Warmup 10/26/15
Tell me a story about roots
Objective
To learn how the roots of
plants function
Tonight’s Homework
pp 310: 1, 2, 3, 4
Notes on Roots
If leaves are for chlorophyll, then what are roots
for?
Notes on Roots
If leaves are for chlorophyll, then what are roots
for?
Roots serve 4 purposes:
- To anchor the plant (not necessarily in soil)
- To absorb water and dissolved minerals
- Transport absorbed substances where needed
- Store food and starches
Notes on Roots
Types of Roots
There are exceptions, but generally roots come
in two basic types:
Notes on Roots
Types of Roots
There are exceptions, but generally roots come
in two basic types:
- A taproot system:
These plants have one large
root.
Secondary roots may or may
not grow out of it, but the main
root is always biggest.
Notes on Roots
- A fibrous system:
In these plants there is no
main root. As the plant
grows, it sends more roots
out from the base or
lengthens the existing roots.
Notes on Roots
As a general rule, roots grow out instead of
down.
A 4-month-old corn plant may have more than
150 meters of roots, barely extending farther
than 5 feet down.
Notes on Roots
Root Growth
Roots have 4 regions that
dictate their growth.
Notes on Roots
Root Growth
Roots have 4 regions that
dictate their growth.
- The root cap is a thick
mass of dead cells. These
protect the root as it
pushes through hard soil.
Notes on Roots
- The meristematic region
is the part going through
new growth. These cells
are rapidly dividing. This
is the part of the root
that is actually new.
Notes on Roots
- The meristematic region
is the part going through
new growth. These cells
are rapidly dividing. This
is the part of the root
that is actually new.
- The elongation region is
where the root becomes
longer. The cells here are
still fairly new and are
filling with water,
stretching out longer as
they go. This pushes the
root cap down more.
Notes on Roots
- The maturation region
is where the cells are
finally stable. These cells
are able to change and
grow into other structures
as needed.
Small hairs grow from
this section. These hairs,
called “root hairs” help
to grab nutrients the plant
would not be able to
reach otherwise.
Notes on Roots
Root Tissues
- Epidermis
The one-cell-thick layer that forms the skin of
the root.
Notes on Roots
Root Tissues
- Cortex
This is a thick layer that usually stores nutrients
for the plant.
Notes on Roots
Root Tissues
- Endodermis
The endodermis is also one layer thick and acts
as a barrier, preventing any nutrients from
getting through
unless they pass
through these
cells.
Notes on Roots
Root Tissues
- Pericycle
This layer is a vascular tissue that helps with
growth. When secondary roots appear, they
grow out from
this tissue.
Notes on Roots
Root Tissues
- Pith
This is the inner core of the root and is used for
water storage, support, and used to be old
tissue.
Notes on Roots
Secondary Growth
At a point, the root can no longer grow any
thicker. When a plant reaches this point, it starts
to grow new xylem and phloem on the outer
edge.
This leaves part of the plant exposed. To protect
itself, the plant grows cork cells to protect the
soft tissue. This gives the root a new outer layer
and the root can continue to grow both longer
and thicker.
Exit Question
What is the difference between a taproot and fibrous
root?
a) Taproots have reached max growth, fibrous haven’t
b) Fibrous roots have reached max growth, taproots
haven’t
c) A taproot is one main root, fibrous roots have many
d) A fibrous root is one main root, taproot is many
e) Taproots and fibrous roots are essentially the same
f) None of the above