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Chapter 3 Life Science
Cells: The Basic Unit of Life
Section 1: The diversity of cells
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A cell is the smallest unit that can perform life processes.
Cells were not discovered until the invention of the microscope in the mid
1600’s.
Robert Hooke was the scientist that discovered cells by looking at cork
under a microscope. He discovered that cells looked like “little rooms”. By
observing plants, he also discovered that some cells are living.
Later Anton von Leeuwenhoek discovered small living organisms in pond
scum. We now call those organisms protists.
Leeuwenhoek also viewed different types of blood cells and bacteria under
a microscope.
Almost 200 years later, Matthias Schleiden concluded all plants were made
of cells and Theodor Schwann concluded all animal tissues are cells.
Rudolph Virchow stated that all cells come from other cells.
With these discoveries, Schwann and Virchow developed the cell theory.
Cell theory
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All organisms are made of one or more cells
The cell is the basic unit of all living things
All cells come from existing cells
Section 1 page 2
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Most cells are too small to see without a microscope.
All cells have the following parts in common:
The cell membrane and cytoplasm. The cell membrane give
the cell shape and protection. The cytoplasm is the fluid part of
the cell.
Organelles are structures in the cell that carry out specific
functions.
All cells contain DNA (the genetic material that carries information
needed to make new cells and new organisms).
The cell membrane controls what materials enter and leave the
cell.
In most cells, DNA is contained in a nucleus which serves as the
control center of the cell.
Cells are divided into two groups: prokaryotic and eukaryotic
Section 1 page 3
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Prokaryotic cells do not have a nucleus.
Two classes of prokaryotes are eubacteria and archaebacteria.
Bacteria live everywhere. Some are beneficial and others are
harmful.
Archaebacteria may live deep in the ocean or near volcanic vents
in the earth’s crust.
Eukaryotic cells are larger than prokaryotic cells. They do contain a
nucleus and membrane bound organelles.
Eukaryotes are multicellular organisms. Humans, animals, and
plants fall into this category.
Section 2
eukaryotic cells
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Some eukaryotic cells have a cell wall. The cell wall is a rigid structure
that gives support to the cell. It will be the outermost structure of the cell.
Plants and algae have cell walls made of cellulose.
The cell wall of plants allows the plant to stand upright and keep their
shape.
Eubacteria and arechaebacteria have cell walls also.
All cells have cell membranes. It separates the cell’s content from its
environment.
The cell membrane contains proteins, lipids, and phospholipids.
The cell membrane controls which materials move in and out of the cell.
Nutrients and water move in while waste products move out.
The cytoskeleton of the cell helps keep it from collapsing and also allows
some cells to move.
The nucleus contains the DNA of the cell.
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Organelles that make proteins within the cells are called ribosomes.
The endoplasmic reticulum or ER is a folded membrane in which
proteins, lipids and other materials are made.
Some ER is smooth while some is rough.
A mitochondrion is the main power source of the cell. Energy is released
by the mitochondria and stored in ATP.
Plant and algael cells contain chloroplast. The process of photosynthesis
takes place in the chloroplasts.
The golgi complex is responsible for packaging and moving material out
of the cell.
Lysosomes carry out digestion within the cell.
The vacuole of the cell stores water for the cell.
Section 3
the organization of living things
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There are some benefits to being a multi-cellular organism.
1. Being a larger organism than single celled organisms
2. The life span of multi-cellular organisms is longer
3. The organisms is very specialized with life functions
A tissue is a group of cells that work together to perform a specific
function. Examples = muscle tissue, nerve tissue, blood etc.
An organ is a group of tissues working together. Examples = stomach,
heart, brain etc.
Organs combine to form organ systems. Examples= digestive system,
circulatory system etc.