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Biology 101 Chapter 4

Cells as the Basic Unit of Life

The Cell Theory

Major Contributors:

Galileo = first observations made with a microscope

Robert Hooke = first to observe small compartments in dead plant tissue, coined the term "cell"

Antony van Leeuwenhoek = first to observe living, mobile cells and bacteria

Robert Brown = first to observe the nucleus

Rudolf Virchow = every new cell comes from a pre-existing cell

Schleiden and Schwann = plants and animals are composed of cells and cell products

Tenements of the Cell Theory:

1) All organisms are composed of one or more cells.

2) The cell is the smallest unit having the properties of life.

3) The continuity of life arises directly from the growth and division of single cells.

Cell size and cell function: Surface area to volume ratio!

- The larger the ratio, the better off the cell!

- Impact of surface area to metabolism

What is the largest cell in the human body? The smallest?

Cell Structures and Their Functions

All cells are placed in one of 2 classes:

Prokaryotic = lack a nucleus (bacteria)

Eukaryotic = have a nucleus (protists, fungi, plants,

and animals)


· very, very small

· very simple structure


A) Plasma (cell) membrane = encloses cytoplasm of cell

B) Nucleoid Region = where DNA is at (not a nucleus)

C) Ribosomes = assembles proteins with info from DNA

D) Bacterial Cell Wall = a rigid outer layer that surrounds

the cell membrane, protects the cell, maintains shape

E) Capsule = a sticky outer layer over cell wall

F) Pili and Fimbriae = numerous short projections that

help with adherence

G) Prokaryotic Flagella = longer projections that help with


H) Plasmids = extra-chromosomal pieces of DNA


· have a nucleus

· very, very large

· complex internal organization

· compartmentalized

· membrane bound organelles

Organelle = "small organ", membrane enclosed structures found inside the cell, each for a specialized function. All chemical activities of the cell occur within organelles.

Benefits of Organelles:

1) Separate environments for chemical reactions

2) Increased membrane surface area

Eukaryotic Cells Broken Up into 3 Regions:

1. Cell Membrane

2. Cytoplasm (cytosol and organelles)

3. Nucleus


1. Nucleus *

2. Endoplasmic Reticulum (ER, smooth and rough)

3. Golgi Apparatus (or Body)

4. Vesicles (lysosomes and peroxisomes)

5. Mitochondria

6. Chloroplasts (only in plants)

7. Storage Vacuole (mainly in plants)

8. Centriolus (only in animal cells)

Other Structures:

1. Ribosomes

2. Cell Wall (in plants)*

3. Cell Membrane

4. Cytoskeleton

a. Microtubules

b. Microfilaments

c. Intermediate Filaments

5. Flagella and Cilia (mainly in animals)

6. Nucleolus

The Nucleus

· Cell's genetic control center

· Double membrane

· Nucleoplasm

· Nuclear envelope

· Nuclear pores

· Chromatin = DNA + associated proteins

· Nucleolus = internal structure of nucleus, site of ribosome assembly

· Chromatin vs. Chromosome

The Cytomembrane System

· Function: internal transport, importing and exporting of cell

· 3 parts:

1. ER

2. Golgi Apparatus

3. Vesicles

Endoplasmic Reticulum

· Single, continuous membrane

· Pipes, tubes and tunnels in cell

· Continuous with nuclear envelope

· Superhighway of the cell

· 2 kinds: Rough ER + Smooth ER

Rough ER

- Flattened connected sacs