7-4 CLASSIFYING ORGANISMS

Science 7

OBJECTIVES Explain why biologists classify

organisms. Relate the levels of classification to the

relationships between organisms. List characteristics used to classify

organisms into groups, including domains and kingdoms.

WHY DO SCIENTISTS CLASSIFY? Classification is the process of

grouping things based on their similarities.

Biologists use classification to organize living things into groups so that the organisms are easier to study.

TAXONOMY The scientific study of how living things

are classified is called taxonomy. Taxonomists sometimes change the way

they classify an organism when new evidence such as DNA shows that the organism belongs in a different group.

THE NAMING SYSTEM OF LINNAEUS Carolus Linnaeus, a Swedish naturalist,

developed a system of naming organisms that is still used today.

Binomial nomenclature is the naming system developed by Linnaeus. The word bionomial means two names.

GENUS AND SPECIES The first word in an organism’s scientific

name is its genus. A genus is a classification grouping that contains similar, closely related organisms.

The second word in a scientific name often describes a distinctive feature of an organism (where it lives, appearance).

The two words together indicate a unique species.

Felis domesticus

Felis concolor

BINOMIAL NOMENCLATURE Binomial nomenclature makes it easy

for scientists to communicate because everyone uses the same name for the same organism, regardless of what language they speak.

LEVELS OF CLASSIFICATION The more classification levels that

two organisms share, the more characteristics they have in common.

8 LEVELS1. Domain-highest level 2. Kingdom- make up domains3. Phyla- make up kingdoms4. Classes- make up phyla5. Orders- make up classes6. Families- make up orders7. Genera- each family contains one or

more genera.8. Species- each genera contains one or

more species.

CLASSIFYING A HUMAN Domain= Eukarya Kingdom= Animalia Phylum= Chordata Class= Mammalia Order= Primates Family= Hominidae Genus= Homo Species= Homo sapiens

DOMAINS AND KINGDOMS Organisms are placed into domains

and kingdoms based on their cell type, their ability to make food, and the number of cells in their bodies.

DOMAIN BACTERIA Members of the domain bacteria are

prokaryotes. Prokaryotes are organisms whose cells

lack a nucleus.

DOMAIN EUKARYA Include, seaweed, mushrooms,

tomatoes, dogs, and people. Organisms in this domain are

eukaryotes, organisms with cells that contain nuclei.

Scientists classify organisms into one of 4 kingdoms: protists, fungi, plants, and animals.