Marine Plants The ocean contains many plants and plantlike organisms. Some are similar to plants we see on land while others are very different. All of these plants have one thing in common they are primary producers. Producers produce their own food through a process known as PHOTOSYNTHESIS Through photosynthesis, plants capture sunlight with special pigments, such as chlorophyll. Plants combine light energy (supplied by sunlight) with water and carbon dioxide to form a sugar called glucose. These sugars fuel the plants life functions. Oxygen is a byproduct of this reaction. Sunlight = Energy All photosynthetic organisms have chlorophyll a (green pigment) Oxygen (O 2 ) Carbon dioxide (CO 2 ) Water (H 2 O) We can write the overall reaction of this process as: Water + Carbon dioxide + Sun energy sugar (glucose) + oxygen 6[H 2 O] + 6[CO 2 ] C 6 H 12 O 6 + 6[O 2 ]
Most of the producers you would be familiar with are on land and are classified as plants, however, most of the producers in the ocean (phytoplankton, seaweed etc) are very different and therefore some say that they are not plants, calling them Protists or Protoctists. Protists are organisms whose cells are very simple. Algae may have just one cell, as do millions of tiny producers that float in the plankton, or grouped together in colonies, or as organisms with many cells, sometimes collaborating together as simple tissues. Marine algae, commonly known as Seaweeds, are the plantlike structures you find on the shore. Algae are very simple chlorophyllcontaining organisms which are divide into three major phyla or divisions which can conveniently be divided by colour as follows: All of these organisms are called Autotrophs, i.e. they are able to produce food (organic matter) for themselves from non-organic substances (water, carbon dioxide) using light or chemical energy. Phaeophyta (brown algae) Rhodophyta (red algae) Chlorophyta (green algae) Phaeophyta These are either olive-green in colour or any shade of brown from golden brown to almost black. Brown seaweeds appear to be brown due to a masking pigment known as fucoxanthin that masks the green chlorpophyll pigments responsible for most of the photosynthesis, and which makes the plant look green. Rhodophyta These show a wide range of colours from red or bright pink to a dark purplish-brown, to almost black. The range of colours are a result of the presence of two extra pigments, phycoerythrin (red) and phycocyanin (blue), which mask the green chlorpophyll and other photosynthetic pigments. Further modification of colour can take place as red seaweeds are often bleached to a light brown or yellow in bright sunlight and can thus be confused with brown algae. Chlorophyta These are usually delicate plants with thin fronds of a grass-green colour. Of the 3 algal divisions, green seaweed show the least variation in colour. They owe this green colour to the presence of the photosynthetic pigment chlorophyll, which is not masked by other colour pigments as in the red and brown algae.
Seaweed Adaptations (physical) Blade - Surface area A large blade surface area increases the light absorbing area of seaweed which in turn increases the rate of photosynthesis, producing fuel for the seaweed. Gas Bladder - Floatation These spherical bladders are filled with gas allowing the algae to remain upright in the water column during submergence. Therefore increasing the amount of sunlight reaching the fronds. Holdfast - Secure attachment Instead of roots, seaweeds have special suckers called holdfasts which cling to rock. Therefore they can live on hard surfaces where plants with roots wouldn t be able to survive. Stipe - Flexibililty Seaweeds living on rocky shores have adapted to being pounded by waves by having a flexible or elastic stipe which allows the seaweed to bend with the wave action and prevent snapping or breaking the stipe. The tide's rise and fall is one of the main factors affecting life on rocky shores. When the tide falls, seaweeds on rocks are exposed to air. They must develop special adaptations to survive until the tide comes in again. Cellulose cell walls also contain gel-forming polysaccharides (algin in brown algae; carrageenan in red algae) which cushion the thalli against wave action and prevent desiccation during low tide. The body of a seaweed is called a thallus (plural thalli). Some seaweeds also produce slimy alginates and tough leathery fronds to deter herbivores. Some red algae retard grazing by marine invertebrates by incorporating large amounts of calcium carbonate into their cell walls. The largest seaweed in the world is a brown algae (kelp) called Macrocystis pyrifera (the giant kelp). The longest recorded length is 54 metres long! M. pyrifera is the type of kelp that makes up the majority of the giant kelp forests off the California coast.
Quick revision: Complete the following statements 1. Plants and plantlike organisms are all, they make their own food. 2. The red seaweeds, or, are used to make soups and seasonings. 3. The Phaeophyta, the largest seaweeds are in colour. 4. The is the leaflike part of an algae that is responsible for photosynthesis. 5. The rootlike part of the seaweed that is used for attachment is the 6. Marine algae such as seaweeds are with very simple, unspecialised cells. 7. The green pigment is found in plants and marine algae to help in photosynthesis. 8. The stemlike part of a seaweed where the blade attaches is the 9. The process by which plants and algae produce heir own food with the help of pigments is called 10. Some red algae retard grazing by marine invertebrates by incorporating large amounts of into their cell walls. 11. allow algae to remain upright in the water column during submergence. 12. Cellulose cell walls contain which cushion the thalli against wave action. 13. Photosynthesis: 6[H 2 O] + 6[CO 2 ] = + 6[O 2 ]
RESEARCH PROJECT: Seaweed Uses Present to your fellow class mates the many uses of seaweeds around the world. (poster or talk) Information to consider including in your project: 1. It is evident that most people unknowingly utilise seaweed products daily in the form of many convenience foods. Identify products that have seaweed-based ingredients What type of products contain agar? What types of products contain algin? What types of products contain carrageenan? 2. How many different categories of products can you find that use seaweed as an ingredient? 3. Historically humans have found uses for seaweed for more than a thousand years - can you find any historical uses in you area? 4. Identify three locations where seaweeds are harvested and processed. 5. Discuss: A) Are seaweeds important economically? B) Do you think that advertisers are wise in promoting sea weed as an ingredient in their products? Tips: Do an internet search and check out sites such as: www.algaebase.org www.teara.govt.nz/earthseaandsky/en www.itmonline.org/arts/seaweed.htm Locate and collect packaged food or other products that have algin, agar, carrageenan, xanthan, gum, alginates, etc. listed as ingredients.