Chapter 3 Cells: The Basic Units of Life

Section 2 The Discovery of Cells

Most cells are not visible with the naked eye

Seeing the First Cells

ü 1665 Robert Hooke and a slice of cork

Seeing Cells in Other Life-Forms

ü 1673 Anton van Leeuwenhoek and pond scum (animalcules – little animals)

The Cell Theory

ü 1839 Theodor Schwann

§ All organisms are composed of one or more cells

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

1858 Rudolf Virchow

ü All cells come from existing cells

Cell Similarities

Although cells come in different shapes and sizes and forms a variety of functions

All things in common include:

ü Cell Membrane

§ barrier between the inside of the cell and the cell’s environment

§ controls the passage of materials into and out of the cell

ü Heredity Material

§ DNA (deoxyribonucleic acid)

Controls all activities of the cell

Contains information needed for that cell to make a new cell

ü Cytoplasm – fluid that surrounds chemicals and structures inside the cell

ü Organelles – Structures and chemicals within the cell which enables it to grow, live, and reproduce

§ Some organelles are surrounded by membranes

ü Size – small

§ You are made up of 100 trillion cells – 50 of these to cover the dot on the letter “i”.

Giant Ameoba Eats New Your City

§ Amoeba:

consists of only a single cell

can’t grow large enough to see without a microscope

… cell grows, needs more food, produces more waste

ü Surface to Volume Ratio – the area of a cell’s outer surface in relation to its volume

§ Growing cells need larger surface to exchange materials

§ Cell volume increases, surface area increases

§ Too large cell – surface has too few openings for materials to go in or out

ü Benefits of Being Multicellular

§ Multiceullar organisms grow by producing more small cells maintaining a high surface to volume ratio

ü Many kinds of Cells

§ Multicellular organism can perform complex functions due to the fact that they are made up of specialized cells

Ex. eye, brain, hand

Two Types of Cells

ü Prokaryotic Cells - a.k.a Bacteria

§ No Nucleus

§ DNA

· one long, circular molecule shaped like a rubber band

§ Cell Wall

· outside wall of the membrane

· hard, rigid

§ Cell Membrane

· soft membrane (liner) presses against the wall of the cell like a balloon

· allows food and waste molecules to pass through

§ Ribosome

· tiny and round – works like a factory to make proteins

Illustration: p 66

Draw and label

ü Eukaryotic Cells – More complex than prokaryotic cells

§ 10 times larger

§ First appeared about 2 billion years ago

§ Non bacteria – ex. plants, animals, fungi, and protoists

§ Nucelus (linear DNA) and many other membrane-covered organelles

§ Cell Wall (some) ex. plants, fungi, some unicellular organisms

§ Cell Membrane (all)

Illustration: p 67

Draw and Label

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

Eukaryotic Cells Nucleus Membrane-covered organelles Linear DNA All other cells