How do you label a 100× microscope sketch of the red alga Polysiphonia sp. (clade, nutrition, reproduction, cellular/structural organization, chloroplast shape, cell types, and characteristic features)?

What you are trying to identify in Polysiphonia at 100×

At 100× total magnification you usually see a thin, hair-like red algal thallus made of chains of cells. The key is to match what you see (branched filaments with many small chloroplasts, no flagella) to the provided checklist options.

Clade: which major group Polysiphonia belongs to

• Correct choice: Rhodophyta
• Why: Polysiphonia is a classic red alga. Red algae do not have flagellated stages and have distinctive pit connections between cells.

Nutrition: how it gets energy

• Correct choice: autotrophic
• Why: it photosynthesizes (using pigments such as phycoerythrin and chlorophyll $a$).

Reproduction: which modes apply

• Correct choice: both
• Why: Polysiphonia has a complex life cycle with sexual reproduction (gametes and fertilization) and asexual spore stages, including tetraspores.

Cellular and structural organization: what the body looks like

• Cellular organization: multicellular
• Structural organization (choose 2): filamentous and branching
• What to draw/label: a main filament (axis) with side branches, made of repeated box-like or cylindrical cells.

Chloroplast shape: matching the best option

• Correct choice: discoid chloroplast
• What to look for: several small, disc-like plastids per cell rather than a single cup-shaped or spiral chloroplast.

Cell types (choose 2): what you can label on a typical specimen

• Vegetative cells: the regular filament cells forming the branches.
• Tetraspores: round to oval spores (often seen in swollen areas of branchlets in tetrasporangia).

Characteristic features (choose 4): best matches for Polysiphonia

Circle these:

1. cell wall (present in all algae, obvious boundary)
2. pit connections (a red-algae hallmark, connections between adjacent cells)
3. starch grains (red algae store floridean starch, visible as granules in cells)
4. vacuole (common plant-like cell feature)

Features to NOT circle from the list (and why)

• flagella: red algae lack flagella in all life stages
• eyespot: typical of some green algae, not Polysiphonia
• conjugation tube: seen in some green algae (e. g., Spirogyra)
• oogonium: not the correct female structure for red algae (they have carpogonia, not oogonia)
• conceptacle: characteristic of certain algae groups (not typical for Polysiphonia lab ID)