World Builders™
World Builders™
Session Five  --  Seaweeds
Session Five  --  Seaweeds

Design and Diversify Your Seaweed
Design and Diversify Your Seaweed

 Families of organisms begin with a basic  body plan and then develop variations.

You may want to review the page on evolution here.

Part One: Design the Basic Ancestral Seaweed

Design Step 1: Create a Single Cell.


one plant cell

Here is a sample cell. It is roughly rectangular and contains a nucleus and some chloroplasts and other structures

I call it greenbox.

Design Step 2: Sketch a Clump of Cells.

a clump of cells

Here we see a loose clump of cells. They don't seem very organized yet.

I used copy and paste.


Design Step 3: Make a tiny simple seaweed.
a very simple plant

Reduce the size of the cell clumps.

Copy them and paste them together.

This green mass that grips a rock.
It is probably about the size of a period.

It is pretty primitive, but it's a start!

Design Step 4: Think! What must the environment be like if this seaweed is going to live?

low plants growing on rockReduce the size of your algal clump  further so that you can make a picture of a group of algae

Copy and paste the group of algae.
Now wait a few million years.

My low growing little seaweeds could be almost half an inch tall. They need to live in shallow water in order to get enough light.

They need to cling to the rocks to avoid being carried away by the waves.

I call these seaweeds scrubbers.

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 Part Two: Diversify into More Biomes

      Biome One: The Ancestral Seaweed Flourishes in Its Environment

Adaptation Step 1: Begin with the Ancestral Seaweed from Step Four Above.


This is the ancestral little seaweed that is about to become an important ancestor!

I called these scrubbers.

Adaptation Step 2: The Seaweed Grows Larger to Make Use of Its Environment

Millions of years have passed.

The seaweed has grown small, tissue-paper thin green sheets of cells.  They are two to three inches tall and grow on rocks in shallow quiet waters.

A few small holdfasts anchor the green sheets of the cells to the rocks.

I call these tiny seaweeds Hi-Guys

    Biome Two: Adapt Plant to Rougher, Deeper Water

Adaptation Step One: Take a Primitive Clump to Work With


primitive plant cell clump

Here is a primitive clump of cells from Step 3 (above).

Adaptation Step Two:   Use tools in your paint program to stretch the clump.

stretched cells

This clump has been stretched and distorted to make a seaweed that will be able to live in deeper water. Make it taller, maybe three to 8 inches tall. Name your plant. I call these plants fans.

     Wait for millions of years.

Design Step 3: Strengthen the Seaweed so that it can Live in Deeper Water
colored plant

Add a stronger holdfast for better attachment to the rocks.

You may need some ridges of plant tissue to stiffen the fans so that the algae will stay together during storms.

  The fans are looking good! 

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 Biome Three:  Adapt Plant to Capture More Nutrients in a Place with a Steady Current

Adaptation Step One: Take a Shallow Water Clump to Work With


colored plant

Start with the deeper water fans that have ridges or ribs of tissue..

You have the makings of several species here!

These plants are about 6 to 16 inches tall. They grow on rocks where the water is up to about three feet deep.

Adaptation Step Two:   The sheets of plant tissue  separate into threads.

flame plants Some of the fans have developed new characteristics. Instead of sheets of tissue they have bunches of  feathery, thread-like tissues that wave in the water. These threads can absorb more food because they have a greater surface area than sheets of tissue.

Improved holdfasts allow them to cling firmly to rocks.

I have called these plants feathers.

     Wait for millions of years.

Design Step 3:   Find  a Way to Photosynthesize in Deeper Water
long stemmed plant

Now a new species has developed from the feather plants.

These plants can grow in deeper water because they have developed short, tough stem-like tubes that allow them to hold onto the rocks below and still get closer to the light at the surface of the water.

I call these invented plants wavers. The whole plant could grow to be four feet tall or even taller.

Scientists think that this the way that evolution works -- a basic organism evolves and changes over the generations so that it has a better chance of survival.

NOTE:  I was thinking of going into deeper water with these seaweeds, but they only have green pigments, so cannot go very deep.  See The Photic Zone to learn about seaweeds and their light requirements.  Remember that single cells adapt by changing their internal chemistry while more complex organisms change their morphology (body shape).  These seaweeds are descended from green algae, and it is too late for them to change their essential pigments.

Biome Four:   Adapt Seaweeds to Live in the Open Ocean

Adaptation Step One: Take a Primitive Clump to Work With


primitive plant cell clump

This is the clump from Step 3 of the first part.

We will see if we can adapt this plant to float.

Adaptation Step Two:  Flatten these Cells so that that can Float on the Surface.

flat mat of cells

Change size, flatten, stretch.

Add little hollow balls of cells so that the whole mat will float. Toughen the cell walls so that the mat will stay together.

Wait, wait, wait for millions of years.

Design Step 3: Add Colors to Help with Photosynthesis in Deeper Water
mats of floating plants

Now we see thin veils of floating plants at the water's surface.

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Well, that isn't too hard!   Actually, it is quite fun!
Let's see what you can come up with!

Part Three: Some Ways to Report Your Results

1. Use a Diagram to Show Evolutionary Relationships

evolutionary chartThis chart shows how the life forms are related.

The new species that develop from a parent species are shown going down, for example, the clump is the ancestor (parent) of the scrubbers.

Species that develop from a common ancestor are shown side by side, for example, Hi-Guys, Veils and Fans  evolved from the scrubbers.


2. You May Use a Table

Notice that I have given the plant's parentage with the name: grandparent/parent/plant

The Development of Water Plants

  Special Adaptations
   single cell microscopic  free-floating  A eucaryote
has chloroplasts
   Clumps microscopic to barely visible  free-floating Cell walls stay conneted together
no differentiation



thin film to about 2 inches clings to stones in shallow water cells cling to rocks with small primitive structures


 2 to 6 inches Rocky bottom

water 5 to 12 inches deep

special structures grip the rocks

some thickening in vertical ribs strengthens plants

  Ribbed Fans

clumps/scrubbers/fans/ ribbed-fans

 3 to 8 inches

Rocky bottom

Water 8 to 24 inches deep

Brown and purple pigments capture light at greater depths
  Feathers clumps/scrubbers/fans/
 6 to 16 inches Rocky bottom

Water 12 to 24 inches deep

Better holdfasts help larger plant cling to rocks

Strand-like structures adapt to currents

small feather gif

Ribbed Feathers

 10 to 24 inches Rocky bottom

Water 18 to 36 inches deep

Brown and orange chlorophyll capture light energy at greater depths.




to four feet or taller  Rocky bottom

Water 3 to 8 feet deep

Strong hollow cord-like structures hold onto rocks to anchor plants


 float on top of water in very thin patches  open water small hollow balls of cells help the mat to float
tougher cells stay together better

PowerPoint Water Plants Rubrics

Water Plants Coordinator Rubrics

Web Pages Water Plants Rubrics Water Plants Coordinator Rubrics

Seaweed Information Menu


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© 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 .