Lower plants
Algae are lower plants. Their body is not divided into root, stem and leaf; such a body is called a thallus. All algae have a chromatophore holding pigment; by pigment type they are divided into green, brown and red algae. One-celled algae include chlorella and chlamydomonas; many-celled ones include ulothrix, spirogyra, porphyra and laminaria. Chlorella is a round green alga that enriches water with oxygen. Chlamydomonas swims with two flagella, and its red eyespot senses light. Ulothrix is a green thread-like alga that holds to the bottom with a rhizoid; in asexual reproduction it forms flagellated zoospores. Spirogyra is also thread-like, with a chromatophore twisted in a spiral, and multiplies by breaking into pieces. Porphyra is a red alga living in the sea; laminaria is a brown sea alga rich in iodine, nicknamed “sea cabbage”. By photosynthesis algae supply water with oxygen and feed aquatic animals; iodine is obtained from some sea algae and some are used as food.
Diagram: from the word “Algae” draw a two-branch tree – “one-celled” (chlorella, chlamydomonas) and “many-celled” (ulothrix, spirogyra, porphyra, laminaria); colour them by pigment colour. If possible the teacher takes a sample of canal water and shows it under the microscope. Safety: stay by water only with adults; never taste algae or drink green water; keep away from the edge; wash your hands with soap if you touched algae.