Plant Internal Structure and Growthocontofallsag.weebly.com/uploads/4/6/0/3/46035517/plant...Plant Internal Structure and Growth B AMBOO is said to be the fastest growing plant. It

Plant Internal Structure and Growth

BAMBOO is said to be the fastest

growing plant. It can grow 3 to 4

feet in height in one day. The General

Sherman Sequoia is the largest living

organism on earth. It is 275 feet tall

and weighs 1,385 tons. How these and

other plants grow is discussed in this

unit.

Objectives:

� 1. Describe plant cells and

tissues.

2. Explain the processes of plant growth.

Key Terms:

�

E-unit: Plant Internal Structure and Growth

Page 1 � www.MyCAERT.com

Copyright © by CAERT, Inc. — Reproduction by subscription only. E040052

apical meristem

bud primordia

cell

cell differentiation

cell division

cell elongation

cell wall

cellulose

chlorophyll

chloroplasts

chromatin

chromosomes

collenchyma cells

companion cells

cork cambium

cork cells

cytoplasm

dermal tissues

endoplasmic

reticulum (ER)

fiber

genes

golgi complex

ground tissue

lateral meristem

leaf primordia

lignin

meristems

mitochondria

nucleolus

nucleus

organelles

parenchyma cells

periderm

phloem

pith

plasma

membrane

plastids

primary plant

growth

ribosomes

rough

endoplasmic

reticulum

sclereid

sclerenchyma

cells

secondary plant

growth

sieve tube

member

smooth

endoplasmic

reticulum

tissues

tracheid cells

vacuole

vascular

cambium

vascular tissues

vessel elements

xylem

Plant Cells and Tissues

The cell is the most basic unit of life. It is the smallest unit that can carry out functions of

life. Interconnected groups of cells that perform similar functions are tissues.

COMPONENTS OF A PLANT CELL

A plant cell is made up of a cell wall, a plasma membrane, cytoplasm, and a variety of

organelles.

Cell Wall

The cell wall is made of multiple layers of cellulose. Cellulose is a polysaccharide, or

complex sugar molecule. The layers of cellulose offer great strength. Cellulose is the primary

ingredient of wood. Once a cell has stopped growing, the cell wall thickens and becomes rigid.

Plasma Membrane

The feature that really defines a cell is the plasma membrane. A plasma membrane, or

cell membrane, is a thin sheet that holds the contents of the cell together and serves as a pro-

tective 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 mem-

brane restricts the movement of some materials, it allows, and even initiates, the movement of

materials into and out of the cell.

Cytoplasm

Cytoplasm is the living semi-fluid material inside the cell membrane. Cytoplasm is the

home to a number of specialized structures called organelles.

Organelles

Organelles are small structures inside the cell that carry out the physiological processes of

the organism. The organelles within a cell have thin membranes used to compartmentalize or

isolate different conditions from other organelles. Within each organelle is a different

intracellular pH, different enzyme systems, and other differences. This enables the cell to carry

out different metabolic activities at the same time.

Plastids are organelles that produce and store food. Chloroplasts are a type of plastid

that contains green pigments called chlorophyll. Chlorophyll traps light energy for photosyn-

thesis. Chloroplasts are found in cells exposed to light. They are abundant in leaves and absent

from root cells. Chromoplasts are plastids that give flowers and fruits their color.

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, the smooth and the rough endoplasmic reticulum. 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. The rough endoplasmic reticulum produces the proteins for

the cell secretion and cell membrane.

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.




Vacuole

Chloroplast

Smoothendoplasmic

reticulum

Roughendoplasmic

reticulum

Cell wall

Golgiapparatus

Mitochondrion

Nucleus

Nuclearmembrane

FIGURE 1. Detailed plant cell.

Mitochondria convert sugars

into energy through cellular res-

piration. It is with mitochondria

that the plant is able to convert

the food it has made and stored

back into a form of energy.

The nucleus is the command

center of the cell. It holds the

genetic information for a cell’s

activities within a nuclear mem-

brane. 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. Chro-

mosomes 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.

Chromatin is a complex of deoxyribonucleic acid (DNA) molecules (35%), RNA (5%), and

protein (60%). 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. A nucleo-

lus is a specialized structure in a nucleus that is the site of ribosome synthesis.

Ribosomes are beadlike structures found on the endoplasmic reticulum. The ribosomes

are the major site for the assembly of amino acids into proteins.

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.

TYPES OF PLANT CELLS

Genetic information and environmental conditions determine the types of cells that a plant

produces. With the appropriate signals, various types of cells are produced.

Parenchyma Cells

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 make up a large portion of the pith

(center part) of a stem. There, the parenchyma cells serve as storage facilities for starches, oils,

water, and salts. The pith is very evident in corn and sugar cane.

Collenchyma Cells

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 sup-

port for the plant.




Nucleolus

Nuclearpores

Chromatin

Nuclearenvelope

FIGURE 2. The nucleus.

Sclerenchyma Cells

Sclerenchyma cells are found throughout a plant. Their role is one of support. They

have a hard, thick secondary cell wall composed, in part, of a material called lignin. Lignin 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.

Tracheid Cells

Tracheid cells are one of four types of cells found in the xylem. The others are vessel ele-

ments, 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 contrib-

ute to the structural support of the plant.

Vessel Elements

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.

Sieve Tube Members

The sieve tube member is a major

element of the phloem. Other cells that

make up phloem tissue are companion

cells, parenchyma cells, 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.

Companion Cells

Companion cells are associated

with sieve tube members. They have

many connections with adjacent sieve




Pores of sieve plate

Sieve plate

Sieve tube member

Companion cell

FIGURE 3. Major elements of the phloem.

tube members. Companion cells do not conduct sugar throughout the plant. They do, how-

ever, play an important role in transporting sugars from photosynthetic parenchyma cells to

the sieve tube members.

Cork Cells

Cork cells are produced to the outside of the cork cambium and result in the outer cover-

ing of secondary growth. Cork cells have waterproof characteristics and fire retardant attrib-

utes.

TYPES OF TISSUES

Vascular plants have three types of mature tissues. They are the dermal (protective) tissues,

the vascular tissues, and the ground (fundamental) tissues.

Dermal Tissues

Dermal tissues consist of

the epidermis (external covering

of the leaves), stems, and roots.

Dermal tissues offer a barrier to

infectious organisms and other

invaders.

The epidermis is made of

closely packed cells that secrete a

waxy cuticle to reduce water loss.

An epidermis is associated with

plants that exhibit primary

growth. The epidermis is a single

layer of cells. Specialized epider-

mal 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.

Dermal tissue on secondary woody growth is a few, to many, cells thick and forms the

familiar bark of trees.

Vascular Tissues

Vascular tissues are the conductive vessels of the plant, and they transport water, miner-

als, foods, and hormones. Specialized vascular tissues include the xylem, which conducts

water and minerals upward from the roots, and the phloem, which transports food.

Ground Tissue

Ground tissue includes all the parts of the plant other than dermal or vascular tissues.

The bulk of a plant consists of ground tissue made up of parenchyma, collenchyma, and

sclerenchyma cells.




Water fromstem

Waterto stem

Cuticle

Xylem

Phloem

Spongymaterial

Epidermis

StomataGuard cell

Air space

FIGURE 4. A cross section of a leaf.

Plant Growth

The growth of a plant takes place in specialized areas of the plant called the meristems.

The meristem tissue consists of unspecialized cells capable of mitosis. There are two types of

growth resulting from cell division in meristem regions. They are termed primary and second-

ary growth.

CELL DIVISION, CELL ELONGATION, AND

CELL DIFFERENTIATION

Growth of higher plants takes place through three essential processes. These are cell divi-

sion, cell elongation, and cell differentiation.

Cell Division

Cell division is simply the increase in the number of cells. This is accomplished through

mitosis.

Cell Elongation

Cell elongation is the enlargement of the individual cells. The elongation of individual

plant cells results in growth of the entire tissue or organ. Both auxins and gibberellins are

responsible for cell elongation.

Cell Differentiation

Cell differentiation allows

cells to take on specific functions.

Cell differentiation is important

to multi-cellular plants, whereas

single-cell plants have no need to

have different types of cells. The

cells of the higher plants are pro-

grammed 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 func-

tion to produce food for the plant.




Root hairs

Xylem

Phloem

Apical meristem

AREA OF CELL

DIFFERENTIATION

AREA OF CELL

ELONGATION

AREA OF CELL

DIVISION

Root cap

Developing

secondary

root

FIGURE 5. Cell division, elongation, and differentiation.

PRIMARY PLANT GROWTH

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 both herbaceous and woody plants.

The meristem of a root is located right behind the root cap. The root cap 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, and so on.

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.

SECONDARY PLANT GROWTH

Secondary plant growth takes place only

in woody plants and occurs in the lateral

meristem. Lateral meristem tissue is found on

the sides of roots and stems. It involves cell divi-

sion in layers ringing the stem. The result is an

increase in the width of the stem or trunk of the

plant. Two lateral meristems involved in sec-

ondary growth are the vascular cambium and

cork cambium.

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.

The cork cambium is located in the outer bark region, and the cells produced there form the

periderm, or 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.

Summary:

� The cell is the most basic unit of life. Plant cells are made up of cell walls, mem-branes, cytoplasm, and organelles, including plastids, endoplasmic reticulum, golgicomplex, mitochondria, nucleus, ribosomes, and vacuole.




Periderms with their cork cambia

Inner bark (secondary phloem)Outer bark

Wood (secondary xylem)

Surface of vascular cambium

Bark

FIGURE 6. Secondary growth occurs in the vascular

cambium of a tree.

Types of cells include parenchyma cells, collenchyma cells, sclerenchyma cells,tracheid cells, vessel elements, sieve tube members, companion cells, and cork cells.

Interconnected groups of cells that perform similar functions are tissues. Threetypes of mature tissues found in vascular plants are the dermal (protective) tissues,the vascular tissues, and the ground (fundamental) tissues.

The growth of a plant takes place in specialized areas of the plant called themeristems. Growth of higher plants takes place through cell division, cell elonga-tion, and cell differentiation.

Primary plant growth occurs in areas called apical meristems. Secondary plant growthtakes place only in the lateral meristem of woody plants. Two lateral meristemsinvolved in secondary growth are the vascular cambium and cork cambium.

Checking Your Knowledge:

� 1. What are the components of a plant cell?

2. What are the types of plant cells?

3. What are three types of mature tissues found in vascular plants?

4. Where does plant growth occur?

5. How do primary plant growth and secondary plant growth differ?

Expanding Your Knowledge:

� Ask your teacher or a biology teacher if they have prepared slides showing differenttypes of cells and meristematic tissues. View these under a microscope. Obtain across section of a woody trunk. Sand it smooth and determine the lateral meristemand cell types.

Web Links:

� Plant Cell Types

http://www.biologie.uni-hamburg.de/b-online/library/plant_biology/celltypes.html

Plant Cells and Tissues

http://arnica.csustan.edu/boty1050/Tissues/tissues.htm

Secondary Growth

http://plantphys.info/Plant_Biology/secondary.html

Primary and Secondary Plant Growth

http://www.cas.muohio.edu/~meicenrd/mudescd/Dendrology/SCDRYGTH/1&2gwrtp2.html

Agricultural Career Profiles

http://www.mycaert.com/career-profiles




Documents

Plant Internal Structure and Growthocontofallsag.weebly.com/uploads/4/6/0/3/46035517/plant...Plant Internal Structure and Growth B AMBOO is said to be the fastest growing plant. It