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Morphology of Stem Class 11: NCERT Notes, Functions & NEET MCQs

🌿 Morphology of Stem — Class 11 Biology

A simple NCERT-focused guide to the structure, functions, regions, modifications and important examples of stems, followed by NEET-style practice questions.

The stem is one of the major vegetative parts of a flowering plant. It develops from the plumule of the embryo and normally grows upward, although modified stems may show very different forms.

For NEET and Class 11 Biology, morphology becomes much easier when you connect structure + function + example instead of memorising isolated facts.

1. Stem: Structure and Main Functions

The stem is generally the ascending part of the plant axis. It bears branches, leaves, flowers and fruits and contains nodes and internodes.

Important Parts of a Stem

Part Meaning
Node The region of the stem where leaves or branches arise.
Internode The portion of stem between two successive nodes.
Terminal bud A bud present at the tip of the stem or branch.
Axillary bud A bud present in the axil of a leaf.

Main Functions of the Stem

  • Supports leaves, flowers and fruits.
  • Helps transport water and minerals.
  • Transports organic substances.
  • Provides mechanical support.
  • May perform photosynthesis when green.
  • Some stems become modified for storage, protection or vegetative propagation.
🧠 Easy Memory Rule:

Node = leaf/branch region
Internode = region between two nodes

2. Stem Modifications: Important NCERT Examples

Stems can be modified to perform functions other than their usual functions. These modifications are particularly important for NEET because students often have to identify the modification from an example.

A. Underground Stem Modifications

Underground stems commonly help in storage and perennation. They may also help in vegetative propagation.

Modification Example Key Feature
Rhizome Ginger Underground horizontal stem
Tuber Potato Swollen underground stem
Bulb Onion Short stem with fleshy storage leaves
Corm Colocasia Short, swollen underground stem

How to Identify Potato as a Stem

Potato is a modified stem because it possesses eyes, which represent buds. The presence of these buds helps distinguish the tuber from a modified root.

🌱 NEET Memory Point:

Potato → Tuber → Modified stem → Eyes = Buds

B. Sub-Aerial Stem Modifications

Some stems develop close to the ground and can help in vegetative propagation. Examples include runner, stolon, sucker and offset.

  • Runner: develops horizontally along the soil surface.
  • Stolon: lateral branches that arise from the base and may produce new plants.
  • Sucker: develops from underground portions and grows obliquely upward.
  • Offset: short lateral branch with distinct nodes and internodes, commonly seen in aquatic plants.

C. Stem Modifications for Protection

In some plants, branches or parts of the stem become modified into thorns. They help protect the plant from herbivores.

Examples include Citrus and Bougainvillea.

D. Stem Tendrils

In some plants, stems become modified into tendrils that help the plant climb.

This modification is useful because the plant can obtain support from surrounding structures.

3. Stem Modifications: Quick Comparison for NEET

Type Function Example
Rhizome Storage / perennation Ginger
Tuber Storage Potato
Bulb Storage Onion
Corm Storage / perennation Colocasia
Thorn Protection Citrus
Tendril Climbing Stem tendrils in climbing plants

4. NEET Biology MCQs on Morphology of Stem

Test yourself before checking the answers. Try to answer each question from memory.

Q1. The region of the stem where leaves arise is called:

A. Internode
B. Node
C. Petiole
D. Lamina

Answer: B. Node

Q2. Potato is considered a modified stem because it possesses:

A. Root hairs
B. Lateral roots
C. Eyes or buds
D. Root cap

Answer: C. Eyes or buds

Q3. Ginger is an example of:

A. Tuber
B. Bulb
C. Rhizome
D. Corm

Answer: C. Rhizome

Q4. Onion represents which type of stem modification?

A. Bulb
B. Tuber
C. Runner
D. Rhizome

Answer: A. Bulb

Q5. Which modification primarily helps climbing plants?

A. Thorn
B. Tendril
C. Tuber
D. Bulb

Answer: B. Tendril

Q6. Thorns in plants such as Citrus are modified:

A. Roots
B. Leaves only
C. Branches or stem structures
D. Flowers

Answer: C. Branches or stem structures

🎯 30-Second Revision

Node → leaf/branch arises
Internode → between two nodes
Potato → tuber + eyes
Ginger → rhizome
Onion → bulb
Colocasia → corm
Citrus → thorn
Climbing → stem tendril

🔗 Continue Your NEET Biology Preparation

This article is part of the NEET Biology for Odisha Students learning series.

Go to NEET Biology Study Hub →

Frequently Asked Questions

What is a node in a stem?

A node is the region of the stem from which leaves or branches arise.

What is an internode?

An internode is the portion of the stem between two successive nodes.

Why is potato considered a stem?

Potato is a modified underground stem because it has eyes, which represent buds.

What is a rhizome?

A rhizome is a modified underground stem that generally grows horizontally and can help in storage and perennation. Ginger is a common example.

Why are stems modified?

Stems may become modified for functions such as storage, perennation, vegetative propagation, protection and climbing.

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