Transcript Unit A - Central CUSD 4

Unit A
Horticultural Science
Horticulture CD
Problem Area 2
Plant Anatomy and Physiology
Lesson 2
Understanding Root Anatomy
Interest Approach
Take a look at this plant that I have just
knocked out of its pot.
How is the soil being held in place?
What can you see in the soil and on the
roots?
Take a look at the roots under a
stereomicroscope. Draw a picture of
what you see.
Why do the roots look hairy?
Vocabulary
Apical meristem
Epidermis
Fibrous root system
Primary root
Root cap
Root hairs
Secondary roots
Taproot system
Student Objectives
1. List the functions of roots in plants.
2. Identify the parts of a root.
3. Identify the two major types of root
systems.
4. Recognize a healthy root system.
What Are the Functions of a
Plant’s Roots?
A plant’s health is directly
related to its roots


A pot bound plant in
need of transplanting
Courtesy of Delmar Publishing
Weak and diseased roots
decrease a plant’s health
Roots need to continuously
grow in order to stay
healthy
 This is why plants become
pot-bound: the roots start
growing out of the pot
because it is too small
Functions of a Root System
1. Absorb water and
minerals from the
environment
2. Anchor the plant in
the ground
3. Store food that has
been made in the
leaves by
photosynthesis

Can be used later by the
plant to grow and
survive
Taraxacum officinale – the
common dandelion
Courtesy of Wm. C. Brown Publishers
What Are the Parts of a Root?
When a seed
germinates, the first
structure to appear is the
root, or radicle

A. It becomes the
primary root
 Usually the most
important root in some
plants
Cotyledon
Radicle = Primary
root; notice all the
root hairs
Courtesy of McGraw Hill

B. Other roots branch out
from the primary root;
called secondary roots
Vascular
cylinder
(xylem &
phloem)

C. The apical
meristem, found at
the root tip, is where
new cells develop
Epidermis
 It is covered by the
root cap – protects it
from damage as it
passes through
coarse soil particles
Apical
meristem
Root Cap
Courtesy of Dorling Kindersley, Inc.
Cortex
(food
storage)

Epidermis
D. The surface of the root
is protected by skin cells
called the epidermis
 Where water and minerals
enter the root by osmosis
& diffusion
 Can grow long, hair like
projections called root
hairs
 They greatly increase
the surface area of the
root to allow more
water intake
Courtesy of Delmar Publishing
There are three major zones of root
development

1. Region of Cell Division – this is where the cells
start to divide through mitosis
 Remember, this is where the apical meristem is located

2. Region of Elongation – in this area just above the
apical meristem, cells become longer and wider
 This action helps to push the root tip through the soil

3. Region of Maturation – at this point, the cells
become specialized, or differentiated, taking on
specific primary functions
 For example, the development of root hairs, xylem,
phloem, etc.
Regions of Cell Development
Region of
Maturation
Region of
Elongation
Root
Cap
Region of
Cell Division
Apical
meristem
Notice that cell
division occurs
at the tip of the
root
Older cells are
found farther
away from the
root tip
Courtesy of McGraw
Hill Publishers
There are several other layers of cells found
within the root



A. Cortex – this is where the root stores the food
produced by the leaves; it is made out of
parenchyma tissue
B. Endodermis – the inner boundary of the cortex;
one cell layer thick; controls the movement of
water and minerals into the xylem and phloem
C. Pericycle – a layer found inside the
endodermis which may produce lateral roots; also
produces vascular cambium in dicots

D. Vascular cylinder, or stele – forms the
central cylinder of the root; it is made out of
two secondary transport tissues
 1. Xylem – carries the water taken in by the
root hairs and epidermis up the plant to the
stems and leaves
 2. Phloem – carries the food produced by the
leaves down to the roots to be stored in the
cortex
Internal Layers of the Root
Lateral Root
Vascular
Cylinder
Xylem
Phloem
Pericycle
Endodermis
Cortex
Root Hairs
What Are the Two Types of Root
Systems?
Plant root systems are organized in two
basic ways; It has to do with primary
and secondary roots

A. A root system comprising one main
primary root and many secondary roots
branching off the primary root is called a
taproot system
 Ex. Carrot, Parsnip, Oak
 Their roots reach far into the ground; they can
be several feet long
Examples of Taproots
Carrot
Beet
Sweet potato
Courtesy of Wm. C. Brown Publishers

B. A system which has no
dominant primary root but is
made of many primary and
secondary roots of similar size
is called a fibrous root system
 Ex. Grasses, Magnolia,
Rhododendron, Euonymus
 The roots are smaller, shorter and
more compact; They usually never
grow below the first 6-12 inches of
soil
Fibrous root system of
grass
Courtesy of McGraw Hill Publishing

These roots form a large network
underground
What Does a Healthy Root
System Look Like?
A healthy root system is white or nearly white
in color and smells fresh, or earthy
If roots are black, brown, or dark orange and
smell rotten or sour, the root system is having
some problems
Watering a plant properly is one of the most
important ways to keep the root system
healthy

If the plants are grown in pots, be sure that there
are drainage holes in the bottom to allow excess
water to drain
 Soak the pot until the growing medium is saturated and
water drips out of the drainage holes
 This encourages the roots to grow through the entire pot

Allow the pot to dry out slightly between watering
 Watering too frequently is a common cause of root death
 Medium that is kept wet has limited air exchange; the
root tissues die for lack of air.
Summary
What are the three functions of a root?
What is another name for a primary
root?
In the tip of the root, what kinds of cells
are the only ones that divide?
What is the epidermis and what is its
function?
Where do root hairs grow from?
Summary
Why does a plant have to have numerous
root hairs instead of just two or three?
Pretend you are a water molecule and you
need to get into the center of the root. What
are all the layers you must go through before
reaching the center?
Describe the functions of the xylem and
phloem.
Where is food stored in the root?