|
A
Quick Review
Life
first appeared on earth about
3.8 billion years ago. The first
life forms were single celled
organisms, and they continued
to be the only life forms here
for 2.8 billion years.
The early life forms
were very small cells called
prokaryotes.
They survived by capturing organic
molecules that were abundant in
the early seas. However, after
a time these molecules became
less abundant, and the tiny cells
needed a new way to capture energy.
Some cells began to use chlorophyll
to make sugar using carbon dioxide
and sunlight, a process called
photosynthesis. Oxygen was produced
as a waste product of photosynthesis.
Oxygen was toxic
to many of the earliest life forms.
Cyanobacteria began
producing oxygen early
in prokaryotic times,
but this oxygen
was absorbed by water,
and most of it united with
iron to form iron
oxide.
This took the oxygen out of
the biosphere so that it was
not readily available to
life forms.
Eventually, however,
atmospheric oxygen very slowly
became more abundant, and more complex
cells, called eukaryotes, appeared.
A eukaryotic cell has a nucleus
enclosed in a membrane, and other
membrane-enclosed components such
as mitochondria and chloroplasts.
The chloroplasts do
photosynthesis inside the
eukaryotic cells, creating
food for them.
Here is
a time line showing the 4.5
billion years since the formation
of the earth.
As
you can see, multicellular organisms
are relative newcomers, and
began to appear only 700 million
years ago in the history of
life.
There are gaps in our
knowledge of the story of
the earth. One gap is
between non-life and life:
we don't know how that gap
was bridged. Another
gap is between unicellular
life forms and multicellular
life forms: we don't really
know how that leap was made.
The
Protists -- A Group of
Eukaryotes
In this
lesson we study the protists,
a group of eukaryotic
organisms that seem to explore the
the possibilities available
to them as larger, more
complex cells. Many are still unicelluar
organisms, in themselves complete and
independent. Others
show the beginnings of
communal living. There
are many protists on earth
today, and scientists are
finding out how unique and
innovative members of this
group are. They all
capture energy, grow, and
reproduce, but they do so in
innovative ways that amaze
us. Some
members of this group are an
important part of the food
chain in the ocean.
Moving
Toward Multicellular
Organisms
For many millions of years, cells would
reproduce by dividing
into two separate individual
cells. However,
sometimes a cell would
divide and then two or more
of the new cells would remain
attached together. There are
strings of cells in pools
and lakes today that are like very thin
spaghetti.. These are
not really multicellular
organisms,
because the cells stick together
but remain self-sufficient and
identical to one another in
what they do..
Truly multicellular
organisms exhibit differentiation.
The land plants that we are
familiar with have cells adapted
to forming stems, roots, leaves,
flowers, and seeds. True
plants evolved from algae in
the water. Have you
looked closely at
seaweeds,
at the beach, or in an aquarium?
Check the Introduction
to Session Five for
some thoughts about the
algae that we call seaweeds.
We will be studying them in
this lesson.
Top
of Page
Information
Read these pages before you begin
making your page.
Plants
and Seaweeds
The
Algae
The
Three Colors of
Seaweeds
Limiting
Factors
Introduction
to Biomes
Protists
How
to Plan Your Seaweeds
Designing
and Diversifying Your Seaweeds
Seaweeds
Evolve
Helpful
Web Sites Be sure
to check out these links.
What
You Should Know: Study Questions
for Test Preparation
Go
to the Rubric Page for PowerPoint Pages see what your
assignment should look like.
Go to the
Coordinator's Rubric Page for a Web Page
to see what information
you need.
Go to the Page
Coordinator's Rubric Page
for PowerPoint
to see what information
you need.
Top
of Page
Assignment
Do
this part in class:
Seaweeds
Think
about your first life forms
and how they could be joined
together
Go
to Chapter 5 of the Work Sheet
Master Pages to Get
Ideas About Making Your
Seaweeds
Evolve
Decide
which biomes your group
will work with.
You need to choose as many
biomes as there are members
in your group.
(Example: 4 people, 4
biomes: 2 people, two
biomes.)
Decide
what the file names of your
pages will be.
The
Page Coordinator should write
a draft of the Water
Algae
page in class tonight. Help
him/her.
Sketch
out the joined cells, and
work towards forms that can
survive in your environments.
Draw
your life forms from stage
to stage as they progress
into aquatic seaweeds
Write
descriptions of your aquatic
plants
Each
person will design and describe
his or her own seaweed and its
three or more evolved species.
Homework:
Bring to class next session:
seaweeds
page with graphics.
See
the Rubric for this page
for a web site.
See
the Rubric for this page
for PowerPoint
Scanned
or computer drawn pictures
of your
seaweed
varieties
A
computer drawn diagram of
how the kinds of
seaweeds
are
related to each other.
©
1996,1997, 1998, 1999,
2000, 2002, 2003.
Elizabeth
Anne Viau.
All rights reserved.
This material may be
used by individuals
for instructional
purposes but not sold.
Please inform the
author if you use it
at
eviau@earthlink.net
.
|