PLANT ORGAN – ROOT AND STEM
Roots
• A plant’s underground root system, which branches out into the soil from the plant’s
central axis, is often more extensive than its aerial parts.
• The extent of a plant’s root depth and spread varies considerably among species and
even among different individuals in the same species.
• Soil conditions greatly affect the extent of root growth.
• Roots generally grow downward, in the direction of gravity. Anchors a plant securely
in the soil.
Root System
• Two types of root systems—a taproot system and a
fibrous root system—may develop from the
embryonic root (the radicle) in the seed.
Taproot
• Consists of one main root formed from the
enlarging radicle with many smaller lateral
branch roots.
• Lateral roots often occur initially in regular
rows along the length of the main root.
• Characteristic of many eudicots and
gymnosperms.
• A dandelion is a good example of a common herbaceous eudicot with a
taproot system.
• A few trees, such as hickory, retain their taproots, which become quite
massive as the plants age.
• Most trees, have taproots when young and later develop large, shallow lateral
roots from which other root branch off and grow downward.
• Gymnosperms are seed-bearing plants that do not produce flowers.
• Examples: Cone-bearing trees such as pines, hemlock and firs
• Eudicots, these are angiosperms that are flowering plants.
• Examples: Oak, Cherry, Bean and Daisy
Fibrous
• Several to many roots of the same size that develop from the end of the stem,
which smaller lateral roots branching off these roots.
• Form in plants in which the embryonic root is short-lived
• Do not arise from preexisting roots but from the stem, they are called
adventitious.
• Adventitious organs occur in unusual locations, such as roots that develop on a
stem or buds that develop on roots.
• Monocots are grass or grass-like flowering plants
• Ex: Onion, Crabgrass
Funtion
A. Anchorage
PHBIOSC201 – Pharm. Botany w/ Taxonomy Lecture
Rody Rica B. Agdipa, RPh
, •Roots anchor a plant securely in the soil.
•Firm anchorage is essential to a plant’s survival so that the stem remains
upright, enabling leaves to absorb sunlight efficiently.
B. Absorption
• Roots absorb water and dissolved minerals (inorganic nutrients), such as
nitrates, phosphates and sulfates, from the soil.
• These materials are the transported throughout the plant in the xylem.
C. Conduction
• The water and minerals absorbed are conducted by the various parts of the
root and shoot system.
D. Storage
• Surplus carbohydrates produced in the leaves by photosynthesis are
transported in the phloem, as sugar, to the roots for storage, usually as sugar
or starch, until needed.
• Carrot roots have an extensive phloem for this purpose.
• Although roots use some photosynthetic products for their own respiratory
needs, most are stored and later transported out of the roots when the plant
needs it.
• Taproot and fibrous roots may be modified for storing food.
o Taproots – Beets, Carrots, Radishes and Turnips
o Fibrous – Sweet Potatoes
• Storage taproots are usually biennials that, as part of the strategy to survive
winter, store their food reserves in the root during the first year’s growth and
use these reserves to reproduce during the second year’s growth.
Structure
A. Root Cap
• A protective thimble like that layers many cells
thick, covers the delicate root apical meristem.
• As the root grows, pushing its way through the
soil, parenchyma cells of the root cap slough
off by the frictional resistance of the soil
particles and replaced by new cells formed by
the root apical meristem toward its outer side.
• The root cap cells secrete lubricating
polysaccharides that reduce friction as the root
passes through the soil.
• Involved in orienting the root so that it grows
downward.
• When a root cap is removed experimentally,
the root apical meristem grows a new cap. However, until the root cap has
regenerated, the root fails to sense gravity as it grows.
B. Root Hairs
• Short-lived, unicellular extensions of epidermal cells near the growing root tip.
Short, typically less than 1cm or 0.4in in length, but are quite numerous.
• Form continually in the area of cell maturation closest to the root tip to
replace those that are dying off at the more mature end of the root hair zone.
• They greatly raise the absorptive capacity of the root by increasing the surface
area in contact with the moist soil.
PHBIOSC201 – Pharm. Botany w/ Taxonomy Lecture
Rody Rica B. Agdipa, RPh
, Roots of Herbaceous Eudicots
Epidermis
• The root epidermis does not secrete a thick, waxy cuticle. The lack of a cuticle and the
presence of root hairs increase absorption.
• Most of the water that enters the root moves along the path of least resistance –
along the cell walls rather than entering the cells.
• One of the major components of cell walls is cellulose, which absorbs water as sponge
does.
• Lacks a pith, a ground tissue in the centers of many stems and roots.
Cortex
• Ground tissue which is composed primarily of loosely arranged parenchyma cells with
large intercellular spaces, makes up the bulk of the root.
• Lacks supporting collenchyma cells, although it may develop some supporting
sclerenchyma cells as it ages.
• The large intercellular air spaces, provide a pathway for water uptake and allow for
aeration of the root. Primary function of the root cortex is storage.
• The oxygen that root cells need for aerobic respiration diffuses from air spaces in the
soil to the intercellular spaces of the cortex, and from there to the cells of the root.
Endodermis
• Inner layer of cortex which controls the amounts and kinds of water and dissolved
materials that enter the xylem in the root’s center.
• Endodermal cells fit snugly against one another and each cell has a special bandlike
region, called a Casparian strip, on its radial (side) and transverse (upper and lower)
walls. : Casparian Strip is a band of waterproof material that ensure water and
minerals enter the xylem only by passing through the endodermal cells. It contains
suberin. Water enters endodermal cells by osmosis, whereas inorganic minerals enter
by passing through carrier proteins in their plasma membranes.
PHBIOSC201 – Pharm. Botany w/ Taxonomy Lecture
Rody Rica B. Agdipa, RPh
Roots
• A plant’s underground root system, which branches out into the soil from the plant’s
central axis, is often more extensive than its aerial parts.
• The extent of a plant’s root depth and spread varies considerably among species and
even among different individuals in the same species.
• Soil conditions greatly affect the extent of root growth.
• Roots generally grow downward, in the direction of gravity. Anchors a plant securely
in the soil.
Root System
• Two types of root systems—a taproot system and a
fibrous root system—may develop from the
embryonic root (the radicle) in the seed.
Taproot
• Consists of one main root formed from the
enlarging radicle with many smaller lateral
branch roots.
• Lateral roots often occur initially in regular
rows along the length of the main root.
• Characteristic of many eudicots and
gymnosperms.
• A dandelion is a good example of a common herbaceous eudicot with a
taproot system.
• A few trees, such as hickory, retain their taproots, which become quite
massive as the plants age.
• Most trees, have taproots when young and later develop large, shallow lateral
roots from which other root branch off and grow downward.
• Gymnosperms are seed-bearing plants that do not produce flowers.
• Examples: Cone-bearing trees such as pines, hemlock and firs
• Eudicots, these are angiosperms that are flowering plants.
• Examples: Oak, Cherry, Bean and Daisy
Fibrous
• Several to many roots of the same size that develop from the end of the stem,
which smaller lateral roots branching off these roots.
• Form in plants in which the embryonic root is short-lived
• Do not arise from preexisting roots but from the stem, they are called
adventitious.
• Adventitious organs occur in unusual locations, such as roots that develop on a
stem or buds that develop on roots.
• Monocots are grass or grass-like flowering plants
• Ex: Onion, Crabgrass
Funtion
A. Anchorage
PHBIOSC201 – Pharm. Botany w/ Taxonomy Lecture
Rody Rica B. Agdipa, RPh
, •Roots anchor a plant securely in the soil.
•Firm anchorage is essential to a plant’s survival so that the stem remains
upright, enabling leaves to absorb sunlight efficiently.
B. Absorption
• Roots absorb water and dissolved minerals (inorganic nutrients), such as
nitrates, phosphates and sulfates, from the soil.
• These materials are the transported throughout the plant in the xylem.
C. Conduction
• The water and minerals absorbed are conducted by the various parts of the
root and shoot system.
D. Storage
• Surplus carbohydrates produced in the leaves by photosynthesis are
transported in the phloem, as sugar, to the roots for storage, usually as sugar
or starch, until needed.
• Carrot roots have an extensive phloem for this purpose.
• Although roots use some photosynthetic products for their own respiratory
needs, most are stored and later transported out of the roots when the plant
needs it.
• Taproot and fibrous roots may be modified for storing food.
o Taproots – Beets, Carrots, Radishes and Turnips
o Fibrous – Sweet Potatoes
• Storage taproots are usually biennials that, as part of the strategy to survive
winter, store their food reserves in the root during the first year’s growth and
use these reserves to reproduce during the second year’s growth.
Structure
A. Root Cap
• A protective thimble like that layers many cells
thick, covers the delicate root apical meristem.
• As the root grows, pushing its way through the
soil, parenchyma cells of the root cap slough
off by the frictional resistance of the soil
particles and replaced by new cells formed by
the root apical meristem toward its outer side.
• The root cap cells secrete lubricating
polysaccharides that reduce friction as the root
passes through the soil.
• Involved in orienting the root so that it grows
downward.
• When a root cap is removed experimentally,
the root apical meristem grows a new cap. However, until the root cap has
regenerated, the root fails to sense gravity as it grows.
B. Root Hairs
• Short-lived, unicellular extensions of epidermal cells near the growing root tip.
Short, typically less than 1cm or 0.4in in length, but are quite numerous.
• Form continually in the area of cell maturation closest to the root tip to
replace those that are dying off at the more mature end of the root hair zone.
• They greatly raise the absorptive capacity of the root by increasing the surface
area in contact with the moist soil.
PHBIOSC201 – Pharm. Botany w/ Taxonomy Lecture
Rody Rica B. Agdipa, RPh
, Roots of Herbaceous Eudicots
Epidermis
• The root epidermis does not secrete a thick, waxy cuticle. The lack of a cuticle and the
presence of root hairs increase absorption.
• Most of the water that enters the root moves along the path of least resistance –
along the cell walls rather than entering the cells.
• One of the major components of cell walls is cellulose, which absorbs water as sponge
does.
• Lacks a pith, a ground tissue in the centers of many stems and roots.
Cortex
• Ground tissue which is composed primarily of loosely arranged parenchyma cells with
large intercellular spaces, makes up the bulk of the root.
• Lacks supporting collenchyma cells, although it may develop some supporting
sclerenchyma cells as it ages.
• The large intercellular air spaces, provide a pathway for water uptake and allow for
aeration of the root. Primary function of the root cortex is storage.
• The oxygen that root cells need for aerobic respiration diffuses from air spaces in the
soil to the intercellular spaces of the cortex, and from there to the cells of the root.
Endodermis
• Inner layer of cortex which controls the amounts and kinds of water and dissolved
materials that enter the xylem in the root’s center.
• Endodermal cells fit snugly against one another and each cell has a special bandlike
region, called a Casparian strip, on its radial (side) and transverse (upper and lower)
walls. : Casparian Strip is a band of waterproof material that ensure water and
minerals enter the xylem only by passing through the endodermal cells. It contains
suberin. Water enters endodermal cells by osmosis, whereas inorganic minerals enter
by passing through carrier proteins in their plasma membranes.
PHBIOSC201 – Pharm. Botany w/ Taxonomy Lecture
Rody Rica B. Agdipa, RPh
