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HOW DO WE KNOW AQUATIC PLANTS PRODUCE OXYGEN IN SUNLIGHT? Objectives: To demonstrate that plant produces oxygen. QCC: S.7.14, S.7.19 Time required: One class period Background:Green plants are critical to other life on this planet because they form the basis of all food webs. Most plants are autotrophic, creating their own food using water, carbon dioxide, and light through a process called photosynthesis. Also, the photosynthesis process produces the all essential life-supporting oxygen that is required by all living organisms. Plants are divided into several kingdoms: Plantae, Protista, and Fungi. Most aquatic plants occur in the kingdoms of Plantae and Protista. Plants in the kingdom "Plantae" include organisms that range in size from a tiny moss to the giant sequoias of California that reach 90 meters (300ft) or more in height. There are approximately 275,000 to 300,000 different species of plants. All plants are multicellular and eukaryotic (i.e., each cell possesses a membrane-bound nucleus that contains the chromosomes). They generally possess chlorophyll and carotenoid pigments, which play a central role in converting the radiant energy of sunlight into sugars, a form of chemical energy, by means of photosynthesis. Plants, therefore, are independent in their nutritional needs (autotrophic) and store their excess food in the form of macromolecules of starch. By aquatic plants we may mean the plants that grow under water, i.e. obligate submersed. But most aquatic plants fall into the group referred to as amphibious plants which are capable of growth both in and under water (submerged) and out of water (emersed), with only their root wet or damp. Aquatic plants are plants that require a water environment to complete all or most of their life cycle. Based upon growth form, these plants can be divided into four types: emergent/emersed, submerged, floating-leaf, and free-floating. Emergent/emersed plants extend above the water surface in shallow areas of lakes, ponds, and ditches. They have relatively rigid stems and do not rely on the water for support. Leaves of this group of plants are essentially like typical leaves of herbaceous angiosperms. The leaves may be amphistomatic (stomata on both surfaces) and have well developed mesophyll to take advantage of the abundant sunlight. Cattails, bulrushes, buttercups, wetland irises are few examples of emergent aquatic plants. Submerged aquatic plants have flexible stems and leaves, are rooted in the sediments, and are completely covered by water. Leaves of underwater plants are often highly dissected to increase the surface area to permit rapid diffusion of carbon dioxide into the chloroplasts of the cell. Examples of submerged aquatic plants are: water buttercups, water milfoils, bladderwort, pond weed etc. Rooted-floating leaf or floating-leaf plants have their roots in the mud or muck while their leaves float on the water. Rooted-floating plants lack stem rigidity and depend on the water for support. These plants usually extend out of the water like emergent plants but have floating leaves. Plants such as bur-reeds, water plantains, and arrow-heads are examples of rooted-floating plants. Free-floating plants obtain their nutrients directly from the water, since they are not rooted to the soil or muck. Examples of free-floating aquatic plants or macrophytes are water hyacinth, water-lettuce and duckweed, a small plant often mistaken for algae. Floating leaves tend to be much broader, without much lobing, and remain flat on the water to take advantage of sun. Stomatas are present on the upper leaf surface for gas exchange, and the upper leaf surface tends to have a very prominent epidermis or cuticle to permit water to roll off or prevent growth of epiphytic algae that interfere with photosynthesis on the leaves. Floating leaves often have lacunae (air chambers) to provide buoyancy, and sclerids (hard cells) within the mesophylls to provide toughness to leaves and prevent from collapsing. Algae (singular alga) are a group of predominantly aquatic, photosynthetic organisms that do not have a precise definition. They range in size from the tiny flagellate Micromonas that is 1 micrometer (0.00004 inch) in diameter to giant kelp that reach 60 meters (200 feet) in length. At one time the photosynthetic aquatic organisms commonly referred to as algae were considered members of the plant kingdom; however the concept of what constitutes a plant has undergone significant change over time. The various major algal groups, such as the green algae, brown algae, and red algae, are now placed in the kingdom "Protista" because they lack one or more of the features that are characteristic of plants. Algae lack true roots, stems, and leaves, but they share this feature with the plant division Bryophyta. The algae have many types of life cycles, from simple to complex. Like all green plants, algae use photosynthesis to form organic food molecules from carbon dioxide and water, and provide oxygen to the atmosphere as a byproduct of photosynthesis. It is estimated that algae produce about 30 to 50 percent of the net (difference between production and use) global oxygen--which is available to humans and other terrestrial animals for respiration, and help burn coal, wood, or oil. Although terrestrial (land) ecosystems produce large amounts of oxygen, the organisms living in these ecosystems consume it relatively rapidly. Therefore the net oxygen production by terrestrial plants over time is low as compared to algae, which are primarily aquatic. Algae are an important food base in the aquatic food-web for almost all aquatic life forms, e.g. fishes, insects and other micro-invertebrates etc. Their importance as the base of the food chain (food web) is even greater for marine organisms, since most plants do not grow or live in oceans. Also, algae has important human use as food and a commercial resource. Knowledge and use of algae is considered as old as humankind (Homo sapiens). Approximately 500 species are eaten by humans, and some 160 are commercially important. Seaweeds are eaten by coastal societies, and algae are considered acceptable foods in many restaurants. Algae are a significant food item in the diets of East Asian and Pacific Island societies, South Americans, North Americans, and northern Europeans. Hawaiians are considered to have the most diverse diet of algae. Besides the importance of algae as the base for aquatic food chain, it is an important source for fossil fuel. Crude and natural gas are the remnants of the photosynthetic products of ancient algae, which were subsequently modified by bacteria. The North Sea Oil deposits and the Colorado oil shales were formed from algae. Today, a green alga (Botryococcus) which blooms in Lake Baikal in Russia produces large amounts of oil which is collected with a special skimming apparatus. Several companies have grown oil-producing algae in high-salinity ponds and have extracted the oil as an alternative to fossil fuels. Aquatic plants provide both benefits and problems. Some benefits from aquatic plants include:
However, aquatic plants cause problems when excessive growth takes place.
Activities Experiment 1. Materials required:
Experiment 2 Materials required:
Aquatic Plants (Types based on growth form, importance of aquatic plants, problem caused by too many aquatic plants, what you can do) Aquatic Plants (Characteristics of a Freshwater Environment, types of leaves, life forms of aquatic plants,) http://www.botgard.ucla.edu/html/botanytextbooks/lifeforms/aquaticplants/fulltextonly.html Uses and Benefits of Aquatic Plants http://www.ecy.wa.gov/programs/wq/plants/native/uses.html Watershed Education Resources on the Internet (Links) Benefits and Detriments of Aquatic and Wetland Plants Algae (General Introduction and Description) Photosynthesis and Transpiration Made Easy Links to Photosynthesis sites Ask a Scientist a Question Plants and Algae Questions http://oceanlink.island.net/ask/algae.html UCMP Glossary of Natural History terms Smith, Roger. 1994. Strands in the Web: 201 Activities for Teaching Environment Awareness. Ontario: Pippin Publishing Limited. |
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