Download Roots, Stems, and Leaves

Name
Date
Class
Section
23.2 Roots, Stems, and Leaves
Indiana Standards Standard B.1.15 Understand and explain that, in biological systems, structure and function
must be considered together.
◗ Before You Read
Salad ingredients include lettuce, tomatoes, radishes, cucumbers, onions, bean sprouts, carrots,
and celery. Botanists might look at a fresh salad and see plant organs. Think of salad ingredients you
are familiar with. Decide whether they are roots, stems, or leaves and list them on the appropriate
line below.
Roots: ____________________________________________________________________________
Stems: ____________________________________________________________________________
Leaves: ___________________________________________________________________________
◗ Read to Learn
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Roots
A root is a plant organ. Roots anchor a plant, usually absorb
water and dissolved minerals, and contain vascular tissues that move
minerals to and from the stem. All roots are not alike. They can be
short or long, thick or thin, massive or threadlike. The surface area
of a plant’s roots can be as much as 50 times greater than the surface area of its leaves. Most roots grow in the soil, but some do not.
There are two main types of root systems—taproots and
fibrous roots. Carrots and beets are taproots. Taproots are single,
thick structures with smaller branching roots. Taproots accumulate and store food. Fibrous roots have many small branching
roots that grow from a central point.
Taproots
READING ESSENTIALS
Fibrous roots
Identify
Details As you skim the section, highlight the structures
of roots, stems, and leaves in
one color. Highlight the functions of roots, stems, and
leaves in another color.
Prop roots
Chapter 23
263
Name
Date
Class
Section
23.2
Roots, Stems, and Leaves, continued
Other types of roots include prop roots, aerial roots, and pneumatophores. Corn has prop roots. They begin above ground and
help support the plant. Some climbing plants have aerial roots.
The aerial roots do not touch the ground. Instead, they cling to
walls to provide support for the climbing stems. Bald cypress trees
grow mostly in swampy soils. They produce modified roots called
pneumatophores, or “knees.” The knees grow upward from the
mud, and out of the water. They help supply oxygen to the roots.
What is the structure of roots?
A Dissolved minerals and water
enter root hairs and travel
through and between the
cells of the cortex.
Pericycle
Endodermis
Cortex
Epidermis
Root hair
Endodermal
cells
Waterproof
seal
B Minerals dissolved in water can
flow between the parenchyma
cells, directly into the root cortex,
then through the cells of the endodermis.
264
Chapter 23
READING ESSENTIALS
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Locate the root hair on the diagram below, which shows a
cross-section of a root. You can see that a root hair is an extension
of an epidermal cell. The epidermal cells are in the epidermis, the
outermost layer of the root. Root hairs increase the surface area
of a root that touches the soil. Root hairs absorb water, oxygen,
and dissolved minerals.
Moving inward from the epidermis, the next layer of cells in the
root is the cortex. The cortex is ground tissue. It helps move water
and dissolved minerals into the vascular tissue. The cortex is made
up of parenchyma cells that sometimes store food and water.
Name
Date
Class
Section
23.2
Roots, Stems, and Leaves, continued
A The xylem in this dicot root is arranged in a
Xylem
Xylem
Phloem
Phloem
Parenchyma
B In this monocot, there are alternating
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
central star-shaped fashion. The phloem is
found between the points of the star.
strands of xylem and phloem that
surround a core of parenchyma cells.
The next layer inward from the cortex is the endodermis. This
is a layer of waterproof cells that form a seal around the root’s
vascular tissues. The waterproof seal of the endodermis forces
the water and dissolved minerals to pass through the cells of
the endodermis. The endodermis controls the flow of water and
dissolved minerals into the root. Next to the endodermis is the
pericycle. Lateral roots develop from the pericycle in older roots.
Xylem and phloem are located in the center of the root. One
of the major differences between monocots and dicots is the
arrangement of the xylem and phloem tissue. In dicot plants,
the xylem forms a central star with phloem cells between the
rays of the star. In monocot plants, strands of xylem alternate
with strands of phloem. The alternating strands form a ring.
Xylem
Sometimes the center of the ring contains parenchyma cells
called a pith.
Phloem
Root hairs
How do roots grow?
There are two areas of cell growth in roots. The root apical
meristem produces cells that cause a root to increase in length.
As these cells begin to mature, they develop into different types
of cells. In dicots, the area between the xylem and the phloem
becomes vascular cambium. The additional cells in the vascular
cambium add to the root’s diameter.
Each layer of new cells produced by the root apical meristem
is left farther behind as new cells are added. The new cells cause
the root to grow forward through the soil. A protective layer of
parenchyma cells called the root cap covers the tip of each root.
As the root grows through the soil, the cells of the root cap
READING ESSENTIALS
Pericycle
Endodermis
Apical meristem
Root cap
Chapter 23
265
Name
Date
Class
Section
23.2
Roots, Stems, and Leaves, continued
wear away. The apical meristem
constantly produces replacement
cells so that the root tip is always
protected.
is a tuber.
B This gladiolus corm
is a thickened,
underground stem
from which roots,
leaves, and flower
buds arise.
C The rhizome of
an iris grows
horizontally
underground.
Stems
Most often stems are the
aboveground part of a plant that
supports leaves and flowers.
Stems have vascular tissues that
move water, dissolved minerals,
and sugars to and from roots and
leaves. Some stems are thin and
green, like those of pansies, basil,
and carnations. Green stems are
soft and flexible. They often
carry out photosynthesis. Trees
and shrubs have thick, woody
stems. The stems of trees can be
quite large. Woody stems are
hard and rigid. They have cork
and vascular cambiums.
Some stems store food. This
helps the plant to survive drought
or cold. Stems that act as foodstorage organs are corms, tubers,
and rhizomes. All three are
underground stems. A corm is a
short thickened stem surrounded
by leaf scales. A tuber is a
swollen stem that has buds from
which new plants grow. Rhizomes
also store food. The figure at left
shows examples of stems that act
as food-storage organs.
What is inside a stem?
The vascular tissue inside stems is arranged differently than the
vascular tissue inside roots. Stems have bundles of vascular tissue
within parenchyma tissue. In monocots, the vascular bundles are
scattered throughout the stem. In dicots, the vascular bundles
form a ring in the cortex.
266
Chapter 23
READING ESSENTIALS
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
A A white potato
Name
Date
Class
Section
23.2
Roots, Stems, and Leaves, continued
Woody Stems Many plants, such as conifers,
produce thick, sturdy stems that last several years
or decades. As the stems of woody plants grow
taller, they also grow in thickness. This added
thickness, called secondary growth, is the result
of cell divisions in the vascular cambium of the
stem. The xylem tissue produced by secondary
growth also is called wood. The annual growth
rings in tree trunks are the layers of vascular tissue produced each year by secondary growth.
As secondary growth continues, the outer
portion of the woody stem develops bark.
Bark is made of phloem cells and the cork
cambium. Bark is a tough, corky tissue that
protects the stem from damage by insects or
plant-eating animals.
Annual growth rings
Cork
Phloem
Vascular
cambium
Xylem
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
What does the stem do?
The stem transports water, sugars, and other compounds. Xylem
1. How does bark protect a
plant?
moves water and dissolved minerals from the roots to the leaves.
Water that is lost as water vapor through the stomata is continually
________________________
replaced by water moving upward in the xylem. Water forms an
unbroken column within the xylem. As water moves up through
________________________
the xylem, it carries dissolved minerals to all living plant cells.
________________________
The phloem carries dissolved sugars. The sugars come from
the photosynthetic tissues that are usually in the leaves. Any part
of the plant that stores
Water lost
these sugars is called a
Source
through leaves
sink, such as the
Sugar
of sugars
parenchyma cells that
make up the cortex in
Phloem
the root. The movement of sugars in
the phloem is called
translocation
Sink
Xylem
(trans lo KAY shun).
The illustration at right
shows the movement of
materials in the vascular
tissues of a carrot.
Sieve plate
Water
A The open ends of the xylem vessel
cells form complete pipelike tubes.
READING ESSENTIALS
Companion cell
B Sugars in the phloem of this
carrot plant are moving to sinks.
Chapter 23
267
Name
Date
Class
Section
23.2
Roots, Stems, and Leaves, continued
How does a stem grow?
2. Does primary growth
lengthen or thicken a
stem?
________________________
Primary growth lengthens a stem. It is similar to primary
growth in a root. The increase in length is due to the production
of cells by the apical meristem at the tip of the stem. Meristems
located along the stem, called nodes, are where leaves and
branches develop.
________________________
Leaves
The primary function of the leaves is photosynthesis. Most leaves
have a relatively large surface area that receives sunlight. Sunlight
passes into the photosynthetic tissues just beneath the leaf surface.
The flat, broad, green surface of a leaf is called the leaf blade.
Sizes, shapes, and types of leaves vary a great deal. Some leaves,
such as those of the Victoria water lily, can be more than two
meters in diameter. Other leaves, such as duckweed, are measured
in millimeters. Some plants produce different forms of leaves on
the same plant.
A blade of grass is joined directly to the stem, but in other
leaves, a stalk joins the leaf blade to the stem. The stalk is called a
petiole (PE tee ohl) and is actually part of the leaf. The petiole
contains vascular tissues that stretch out from the stem into the
leaf and form veins. You can often see the veins if you look closely
at a leaf. They look like lines or ridges.
Leaves vary in shape. A simple leaf is one with a blade that is
not divided. Maple leaves and tulip poplar leaves are examples of
simple leaves. When a leaf blade is divided into leaflets it is called
a compound leaf. The leaves of the walnut are an example of
compound leaves.
A The leaves of the
walnut are compound
with many leaflets.
268
Chapter 23
B The needlelike leaves of the
evergreen yew can receive
sunlight year round.
C The tulip poplar is a deciduous
tree with broad, distinctive,
simple leaves.
READING ESSENTIALS
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
________________________
Name
Date
Class
Section
23.2
Roots, Stems, and Leaves, continued
Not all leaves grow on a stem in the same way. When two
leaves grow directly opposite each other on a stem, the arrangement is called opposite. If the leaves are on opposite sides of the
stem, but one is higher than the other, the arrangement is called
alternate. When three or more leaves grow around a stem at the
same position, the arrangement is called whorled.
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
What is the structure of a leaf?
Use the illustration at right as you
study the internal structure of a typical
leaf. Notice the cuticle and the upper and
lower epidermis. Between the epidermal
layers are two layers of mesophyll.
Mesophyll (MEH zuh fihl) is the photosynthetic tissue of a leaf. It is usually made
up of two types of parenchyma cells—
palisade mesophyll and spongy mesophyll.
Most photosynthesis takes place in the
palisade mesophyll. These cells receive
maximum exposure to sunlight and have
many chloroplasts. The spongy mesophyll
cells are surrounded by many air spaces
that allow carbon dioxide, oxygen, and
water vapor to flow freely. Gases also can
move in and out of the stomata.
Cuticle
Upper
epidermis
Palisade
mesophyll
Vascular
bundle
Xylem
Phloem
Lower epidermis
Stomata
Spongy mesophyll
Guard cell
What is transpiration?
The waxy cuticle and stomata help reduce water loss. Guard
cells control the size of a stoma. The loss of water through the
stomata is called transpiration. The opening and closing of guard
cells regulates transpiration. The proper functioning of guard
cells is important because plants lose up to 90 percent of all the
water they transport from the roots by transpiration.
3. What regulates
transpiration?
________________________
________________________
________________________
What are some modifications in leaves?
The pattern of veins in leaves is one way to distinguish different groups of plants. Veins are vascular tissues that run through
the mesophyll of a leaf. The patterns can be parallel or netlike as
shown on page 270. Parallel veins are found in many monocots.
Many dicots have netlike veins. The leaves of ginkgoes are
dichotomously veined.
READING ESSENTIALS
Chapter 23
269
Name
Date
Class
Section
23.2
Roots, Stems, and Leaves, continued
Leaf venation
Parallel
Many plants have leaves that have functions besides photosynthesis. Some leaves, when crushed or broken, release substances
that cause pain or swelling. Animals and humans learn to avoid
such leaves. Cactus spines are modified leaves that help reduce
water loss and provide protection from plant-eaters.
Carnivorous plants have leaves with adaptations that can trap
insects or other small animals. Other leaf modifications include
the curling tendrils in sweet peas, the colorful bracts on poinsettias, and the overlapping scales that enclose and protect buds.
Leaves often act as water or food storage sites. The leaves of
Aloe vera, for instance, store water. A bulb, on the other hand,
provides an example of leaves storing food. A bulb consists of a
shortened stem, a flower bud, and thick immature leaves. Food
is stored in the base of the immature leaves. Onions, tulips, and
narcissus grow from bulbs.
◗ After You Read
Mini Glossary
cortex: layer of ground tissue in the root that is
involved in the transport of water and dissolved minerals into the vascular tissue of
the root
endodermis: single layer of cells that forms a
waterproof seal around a root’s vascular tissue; controls the flow of water and dissolved minerals into the root
mesophyll (MEH zuh fihl): photosynthetic tissue
of a leaf
pericycle: in plants, the layer of cells just within
the endodermis that gives rise to lateral roots
270
Chapter 23
petiole (PE tee ohl): in plants, the stalk that joins
the leaf blade to the stem
root cap: tough, protective layer of parenchyma
cells that covers the tip of a root
sink: any part of a plant that stores sugars produced during photosynthesis
translocation (trans loh KAY shun): movement
of sugars in the phloem of a plant
transpiration: in plants, the loss of water
through stomata
READING ESSENTIALS
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Netlike
Name
Date
Class
Section
23.2
Roots, Stems, and Leaves, continued
1. Read the key terms and definitions in the Mini Glossary on page 270. Circle any three of the
terms that describe the structure or function of leaves. In the space provided explain in your
own words how those three terms relate to leaves.
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
2. For each plant part listed in the first column, write the name of one related structure in the
second column and one function in the third column.
Structure
Function
Roots
Stems
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Leaves
Visit the Glencoe Science Web site at science.glencoe.com to find
your biology book and learn more about roots, stems, and leaves.
READING ESSENTIALS
Chapter 23
271