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Classifying Organisms



What is a species?

A huge variety of organisms live on our planet.

Scientists have put living things into groups to make them

easier to identify. This is called classification.

Organisms can be classified into

different species.

So far, scientists have identified around 290,000 species of

plants, 1,250,000 species of animals and 5 million species of

bacteria living on our planet.

A species is a group of organisms

that are capable of interbreeding to

produce fertile offspring.


Problems with classifying species

Sometimes it is not easy to classify organisms into species.

Bacteria usually reproduce asexually. However, our definition

of ‘species’ is based on organisms that can breed together. This definition therefore does not work for bacteria.

Many common duck species can breed together to

produce hybrids. There have been over 400 types

of duck hybrid recorded.

These are often fertile, and can

breed with each other or the native

ducks, producing ducks with a

variety of characteristics.


Problems with classifying species

Mules are hybrids, made by breeding a donkey with a horse.

Most are infertile, but occasionally female mules do mate with

donkeys or horses to produce offspring. This does not fit with

our definition of species, and makes it hard to classify

the animals.

+ =


Ring species



Levels of classification


Binomial classification

The classification system that scientists

use today was developed by

Carl Linnaeus in the 18th century.

This system is known as binomial

classification. It uses Latin names, so

scientists around the world can use the

same names without confusion.

The first part of an organism’s scientific name is its genus, and the second part is the species.

e.g. Tyrannosaurus rex

Genus species


Binomial classifications


How do we classify organisms?

There are far too many organisms in the world for scientists

to be able to understand each one.

Classification helps them to make sense of this vast variety of

organisms by putting species together if they share

characteristics.

Questions that might be asked include:

does the organism have a

structure, like a backbone or

flowers, that suggest that it belongs

in a certain classification?

how is its DNA similar to and different from the

other organisms that have already been classified?


Plant and animal kingdoms


Other kingdoms

Originally, scientists tried to fit all organisms into the plant or

animal kingdoms.

However, they had problems

classifying some organisms,

which didn’t fit clearly into either kingdom.

Three new kingdoms were created to deal with this problem:

the prokaryote kingdom, the protoctist kingdom and the

fungi kingdom.


Other kingdoms


Classifying animals

Animals can be divided into two groups.

Vertebrates have a backbone. They have a firm body

because of the muscles that are attached to their skeleton.

Invertebrates do not have a backbone. They have soft inner

bodies that are held in shape either by a flexible covering of

outer cells or by a hard covering called an exoskeleton.

animals

vertebrates invertebrates


Animal classification


Vertebrate classification


Archaeopteryx

Archaeopteryx has been extinct for approximately

150 million years. Based on fossil evidence, this creature is

very difficult to classify.

Archaeopteryx had some features of

a reptile:

hollow bones

feathers.

However, it also had bird

features:

teeth

three claws on each wing

a long, bony tail.

How would you classify it?



Evolution and classification

Classification enables us to explore the evolutionary origins

of an organism.

Two organisms in the same genus are

generally very similar, and are therefore

likely to share an ancestor in the recent past.

For example, the genus Canis includes

dogs, jackals and wolves.

Two organisms in the same kingdom (e.g. dogs

and spiders) share some characteristics, but are

different in many ways. Consequently, their

common ancestor is likely to be in the distant past.


Evolutionary trees

An evolutionary tree represents the evolutionary relationship

between organisms. Organisms with recent common

ancestors are closer together on the tree.

Scientists use the following evidence to construct

evolutionary trees:

genetics and DNA

fossil records

the structures of organisms

patterns of embryonic

development.


A simple evolutionary tree


Evolutionary tree – mammals

This evolutionary tree shows some examples of mammals.

cow

mouse

rat

platypus

opossum

human

chimp

monkey

horse

dog

Which animal is

most closely related

to the human?

Which animal is

most closely related

to the horse?

Which animal

branched out from

the others furthest

back in evolutionary

time?


Evolution and ecology

Some organisms that share a distant ancestor live in the

same environment. They may evolve similar characteristics

and structures to help them survive.

However,

scientists can

tell that they are

not closely

related because

their DNA is not

very similar.


Whales and sharks

Whales and sharks both live in the sea, and could be

considered to look quite similar. However, they are entirely

different species:

Whales and sharks look similar because they have

developed structures such as fins and a streamlined body to

help them to live in the sea environment.

whales sharks

have lungs have gills

warm-blooded cold-blooded

give birth to

live younglay eggs

mammal fish


The importance of habitat

Sometimes organisms with a recent common ancestor live in

different environments. They may evolve quite differently,

even though their DNA is similar.

The Galapagos Islands are home to

many species of finch that all evolved

from a recent common ancestor.

However, today the finch species

have different features to help them

survive on their particular islands.

Some finches have beaks that are best for eating fruit, while

others have beaks adapted to eating seed or insects. This

varies according to what the main source of food is on the

island where they live.



Why is classification so important?

Why is classifying species is so important?

It helps scientists to identify and study organisms.

It makes it easier for us to know how many different

species live in an area, and recognize the places that

have the greatest diversity. It is important to conserve

these locations.

It indicate the population of

each species. This helps us to

determine which species are

endangered, and take

measures to protect them.


Endangered species



Glossary


Anagrams


Multiple-choice quiz

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Classifying Organismstodhigh.com/.../wp-content/uploads/2018/03/Classifying_Organisms.pdf · A species is a group of organisms ... organisms by putting species together if they share