LIVING THINGSAND

HOW ARE LIVING THINGS CLASSIFIED?

What are living things like?

Any living thing is called an organism. Organisms

vary in size are found just about everywhere have different behaviors and food needs. However, all organisms have similar traits that

determine what it means to be alive.

How are living things organized?

Living things are made up of small units called cells.

cell : is the smallest unit of an organism that carries on the functions of life. Some organisms are made up of just one cell, others are made up of many cells. Cells take in materials from their surroundings. Each cell has an orderly structure and has hereditary material. All the things organisms can do are possible because of what their cells can do.

How do living things respond?

Living things interact with their surroundings. Anything that causes some change in an organism is a stimulus (plural, stimuli). The reaction to a stimulus is a response. Often that response results in movement.

Response to Stimuli

To carry on its daily activity and to survive, an organism must respond to stimuli. Organisms respond to external stimuli such as movement and light. Living things also respond to stimuli that occur inside them. The organisms then make internal changes to keep the right amounts of water and food in their cells. An organism’s ability to keep the proper conditions inside no matter what is going on outside the organism is called homeostasis.

How do living things grow and develop?

Organisms grow by taking in raw materials. One-celled organisms grow by increasing in size. Most growth in many celled organisms is due to an increase in

the number of cells. Organisms change as they grow. All of the changes that take place during an organism’s life are

called development. Complete development can take a few days for the butterfly

shown below, or several years for a dog. The length of time an organism is expected to live is its life span. Some organisms have a short life span. Some have long life

spans.

Why do living things reproduce?

Organisms eventually reproduce. They make more of their own kind. Some bacteria reproduce every 20

minutes. A pine tree might take two years to

produce seeds. Without reproduction, living things would

not exist to replace those individuals that die.

What raw materials do organisms need?

Water is important for all living things. Most organisms are made of more than

50 percent water. Humans are made of 60 to 70 percent

water. Plants and animals take in and give off

large amounts of water each day. Organisms use homeostasis to balance

the amount of water taken in and lost.

What raw materials do organisms need?

Organisms use water for many things. Blood is about 90 percent water. Blood transports food and wastes in animals. Plants use water to transport materials

between roots and leaves.

What raw materials do organisms need?

Living things are made up of substances such as sugars,

proteins, and fats. Animals get these substances from the food they eat. Plants and some bacteria make the substances using

raw materials from their surroundings. These important substances are used over and over

again. When organisms die, substances from their

bodies are broken down and released into the soil or air.

The substances can then be used again by other organisms.

Classification

When similar items are placed together, they are being classified.

Organisms also are classified into groups. Early classifications of organisms

included grouping plants that were used in medicines.

Animals were often classified by human traits. For example, lions were classified as

courageous animals and owls were classified as wise

Classification

More than two thousand years ago, Aristotle, a Greek, decided that any organism could be classified as either a plant or an animal.

Then he broke these two groups into smaller groups. For example, his groups included animals that

had hair and animals that did not have hair, and animals with and without blood.

Who was Carolus Linnaeus?

In the late 1700s, Carolus Linnaeus, a Swedish naturalist, developed a new system of grouping organisms.

His system was based on organisms with similar structures. For example, plants that had a similar flower

structure were grouped together. His system was accepted and used by

most other scientists.

What classification do modern scientists use?

Modern scientists use similarities in structure to classify organisms use similarities in both external and internal features.

For example, scientists use the number of chromosomes in cells to understand which organisms may be genetically related to each other

study fossils, hereditary information, and early stages of development.

Scientists use the information to determine an organism’s phylogeny.

Phylogeny (fi LAH juh nee) is the organism’s evolutionary history. This tells how the organism has changed over time. It is the basis for the classification of many organisms.

How are organisms grouped?

A classification system commonly used today groups organisms into six kingdoms.

A kingdom first and largest category divided into smaller groups. the smallest classification is a species.

Organisms in the same species can mate and produce fertile offspring.

Scientific Names

If scientists used only common names of organisms, it would be confusing. For example, a jellyfish is neither a fish nor

jelly. A sea lion is more closely related to a seal

than a lion. To avoid confusion, scientists use a

naming system developed by Linnaeus when referring to a particular species.

Each species has a unique, two-word scientific name.

What is binomial nomenclature?

The two-word naming system used to name organisms is called binomial nomenclature (bi NOH mee ul ·

NOH mun klay chur). The first word of the two-word name

identifies the genus of the organism. A genus is a group of similar species. The second word of the name might tell you

something about the organism. It might tell what it looks like or where it is

found.

Why are scientific names used?

Two-word scientific names are used for four reasons. They help avoid mistakes. Animals with similar evolutionary history are

classified together. Scientific names give descriptive information

about the species. Scientific names allow information about

organisms to be organized easily and efficiently.

Tools for Identifying Organisms

Tools used to identify organisms include field guides and dichotomous (di KAH tuh mus) keys.

Field guides include descriptions and pictures of organisms give information about where each organism

lives to identify species from around the world.

What are dichotomous keys?

A dichotomous key is a detailed list of identifying characteristics that includes scientific names.

The keys are set up in steps. Each step has two descriptive

statements, such as hair or no hair. You can use a dichotomous key to identify

and name a species.