M-10 Kelp
Overview: Students will observe visual aids and dried samples to
understand how seaweeds are adapted to their watery environment as
compared to a soil plant and to understand the importance of a kelp
forest as a habitat for many marine animals, as an economic resource
and as a base for the marine food chain.
Grade Levels: 3 – 8
ACTIVITY
Key Concepts:
1. Seaweed’s structure differs
from that of soil plants due
to its water environment.
2. It has been used as food by
humans for hundreds of
years and contains protein,
vitamins, and minerals.
3. The brown algae, or kelp,
that makes up the kelp
forests along the pacific
coast is harvested
commercially to provide a
variety of useful products.
4. The kelp–otter–urchin
relationship is a delicate
balance that affects the
health of the kelp forests.
5. The kelp forests are
important to the entire food
chain, from small fish and
marine invertebrates to birds
and large mammals.
I. Comparing seaweed structure to soil plants: (5-10 minutes)

Show students the dried samples of seaweed and let them feel
and observe the samples. You can refer to the visual aid that
shows parts of a kelp plant. You can show sample soil plant.

Ask students what four things all plants (and living
organisms) need in order to survive.
Earth (nutrients), air (carbon dioxide), sun, and water.

Have students identify a holdfast and ask what purpose it
serves. How does the seaweed get water and nutrients?
It is similar to a soil plant root in that it holds the plant
in place. This is its only job, which is extremely
important due to the force of currents and tides. Roots
also acquire water and nutrients for the soil plant.
Seaweed does not need this since both can be directly
absorbed through the blades or fronds.

Have students identify a stipe and ask what purpose it serves.
It is similar to a soil plant stem and supports the kelp
and defines its structure. However, it does not need to
transport water and nutrients, so its structure is
simpler.

Have students identify blades and ask what purpose they
serve.
Blades are similar to soil plant leave. They are the
primary location of photosynthesis.

Have students identify air bladders and ask what purpose they
serve.
Air bladders help float the blades to the surface of the
ocean for better access to sunlight.

Ask why kelp grows where wave action is the greatest.
This is where the shallow water begins and seaweed
needs access to sunlight. Also, nutrients needed by
seaweed are stirred up by waves and are more
accessible.
Grade Level Options:
Primarily, for older grades one
wants to skip or move quickly
through the simple, obvious
questions and add more complex
questions. These appear at the
end of each activity section.
1. While discussing the structure
of kelp, you can also talk about
the three different types of
marine algae: red, green and
brown. Show samples of these
and talk about the differences.
2. While discussing the
economic importance of
seaweed, discuss what products
come from what type of algae.
Kelp
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California Science Standards:
ACTIVITY – Continued

Helpful Hints:
Keep in mind the difference
between “kelp” and “seaweed”.
Show sample of seaweed that has been soaked.
Take a small sampe of seaweed from the kit and
soak it for a couple hours in water. Let students
feel it. Gives students a feel for what seaweed is
like – slippery, tough (especially lengthwise).
Following are for older grades:
 Identify red, green and brown algae in the samples. Ask
why they are not all green, since there is photosynthesis.
Note red and green are not as thick and tough as
brown. Other pigments mask the green of
chlorophyll. Note that only the brown algae are
called kelp.
 Ask how each plant reproduces itself.
Flowering plants produce flowers and seeds. Seaweed
don't, but it does reproduce by gametes – male/female
sex cells or by regeneration from the holdfast. This is
similar to mosses and ferns.
II. The economic importance of seaweed: (5-10 minutes)
Kelp

Ask if any student has eaten seaweed.
Most will say “No” since they don’t recognize seaweed
in what they eat.

Tell the students that communities that live near an ocean
since man first became homo sapien have eaten seaweed.
Show food product packages (soup, sushi wrap, crackers,
etc.). Ask if any have eaten similar foods.
Most will now realize some of what they have eaten is
seaweed. Many of these samples are not kelp (see
background information).

Use visual aid with ocean and Velcro spots to describe how
kelp is harvested. Place picture of harvest barge on visual
aid. Mention that there are regulations on how much can be
harvested (no deeper than 4’) and ask students if they can tell
you why such controls are necessary.
Cut too much in general and you can kill the plant. Cut
too deep and you can limit how much sun the plant gets
and so stunt its growth. These can have a negative
impact on the health of the kelp forest and thus the
entire local food chain (see section 3).
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Glossary:
ACTIVITY – Continued
agar – a jellylike substance
extracted from red algae. It is
used as a culture medium and as
a gelling and stabilizing agent in
foods.

algae – any of a group of lower
plants having chlorophyll but no
vascular system, including many
seaweeds and related fresh water
plants.
algin – a substance extracted
from brown algae (kelp) and
used as a thickening and
emulsification agent.
bladder – structure containing
air that is attached to a stipe and
helps raise the blades toward the
surface of the ocean.
blade – a flat, elongated organ
resembling a leaf. This organ is
where most photosynthesis takes
place.

emulsion – a mixture of
mutually insoluble liquids, such
as oil and water, in which one is
dispersed as droplets throughout
the other.
flagella – organelles that project
singly or in groups from a cell
and are the primary means of
motions for many
microorganisms.
Kelp
Ask students why kelp is the primary seaweed in this
harvest. Remember that kelp can grow up to 20
centimeters, or 8 inches, in a day.
It is extremely fast, large and abundant. It renews
itself easily.
Following is for older grades:
 Ask students how much kelp could be harvested in a
season.
If you harvest 4 feet deep and kelp grows 8 inches
in a day, it will re-grow every week or so.
 Discuss uses of other seaweeds.
1. Red: looks like a delicate fern. Make agar-agar. Doctors
use this for throat cultures by taking a swab of suspected
bacteria & incubating it in the petri dish. Orchids are
cloned in test tubes filled with sugar agar for a nutrient
gel to hold delicate, growing plant.
2. Green: Soak green Wakame brand at home to show it
dry, then wet -can feel vegetable protein (slippery).
carrageenan – a colloidal
extract from red algae used in
food to stabilize and thicken.
chlorophyll – the organelle in
plants that functions in
photosynthesis.
State that the products made from the harvested kelp are used
extensively in food and other manufactured items for
emulsification (blending oil and water), thickening, and
texture. List some of these products by having students take
turns placing a product picture on the visual aid and guessing
what use is made of kelp in the product.
There are also a few product packages that you can
show the students. The ice cream cartons in particular
list algin and carrageenan, both extracts from kelp.
III. The kelp forest food chain (5 minutes)

Using the kelp forest visual aid, give each child an animal
to place on the poster to make a food chain. Discuss
where the animal fits on the food chain.
What are the major producers (kelp)? What are the
major herbivores (urchins)? What are the major
predators (otters, humans)? How do other animals
fit in?

Remove sea otter from the poster. Ask what would
happen if sea otters were not protected from hunting.
Kelp beds might disappear again due to destruction by
urchins. Other animals will disappear due to lack of the
kelp forest environment.
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Glossary (continued):
food chain – a sequence of
plants and animals that depend
on one another for food. The
lower elements of the chain (the
producers) serve as food for the
higher elements (the consumers).
frond – a connected set of
blades attached to a stipe.
gamete – a mature reproductive
cell. It can be either male
(sperm) or female (egg).
ACTIVITY - Continued

Ask what dangers can be foreseen if the otter population
grows too large? A herd of 2,000 otters eats 20 million
pounds of invertebrates in a year!
Reduce numbers of abalone; then as otters deplete abalone
supply, they switch to digging for clams.

Ask who besides marine animals would feel the loss of
kelp beds?
People — economic loss of kelp products.

Ask how an oil spill off California would affect this food
chain?
Otters would die because oil removes air insulation, the
trapped air from their fur, and otters do not have
subcutaneous fat to keep them warm.

Ask what effect another El NiÑo would have on this
delicate relationship.
Urchin population would increase; otters may not be able
to eat sufficient urchins to maintain a balance.
holdfast – the organ that
attaches a seaweed to a solid
support, usually a rock.
kelp – macroscopic brown algae.
photosynthesis – the process by
which plants turn water and
carbon dioxide into sugars, using
the power of sunlight. This
process occurs in the chlorophyll
organelle.
spore – a primitive, usually one
celled, reproductive body
produced by some lower plants
and animals.
stipe – the stem-like organ of a
seaweed that connects the fronds
to the holdfast.
Links to Other Kits:
One can use the information
in kit G-P (new plant kit) for
an understanding of soil
plants.
Kelp
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Background Information
I. Comparing seaweed structure to soil plants:
Since seaweed exists in a water environment, it does not require strong support or a water
conducting system. Seaweed does not contain roots but lives attached to a stable support,
usually a rock. The organ of attachment is called a holdfast. Without this holdfast, wave and
current action would carry kelp away from the shore. Kelp needs to remain in the intertidal zone
to receive the appropriate nutrients and salt content. Instead of water conducting stems, kelp has
hollow, flexible stipes, which move with wave action and serve to keep the blade-like fronds
upright for increased exposure to sunlight. Since water is used for support of the stipe, it does
not have to be rigid like the stem of a soil plant. At the end of each stipe are gas-filled bladders
which keep the plant afloat, near the surface for photosynthesis. At the end of the air-bladders
hundreds of structures emerge that resemble leaves but are called blades. It is within the blades
that most photosynthesis occurs. Blades may be different shapes, but their large, elongated form
allows them to spread across the water to capture the maximum amount of sunlight.
During severe storms, stipes may break and plants are washed ashore. Usually the holdfast
remains in place and a new stipe can grow. Kelp plants also reproduce from spores dropped
from the blades. These spores have flagella (moving hairs for swimming). Spores develop into
male (sperm) and female (egg) gametes which combine to produce a miniature kelp plant.
II. The economic importance of seaweed:
The word kelp is derived from Middle English word referring to ash. During this era brown
algae, now called kelp, was burned to produce ash for soap-making.
Seaweed is primarily complex algae, and has been used as food for hundreds of years. It contains
protein, vitamins and minerals. (There are small amounts of seaweed that are vascular plants that
have moved back into the water, such as eelgrass.) There are three varieties of marine algae: red
(agar-agar), green (sea lettuce), and brown (macroscopic browns are called kelp and have many
uses).
Here is a more detailed discussion of the three varieties of marine algae (note: other products
come from each variety of algae, the descriptions only give a sample):
Kelp

Red (phylum: rhodophyta) produces Nori (used in many oriental foods),
agar (a thickening agent and a growth medium), and carrageenan
(similar to agar). The blade of these algae is very thin, only a few cells
thick.

Green (phylum: chlorophyta) produces Anori (used for food similarly to
Nori) and ulva (green sea lettuce, which is also edible). The blades are
always 2-cells thick.

Note: Together, red and green algae make up a significant part (on the
order of 50%) of what is washed up on the beach or found in tide pools.
Thus what is seen on a field trip is as likely to not be kelp as to be kelp.
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
Brown (phylum: phaeophyta), called kelp, produces algin (a thickening
and emulsifying agent used in many products) and laminaria (used in
soups and other foods). The blades of these algae are often thicker than
the other two.

Note: 70% of the earth’s surface is covered with water. This water
contains algae! More than half (and maybe as much as 80%) of the
oxygen we breathe comes from these algae. To solve the air quality
problem, we need to save the oceans as well as the tropical forests!
The brown algae, or kelp, that makes up the kelp forests along the Pacific Coast is harvested
commercially to provide a variety of useful products. It is an extremely rapid growing plant,
reaching 200-300 ft. in length. If conditions are right (nutrients, sunlight) each stipe may grow 20
centimeters per day. In Southern California barges with an underwater mowing machine cut the
upper portion of the kelp (sample picture). State regulations limit cutting to 4 ft. depth. Conveyor
belts haul the kelp aboard. Photosynthesis of kelp is increased after cutting as more sunlight
reaches the canopy. Approximately 150,000 wet tons of kelp are harvested in California waters
by this method.
Once harvested, the brown algae, or kelp, are processed to produce algin, a dry powder that acts
as a stabilizer and emulsifier in many foods. Algin keeps pigment particles mixed with
accompanying liquid (cosmetics, paints). As an emulsifier, the algin binds oily and watery fluids
together (salad dressings do not separate). As a stabilizer it thickens and smoothes products such
as ice cream, instant puddings and soups. Other uses are fodder for animals, fertilizer for plants,
and softens leather for tanning.
Green and brown algae are both used in soups, stews, crackers, cookies for flavoring and nutrient
content.
Red algae are a source of carrageenan and agar. Nori is probably the most popular type, used in
soups and stew. Industrially, agar is used a gel for a media base (microbiology) or as a sugar
media for cloning flowers such as orchids.
III. The kelp forest food chain:
Kelp grows in cold waters within the intertidal zone where conditions are just right (nutrient runoff, specific salinity and wave action). The Pacific Coast has one of the greatest diversities of this
plant.
The kelp–otter–urchin relationship is a delicate balance (symbiosis — 2 dissimilar organisms
living together). Reduce one part of this relationship and the delicate chain falls apart. Sea
urchins are the only marine animal to directly devour kelp beds. Sea otters help kelp beds
flourish by feeding on urchins. Otters have pockets under forearms to carry food to the surface.
The absence of sea otter populations, due primarily to fur hunters (see handout), has been shown
to have significant consequences for all marine life in the intertidal zone. Without the otters,
kelp beds rapidly disappear as sea urchins not only eat the large plants, but also devour any new
plants before they can become established. Otters rely on the kelp forest for an urchin food
supply, as a safe habitat, and as a safe haven for their young (otters wrap kelp around themselves
and young as protection against wave action. Sea otters are one of the animals capable of using a
rock as a tool to crack open another of its favorite food, abalone & crabs.
Kelp
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Disappearance of kelp beds means loss of habitat and food for many fish species, mollusks, and
small marine invertebrates. These animals, in turn, are eaten by crabs, sea stars and larger fish.
Going up the food chain, larger mammals (sea lions, otters) and birds (cormorants, gulls) eat the
crab, abalone and small fish with the ingested kelp. Fish such as the kelp bass live within the
kelp forest, well protected from predators.
Kelp provides more carbon to the food chain than do phytoplankton, thus adding to the base of
the food chain. In areas where kelp beds are prevalent, many sea animals are fed. Wave action
rips kelp blades into small pieces that decompose to become food for filter feeders and small
invertebrates. Currents carry this food to surrounding areas. The kelp forest attracts many fish
species not only for food but also for protection. However, the dense canopy of kelp limits the
amount of sunlight that can penetrate deep waters, thus inhibiting growth and habitat of some
fish species.
IV. Photosynthesis:
This is for information only. There is a separate photosynthesis kit if you need to
actually teach students about this.
Plants and animals both need carbohydrates for energy. Animals (including humans)
eat carbohydrates which in turn are converted into sugar molecules that body cells use
to make energy (a process called cellular respiration). Plants can't eat carbohydrates so
they must make their own sugar molecules by using the sun's energy, nutrients from
the water and the help of special plant cells called chloroplasts which contain a pigment
called chlorophyll (a process called photosynthesis).
Seaweeds belong to a group of plants known as autotrophic (self-feeding) because they
feed themselves from the sun's energy. The sun's energy produces photons (energy)
that are utilized by the chloroplasts to convert water and carbon dioxide into sugar
molecules and oxygen. The more photons that are delivered to a frond, the more
energy can be absorbed and more sugar can be produced. To insure that sufficient
sunlight reaches chloroplasts in the blade-like fronds, special adaptive gas-filled
bladders are located at the end of a stipe to lift the plant to the water's surface. Large,
flat fronds (increase the surface area) grow from each air bladder and spread for better
exposure to sunlight (read learning station on kelp structures for more information).
Photosynthetic plants such as kelp are the backbone for marine food chains as these
plants grow at tremendous rates, providing food, oxygen and shelter for many forms of
marine life as well as humans.
The process of photosynthesis is as follows:
Seaweed is able to absorb the sun's light energy (photons) due to a green substance
called chlorophyll that is located in special cells within the blades called chloroplasts.
Once light energy has been captured, it is released to the chloroplast within the cell to
be used as chemical energy for the production of sugar molecules. The same
chlorophyll can be used over and over again to absorb more light energy. Most of
Kelp
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photosynthesis takes place in chloroplasts within the blades. The surrounding water
(H2O) provides carbon dioxide (CO2), nitrogen (N) and phosphates that are absorbed
through the blades into the chloroplasts to be converted into sugar and oxygen
molecules. The sugar molecules are used by the plants for energy to grow and
reproduce. The oxygen molecules are by-products, released back into the water, to be
used by other animals. All plants contain chlorophyll, so most plants are green. But
some plants contain other colored pigments (brown, yellow, red), which can mask the
green chlorophyll. An example is kelp, which is usually brown because other pigments
overrule its green chlorophyll.
The chemical equation for photosynthesis is:
6H 2 O + 6 CO 2 + light energy----> C 6 H 12 O 6 + 6O 2
Kelp
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Material List






Kelp
Kelp poster
Flowering plant poster (optional- from Nature in Your Neighborhood)
Samples of kelp plants
Bring a flowering plant from home for comparison (optional)
Samples of seaweed-related products i.e.: toothpaste, agar, chips, ice cream cartons
petri dish (agar) for throat cultures
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Karla Martin, January 2005