Discovery of Cells Chapter 3-Section 2

Tiny Most Cells are so tiny they are not visible to the naked eye.

What would make someone think that something is made up of tiny parts that cannot be seen?

Actually… The first person to see cells was not even looking for them.

Robert Hooke In 1665, a British scientist named Robert Hooke was trying to find something interesting to show other scientists at a meeting.

Microscope Earlier, he had built a crude microscope that allowed him to look at very tiny objects.

Cork One day Hooke decided to look at a thin slice of cork, a soft plant tissue found in the bark of trees.

Cells To Hooke’s amazement, the cork looked like hundreds of little boxes, which he described as looking like honeycomb.

Cells He named the tiny boxes cells, which is the Latin word for “little rooms”.

Outer Layers Left Behind Although Hooke did not realize it, the boxes were actually the outer layers of the cork cells that were left behind when the cells died.

Plants Later he looked at thin slices of plants and saw that they too were made up of tiny cells. Some of them were even filled with “juice” (these were living cells)

Hooke Hooke also used his microscope to look at feathers, fish scales, and the eyes of house flies, but he spent most of his time looking at plants and fungi.

Hooke Hooke thought cells were only found in these types of organisms…NOT IN ANIMALS!!!!

Seeing Cells in Other Life-Forms In 1673, a Dutch merchant named Anton van Leeuwenhoek used one of his own handmade microscopes to get a closer look at pond scum.

Animalcules-”Little Animals” He was amazed to see many small creatures swimming around in the pond scum!

Blood Leewenhoek also looked at blood he took from different animals.

Blood Cells He observed that the blood cells of fish, birds, and frogs are oval-shaped, while those in humans and dogs are flatter.

Tartar Leewenhoek also did the same experiment by scraping tartar off both his own teeth and the teeth of animals!

Great Job!!! Leeuwenhoek was the first man to see bacteria! And, he discovered that yeasts used to make bread dough rise are actually unicellular organisms!

The Cell Theory After Hooke saw the first cells, almost a century passed before anyone realized that … CELLS ARE PRESENT IN ALL LIVING THINGS!

Matthias Schleiden Looked at many slides of plant tissue and read what other scientists had seen under the microscope.

Matthias Schleiden 1838: Concludes that all plant parts are made of cells.

Theodor Schwann 1839: Wrote Cell Theory

Cell Theory All organisms are composed of one or more cells. The cell is the basic unit of life in all living things.

Rudolf Virchow 1858: Saw that cells could not develop from anything but other cells…so he added to cell theory….

Cell Theory All cells come from existing cells.

Cell Similarities Cells come in many shapes and sizes and perform a variety of functions.

Things In Common 1. All cells have a cell membrane that acts as a barrier between the inside of the cell and the cell’s environment. It also controls the passage of materials into and out of the cell.

Things In Common 2. Heredity Material : Part of the cell theory states that all cells are made from existing cells. –When new cells are made, they receive a copy of the hereditary material of the original cells called DNA.

Things In Common Cytoplasm and Organelles: All cells have chemicals and structures that enable the cell to live, grow and reproduce. These structures are called organelles. –The chemicals and structures of a cell are surrounded by fluid. This fluid and almost everything in it are called cytoplasm.

SO SMALL Almost all cells are too small to be seen with a naked eye. You are made up of 100 trillion cells, and it would take fifty of these cells to just cover up the dot on the letter i.

Surface to Volume Ratio When cells grow they need more food and produce more waste.

Surface to Volume Ratio As the cell’s volume increases, it’s outer surface increases as well. The surface to volume ratio decreases as cell volume increases. Increasing the number of cells but not their size maintains a high surface to volume ratio.

Surface to Volume Ratio The area of a cell’s outer surface in relation to it’s volume.

Nucleus A nucleus is a membrane-covered organelle that holds the cells DNA.

2 Types of Cells 1. In one group, cells have a nucleus. 2. In other group, the cells DNA is not contained in the nucleus.

2 Types of Cells Prokaryotic: Cells that do not have a nucleus. Eukaryotic: Cells that have a nucleus.

Prokaryotic Cells Example: Bacteria Bacteria have tiny organelles called ribosomes. –These organelles work like little factories to make protiens.

Bacteria Most bacteria are covered by a hard cell wall outside a softer cell membrane. Bacteria were probably the first kinds of cells on Earth. The oldest fossils ever found were of prokaryotic cells (3.5 billion years old)

Eurkaryotic Cells Are more complex than prokaryotic cells. Ten times larger than prokearyotic cells. First appeared about 2 billion years ago. All living things that are not bacteria are made of one or more eukaryotic cells.

Eukaryotic Cells Examples: Include plants,animals, fungi and protists.

Eukaryotic Cells Have a nucleus and many other membrane covered organelles. –This allows many different chemical processes to occur at the same time.

Eukaryotic Cells There is more DNA in eukaryotic cells than in prokaryotic cells, and it is stored in the nucleus.

Eukaryotic Cells All eukaryotic cells have a cell membrane, and some of them have a cell wall.

Prokaryotic Cells Prokaryotic –No nucleus –No membrane covered organelles –Circular DNA –Bacteria

Eukaryotic Nucleus Membrane Covered Organelles Linear DNA All other cells