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MAKING SENSE OF CLASSIFICATION

IGCSE Biology1.2 The Variety of Living

Organisms

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Learning Objectives• Can you describe the common features shared

by organisms within the following main groups: plants, animals, fungi, bacteria, protoctists and viruses?

• What does the term ‘pathogen’ mean?• Understand that pathogens may be fungi,

bacteria, protoctists or viruses.


Classification• All living organisms can be classified into

groups based on certain criteria. • One of the simplest forms of classification is to

split all living things into 5 Kingdoms.• Animals, plants, fungi, protoctists and

bacteria.• We will also look at viruses which are non-

living and therefore classified separately.


Classification

Plants Animals Fungi

Protoctists Bacteria Viruses


Plants• They are multicellular.• Cells contain chloroplasts.• Carry out photosynthesis and therefore make

their own food (autotrophic).• Have cellulose cell walls.• Store sugar as starch.


Animals• They are multicellular.• Get their nutrition from feeding on other

organisms (heterotrophic).• They are capable of movement.• Store sugar as glycogen.


Fungi• Can be multicellular or unicellular.• Cell wall made of CHITIN.• Made of a network of fibres called a

MYCELIUM of HYPHAE.• Feed by SAPROPHYTIC nutrition using

EXTRACELLULAR enzymes.


Protoctists• A strange collection of simple organisms that

do not fit into the other groups therefore often known as the ‘dustbin’ kingdom.

• Mostly single celled.• E.g. protozoa like amoeba or Algae.


Bacteria (Prokaryotes)• Small single celled organisms.• Three basic shapes: spheres, rods and spirals.• Cell wall made of polysaccharides and

proteins (peptidoglycan).• Some have a capsule or slime layer.• Has no nucleus.• Some species have flagella.• Some contain plasmids (loops of DNA) which

we can use in genetic engineering.


Bacteria

A typical bacteria


Viruses• All are parasites.• Much smaller than bacteria cells.• Not made of cells, and do not carry out any of

the normal ‘characteristics’ of living organisms.

• Made of genetic material surrounded by a protein coat.

• All natural viruses cause disease.


What is a pathogen?


What is a pathogen?


A pathogen is an organism that causes

disease.

Pathogens• It could be a virus e.g. influenza.

• It could be a fungus e.g. athlete’s foot

• It could be a bacteria e.g. cholera

• It could be a protoctists e.g. malaria

• These pathogens can often be passed from person to person.


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