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38215_Ward's World+Biology Power Pack

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Page 12 + ward ' s science Make Your Own Algae Beads Recommended Grade Level(s): Appropriate for: 6th Grade–12th Grade Time Requirements: Prep Time: 1 month (mostly passive time while culture incubates) Activity Time: 1 hour (fully prepped) Teaching Topics & Concepts: In this procedure you will create a gel-like bead of algae mixed with sodium alginate; a polysaccharide derived from brown algae (seaweed) that is often used as a thickening agent in food. A drop of this algae mixture will become rigid and "bead-like" by exposing it to Calcium Chloride. Calcium ions (Ca2+) are exchanged with sodium ions (Na+) and replace them in the poly- mer. However, unlike Na+ which can form only one bond, Ca2+ can form two. This allows for cross-linking to occur among the polymer chains which leads to rigidness of the drop and an algae bead as a result! Materials: Safety • Always read the SDS for all chemicals before handling them. • Wear safety glasses, gloves and lab coat or apron. ! Procedure: Day 1—Start Algae Stock Culture • Pour algae Starter Stock into ~1L flask • Place in front of a light source (shouldn't get warm to the touch) • Aerate using an aquarium pump and diffusion stone • Cover the flask opening with foam/cotton to keep out dust. • Allow to grow for approximately 4 weeks. Over this time, it will turn dark green. • As evaporation occurs, add fresh media to the flask to replenish nutrients. Day 28—Prepare Solutions and Equipment 2% Sodium Alginate (by mass) • Add 5g of Sodium Alginate to 250 mL water • Add the alginate to room temperature water while stirring and agitate with stir plate until fully dissolved. This may require up to 24 hours on the stir plate. 3% Calcium Chloride (by mass) • Add 7g CaCl2 to 250mL water • Chill overnight in refrigerator Start Concentrating Your Algae Stock Culture • Your solution should now be a dark green. Remove air tube and re-cover with foam/cotton. • Move the culture to your workspace (room temperature) and allow to sit overnight to settle. • Distilled water (bottled water is also ok) • Powdered Sodium Alginate (for 2% Sodium Alginate Solution) • Stir Plate and Magnetic Stir Bar (for 2% Sodium Alginate Solution) • Powdered Calcium Chloride (for 3% Calcium Chloride Solution) • Culturing Equipment – Algae Starter Stock – 1L flask – Aquarium pump with tubing and air stone – Light (ideally full-spectrum) – Foam/Cotton Plug • Algae Bead Collecting Equipment – Ring Stand – Separatory Funnel – 500mL flask (or larger) – Tea Strainer or Spoon Find materials for this activity at wardsci.com. Discover more free activities at wardsworld.com

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