Chapter 1 Section 2. Cells were discovered in 1665 by Robert Hooke. He observed them by looking at...

Chapter 1 Section 2

Cells were discovered in 1665 by Robert Hooke.

He observed them by looking at a thin slice of cork.

He saw hundreds of Little boxes and called them cells, which means “little rooms.”

Hooke believed that cells were only found in plants.

In 1673, Anton van Leeuwenhoek observed pond water and scum and saw small creatures he named animalcules, which means “little animals.”

He also observed blood from different animals and teeth scrapings.

He was also the first person to see bacteria, a unicellular organism.

It took nearly two centuries after Hooke’s discovery of cells that anyone realized, cells are present in all living things.

Matthew Schleiden, a German scientist who studied animals also stated that they are made of cells.

Schleiden wrote the first two parts of what is known as the Cell Theory.

In 1858, a German doctor, Rudolf Virchow wrote the third part of the Cell Theory.

All organisms are composed of one or more cells.

The cell is the basic unit of life in all living things.

All cells come from existing cells.

Cells come in different shapes, sizes, and perform different functions but they share many similarities.

• Cell Membrane• Hereditary Material• Cytoplasm and Organelles• Small size

All cells are surrounded by a cell membrane.

This membrane acts as a barrier between the inside and outside of the cell.

It controls the passage of materials into and out of the cell.

When new cells are made, they receive a copy of the hereditary material of the original cells.

DNA

All cells have organelles, chemicals and structures that enable it to live, grow, and reproduce.

The chemicals and structures of a cell are surrounded by fluid called the cytoplasm.

Almost all cells are too small to be seen with the naked eye and must be observed under high power of a microscope.

A cell’s outer wall (surface area) needs to be able to accommodate its inner activities (volume).

If a cell gets too large, its surface will have too few openings to allow enough materials into and out of it.

A single cell as big as us would have an incredibly small surface-to-volume ratio.

The cell would not survive because its outer surface would be too small to allow in the materials it would need.

Multicellular organisms grow by producing more small cells, not by getting larger.

Multicellular organisms have cells that specialize in a particular area and do a particular job.

These cells can form tissues and organs with different functions.

Prokaryotic Cells No membrane-covered nucleus, free

floating DNA

Eukaryotic Cells Membrane-covered nucleus that

contains DNA

These cells are also called bacteria and are the world’s smallest cells.

Their DNA is one long, circular strand.

They do not have any membrane-covered organelles.

Most bacteria are covered by a hard cell wall outside a softer cell membrane.

These cells were probably the first types of cells on Earth.

These cells are more complex than prokaryotic cells and about 10 times larger.

These cells first appeared about 2 billion years ago.

All living things that are not bacteria are made of one or more eukaryotic cells (plants, animals, fungi, and protists.)

They have a nucleus and several membrane-covered organelles.

Prokaryotic Cells Eukaryotic Cells

*No nucleus *Nucleus

*No membrane *Membrane-covered organelles covered

organelles

*Circular DNA *Linear DNA

*Bacteria *All other cells