Transcript Plant Structure and Growth

ANIMAL, PLANT &
SOIL SCIENCE
E4-2
PLANT INTERNAL
STRUCTURE AND
GROWTH
Interest Approach
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Take the students outside to see a small tree, bring
a small tree to class, direct attention toward a small
tree outside the window, or show an image of a
small tree. Identify a small lower limb on the tree.
Then, ask the students where that limb will be in 50
years if the tree continues to grow. Students often
assume that a tree grows from the ground and that
it begins by enlarging at the ground level; they fail
to realize that growth occurs from meristem tissues.
Objectives
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1 Review the functions of plant cell components.
2 Examine the role of cell division, cell elongation,
and cell differentiation in plant growth and the
different types of plant tissue.
3 Identify and describe the basic types of plant
cells.
4 Compare and contrast primary and secondary
plant growth.
Terms
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_ apical meristem
_ bud primordia
_ cell
_ cell differentiation
_ cell division
_ cell elongation
_ cell wall
_ cellulose
_ chlorophyll
_ chloroplasts
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_ chromatin
_ chromosomes
_ collenchyma cells
_ companion cells
_ cork cambium
_ cork cells
_ cytoplasm
_ dermal tissues
Terms
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_ endoplasmic reticulum
_ fiber
_ genes
_ golgi complex
_ ground tissue
_ lateral meristem
_ leaf primordia
_ lignin
_ meristems
_ mitochondria
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_ nucleolus
_ nucleus
_ organelles
_ parenchyma cells
_ periderm
_ phloem
_ pith
_ plasma membrane
Terms
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_ plastids
_ primary plant growth
_ ribosomes
_ rough endoplasmic
reticulum
_ sclereid
_ sclerenchyma cells
_ secondary plant
growth
_ sieve tube member
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_ smooth endoplasmic
reticulum
_ tracheid cells
_ vacuole
_ vascular cambium
_ vascular tissues
_ vessel elements
_ xylem
What are the functions of plant cell
components?
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I. The cell is the most basic unit of life. It is the
smallest unit that can perform functions of life.
Plant cells are composed of the following items.
A. The cell wall is made of multiple layers of
cellulose, which is a polysaccharide or complex
sugar molecule. The layers of cellulose offer
great strength. Therefore, it is no surprise that
cellulose is the primary ingredient of wood. Once
a cell has stopped growing, the cell wall thickens
and becomes rigid.
What are the functions of plant cell
components?
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B. The feature that really defines a cell is the
plasma membrane or cell membrane, which is a thin
sheet that holds the contents of the cell together and
serves as a protective barrier from the surrounding
environment. The fluid mosaic model of the plasma
membrane consists of a lipid bi-layer in which
proteins are imbedded. While the plasma
membrane restricts the movement of some materials,
it allows and even initiates the movement of other
materials into and out of the cell.
What are the functions of plant cell
components?
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C. Cytoplasm is the living semi-fluid material inside
the cell membrane and is home to a number of
specialized structures called organelles.
D. Organelles are small structures inside the cell that
carry out the physiological processes of the
organism.
What are the functions of plant cell
components?
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1. Plastids are organelles that
produce and store food.
a. Chloroplasts are a type of
plastid that contains green
pigments called chlorophyll.
Chlorophyll traps light energy for
photosynthesis. Chloroplasts are
found in cells exposed to light, so
they are abundant in leaves and
absent from root cells.
 b. Chromoplasts are plastids that
give flowers and fruits their color.
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What are the functions of plant cell
components?
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2. The endoplasmic reticulum (ER) is an internal network
of membranes extending throughout the cytoplasm. The
endoplasmic reticulum contains many types of enzymes
that catalyze different types of chemical reactions.
There are two distinct forms of endoplasmic reticulum:
smooth and rough.
a. The smooth endoplasmic reticulum is the site for the
production of lipids (fats) and hormones. It is also a site that
breaks down toxic chemicals.
 b. The rough endoplasmic reticulum produces the proteins for
the cell secretion and cell membranes.
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What are the functions of plant cell
components?
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3. Proteins are processed, sorted, or modified in the
golgi complex. These processes result in the complex
molecules needed for plant growth. Many proteins
manufactured in the ER pass through the golgi
complex.
4. Mitochondria convert sugar into energy through
cellular respiration. With mitochondria, the plant is
able to convert the food that it has made and
stored into a form of energy.
What are the functions of plant cell
components?
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5. The nucleus is the command center of the cell. It holds the
genetic information for a cell’s activities within a nuclear
membrane.
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a. The nucleus is surrounded by a nuclear membrane. Flowing
through the nuclear membrane are materials needed for protein
synthesis and fluids carrying chemical messages between the
cytoplasm and the nucleus.
b. Chromosomes contained in the nucleus hold the genetic blueprint
of the organism and direct all functions of the cell, including protein
synthesis. Chromosomes are made of chromatin.
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(1) Chromatin is a complex of deoxyribonucleic acid or DNA molecules
(35 percent), RNA (5 percent), and protein (60 percent).
(2) Segments of chromosomes, or genes, are units of hereditary data
that dictate the activity and structure of a cell. Each chromosome
contains thousands of genes.
c. A nucleolus is a specialized structure in a nucleus that is the site of
ribosome synthesis.
What are the functions of plant cell
components?
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6. Ribosomes are bead-like structures
found on the endoplasmic reticulum.
Ribosomes are the major site for the
assembly of amino acids into proteins.
7. The vacuole is a large sac bound by a
membrane. It may occupy up to 90
percent of the cell. It serves to transport
and store water, foods, salts, minerals,
pigments, proteins, and wastes.
What are the functions of plant cell
components?
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E. The organelles within a cell have thin membranes
used to compartmentalize or isolate different
conditions from other organelles. For example,
mitochondria and chloroplasts are bound with
membranes. Different intracellular pH, enzyme
systems, and more can be noted within each
organelle. This enables the cell to perform different
metabolic activities at the same time.
What is the role of cell division, cell elongation, and cell
differentiation in plant growth? What are the different
types of plant tissue?
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II. Growth of higher plants takes place through three
essential processes, and vascular plants have three
types of mature tissues.
A. Cell division is simply the increase in the number of
cells, which is accomplished through mitosis.
B. Cell elongation is the enlargement of the individual
cells, which results in growth of the entire tissue or
organ. Auxins and gibberellins are responsible for cell
elongation.
What is the role of cell division, cell elongation, and cell
differentiation in plant growth? What are the different
types of plant tissue?
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C. Cell differentiation allows cells to take on specific
functions. Cell differentiation is important to
multicellular plants, whereas single-cell plants have
no need to have different cell types. The cells of the
higher plants are programmed to become
specialized and make up the various plant organs.
Some cells specialize as root cells that absorb water
and nutrients. Some conduct water and minerals
throughout the plant. Others become leaf cells
containing chloroplasts and function to produce food
for the plant.
What is the role of cell division, cell elongation, and cell
differentiation in plant growth? What are the different
types of plant tissue?
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D. Vascular plants have three types of mature tissues.
1. Dermal tissues consist of the epidermis or external
covering of the leaves, stems, and roots. Dermal tissues offer
a barrier to infectious organisms and other invaders.
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a. The epidermis is made of closely packed cells that secrete a
waxy cuticle to reduce water loss. The epidermis is a single layer
of cells associated with plants that exhibit primary growth.
Specialized epidermal cells called guard cells control the opening
and closing of the stomata through which the diffusion of carbon
dioxide, oxygen, and water vapor is allowed.
b. Dermal tissue on secondary woody growth is a few too many
cells thick and forms the familiar bark of trees.
What is the role of cell division, cell elongation, and cell
differentiation in plant growth? What are the different
types of plant tissue?
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2. Vascular tissues are the conductive vessels of the
plant. They transport water, minerals, food, and
hormones. Specialized vascular tissues include the
xylem, which conducts water and minerals upward
from the roots, and the phloem, which transports
food.
3. Ground tissue (fundamental tissue) includes all the
parts of the plant other than dermal or vascular
tissues. The bulk of a plant consists of ground tissue
consisting of parenchyma, collenchyma, and
sclerenchyma cells.
What are the basic types of plant
cells?
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III. Genetic information and environmental
conditions determine the types of cells that
a plant produces. With the appropriate
signals, various types of cells are produced.
A. Parenchyma cells are found throughout a
plant and typically lack a secondary cell
wall associated with rigid strength for
support. The palisade layer and spongy
mesophyll cells in leaves are parenchyma
cells. Modified parenchyma cells compose a
large portion of the pith (the center part of
a stem). There they serve as storage
facilities for starch, oil, water, and salt. The
pith is very evident in corn and sugar cane.
What are the basic types of plant
cells?
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B. Collenchyma cells are located under the epidermis
of the stem, along leaf veins, and at corners of
angular stems. They have thick, yet flexible cell walls
that provide structural support for the plant.
C. Sclerenchyma cells are found throughout a plant
and function as a support. These cells have a hard,
thick secondary cell wall composed, in part, of a
material called lignin, which is a molecule that
provides strength and rigidity to the cell. A long type
of sclerenchyma cell is called fiber. Fiber cells are
abundant in wood and bark. A form of sclerenchyma
cell that is short and cubical is the sclereid. It is found
in the shell of nuts and the stones of fruit, such as
peaches.
What are the basic types of plant
cells?
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D. Tracheid cells are one of four types of cells found
in the xylem. The others are vessel elements,
parenchyma, and fibers. Tracheids are long and
tapering in shape. They are dead cells and hollow.
Their role is to conduct water and minerals
throughout the plant. Water passes from one cell to
another through thin places in the cell wall called
pits. Tracheids also contribute to the structural
support of the plant.
What are the basic types of plant
cells?
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E. The vessel elements are found in the xylem where
they conduct water and minerals and provide
structural support for the plant. Vessel element cells
are hollow. At the end of the cell walls, there are
perforations or holes that allow the free flow of
water from one cell to the next. Vessel cells also
have pits along the sides of the cells that permit the
lateral movement of water.
What are the basic types of plant
cells?
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F. The sieve tube member is a major element of the
phloem. Other cells that compose phloem tissue are
companion cells, parenchyma, and fibers. Sieve
tube members are stacked end to end to form sieve
tubes. There are holes at the end of each cell called
sieve plates through which sugars are moved. Sieve
tube members are living cells at maturity, but many
organelles—including the nucleus, vacuole, and
ribosomes—vanish as the cell matures.
What are the basic types of plant
cells?
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G. Companion cells are associated with sieve tube
members. They have many connections with
adjacent sieve tube members. Companion cells do
not conduct sugar throughout the plant. They do,
however, play an important role in transporting
sugars from photosynthetic parenchyma cells to the
sieve tube members.
What are the basic types of plant
cells?
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H. Cork cells are produced to the outside of the cork
cambium and result in the outer covering of
secondary growth. Cork cells have waterproof
characteristics and fire-retardant attributes.
How do primary and secondary plant
growth compare?
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IV. The growth of a plant takes place in specialized
areas of the plant called the meristems. The meristem
tissue consists of unspecialized cells that are capable of
mitosis. Two types of growth result from cell division in
meristem regions: primary and secondary growth.
A. Primary plant growth occurs in areas called apical
meristems. Apical meristem tissue is found at the tips of
roots and at the end of stems. Growth at the apical
meristem increases the length of the plant. Primary
growth occurs in herbaceous and woody plants.
How do primary and secondary plant
growth compare?
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1. The meristem of a root is located right behind the root
cap, which is a layer of cells that protect the meristem as the
root grows through the soil. Just behind the root cap is the
area of cell division. Further back is an area of cell
elongation. As the cells in the root mature, they differentiate
to perform specific functions. In a root system, the cells might
become root hairs, xylem, phloem, etc.
2. The meristem of the shoot has areas of cell division, cell
elongation, and cell maturation. The structure of the stem
apical meristem differs from the root apical meristem in that
it has embryonic leaves known as leaf primordia and
embryonic buds called bud primordia. As the cells in these
immature structures divide, elongate, and mature, they
become the leaves and stems of the plant.
How do primary and secondary plant
growth compare?
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B. Secondary plant growth takes place only in woody
plants. It takes place in the lateral meristem; this
tissue is found on the sides of roots and stems.
Secondary plant growth involves cell division in
layers ringing the stem. The result is an increase in
the width of the stem or trunk of the plant. Two
lateral meristems are involved in secondary growth.
How do primary and secondary plant
growth compare?
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1. Vascular cambium is a layer of meristematic tissue
found between the wood and the bark. It produces
secondary xylem to the inside of the vascular cambium
and secondary phloem to the outside. Cell division
occurs only when the plant is actively growing, primarily
during the spring and summer.
2. The cork cambium is located in the outer bark region,
and the cells produced there form the periderm (the
outer bark). Cork cambium produces cork cells that
replace the epidermis present during primary growth.
The periderm ranges from several cells in thickness to
many cells.
REVIEW
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1. What are the functions of plant cell components?
2. What is the role of cell division, cell elongation,
and cell differentiation in plant growth? What are the
different types of plant tissue?
3. What are the basic types of plant cells?
4. How do primary and secondary plant growth
compare?