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The Diversity of Living Things An Introduction. How many species exist on Earth?. Estimated = 8.7 million. Actual number identified by scientists = 2 million. Species – a group of organisms that can interbreed in nature & produce fertile offspring. How do scientists identify a species?.

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The Diversity of Living Things An Introduction

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The diversity of living things an introduction

The Diversity of Living ThingsAn Introduction

How many species exist on earth

How many species exist on Earth?

Estimated = 8.7 million

Actual number identified by scientists = 2 million

Species – a group of organisms that can interbreed in nature & produce fertile offspring.

How do scientists identify a species

How do scientists identify a species?



- Structural features (body shape, size, etc.)

2. Biological

- Whether or not two organisms can produce fertile offspring

3. Phylogenetic

- Evolutionary history of a species

Naming species

Naming Species

A problem???

Many organisms have been given several names that differ from place to place.

  • The animals to the right have been called:

  • Woodchucks

  • Groundhogs

  • Whistle Pigs

  • Forest Marmots

Scientific Name: Marmotamonax

The standard system of naming

The Standard System of Naming

Taxonomy – a branch of biology that identifies, names, & classifies species.

Binomial Nomenclature – a system of giving a two-word Latin name to each species



Canis lupus

Aka “grey wolf

Genus – a taxanomic group of closely related species

Taxonomic classification is hierarchical

Taxonomic Classification is “hierarchical”

Species are arranged in categories from most general to most specific.

















Taxon – a named group of organisms

Carolus linnaeus the father of taxonomy

Carolus Linnaeus, “The Father of Taxonomy”

Why classify

Why Classify?

  • Scientists have determined that the Earth has 8.7 million species of living things.

    • Biologists have described only 2million of these

    • Only a small percentage (22%) of the estimated life on earth

  • To understand the diversity of life a system of biological classification that names and groups organisms into meaningful categories was needed.

  • Helps us understand how things are similar and different from one another

Class challenge

Class Challenge!

  • Look at the type of footwear you have on today.

  • Look around at other peoples footwear.

  • How could the class be split into two different groups based on footwear?

  • Can the two newly formed groups be further separated?

  • Can the groups split yet again?

The diversity of living things an introduction

  • In biology, what do we use to help us with classifications?

    • Dichotomous Keys

Dichotomous classification keys

Dichotomous Classification Keys

Dichotomous keys

Dichotomous Keys:

  • Means – divided into two parts.

  • Tool that allows the user to determine the identity of items in the natural world such as trees, wildflowers, mammals, reptiles, rocks, and fish.

  • Keys consist of a series of choices that lead the user to the correct name of a given item.

  • Always give two choices in each step.

When constructing keys

When Constructing Keys:

  • Use constant characteristics rather than variable ones.

  • Use measurements rather than terms like "large" and "small".

  • Use characteristics that are generally available to the user of the key rather than seasonal characteristics or those seen only in the field.

  • Make the choice a positive one - something "is" instead of "is not".

  • If possible, start both choices of a pair with the same word.

  • If possible, start different pairs of choices with different words.



  • Suppose you have four insects a ladybug, a housefly, a dragonfly and a grasshopper. After studying the insects, you might use:

    • wing covering

    • body shape

    • where the wings point towards.

The diversity of living things an introduction

  • To begin the key, you could start separating the four insects based on wing covering "wings covered by exoskeleton" vs. "wings not covered by exoskeleton."

  • A sample dichotomous key might look like:

The diversity of living things an introduction

Step 1. a. wings covered by an exoskeleton……go to step 2

b. wings not covered by exoskeleton….go to step 3

Step 2. a. body has a round shape .………………..ladybug

b. body has an elongated shape .…….…grasshopper

Step 3. a. wings point out from side of body …dragonfly

b. wings point to posterior of body.……housefly

Notice that there were four organisms to be identified and it only took three steps. Usually, there should be one less step than the total number of organisms to be identified in your dichotomous key.

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