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Activity: Structure of Algae with Comparisons to Vascular Plants
NGSS Science and Engineering Practices
NGSS Crosscutting Concepts
NGSS Disciplinary Core Ideas


  • Table 2.4
  • Table 2.5
  • Algae (three types)
  • Aquatic and/or terrestrial vascular plants (optional)
  • Seawater
  • Containers to hold algae at your table
  • Tools provided by your instructor to investigate algae
  • Towels


A. Identify parts of algae

  1. Choose one type of algae to observe.
  2. Fill out the first two columns of Table 2.4 for your alga.
    1. In the ‘Describe’ column of Table 2.4, record general and specific features of your alga.
    2. In the ‘Draw and Label’ column of Table 2.4, draw your alga and label its parts. Label the thallus, blade, holdfast, stipe, and pneumatocysts (using the definitions in Table 2.3 and diagram in Fig. 2.20), when possible, in your drawing.

Fig. 2.20. (A) Diagram showing general alga morphology

Image by Byron Inouye

Table 2.3. Common algae terms
Blade – a large, flattened branch of the thallus (Fig. 2.20)
Calcified – describes an organism with calcium carbonate in its tissue, which often gives it a hard texture
Calcium carbonate – a chemical compound found in some organisms for structure and defense
Dichotomous – a branching pattern where branches are divided in two (Fig. 2.24 C)
Filaments or filamentous –very thin branches that are usually chains of connected single cells (Fig. 2.24 B)
Holdfast – part of the thallus that anchors the plant to the bottom (rock, sand, coral rubble, other plants, or animals; Fig. 2.20)
Midrib – a thickened portion in the center of an alga blade or stipe. The mid rib may look similar to a vein, however it is not true vascular tissue (Fig. 2.21 A).
Pneumatocyst – air bladders used to hold the alga upright in the water (Fig. 2.22 A).
Segmented – visibly divided into separate uniform parts or sections (Fig. 2.22 A).
Stipe – a stem-like structure. Unlike terrestrial plants, the stipe does not have true vascular tissue (Fig. 2.20).
Thallus – main body of the alga
  1. Repeat steps 1 and 2 for at least two more algae.
  2. Ask your instructor where the algae you are examining were collected and for some information about the habitat (if they have not already shared this information with you).
  3. In the “Features that Allow for Survival and Reproduction” column of Table 2.4, list the features that allow the algae to survive and reproduce in its habitat.


B. Compare algae and vascular plants.

  1. Visually inspect the algae and compare it to a vascular plant (from memory, a diagram, or a specimen).
  2. In your group, discuss the similarities and differences between algae and vascular plants.
  3. Fill out Table 2.5 comparing the environment, energy acquisition, structure, movement, dispersal, and reproduction of algae and vascular plants.


Activity Questions
  1. How does the environment of algae differ from the environment of a vascular land plant?
  2. Not all algae have an obvious thallus, blade, holdfast, or stipe. What other algae features would help you distinguish one alga species from another?
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.