The organism with spiral chloroplasts and nucleus suspended by cytoplasmic strands is

Analyze the question: We need the organism with two features: (1) chloroplasts shaped like a spiral ribbon, and (2) a nucleus suspended in the cell's center by cytoplasmic strands.

Explain the concept: Spirogyra is a filamentous green alga found in ponds and slow-moving freshwater. Its name comes from its spiral (helical) chloroplasts. Each cell has a large central vacuole, and the nucleus is held in the middle of the cell by thin strands of cytoplasm that stretch across the vacuole.

Go through the options:

• A. Volvox: A spherical colony of many flagellated cells. Each cell has a single cup-shaped chloroplast, not a spiral one.
• B. Spirogyra: Has ribbon-like spiral chloroplasts, and its nucleus is suspended in the center by cytoplasmic strands. This fits both clues.
• C. Paramecium: A slipper-shaped protozoan with no chloroplasts at all. It is not photosynthetic.
• D. Euglena: Has several disc-shaped or star-shaped chloroplasts and a flagellum. Its nucleus is not suspended by strands.

Answer: The correct option is B. Spirogyra.

Tip: Link the name to the feature: Spiro-gyra means "spiral" (think of a coil). If a question mentions spiral or ribbon-shaped chloroplasts, think Spirogyra right away.