,
CONCEPTUAL Life Science
Cells and Tissues
roJl unit in 1M course 15 J teach it. The pIJ15 ell lIIimaJ dssucs couJd be caily ilKlOqlOJ'llled inIo the
inuodudion to SCClion 011 the human lIIilllll. Not 10 CISY to do with tbe p1llllS because die only real emphasis on pllln1S 1hlIt 1bac is
will be wi1h tbe enersY 8IId photosynthesis Wlil So, lun cnterin& it heR. We 1liiy WII'IIIO 1hink IbouI die pboIosyntbcsis IOIlIC II1CR
end come up wi1h somdhin& tike the BJCCI!. pllll~ makes food for us, or IJ'CCII pllll15 IIId photos)'nlhcsis.
[ln1rodUClOIy note: This is •
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in all ofthe notes that I use with my studcn1s. In _ lecture book I usc, there Ire drawinp for IICIriy
nery tissue. 1bcsc hIVe been oml1lcd bere. I till always dnIw diem later if we decide to 10 tblllOUtf. FHO 3/J1104)
AI, III expedient, J h."e typed
PYRAMID OF BIOLOGICAL STRUcnJRE
Organism
Organ
Systems
. Organs
Tissues
Cells
Figure CT-1. The ~yramid ofbiological structure.
Living things exhibit stnlcture and organization. The basic unit of structure and
function is the cell. CeJls are organized into units containing similar cells. These are
called tissues. Different types oftissues are found in an organ. For example, an organ
. such as the stomach has epithelium, muscle and nerve tissue in it Organs are organized
into structmal· units called organ systems. The stomach is part ofthe digestive system.
The digestive system also contains other organs. Therefore, a living creature, such as a
human, is an organism containing various organ systems with their component organs,
made oftissues ofwhich the basic units are the cells.
PLANT TISSUES
I.
Meristematic tissues
Meristematic tissues have embryonic, undifferentiated cells. Undifferentiated is a
tenn used to mean that the cells have not changed into other cells yet•.
CT-1
.
C1-2
When embryonic cells change into other cells they undergo a process called
differentiation. Differentiation is the process ofbecoming different. In meristematic
tissue, the ceJls have the ability to divide using mitosis but they have not chBnged into
other tissue types yet. They eventually will become cells of other types. Flowering
plants such as trees have meristems located in three places: the shoot tip, the root tip and
the cambium layer between the bark ofthe tree and the wood.
A.
Shoot tip
There is a meristem at the end ofeach branch ofa tree. It is protected by a bud.
The ceJlsin the shoot tip meristem (also known as,the' apical meristein) prod~ce
embryonic cells that will eventually develop into the stems, branches and leaves ofthe
tree. The bud has one year's worth of growth inside. In the spring when the trees deploy
their leaves, the bud begins to grow and the leaves develop and deploy quickly. During
the summer, the tree makes another set ofleafbuds for next year so that next spring, it is
ready to deploy its leaves a~ the appropriate time.
B.
Root tip
There is a meristem at the tip of each root. The meristem enables the I'QOt to grow
deeper into the soil. It also produces the other root tissues. The root tip meristem is
protected by a root cap so that friction with the soil does not wear it down.
After the cells ofthe root tip divide, they begin to elongate. This produces a zone
of elongation in the root. This production of new cells and elongation process permits the
root to penetrate deeper into the soil.
.
C.
Cambium
The cambium is found between the xylem and phloem layers of woody stems. It
produces new xylem and phloem cells. This activity increases the diameter ofthe ~.
Since cambium is active only dming the growing season, the xylem tissue forms in rings.
A tree generally produces one ring ofxylem per year. Therefore you can
detennine the age ofthe tree by counting the rings. The appearance ofrings is produced
by placing this spring's new, large-diameter cells immediately adjacent to last summer's
old, small-diameter cells.
D.
Pennanent tissues
A.
Surface tissues
1. .
Epidermis
. .
CT-3
The epidermis contains living cells and is found on the surfaces ofyoung stems
and leaves. The lower epidennis ofleaves contains specialized occlusive cells known as
guard cells that SlDTOund openings in the leaves called stomates. "Stomate" is derived
from Latin and means hole. The guard cens regulate the size ofthe holes in the leaves
and pennit exchange of gases (CO2. 02) and water vapor with the air. The epidermis
generally has a waxy outer surface to prevent loss ofwater by the plant except when the .
stomates are open.
2.
Periderm
The periderm contains non-living cells that have thick secondary walls. The walls are
waterproofed and made impenneable with a material called suberin. Periderm is a tissue
that replaces the epidermis on older stems ofthe plant. The suberin-containing secondary
walls ofthe peridenn prevent loss ofwater by the plant
B.
Fundamental tissues
1.
ParenChyma
Parenchyma contains living cens that are capable ofceD division. It is the least
specialized ofthe plant tissues. These cells have thin primary waIls. Parenchyma is \ISed
as a filler tissue in such plant structures as com stalks.
2.
Collencl1yma
The cells ofcollenchyma are usually alive. They have secondary wall material
that is deposited in the comers giving them a characteristic appearance under the
.microscope. This type oftissue is.found in c~ types of stems. It serves as a support
tissue.
3.
Sclerenchyma
a.
Fibers
The fibers ofsclerenchyma are dead. These cells have very thick secondary walls
and very small lumens. A lumen is a cylindrical space surrounded by a cylindrical
structure. The space inside a garden hose is a Imnen. "Lumen" means light-sort oflike
the light at the end ofthe twmel.
The very thick waIls offiber cells give them much strength. This type oftissue
serves as a structural support tissue in stems. It is often associated with vascular bw1C:Ues.
CT-4
b.
Sclereids
The cells of sclereidsare'also dead. Like the fibers, they have very thick
secondary walls with very tiny lumens. Sclereids are spherical. They are part of such .
plant stJUctures as peach pits.
4;
Endodennis
The endodermis is a layer of living cells found in the root. It has a waterproofing
layer known ~ the Casparian strip containing lignin and suberin, two impermeable
materials. The Casparian strip prev~ts materials from leaking .from the outer tissues of
the root into the center where the vascular tissue is located. The plant uses the
endodermis to regulate what materials enter the plant and are transported up to the stem
and leaves.
C.
Vascular tissues
1.
Xylem
Xylem ~lls are dead. Xylem is a transport tissue that conducts water and
minerals upward in the plant. It also serves as a support tissue. Xylem is the major
component ofwood. Xylem tissue in a woody stem (such as a tree trunk)has rays of
parenchyma cells in it.
2.
Phloem
Phloem contains Uving cells that conduct nutrients both upward. and downward.
Phloem cells always are found in pairs. There is a large conducting cell called a sieve
tube and a smaller cell alongside known as the companion cell. The cytoplasm
communicates between the sieve tube and the companion cell. The sieve tube is
. responsible for conducting materials. 'The companioD cell contains the nucleus that
controls the pair ofcells.
In a tree, the phloem is found in the bark. When the vascular tissues, xylem and
phloem, tmn to the outside to connect to stems and leaves, the phloem is always on the
bottom and the xylem is always on top. This is apparent in a microscopic view of a
cross-section ofa leaf. In the leaf, the vascular bundles always have the xylem on the top
and the phloem underneath the xylem.
ANIMAL TISSuES
I.
Epithelium.
·
.
CT-5
Epithelium is a tissue that lines or covers alI" body surfaces, both inside and
outside. This includes the skin, the inside and outside ofthe blood vessels, cuctgs, the
digestive tract and other body organs.
A.
Simple epithelium
Simple epithelium always contains a single layer of cells attached to a membrane.
As this membrane is underneath the cells, it is called the basement membrane. There are
three kinds of epithelial cells that differ in their shapes.
1.
Simple squamous epi~elimn
"Squamous" meansjlat. Simple squamous epithelium contains a single layer of
flat cells attached to a basement membrane. An example ofthis type oftissue is
peritoneum, the tissue that surrounds and suspends the digestive organs in the abdominal
cavity.
2.
Simple cuboidal epithelium
"Cuboidal" means having the shape of a cube. 'IJUs tissue contains a single layer
of cube-shaped cells on a basement membrane. An example ofthis type of tissue is the
lining ofthe collecting duct in the kidney.
3.
Simple columnar epithelium
"Columnar" means that the cells are tall~ like columns. This tissue contains a
single layer oftaJl cells on a basement membrane. An example ofthis type oftissue is
the intestinal lining.
B.
Stratified epithelium .
"Stratified" means that the cells ofthe tissues are found in layers. All three types
of stratified epithelium start out as several layers ofcuboidal cells on a basement
membrane. The other layers detennine which type oftissue it is.
I.
Stratified squamous epithelium
Stratified squamous epithelium contains several layers ofcuboidal cells on a
basement membrane. As you proceed away from the membrane the cells get
progressively flatter.. An example is skin.
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2.
Stratified cuboidal epithelium
In stratified cuboidal epithelium, the cells in all layers ofthe tissue are cuboidal.
An example is the lining ofthe ducts of the sweat glands.
3.
Stratified columnar epithelium
In stratified columnar epithelium, all layers ofthe tissue are cuboidal except for
the top layer that contains tall cells. An example is the lining ofthe duets ofthe
·mammary glands.
n.
Connective tissue
Connective implies holding things together or joining things. Thus we -expect to
find tendons, ligaments and cartilage classified as connective tissue. In addition, the
category ofconnective tissues contains body-wide tissues such as bone, blood and lymph.
In most cases, the cells that make up the tissue are SUITOunded by some kind of matrix or
material characteristic ofthe tissue.
A.
Tissues that connect body structures
1.
Loose connective tissue (areolar)
Loose connective tissue contains cells surrounded by a matrix ofcollagenous
fibers, elastic fibers and lymph. Collagenous fibers are made of collagen, a type of
structural body· protein. Lymph is also called tissue fluid. It is a liquid that is found in
between the different parts ofthe body in the spaCes known as the connective tissue
· spaces.
2.
Dense connective tissue
Dense connective tissue is composed primarily ofcollagenous fibers. DeDse
connective tissue is found in the dennis ofthe skin, tendons and ligaments. A tendon
connects a muscle to a bone while a ligament l:onnects one bone to another bone. .
3.
Adipose tissue
Adipose tissue is made offat cells. Each cell has a thin ring ofcytoplasm that
SWTounds a large vacuole containing a rat droplet.
4.
.Cartilage
There are three kinds ofcartilage. Each consists ofcells SUJ1'OUDded by a matrix .
...
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· of small fibers.
-.,.
'.
. .
CT-'
• Yellow elastic cartilage is found in the arteries and between the rungs ofthe
.
w~~.
• Hyaline cartilage forms the ridge of the nose and the rings of the trachea.
• Elastic cartilage is found in the external ear, the epiglottis and the Eusiachian
tube.
B.
Bone
1.
Description ofbone tissue
Bone cells are sUJTounded by a matrix of calcium phosphate. There are tunnels in
the bone called Haversian canals that contain the blood vessels that supply blood to the
bone cells. Bone has the most mineral matter. There are two types of bone tissue known
as spongy bone and compact bone.
2.
Spongy bone
The ends ofthe long bones are made of spongy bone. "Spongy," when it is used
in biology, means "having the appearance of a sponge." It does not mean that the tissue
is soft and flexible. Spongy bone is hard but has the appearance ofa sponge..
3.
Compact bone
Compact bone does not have the spaces in it that give it a spongy appearance.
The long parts ofthe long bones are composed of compact bone tissue.
C.
Vascular tissue
Vascular tissue consists ofcells surro\D1ded by a liquid matrix. There are two
types ofvascular tissue that are called blood and lymph.
1.
Blood
Blood is found in blood vessels. It is carried by the circulatory system.
2.
Lymph
Lymph consists offluid that is fOlUld outside of the blood vessels. ]t isaJso
known as tissue fluid. It is collected via the lymphatic system and eventually returns to
the circulatory system. •
..
III.
Muscles
,A.
Smooth muscle
CT-8
Smooth muscles are found in all involuntary organs except the heart. Examples
oforgans include the diaphragm and the arteries. Smooth muscle does not contain
striations.
B.
Striated muscle
Striated muscles are attached to the bones ofthe skeleton. Each striated muscle
cell is multinucleate because it has many nuclei. Striated muscles contain striations,
which are lines that produce a cross-banding effect. These lines result from $e
orientation of the muscle proteins within the eell. The striated skeletal muscles are also
known as voluntary muscles.
C.
Cardiac muscle
The heart is the only organ that contains cardiac muscle. This muscle cell type
has distinct cells that are separated by intercalated discs. The intercalated discs partition
the muscle into cells. Cardiac muscle cells also contain striations.
IV.
Nerve tissue
The neuron is the cell ofthe nervous·system. Each axon is surrounded by a
sheath of membranes.