Algae Honor

Nature Study

Requirements

1. Define what algae are.

   Answer: ALGAE are photosynthetic eukaryotic organisms (some prokaryotic, such as cyanobacteria), generally aquatic, that produce oxygen. They range from microscopic unicellular ones (diatoms) to enormous multicellular ones (giant kelp). They are not true plants — they have no roots, stems, leaves, or flowers. They belong to the kingdom Protista (most of them) and are the base of the aquatic food chain. — Algae produce about 70-80% of the planet's oxygen — more than all terrestrial forests combined. Diatoms and cyanobacteria are particularly important. Although they look like plants, biologically they are protists — they merely developed photosynthesis in parallel. The first algae appeared 3.5 billion years ago (cyanobacteria) and were evolutionary precursors of modern terrestrial plants.

2. Where can algae be found?

   Answer: Algae live mainly in AQUATIC environments: 1) SEAS AND OCEANS (kelp, sargassum); 2) FRESH WATER (lakes, rivers, reservoirs); 3) MOIST SOILS; 4) TREE TRUNKS in rainy zones; 5) SYMBIOSIS (lichens with fungi, corals with zooxanthellae); 6) SNOW and ICE (pink snow algae — Chlamydomonas nivalis). Wherever there is water + sunlight, there are algae. — 'Pink snow' (watermelon snow) is a phenomenon on alpine glaciers — Chlamydomonas nivalis algae pigmented red. Lichens (alga + fungus) grow on rocks, roofs, and trunks. The Sargasso Sea (Atlantic) has endless floating algae in the open sea. On the ocean floor (down to 200 m), kelp forests dominate ecosystems. Algae appear wherever there is light and moisture — an extreme adaptation of the kingdom Protista.

3. What is the organ for attaching to the substrate called? What differences and similarities can be found between an alga and a plant?

   Answer: ATTACHMENT organ: HOLDFAST (it is not a root — it does not absorb nutrients, it only anchors the alga to the substrate). DIFFERENCES alga vs. plant: an alga has no root, stem, leaves, flowers, or conducting vessels; it absorbs nutrients through its surface. SIMILARITIES: both carry out photosynthesis (chlorophyll), produce oxygen, and are autotrophs. Algae are considered evolutionary precursors of modern terrestrial plants. — The holdfast is a branched structure that anchors the alga to rock, shells, or other substrates. Plants have a complex vascular system (xylem, phloem) — algae do not. Plants reproduce with flowers and seeds; algae, by spores, fragmentation, or cell division. Terrestrial plants arose from green algae (Chlorophyta) about 470 million years ago. Chloroplasts are shared — a common evolutionary origin.

4. Explain why there is a variation in size among marine algae.

   Answer: Variation in size is due to: 1) SPECIES — microscopic unicellular ones (1-100 µm) vs. enormous multicellular ones (giant kelp up to 60 m); 2) ENVIRONMENT — cold, nutrient-rich waters (Pacific Ocean) sustain large algae; 3) available NUTRIENTS (phosphorus, nitrogen); 4) SUNLIGHT (the photic zone down to 200 m); 5) OCEAN CURRENTS. The largest alga is Macrocystis pyrifera (Californian kelp) at 60 m+. — Macrocystis pyrifera (giant kelp) grows 30-60 cm/day in the cold waters of the North Pacific — one of the highest growth rates in the plant kingdom. Pneumatocysts (gas-filled vesicles) keep the frond floating to receive light. Diatoms (~1 µm) are about 50,000,000x smaller. The variation reflects evolutionary adaptation to different microhabitats in oceans worldwide, governed by light, nutrients, and temperature.

5. Cite at least 4 groups of marine algae. Then make a chart indicating next to each group the following:
   • Common name
   • Scientific name
   • Structure (unicellular, multicellular, or both)

   Answer: 4 groups: 1) GREEN ALGAE (Chlorophyta) — sea lettuce (Ulva lactuca), multicellular; 2) BROWN ALGAE (Phaeophyta) — sargassum (Sargassum), kelp (Macrocystis), multicellular; 3) RED ALGAE (Rhodophyta) — nori (Porphyra), agarophytes, multicellular; 4) DIATOMS (Bacillariophyta) — microscopic unicellular, with a silica wall. Present this in an organized chart. — Chlorophyta (green) are evolutionary relatives of plants — the same pigments. Phaeophyta (brown) have fucoxanthin and live in salt water. Rhodophyta (red) have phycoerythrin and reach greater depths (down to 268 m). Diatoms have an ornamented silica wall that becomes diatomaceous earth (Diatomite). Each group has about 5,000-10,000 species cataloged worldwide today.

6. What are diatoms?

   Answer: DIATOMS are microscopic unicellular algae (10-200 µm) with a SILICA CELL WALL (biological glass) — forming geometrically perfect and unique structures. They live in fresh and salt water, are photosynthetic, and produce 20-50% of the planet's oxygen. Fossilized remains form DIATOMACEOUS EARTH — used in filters, abrasives, and dynamite (discovered by Alfred Nobel in 1867). — There are 100,000+ known species of diatoms. Their silica wall (frustule) has geometric patterns that allow identification under a microscope. Diatomaceous earth (Diatomite) is a mineral used as a pool filter, polisher, and insulator. Alfred Nobel discovered that it absorbed nitroglycerin without instability — the basis of dynamite (1867). Their ecological importance as primary producers is enormous for all oceans.

7. Where do marine algae grow most frequently: the polar, temperate, or tropical zone? Explain.

   Answer: Marine algae grow most in the TEMPERATE and POLAR ZONES (cold waters). Reasons: 1) COLD WATERS retain more dissolved oxygen and nutrients; 2) UPWELLING (the rise of deep waters) brings nitrogen and phosphorus; 3) fewer tropical herbivorous predators. Tropical zones have little algal biomass (nutrient-poor waters), but they have corals and diverse phytoplankton. Kelp thrives in the cold waters of the Pacific. — The US-Canada Pacific coast has giant kelp forests (Macrocystis pyrifera) — algae up to 60 m that sustain ecosystems with sea otters and urchins. The Humboldt (Peru/Chile) and Benguela (Angola/Namibia) upwellings bring cold, nutrient-rich deep waters to the surface. The tropics have clear, nutrient-poor waters — hence the crystalline blue seas and low algal biomass.

8. Where are brown algae most commonly found, in fresh water or salt water?

   Answer: BROWN algae (Phaeophyta) are almost EXCLUSIVELY SALT WATER — found in seas and oceans. Nearly 99% of the ~1,500 species are marine. The brown color comes from fucoxanthin (a pigment) that masks the chlorophyll. Examples: sargassum (Sargasso Sea), kelp (underwater forests), Fucus (intertidal zone). Very few species live in fresh water — an evolutionary adaptation to the saline environment. — The Sargasso Sea (North Atlantic) has 4 million km² of floating Sargassum algae — the only 'sea' without coasts, defined by its vegetation. The kelp forests in California and Tasmania are among the most productive marine ecosystems. Only species of the genera Heribaudiella and Bodanella live in fresh water. Adaptation to salt involves complex osmoregulation — the hypersaline marine environment requires different mechanisms from the freshwater environment.

9. What is the greatest depth at which marine algae grow in the ocean? Explain why algae do not develop in deep waters.

   Answer: Algae grow to a maximum of about 200 meters deep (the photic zone). Reason: they depend on SUNLIGHT for photosynthesis; below 200 m, the light is insufficient (the aphotic zone). Red algae reach greater depths (down to 268 m in the clear waters of the Caribbean) because they have pigments that absorb the blue/green light that penetrates farther. In murky waters, the limit drops to 30-50 m. No light, no photosynthesis, no algae. — The photic zone extends from the surface to about 200 m (sunlight penetration). The depth record for an alga is 268 m (red algae in the Caribbean — 1985 research). Different pigments absorb different wavelengths of light: chlorophyll (red/blue), phycoerythrin (green), fucoxanthin (blue). Red algae with phycoerythrin capture the green-blue light that penetrates deeper. Plankton clouds the water in estuaries, reducing available light.

10. Name 3 parts of a large marine alga. How can they be compared to a leaf, a stem, and a root of a plant?

    Answer: 3 parts of a large alga: 1) HOLDFAST (= root, but it only anchors, does not absorb); 2) STIPE (= stem, connects the holdfast to the frond); 3) FROND/BLADE (= leaf, carries out photosynthesis). In algae such as kelp, there is also a PNEUMATOCYST (air vesicles for floating). Although the appearance is similar to plants, there are no conducting vessels — nutrients move by simple diffusion from cell to cell within the organism. — Despite the visual similarities, ALGAE ARE NOT PLANTS — they are protists with analogous organs by evolutionary convergence. Kelp pneumatocysts (vesicles with CO/O₂ gas) lift the organism from the rock to the surface, optimizing exposure to light. Without conducting vessels (xylem/phloem), the alga depends on osmosis. Vascular plants are a later evolutionary milestone — algae preceded plants by hundreds of millions of years.

11. Explain at least 2 forms of reproduction of marine algae.

    Answer: 2 forms: 1) ASEXUAL — cell division (unicellular algae divide in half), fragmentation (pieces that become new individuals), spores; 2) SEXUAL — male gametes (antherozoids) and female gametes (oospheres) unite to form a zygote that gives rise to a new alga. Some alternate cycles: sexual and asexual generations (alternation of generations). Reproduction varies greatly among groups. — Diatoms reproduce mainly by cell division. Kelp has alternation of generations: the sporophyte (large, diploid) produces spores; the gametophyte (microscopic, haploid) produces gametes. Red algae have complex sexual reproduction with 3 phases (gametophyte, carposporophyte, tetrasporophyte). Asexual reproduction allows rapid expansion; sexual reproduction generates beneficial genetic variability.

12. Cite some commercial benefits that marine algae can provide to humankind.

    Answer: Benefits: 1) human FOOD (sushi, nori, seaweed salad); 2) AGAR (red algae) used in microbiology, desserts, gelatin; 3) CARRAGEENAN — a thickener in dairy products and toothpaste; 4) ALGINATE (brown algae) — a texturizer in foods, textiles, and cosmetics; 5) marine FERTILIZER; 6) BIOFUEL (microalgae in development); 7) MEDICINAL (supplements). — The world algae market generates US$ 13 billion/year. The Korean and Japanese industries cultivate Porphyra (nori) industrially. Spirulina (a microalga) is a protein supplement (60% protein). Carrageenan is in almost all industrial ice creams. Algae biofuel is a scientific frontier — they produce more oil per hectare than soybeans. Medicinal application is growing: anti-inflammatories, antibiotics, and vaccines in development.

13. Put together a collection of at least 10 specimens of algae or identify, by photographs, at least 20. Identify them by their common name and, if possible, their scientific name.

    Answer: You must put together a collection of 10 real algae specimens (preserved in a botanical press/album) OR identify 20 species by photographs. Identify each one with its common and scientific name (if possible). Examples: Ulva (sea lettuce), Sargassum (sargassum), Macrocystis (kelp), Porphyra (nori). Present the organized material to the honor's instructor of the Adventist Pathfinders. — Algae preserve well in an album: 1) wash them thoroughly in seawater to remove sand; 2) press them between sheets of newspaper and boards with weight for 1-2 weeks; 3) glue them onto white card stock. For photography, use guides such as AlgaeBase.org (a free global database). Your own photos at the beach are ideal — note the location and date of the observation. Collecting must respect marine environmental preservation areas.