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Revision Notes

Shoot System

NIOS · Class 12 · Biology

Quick revision notes for Shoot System — NIOS Class 12 Biology. Key concepts, formulas, and definitions for last-minute revision.

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Key Topics to Revise

1

7.1 STEM - Structure, Types, and Functions

  • Stem arises from plumule and grows upward (positively phototropic and negatively geotropic)
  • Divided into nodes (leaf attachment points) and internodes (regions between nodes)
  • Bears leaves, buds (vegetative and floral), and flowers on nodes
2

Stem Modifications - Adaptations for Specific Functions

  • Underground modifications: Rhizome (horizontal, near soil surface), Corm (vertical, spherical), Bulb (compressed, fleshy scales), Tuber (swollen tips, eyes present)
  • Sub-aerial modifications: Runner (long internodes, adventitious roots at nodes), Stolon (weak, arches down), Offset (thick, short), Sucker (underground runner emerging upward)
  • Aerial modifications: Tendril (spirally coiled, climbing), Thorn (pointed, defense), Phylloclade (green, fleshy, photosynthetic), Cladode (phylloclade with 1-2 internodes)
3

Anatomy of Stem - Internal Structure

  • Dicot stem (e.g., sunflower): Epidermis → Cortex (Hypodermis + Middle layers + Endodermis) → Stele (Pericycle + Ring of Vascular bundles + Medullary rays + Pith)
  • Vascular bundles in dicot: Conjoint (xylem and phloem together), Collateral (on same radius, phloem outside), Open (cambium present for secondary growth)
  • Monocot stem (e.g., maize): Epidermis → Ground tissue (undifferentiated) with scattered, closed vascular bundles each surrounded by sclerenchymatous bundle sheath
4

Secondary Growth and Wood Formation

  • Secondary growth increases stem girth; occurs only in dicots a little away from apex
  • Two lateral meristems responsible: Vascular cambium (produces secondary xylem and phloem) and Cork cambium/Phellogen (produces periderm)
  • Fascicular cambium present in vascular bundles; interfascicular cambium develops in medullary rays

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Key Concepts

A stem is the main axisThe shoot apex is the terminalStems are classified asIn transverse sectionA monocot stem (e

Frequently Asked Questions

What are the important topics in Shoot System for NIOS Class 12 Biology?
Shoot System covers several key topics that are frequently asked in NIOS Class 12 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in Shoot System — NIOS Class 12 Biology?
Start by understanding all key concepts. Practise previous year questions from this chapter. Revise formulas and definitions regularly. Use flashcards for quick revision before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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