ROOT ANATOMY

• The main function of roots is the absorption of water and dissolved nutrients.
• Starting from the outermost layer in a root the first thing we find is the cuticle, which is not a tissue, but a waxy substance that covers all external parts of a plant. Its main function is to protect the plant from water loss and bacterial or fungal infection. In the roots, the cuticle is thin to allow water absorption.
• After the cuticle we find the true tissues of the root, starting on the outside of the cross-section to the inside we find: epidermis, cortex, endodermis with Casparian strips, and the stele or vascular cylinder which is composed of pericycle, xylem and phloem
• Literally translates as outer skin, and it delimits the root, protecting the inner tissues from the outer environment and physical damage. It usually is one cell layer thick.

  Epidermis
• This is the tissue just underneath the epidermis and it is several cell layers thick. The function of this is to store food and water.

  Cortex
• It is literally means the inner skin. It delimits the inner cylinder of the root and it is one single layer of cells. ?

  Endodermis
• The cells of the endodermis are thicker than those in the cortex because the cell walls of the endodermal cells have lignin and suberin (structural plant compounds) that form bands called?


  Casparian trips
• These are a cellular feature found in the roots of all higher plants. They are ring-like, hydrophobic cell wall impregnations. These impregnations occur in the endodermis, an inner cell layer that surrounds the central vascular strand of roots.

  Casparian strips
• The tissue found just inside of the endodermis, commonly one cell thick and it is the first one found on the stele or vascular cylinder. Its main function is to produce lateral roots.


  Pericycle
• The tissue in the middle of the root, usually looking as an X in young eudicots, and arranged in a ring around a central pith in monocots.


  Xylem
• Responsible for water and dissolved nutrient transportation. It transports water upward from the roots to the leaves.


  Xylem
• The tissue that transports the carbohydrates (sugars) produced in photosynthesis throughout the plant. 

  Phloem
• In roots it is usually found in between the xylem in the vascular cylinder.


  Phloem
• Water moves from the soil to the root hairs through a process called 

  Osmosis
• These are essential components of plants and they are available in large quantities.

  Macronutrients 
• In osmosis, water moves through a ______ from a place with more water to a place with less water. Because of the presence of salts and other minerals inside of the root hairs, water is less abundant inside of the cells than on the outside in the soil, where there are less salts and minerals: therefore the water present in the soil moves to the inside of the root hairs. 

  plasma membrane
• Water is transported by the _____?

  xylem
• It is the innermost tissue, found in the middle of the vascular cylinder.

  Xylem
• After water is absorbed by the root hairs it can move through the root tissues using two different routes: between the porous cell walls of the cells (apoplastic transport) or directly from cell to cell (symplastic transport), through tiny pores that join the cells called plasmodesmata. 
• In the dicot root, the xylem is often star-shaped with several arms, and the phloem is situated between the arms of the xylem. In the monocot root, the vascular tissues are arranged in a ring around the central pith.
• Can you identify the following?

  A) Dicot Root

  B) Epidermis

  C) Xylem

  D) Phloem

  E) Cortex

  F) Pericycle

  G) Endodermis

  
• Can you identify the following?

  A) Monocot Root

  B) Epidermis

  C) Cortex

  D) Endodermis

  E) Pericycle

  F) Xylem

  G) Phloem

  H) Pith