GCE Biology CIE 5090
2.1 Concept and use of a classification system
CONTENTS
1 Understand that organisms can be classified into groups by the features
they share
2 Describe a species as a group of organisms that can reproduce to produce
fertile offspring
3 Describe the binomial system of naming species as an internationally
agreed system in which the scientific name of an organism is made up of two
parts showing the genus and species
4 Construct and use dichotomous keys based on identifiable features
2.1 Concept and use of a classification system
2.1 Concept and Use of a Classification System
Classification: The process of sorting living organisms into groups based
on their shared features. This helps scientists to identify organisms,
predict their characteristics, and find evolutionary links between them.
Species: Defined as a group of organisms that can reproduce to
produce fertile offspring.”
Paper 2 Tip: The keyword in the definition of a species is fertile. Different
species can sometimes reproduce (e.g., a horse and a donkey produce a
mule), but their offspring are infertile. Omitting this word will lose you the
mark.
Binomial System: An internationally agreed system for naming organisms.
Each species is given a unique two-part scientific name.
o Part 1: The Genus name, which always starts with a capital letter.
o Part 2: The species name, which always starts with a lower-case
letter.
o The entire name is written in italics (or underlined if handwritten).
o Example: Humans are Homo sapiens. Homo is the genus,
and sapiens is the species.
Dichotomous Keys: A tool used to identify organisms by working
through a series of paired, contrasting statements. Each step presents two
choices; the correct choice leads either to the organism's name or to the
next pair of statements.
Paper 4 Tip: When using a dichotomous key, read both statements in a pair
carefully before making a choice. When constructing one, ensure each step
offers only two mutually exclusive choices (e.g., "Wings are present" vs.
"Wings are not present") and that your key successfully separates all the
given organisms.
Past Paper Practice (Topic 2.1)
Question 1 (MCQ): [Nov 2021, Paper 12, Q2]
What is a feature of all organisms in the same species?
A. They can all breed with each other.
B. They can all produce fertile offspring.
C. They are all in the same ecosystem.
D. They are all the same age.
Solution: B
o Explanation: The biological definition of a species is a group of
organisms capable of interbreeding to produce fertile offspring.
While they can breed (A), the key is that the offspring must also be
able to reproduce.
Question 2 (MCQ): [June 2020, Paper 12, Q1]
Which statement about the binomial system of naming is correct?
A. The first name is the genus and the second name is the species.
B. The first name is the species and the second name is the genus.
C. The names are written in italics with a capital letter for the species.
D. The names are written in italics with a capital letter for the genus and for the
species.
Solution: A
o Explanation: This tests the rules of the binomial system. The order
is always Genus then species. The Genus is capitalised, but the
species is not.
Question 3 (Paper 2): [Nov 2020, Paper 22, Q6a]
(a) The scientific name for the leopard is Panthera pardus. State the genus of the
leopard. [1]
(b) A lion has the scientific name Panthera leo. Explain what the scientific names
of the leopard and the lion suggest about their relationship. [2]
Solution:
(a) The genus is Panthera.
(b) They both belong to the same genus (Panthera). This means they are
closely related and share a recent common ancestor.
Examiner's View (P2):
(a) A direct recall of the binomial system rules.
(b) The key is to state that sharing a genus means they are closely related.
Simply saying "they are related" might not be specific enough for full marks.
2.2 Features of organisms
CONTENTS
1 State the main features used to place all organisms into one of the five
kingdoms: Animal, Plant, Fungus, Prokaryote, Protoctist
2 State the main features used to place organisms into groups within the
animal kingdom, limited to:
(a) the main groups of vertebrates: mammals, birds, reptiles, amphibians, fish
(b) the main groups of arthropods: myriapods, insects, arachnids, crustaceans
3 State the main features used to place organisms into groups within the
plant kingdom, limited to ferns and flowering plants (dicotyledons and
monocotyledons)
4 Classify organisms using the features identified in 2.2.1, 2.2.2 and 2.2.3
5 State the main features of viruses, limited to protein coat and genetic
material
6 Understand that viruses can only replicate in living cells
2.2 Features of organisms
2.2 Features of Organisms
The Five Kingdoms: All organisms can be classified into one of
five kingdoms based on their cellular structure and features.
Kingdom Key Features
Animal Multicellular, no cell walls, no chloroplasts, feed by
ingesting other organisms.
Plant Multicellular, have cellulose cell walls, have chloroplasts for
photosynthesis.
Fungus Mostly multicellular (e.g., mushrooms) or single-celled (e.g.,
yeast), have cell walls made of chitin (not cellulose), feed
by saprotrophic nutrition (secreting enzymes externally and
absorbing the digested products), have a body made of
thread-like hyphae which form a mycelium.
Prokaryo Single-celled, have a cell wall (not cellulose), no
te nucleus (have a circular loop of DNA instead), may have
plasmids. (e.g., bacteria).
Protoctis Mostly single-celled microscopic organisms. Some are
t "animal-like" (e.g., Amoeba), while others are "plant-like"
and have chloroplasts (e.g., Chlorella).
Groups within the Animal Kingdom:
o Vertebrates (animals with a backbone):
Mammals: Have fur/hair, produce milk, have a placenta,
endothermic (warm-blooded).
Birds: Have feathers and a beak, lay hard-shelled eggs,
endothermic.
Reptiles: Have dry scales, lay soft-shelled eggs,
ectothermic (cold-blooded).
Amphibians: Have smooth, moist skin; adults have
lungs, larvae have gills; ectothermic.
Fish: Have wet scales and fins, breathe with gills,
ectothermic.
o Arthropods (invertebrates with jointed legs and an
exoskeleton):
Insects: 3 pairs of legs, 3 body parts (head, thorax,
abdomen), 1 pair of antennae.
Arachnids: 4 pairs of legs, 2 body parts (cephalothorax,
abdomen), no antennae.
Crustaceans: More than 4 pairs of legs, chalky
exoskeleton, 2 pairs of antennae.
Myriapods: Many pairs of legs, segmented body.
Groups within the Plant Kingdom:
o Ferns: Have leaves called fronds. Reproduce using spores.
o Flowering Plants: Reproduce using seeds produced by
flowers.
Monocotyledons: One cotyledon, parallel leaf veins,
flower parts in multiples of 3.
Dicotyledons: Two cotyledons, branching/reticulate leaf
veins, flower parts in multiples of 4 or 5.
Viruses:
o Viruses are not classified in any kingdom as they are not
considered truly living.
o Structure: A simple structure consisting of a protein
coat surrounding a core of genetic material (either DNA or
RNA). They have no cellular structure (no cytoplasm, nucleus,
etc.).
o Replication: They are parasites that can only replicate inside
living host cells. They take over the host cell's machinery to
make new copies of themselves, often destroying the host cell
in the process.
Past Paper Practice (Topic 2.2)
Question 1 (MCQ): [June 2021, Paper 12, Q2]
Which type of organism has a body consisting of a mycelium of hyphae?
A. an animal
B. a bacterium
C. a fungus
D. a plant
Solution: C
o Explanation: This is a key structural feature of the Fungi
kingdom. The network of thread-like hyphae is called a
mycelium.
Question 2 (MCQ): [Nov 2021, Paper 12, Q3]
The diagram shows an animal.
Using the dichotomous key, what is this animal?
1 (a) has six legs......................... go to 2
(b) has eight legs...................... go to 3
2 (a) has wings............................. A
(b) has no wings....................... B
3 (a) has a segmented body........ C
(b) has an unsegmented body... D
(The diagram provided would show an insect like a beetle or
fly)
Solution: A (assuming the diagram showed a winged insect).
o Explanation: This tests the use of a key and knowledge of
arthropod features. An insect has six legs (go to 2). If it has
wings, it is organism A. This is a typical dichotomous key
question.
Question 3 (Paper 2): [Based on 5090 Syllabus]
State two structural features that are present in viruses but not in
bacteria. [2]
Solution: Viruses do not have any features that are not also
present in bacteria in some form. The question is likely intended to
be reversed.
Revised Question: State two structural features that are present
in bacteria but not in viruses.
Solution:
1. Cell wall
2. Cell membrane / Cytoplasm / Ribosomes / Plasmids
Examiner's View (P2): The key difference is that viruses are non-
cellular. Therefore, any cellular component (cell wall, cell membrane,
cytoplasm, ribosomes) is a valid feature that bacteria have and viruses
lack.
