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Roots—Chapter 5
vocabulary
 Adventitious root
 Fibrous root system
 Lateral root
 Mycorrhiza
 Prop root
 Radicle
 Root apical meristem
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Root cap
Root hair
Tap root
Zone of elongation
Pericycle
Endodermis
Root nodule
Function of Roots

Three main functions
◦ Anchor the plant in the ground
◦ Absorb water and minerals
◦ Produce hormones
Root System types

Taproot system-a single prominent root
that is bigger than the rest
◦ Examples: radish, carrot

Fibrous root system- mass of roots that
are very similarly sized
◦ Examples: onions, Palm trees, grasses

Monocots have only fibrous roots
because they are not capable of
secondary growth. Therefore, they only
grow primarily, or upward (downward)
once.

Dicots are capable of secondary growth,
or growing outward, so a large primary
root could grow very large. May have
both types of roots
Fibrous v. Tap Roots

Root systems will generally exist as a
function of the environment and the
organism.
◦ Plants that grow where rain is plentiful will often
grow roots closer to the surface.
◦ Plants that grow where rain is seasonal will often
grow deep roots top access under ground water.
Taproots
 Develops
from a
radicle, or
embryonic seed
root
 Lateral Roots:
Roots that branch
off of the primary
root.
Fibrous Root system
 Roots
do not grow from a
radicle.
 Radicle disappears shortly
after germination
Adventitious Roots

Roots that
do not arise
on preexisting
roots and
not part of
the radicles
Tubers

A tuber is a thickened
underground stem, and
the stem tissue serves
as the primary storage
tissue. Meristems
(where new shoots
grow) occur on the
tuber and are
commonly called "eyes"
on a potato.
Rhizome
A
rhizome is a
modified stem, and
the stem tissue itself
is the primary storage
tissue. The rhizome,
however, is unique in
that it grows
horizontally through
soil
Prop Roots
 Roots
that are partly exposed in the air
 Used to help support the plant
Aerial Roots
 Roots
that are
entirely exposed
above the ground.
 Special cells on the
outside of the root,
called velamen,
prevent the roots
from drying out
Mycorrhizae
 Roots
of 80% of all seed plants have a
symbiotic relationship with soil fungi,
both benefit.
 Plant gains phosphorus and other
minerals that it normally can’t absorb
efficiently
 Fungi gets sugars from photosynthesis
in return
Root Nodules
 Some
plants have the ability to grow
nitrogen fixing bacteria in their roots.
(The original farmers?)
 Roots swell to accommodate bacteria
 Even though 78% of the atmosphere is
nitrogen, plants can’t use it.
 The bacteria can take it out of the
atmosphere a fix it into usable forms like
ammonia
Parasitic plants
 Some
plants can actually be parasites
on other types of plants
 Haustoria- Roots of parasitic plants
are modified to penetrate other
plants and absorb nutrients.
---------------------------------------------- Dodder—parasitic on wheat
 Mistletoe—parasitic on
trees…hmmm
Root hairs

Root hairs are extensions of the epidermis
◦ Greatly increases surface area.
 Aids in anchoring the plant
 Aids in absorbing water and nutrients