Shoot System — Revision Notes

⚡ 30-Second Revision

Shoot System: — Plumule origin, aerial part.
Components: — Stem, leaves, flowers, fruits.
Stem: — Nodes, Internodes, Buds (Apical, Axillary).
Underground Stems (Storage/Perennation):

- Rhizome: Ginger, Turmeric (horizontal) - Corm: Colocasia, Gladiolus (vertical) - Tuber: Potato ('eyes' = buds) - Bulb: Onion, Garlic (reduced stem disc, fleshy leaves)

Sub-aerial Stems (Vegetative Propagation):

- Runner: Grass, Strawberry (creeping) - Stolon: Mint, Jasmine (arches down) - Offset: Pistia, Eichhornia (aquatic, short thick) - Sucker: Banana, Chrysanthemum (underground base, grows up)

Aerial Stems (Support/Protection/Photosynthesis):

- Tendrils: Grapevine, Gourds (axillary bud modified) - Thorns: Citrus, Bougainvillea (axillary bud modified) - Phylloclade: Opuntia, Euphorbia (multiple internodes, photosynthetic) - Cladode: Asparagus, Ruscus (1-2 internodes, photosynthetic)

Apical Dominance: — Apical bud inhibits lateral bud growth.

2-Minute Revision

The shoot system, originating from the plumule, is the plant's above-ground structure, comprising the stem, leaves, flowers, and fruits. The stem, characterized by nodes and internodes, supports leaves and reproductive structures, and facilitates transport.

Buds (apical, axillary) are crucial for growth and branching. A key concept is apical dominance, where the apical bud inhibits lateral bud growth. Stems undergo various modifications for specialized functions.

Underground stems like rhizomes (ginger), corms (Colocasia), tubers (potato), and bulbs (onion) primarily store food and aid perennation. Sub-aerial stems such as runners (grass), stolons (mint), offsets (Pistia), and suckers (banana) are vital for vegetative propagation.

Aerial stem modifications include tendrils (grapevine) for support, thorns (Bougainvillea) for protection, and photosynthetic structures like phylloclades (Opuntia) and cladodes (Asparagus), which are adapted to reduce water loss in arid environments.

Remembering specific plant examples for each modification is critical for NEET.

5-Minute Revision

The shoot system, the aerial part of a plant, develops from the embryonic plumule and is essential for photosynthesis, reproduction, and transport. Its main components are the stem, leaves, flowers, and fruits.

The stem is the central axis, featuring nodes (points of origin for leaves/branches) and internodes (segments between nodes). Buds are undeveloped shoots: apical buds at the tip drive vertical growth, while axillary buds in leaf axils can form branches or flowers.

Apical dominance, mediated by auxin, is the phenomenon where the apical bud suppresses lateral bud growth.

Stem modifications are a high-yield area. They are categorized by their position and function:

1
Underground Stems (Storage & Perennation):

* Rhizome: Horizontal, fleshy stem with nodes/internodes. Ex: Ginger, Turmeric. * Corm: Vertical, condensed, fleshy stem. Ex: Colocasia, Gladiolus. * Tuber: Swollen tip of an underground branch, with 'eyes' (buds). Ex: Potato. * Bulb: Reduced disc-like stem with fleshy scale leaves. Ex: Onion, Garlic.

1
Sub-aerial Stems (Vegetative Propagation):

* Runner: Creeping stem, roots at nodes. Ex: Grass, Strawberry. * Stolon: Arches down to form new plant. Ex: Mint, Jasmine. * Offset: Short, thick runner in aquatics. Ex: *Pistia*, *Eichhornia*. * Sucker: Arises from underground base, grows obliquely up. Ex: Banana, Chrysanthemum.

1
Aerial Stems (Support, Protection, Photosynthesis):

* Stem Tendrils: Coiled structures for climbing, from axillary buds. Ex: Grapevine, Gourds. * Thorns: Hard, pointed, woody structures for protection, from axillary buds. Ex: *Citrus*, *Bougainvillea*. * Phylloclade: Flattened/cylindrical green stem, multiple internodes, photosynthetic. Ex: *Opuntia*, *Euphorbia*. * Cladode: Phylloclade with 1-2 internodes. Ex: *Asparagus*, *Ruscus*.

Worked Example: Identify the stem modification in a potato. A potato is an underground, swollen structure. Upon closer inspection, it has 'eyes' which are actually nodes with axillary buds. This confirms it is a stem tuber, not a root, as roots lack nodes and buds. Its primary function is food storage (starch) and vegetative propagation through these buds.

Prelims Revision Notes

Shoot System: NEET Quick Recall Notes

I. Basic Structure & Components:

Origin: — Plumule of embryo.
Main Axis: — Stem.
Stem Features:

* Nodes: Points where leaves/branches arise. * Internodes: Region between two nodes. * Buds: Undeveloped shoots. * Apical (Terminal) Bud: At stem apex, for vertical growth. Exhibits apical dominance. * Axillary (Lateral) Bud: In leaf axil, forms branches/flowers. * Accessory Buds: Extra buds in axil. * Adventitious Buds: Develop at unusual places (e.g., roots, old stems).

Leaves: — Photosynthetic organs, borne at nodes.
Flowers: — Reproductive structures.
Fruits: — Developed ovary, encloses seeds.

II. Functions:

Photosynthesis (leaves)
Support (stem)
Conduction (xylem, phloem)
Reproduction (flowers, vegetative propagation)
Storage (modified stems)
Protection (thorns)

III. Stem Modifications (Crucial for NEET):

A. Underground Stem Modifications (Storage & Perennation):

1
Rhizome: — Horizontal, fleshy, nodes, internodes, scale leaves, axillary buds. Ex: Ginger, Turmeric, Banana, Canna.
2
Corm: — Vertical, condensed, fleshy, nodes, internodes, dry scale leaves. Ex: Colocasia (Arvi), Amorphophallus (Suran), Crocus, Gladiolus.
3
Tuber: — Swollen terminal part of underground branch, stores food (starch), has 'eyes' (nodes with axillary buds). Ex: Potato.
4
Bulb: — Highly condensed disc-shaped stem, fleshy scale leaves store food, adventitious roots at base. Ex: Onion, Garlic.

B. Sub-aerial Stem Modifications (Vegetative Propagation):

1
Runner: — Slender, prostrate, creeps on ground, roots at nodes, new plants at intervals. Ex: **Grasses (*Cynodon dactylon*), Strawberry, Oxalis.**
2
Stolon: — Slender lateral branch, grows aerially then arches down to ground. Ex: Mint, Jasmine.
3
Offset: — Short, thick, prostrate lateral branch, aquatic plants, rosette of leaves & roots at apex. Ex: Pistia, Eichhornia (Water Hyacinth).
4
Sucker: — Lateral branch from underground base, grows obliquely upwards. Ex: Chrysanthemum, Banana, Pineapple.

C. Aerial Stem Modifications (Support, Protection, Photosynthesis):

1
Stem Tendrils: — Thin, wiry, spirally coiled, from axillary bud, for climbing. Ex: Gourds (Cucumber, Pumpkin, Watermelon), Grapevine.
2
Thorns: — Hard, pointed, woody, from axillary bud, for protection. Ex: Citrus, Bougainvillea.
3
Phylloclade: — Flattened/cylindrical, green stem, multiple internodes, photosynthetic. Ex: Opuntia, Euphorbia.
4
Cladode: — Phylloclade with 1-2 internodes, photosynthetic. Ex: Asparagus, Ruscus.

IV. Key Distinctions & Misconceptions:

Potato vs. Sweet Potato: — Potato = stem tuber (has 'eyes'); Sweet Potato = root tuber (no 'eyes').
Onion: — Bulb (modified stem + fleshy leaves), not a root.
Stem Tendril vs. Leaf Tendril: — Stem tendril (axillary bud, e.g., Grapevine); Leaf tendril (leaf/leaflet, e.g., Pea).
Phylloclade vs. Cladode: — Phylloclade (multiple internodes); Cladode (1-2 internodes).

Vyyuha Quick Recall

To remember the common underground stem modifications and their examples:

Really Cool Teachers Bring Good Potatoes Often.

Rhizome: Ginger
Corm: Gladiolus (or Colocasia)
Tuber: Potato
Bulb: Onion