Roots

1. Core Definition

  • Root = underground organ responsible for:

    • Anchorage

    • Absorption (water + minerals)

    • Transport

    • Storage

  • Found in vascular plants (have xylem + phloem)

2. Major Functions

A. Anchorage

  • Roots grow downward (positive gravitropism)

  • Spread laterally → stability

  • Prevent soil erosion

B. Absorption

  • Occurs mainly in root hairs

  • Increases surface area

  • Water enters via osmosis

  • Minerals enter via active transport (ATP required)

C. Transport

  • Water + minerals → xylem → shoot

  • Moves through:

    • Symplastic route (cytoplasm, plasmodesmata)

    • Apoplastic route (cell walls, spaces)

D. Storage

  • Stores carbohydrates (starch, sugars)

  • Examples:

    • Carrot

    • Sweet potato

E. Gas Exchange

  • Occurs via:

    • Root hairs (young roots)

    • Lenticels (older roots)

3. Root Structure (Order Matters)

1. Radicle

  • First root from seed (embryonic root)

2. Primary root

  • Main central root (in dicots)

3. Secondary roots

  • Branches from primary root

4. Root Tip Regions (Critical)

A. Root cap

  • Protects tip

  • Pushes through soil

B. Apical meristem

  • Cell division

  • Primary growth (length)

C. Region of elongation

  • Cells lengthen

  • Growth direction controlled by gravity

D. Region of differentiation

  • Cells specialize into tissues:

Tissue

Function

Epidermis

outer layer, absorption

Cortex

storage, transport

Endodermis

selective barrier (Casparian strip)

Stele

vascular system (xylem + phloem + cambium)

5. Casparian Strip (High Yield)

  • Located in endodermis

  • Blocks passive flow

  • Forces materials into symplast

  • Prevents backflow

  • Ensures selective uptake

6. Water & Mineral Uptake

Water

  • Enters via osmosis

  • Moves:

    • Apoplast → blocked at Casparian strip

    • Then forced into symplast

Minerals

  • Enter via active transport

  • Against concentration gradient

  • Requires ATP

  • Causes water to follow (osmosis)

7. Symbiosis

  • Mycorrhiza (fungi) → increase absorption

  • Rhizobium (bacteria) → nitrogen fixation

8. Root Systems

A. Taproot (Dicots)

  • One main root + branches

  • Deep, strong anchor

  • Storage

  • Example: carrot, oak

B. Fibrous (Monocots)

  • Many thin roots

  • Shallow, widespread

  • Prevent erosion

  • Example: grass, corn

9. Specialized Roots

Type

Function

Example

Adventitious

from stem

grasses

Nodal

from nodes

corn

Aerial

above ground

orchids

Pneumatophores

gas exchange

mangroves

Haustorial

parasitic

mistletoe

Storage

food storage

carrot

10. Monocot vs Dicot Roots (Structure)

Feature

Monocot

Dicot

Root type

Fibrous

Taproot

Xylem

Ring

X-shaped center

Pith

Present

Usually absent

Growth

Primary only

Primary + secondary

11. Growth in Roots

Primary Growth

  • From apical meristem

  • Increases length

Secondary Growth

  • From lateral meristems:

    • Vascular cambium → xylem + phloem

    • Cork cambium → protective layer

  • Increases girth (thickness)

12. Key Mechanisms to Memorize

  • Osmosis → water movement

  • Active transport → mineral uptake

  • Casparian strip → control point

  • Apical meristem → length growth

  • Vascular cambium → thickness growth

13. Cause–Effect Logic (Exam Focus)

  • No roots → no water/nutrients → plant dies

  • More root hairs → more absorption

  • Active transport ↑ → mineral uptake ↑ → water follows

  • Removing roots → loss of anchorage + uptake

14. Ultra-Compact Summary

  • Roots = anchor + absorb + transport + store

  • Root hairs = absorption

  • Casparian strip = control

  • Xylem = water up

  • Primary growth = length

  • Secondary growth = thickness

  • Dicots = taproot + secondary growth

  • Monocots = fibrous + primary only