochondria
• Some of the protoctista, e.g. Euglena, possess chloroplasts and make their
food by photosynthesis
• These protoctista are often referred to as unicellular ‘plants’ or Protophyta
• Organisms such as Amoeba and Paramecium
take in and digest solid food and thus
resemble animals in their feeding
• They may be called unicellular ‘animals’ or
protozoa
• Amoeba is a protozoan which moves by a
flowing movement of its cytoplasm
• It feeds by picking up bacteria and other microscopic organisms as it goes
Viruses
Features of Viruses
• Viruses are not part of any classification system as they are not considered living things
• They do not carry out the seven life processes for themselves, instead they take over a host cell’s
metabolic pathways in order to make multiple copies of themselves
• Virus structure is simply genetic material (RNA or DNA) inside a protein coat
Capsomeres
RNA or DNA
strand
Protein coat
(capsid)
Structure of a typical virus
Classifying Animals
Kingdom Animalia/Animal Kingdom
• Animals can be classified into vertebrates and invertebrates
• Animals are classified into this two groups based on whether or not they have a backbone
• Vertebrates are animals with a vertebral column or backbone and invertebrates are animals
without a vertebral column or backbone
• All vertebrates are classified into their own phylum known as Phylum Vertebrate, or Phylum
Chordata/Chordates
• Invertebrates are classified into
four phyla:
 Mollusca/Molluscs
 Annelida/Annelids
 Nematoda/Nematodes
 Arthropoda/Arthropods
• This means each animal that is without a backbone is classified under one of the above four phyla,
and all the animals with a backbone are classified under Phylum Vertebrate
Phylum Vertebrate
• All vertebrates have a backbone. The backbone is also known as the vertebra and it is a series of bones or
pieces of cartilage that are connected to form the spine in some animals, including humans
• There are 5 classes of vertebrates shown in the table below:
Vertebrate class
Fish
Amphibia
Examples
Trout, catfish,
Frog, toad, newt,
shark, carp,herring salamanders
Lizards,
snakes, Penguins, eagles, Whales, bats, cats,
tortoises,
ostriches, chickens humans, elephants
crocodiles
Body covering
Moist skin covered Moist skin, no
in scales
scales
Dry skin with
scales
Movement
Fins which they
use for swimming
and balance
Have four limbs Have two wings Four limbs
except for snakes and two legs
Four limbs, back
feet often webbed
to make
swimming more
efficient
Reptiles
Birds
Dry skin covered
with feathers
Mammals
Dry skin covered
with fur or hair
Vertebrate class Fish
Amphibia
Reptiles
Birds
Mammals
Reproduction
Produce jelly-covered Produce jellyeggs in water
covered eggs in
water
Produce eggs with Produce eggs with Produce live young
leathery
a hard shell laid on
waterproof shell
land
laid on land
Sense organs
Eyes, no ears, lateral Eyes, ears
line along body for
detecting vibrations
Eyes, ears
Other details
Cold blooded, gills
for breathing
Cold blooded,
Warm blooded,
lungs for breathing lungs for
breathing, has
beak
Cold blooded,
lungs and skin for
breathing
Eyes, ears
Eyes, ears with a
pinna
(external
flap)
Warm blooded,
lungs for
breathing, females
have mammary
glands to produce
milk to feed young
ones, four types of
teeth
NB: A cold-blooded animal cannot maintain its own body temperature and so has a body temperature which is
the same as the environment. Warm-blooded animals can maintain their own body temperature even if the
temperature of the environment changes
Vertebrate classification
Invertebrates
• Any animal that does not have a backbone is classified as an invertebrate
• One of the morphological characteristics used to classify invertebrates is whether they have legs or
not
• Invertebrates can be classified into the following groups;
 Annelids
 Molluscs
 Nematodes
 Arthropodes
Annelids
• They are worms with a segmented body
• Have a body cavity and their bodies are symmetrical along their length
• Common example is the earthworm found in soil of many gardens
• Found in most habitats on earth including sea, fresh water and on land
earthworm
Molluscs
• Have soft, smooth (unsegmented) body
• Body usually protected by hard outer shell
• Examples are garden snail, mussels, oysters and other shellfish
found in the sea
Snail
Nematodes
• Have a thread-like, round, smooth (unsegmented) body
• Usually parasitic (can cause disease in humans, animals and plants)
• When you say an animal has worms, the type of worms that are
affecting the animal are nematode worms
• Example is the roundworm
Roundworm
Arthropods
• All invertebrates with jointed legs are part of the phylum Arthropods
• Arthropods also have a symmetrical body along their length and the body is divided into three
segments;
 The head
 Thorax
 Abdomen
• Bodies have a tough external covering or exoskeleton which is made from a substance called chitin
• They are classified further into the following classes, insects, arachnids, crustaceans and myriapods:
Insects
Arachnids
Crustacea
e.g bees, beetles,
butterflies, dragonfly
e.g spider, scorpions, mite
e.g
craps,
lobsters, e.g millipede, centipede
woodlouce, shrimps
Three pairs of legs
Four pairs of legs
Five or more pairs of
legs
Ten or more pairs of
legs, usually one pair per
segment
Body divided into
cephalothorax and
abdomen
Body consists of many
segments

Body divided into head, Body divided into
thorax and abdomen
cephalothorax and
abdomen
Myriapods
Insects
Arachnids
Crustaceans
Myriapods
One pair of antennae
 No antennae
Two pairs of antennae
One pair of antennae
One pair of compound
eyes
Several pairs of simple
eyes
One pair of compound
eyes
Simple eyes
Usually have two pairs  Chelicerae for bitting  Exoskeleton often
of wings (one or both
and poisoning prey
calcified (formed from
pairs may be vestigialcalcium)
meaning non-functional
 Breathe through gills
and undeveloped)
Arthropod classification
Classifying Plants
Ferns & Flowering Plants
• At least some parts of any plant are green, caused by the presence of the pigment chlorophyll which
absorbs energy from sunlight for the process of photosynthesis
• The plant kingdom includes organisms such as ferns (non-flowering) and flowering plants
Ferns:
• Have leaves called fronds
• Do not produce flowers but instead reproduce by spores produced on the underside of fronds
Ferns
Ferns reproduce by spores found in the underside of their fronds
Flowering plants:
• Reproduce sexually by means of flowers and seeds
• A flower is a reproductive organ of a plant
• Seeds are produced inside the ovary found at the base of the flower
• In adult plants the flowers develop into fruits and seeds and these then grow into new plants
• Flowering plants an be divided into two groups – monocotyledons and dicotyledons
Wheat plants are monocotyledons
Sunflowers are dicotyledons
Comparing monocotyledons and dicotyledons
Monocotyledons
Dicotyledons
One cotyledon
Two cotyledons
Leaves are narrow
Leaves are broad
Veins in leaves are parallel
Veins in leaves are branched
Roots form a fibrous root system
Roots form a central tap root system
Flower parts are in multiples of 3 e.g flowers
will have 3,6 or 9 petals
Flower parts are in multiples of 4 or 5
Stems often hollow and soft
Stems often solid, thickened and hard
Examples are maize, grasses, sorghum and
onions
Examples are beans, daises and trees such as
marula trees
Comparing monocots and dicots
Dichotomous Keys
Constructing & Using a Key
• Keys are used to identify organisms based on a series
of questions about their features
• Dichotomous means ‘branching into two’ and
it leads the user through to the name of the
organism by giving two descriptions at a
time and asking them to choose
• Each choice leads the user onto another two
descriptions
• In order to successfully navigate a key, you
need to pick a single organism to start with
and follow the statements from the
beginning until you find the name
• You then pick another organism and start at
the beginning of the key again, repeating
until all organisms are named
Example of a dichotomous key #1
Example of a dichotomous key #2