Which of the following is a stem?

Ginger is the correct answer. The part we use is a rhizome, an underground stem that grows horizontally, has nodes and scale leaves, and sends out roots and shoots from its nodes. If you see nodes or buds, you are looking at a stem.

• Turnip is a taproot. The swollen part is the primary root storing food, so it is a root.
• Carrot is also a taproot, with the storage organ formed from the primary root.
• Sweet potato is a tuberous root, an adventitious root swollen with stored starch. Do not confuse it with the potato, which is a stem tuber.

The core concept is modification of plant parts for storage and vegetative propagation. Rhizomes (ginger, turmeric), stem tubers (potato), corms (colocasia) and bulbs (onion) are modified stems. Taproots (carrot, radish) and tuberous roots (sweet potato) are modified roots. This connects to Botany in General Studies and to crop propagation questions in Agriculture optional, where ginger and turmeric are propagated through rhizome pieces.

Trap: Candidates see a swollen underground organ and assume it must be a root. Check for nodes, buds and scale leaves before deciding.