HOW LIVING THINGS ARE ORGANIZED

Multicellular living things are very organized. In fact, levels of organization exist:

The smallest living unit that makes up a living thing is the CELL.
Look at these human cells:

CELLS group together to form tissues.

TISSUES are made up of similar cells that carry out a common function. For example, muscle tissue is made up of hundreds of muscle cells grouped together.

 Tissues form ORGANS. Organs are made up of a group of tissues that work together to carry out a common function. For example, muscles and bones are organs.

Organs form SYSTEMS. Systems are made up of a group of organs that work together to carry out a common function. For example, the skeletal system is made up of bones.

When all systems work together, they form an ORGANISM. An organism is a COMPLETE LIVING THING.

The Internal Organization of Living Things

What is a cell?

Living things are made up of a large number of very small units called CELLS.

A cell is the smallest living unit that makes up a living thing.

Most cells are very small, so we need a microscope to see them.

The number of cells in a living thing varies.

• Some living things are made up of a single cell. They are called UNICELLULAR: they can only be seen with a microscope. For example: a paramecium.

• Other living things are made up of many cells: they are called MULTICELLULAR. For example: an elephant.

What are cells like?

Cells are living things. This means that, like other living things, they carry out the life processes of nutrition, reproduction and sensitivity.

However, not all cells are alike. They differ in shape, in size and in the tasks they carry out. For example, skin cells are differente from bone cells.

Cells have three main parts:

• The membrane is a covering that surrounds the cell, and separates it from the exterior.
• The nucleus is the part that controls the function of the cell.
• The cytoplasm is the space between the nucleus and the membrane.

Plant cells also have a hard cell wall around the membrane.
         

             Animal Cell                                      Plant Cell

Click on the image above to learn more about each cell part.

Now, click the following image. Read the tutorial, play the game and answer the quiz questions.

WHAT LIVING THINGS ARE LIKE

PRINCIPAL CHARACTERISTICS

We can recognize living things because they share the following characteristics:

• They are born. All living things come from other living things.

 

 Chicks are hatching from eggs.

• They eat. All living things need food. The type of food may vary.

The squirrel is eating a nut.

• They grow. All living things increase in size during their lifetime. Sometimes they change appearance.

Plants growing.

 

Click on the image below to play a game about "Growth".

 

• They react. Living things can perceive what is going on around them, and they react to what they perceive.

A zebra running away from a hungry lion.

• They reproduce. Living things can create offspring similar to themselves.

A mother, a father and their baby.

• They die. At some time, all living things stop functioning and cease to live.

Dead trees in a desert.