This document provides an overview of key concepts in biology, including: 1) The eight main characteristics shared by living organisms: movement, respiration, sensitivity, growth, reproduction, excretion, nutrition. 2) There are estimated to be millions of living species, but only a small fraction have been identified and classified. 3) Classification systems group organisms into a hierarchy of kingdoms, phyla, classes, orders, families, genera, and species to show evolutionary relationships. The scientific name uses binomial nomenclature to identify each species.

1. IGCSE BIOLOGY
SECTION 1 LESSON 1

2. Content
Section 1
The nature
and variety of
living
organisms
a) Characteristics of living
organisms
b) Variety of living organisms

3. Content
Lesson 1
a) Character-
istics of
living
organisms
a) Characteristics of living
organisms
1.1 Understand that living organisms share the
following characteristics:
– they require nutrition
– they respire
– they excrete their waste
– they respond to their surroundings
– they move
– they control their internal conditions
– they reproduce
– they grow and develop.
BONUS: Classification of
living organisms

4. How
many
species?

6. About 1.4 million
species have been
described.

7. It has been
estimated that
there may be as
many as 8.7 million
species!

8. The vast majority
have therefore not
been identified.

9. Group
Estimated total
number of
species
Percentage of
total already
described
Animals 7.7 million 12%
Fungi 0.61 million 7%
Plants 0.30 million 70%
Protozoa 0.04 million 22%
Chromists
(plant-like)
0.03 million 50%

10. Suppose you
landed on
another
planet in our
galaxy.

11. What signs
of life would
you look for?

12. What are the
characteristics
of living
organisms?

13. MRS GREN

14. Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition

15. Movement
Most single-celled creatures,
and larger animals, move
about as a whole. Fungi and
plants make movements with
parts of their bodies.
Movement does not
necessarily involve
locomotion (movement of an
organism from place to
place)

16. Respiration
All living organisms break
down food to obtain energy.
Most organisms need oxygen
for this (aerobic respiration)
whereas others are able to
respire without oxygen
(anaerobic respiration).
Taking in oxygen and
removing carbon dioxide is
the process of breathing.
Glucose + oxygen 
Carbon dioxide + water
C6H12O6 + 6O2 
6CO2 + 6H2O

17. Sensitivity
All living organisms respond
to their environment.
Sensitivity is the ability of
living organisms to respond
to stimuli. A stimulus is a
change in the external or
internal environment of an
organism. Plants, for
example, respond to gravity.
This is known as geotropism.

18. Sensitivity
Living organisms are also
aware of their internal
environment and are able
to respond to changes and
restore the body to its
normal state. This
regulation of the internal
environment is known as
homeostasis.

19. Growth
Bacteria and single-celled
creatures increase in size.
Many-celled organisms
increase the number of
cells in their bodies,
become more complicated
and change their shape as
well as increasing in size.

20. Reproduction
Off spring are produced
by the process of
reproduction. Single-
celled organisms and
bacteria may simply keep
dividing into two (eg.
binary fission). Many-
celled plants and animals
may reproduce sexually or
asexually.

21. Excretion
Excretion involves the
removal of waste
products from the body,
such as carbon dioxide ( a
product of respiration).
Living organisms expel
these substances from
their bodies in various
ways.

22. Nutrition
Nutrition is the process
of obtaining food. There
are two main methods of
obtaining food –
aututrophic nutrition
(green plants) and
heterotrophic nutrition
(organisms use ready-
made organic compounds
as their food source).

23. MRS GREN

24. Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition

25. CLASSIFICATION – a method
of scientific taxonomy used to
group and categorize organisms
into groups such as a genus or
species.

26. CLASSIFICATION – a method
of scientific taxonomy used to
group and categorize organisms
into groups such as a genus or
species.
These groups are known as taxa.

27. The modern system of
putting different organisms
into certain groups was
developed by the Swedish
botanist and zoologist Carl
Linnaeus in the eighteenth
century.
He gave each species a
Latin name, consisting of
the genus and the species.
This is known as binomial
nomenclature.

28. For example, the scientific
name for the rabbit is
Oryctolagus cuniculus. It is
known by this name all over
the world by the scientific
community.
Similarly, the binomial name
for human beings is Homo
sapiens.
Homo is the genus, and
sapiens is the species.

29. Classification
Kingdom The largest group of
organisms recognised by
biologists. But how many?

30. Classification
Kingdom The largest group of
organisms recognised by
biologists. But how many?
For many years most
biologists favoured the use
of two kingdoms, Plants and
Animals.

31. Classification
Kingdom The largest group of
organisms recognised by
biologists. But how many?
For many years most
biologists favoured the use
of two kingdoms, Plants and
Animals.
Modern classification tends
to favour the adoption of 5
kingdoms – Prokaryotes
(Monera), Protoctista,
Fungi, Plants and Animals

32. Classification
Kingdom
Monera
(Prokaryotes)
Bacteria and Blue-green algae
Protoctista Amoeba, Paramecium
Fungi Moulds, Mushrooms, Yeast
Plants
Algae, ferns and mosses,
conifers and flowering plants
Animals
Jellyfish, worms, arthropods, molluscs,
echinoderms, fish, amphibia, reptiles,
birds and mammals.

33. Classification
Kingdom
Viruses are not
considered to
be living, so are
not included in
this
classification
scheme.

34. Classification
Eg. Lion

35. Classification
Kingdom Animalia

36. Classification
Kingdom Animalia
Phylum Vertebrates

37. Classification
Kingdom Animalia
Phylum Vertebrates
Class Mammals

38. Classification
Kingdom Animalia
Phylum Vertebrates
Class Mammals
Order Carnivores

39. Classification
Kingdom Animalia
Phylum Vertebrates
Class Mammals
Order Carnivores
Family Felidae (cats)

40. Classification
Kingdom Animalia
Phylum Vertebrates
Class Mammals
Order Carnivores
Family Felidae (cats)
Genus Panthera

41. Classification
Kingdom Animalia
Phylum Vertebrates
Class Mammals
Order Carnivores
Family Felidae (cats)
Genus Panthera
Species leo

42. Classification
Panthera leo

43. End of Section 1 Lesson 1
In this lesson we have covered:
• Species diversity
• Characteristics of living organisms
• Classification