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Supports And Movement
Biology Class IX
7/15/2015
Educast
Lubna Naz
Chapter #13
Supports And Movement
Contents:
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
Support In Plants
Physical Nature Of Xylem
Supporting Tissues Of Young Dicotyledonous Stem
Movement In Plants
Sessile And Motile
Locomotion In Protoctists
Locomotion In Volvox
Support And Movement In Animals
Support And Movement In Animals
Action Of Flexors And Extensor As A Pair Of Opposing
Muscles
k. Role Of Tendons And Ligaments In Movements
Supports And Movement
All living things move in some way. This may be obvious, such as animals that are able to walk,
or less obvious, such as plants that have parts that move to track the movement of the sun.
Turgidity of cells
Turgor pressure of the cell acts onto the neighboring cells:
(turgor pressure is the presence of water exerted and outward pressure from the inside of a fully
turgid cell)
As parenchyma cells in cortex and pith of the stem are closely packed together, the pressing
effect they act against one another keep the whole tissue in a tense state
stem becomes erect
This occurs is all plants, especially important for herbaceous plants and young plant / seedling of
woody plants which lack mechanical tissues
If the plant received too little water, turgor pressure decreases and the plant wilt.
THE DISTRIBUTION OF XYLEM AND PHLOEM IN PLANTS
These 2 conducting tissues are to be found in roots, stems and also in leaves. However, the
pattern of their arrangement differs in each.
Root structure
When you were studying cell division, you were shown a vertical section of a root.
You should be able to label the various tissues in the transverse section of a root
below. Note that the parts coloured yellow, and light brown, are also composed of
cells, of different types.
Stem structure
The diagram of a stem similarly shows a transverse section of a stem. Here you see
that the conducting tissue is grouped differently, into vascular bundles.
Leaf structure
The diagram above shows the distribution of conducting tissues (again in vascular
bundles), and green tissue in the centre of the leaf, which is in some ways like the
packing tissue in the other parts of the plant.
Stems
Stems are usually above ground organs and grow towards light (positively
phototropic) and away from the ground (negatively geotropic), except in the case of
certain metamorphic (modified) stems.
The main stem develops from the plumule of the embryo, while lateral
branches develop from auxillary buds or from adventitious buds. In normal stems
clearly defined internodes and nodes can be distinguished, the latter being the regions
where the leaves are attached. In younger stems stomata are found in the epidermis
while in the mature stems lenticels are evident. Depending on the hardness of the stem
one can also distinguish between herbaceous and woody stems.
In
this
section
we
will
discuss
the internal
structures of
young dicotyledonous and monocotyledonous stems, secondary thickening in the
stems of dicots, anddifferences in the internal structures of dicots and monocots.
Stem of a Dicotyledonous Plant: Internal Structure
From the study of the transverse section of the dicotyledonous stem you will identify
the following three regions of tissues: epidermis, cortex, and vascular cylinderor stele.
Epidermis
The epidermis consists of a single layer of living cells which are closely packed. The
walls
are thickened and
covered
with
a thin
waterproof
layer called
thecuticle . Stomata with guard cells are found in the epidermis. In some stems
either unicellular or multicellular hair-like outgrowths, trichomes, appear from the
epidermis.
Functions
1. The epidermis protects the underlying tissues.
2. The cuticle prevents the desiccation of inner tissues and thus prevents water
loss.
3. The stomata allow gaseous exchange for the processes of respiration and
photosynthesis.
Cortex
This region comprises the collenchyma, parenchyma and endodermis. It is situated to
the inside of the epidermis.
Collenchyma
These cells lie under the epidermis and constitute three to four layers of cells
with cell walls thickened at the corners. The collenchyma cells contains
chloroplasts
Functions of the Collenchyma
1. This tissue serves to strengthen the young stem.
2. The chloroplasts are responsible for the synthesis of organic food during
photosynthesis.
Parenchyma
Beneath the collenchyma cells are a few layers of thin-walled cells,
parenchyma, with intercellular spaces. The parenchyma cells make up
the bulk of the cortex.
Functions of the Parenchyma
3. The synthesized organic food (mainly starch) is stored here.
4. The intercellular air spaces are responsible for gaseous exchange.
Endodermis or Starch Sheath
The endodermis or starch sheath forms the innermost layer of the cortex. This is
a single layer of tightly-packed rectangular cells bordering the stele of the stem.
Functions of the Endodermis
5. The cells of this tissue store starch.
6. It allows solutions to pass from the vascular bundles to the cortex.
Vascular Cylinder or Stele
This region comprises the pericycle, vascular bundles and pith (medulla).
Pericycle
The pericycle is made up of sclerenchyma cells which are lignified, dead fibre cells .
These cells have thick, woody walls and tapering ends.
Functions of the Pericycle
1. It strengthens the stem.
2. It provides protection for the vascular bundles.
3. Vascular Bundles
The vascular bundles are situated in a ring on the inside of the pericycle of the plant. This
distinct ring of vascular bundles is a distinguishing characteristic of dicotyledonous
stems. A mature vascular bundle consists of three main tissues - xylem, phloem and
cambium. The phloem is located towards the outside of the bundle and the xylem towards
the center. The cambium separates the xylem and phloem which bring about secondary
thickening.
Functions of the Vascular Bundles
1. The xylem provides a passage for water and dissolved ions from the root system
to the leaves.
2. The xylem also strengthens and supports the stem.
3. The phloem transports synthesized organic food from the leaves to other parts of
the plant.
4. The cambium, divides to produce new xylem and phloem cells, making secondary
thickening possible.
Pith (Medulla)
The pith occupies the large central part of the stem. It consists of thin-walled parenchyma
cells with intercellular air spaces. Between each vascular bundle is a band of
parenchyma, the medullary rays, continuous with the cortex and the pith.
Functions of the Pith or Medulla
1. The cells of the pith store water and starch.
2. They allow for the exchange of gases through the intercellular air spaces.
3. The medullary rays transport substances from the xylem and phloem to the inner
and outer parts of the stem.
Secondary Thickening in Dicotyledonous Stems
In herbaceous dicots a limited amount of secondary thickening occurs, while it is more
evident in perennial, woody dicots. The stem increases in thicknessas it grows older. In
the vascular bundle of a young dicot stem the xylem and phloem are separated
by cambium.
Secondary thickening begins when mature parenchyma cells in the medullary rays which
lie between the adjacent vascular bundles become meristematic and form the fascicular
cambium. The fascicular cambium forms a continuous ring of cambium as it joins up
with the fascicular cambium. This cambium ring undergoes division to form secondary
phloem to the outside and secondary xylem to the inside. The secondary xylem and
secondary phloem are laid down in the form ofconcentric cylinders on either side of the
cambium ring. At certain points the cambium forms parenchyma, which radiates from the
middle of the stem through the secondary xylem and secondary phloem to form vascular
rays. As a result of these changes the stem increases in thickness. The primary xylem and
phloem are pushed further and further apart. The pith remains alive.
Some of the parenchyma cells between the vascular bundles continue to exist to form
radially directed vascular rays. Annual rings develop in the secondary xylem, each
consisting of a layer of spring wood and a layer of autumn wood. A cylindrical meristem
develops in the cortex, the cork cambium (phellogen). The cork cambium gives rise to
the cork cells (phellem) on the outside and the secondary cortex (phelloderm) on the
inside. Together this is known as the periderm. Opposite the stomata the cork cells
(phellem) give rise to lenticells for gaseous exchange.
 The movement of higher plants are chiefly in the form of bending, twisting, and elongation
of certain plant parts or organs.
 Spontaneous movement: There are other plant movements which take place spontaneously,
without any external stimuli. These movements are described spontaneous or autonomic
movements.
 Induced movement: Some plant movements are caused in response to certain to certain
stimuli and they are said to be induced or plant movement which take place spontaneously,
without any irritability and sensitivity of protoplasm.
 There are the following three types of autonomic movements:1. Movements and locomotion
2. Growth and curvature movement
3. Variation movements
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Similarly, paratonic movements also of three kinds:Tropic movements
Tactic movements
Nastic movements
TROPIC MOVEMENTS :
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Growth movements, which occur in response to unidirectional external stimuli & result in
positioning of the plant part in the direction of the stimulus, are said to be tropic
movements.
Depending upon the nature of stimuli, these movements are of following types:A) Phototropism
B) Geotropism
C) Hydrotropism
D) Chemotropism
A. Phototropism:
These curvature movements occur when a plant is provided with artificial or natural light only
from one direction. Stems which generally show a curvature toeard the source of light are said
to be positively phototropic. Roots which grow away from the source of light are called
negatively phototropic.
B. Geotropism
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Growth movements induced by stimulus of gravity are said to be geotropism. Primary
roots always grow downward in the direction of gravity and thus are positively
geotropic, whereas the main shoots grow upward away from the gravity and are thus
negatively geotropic.
The secondary lateral roots and shoots show a weaker response to gravity and thus take
up a position at an angle to the gravitational stimulus and are called diageotropic.
Demonstration of geotropism:
Geotropism can be demonstrated in the laboratory with the instrument known as
Klinostat. It can allow a potted plant fixed on it to rotate at a definite speed.
Two klinostats are taken and a potted plant on each is fixed on a horizontal position.
One klinostat is rotated and the other is kept stationary. Observations made after
sometime will show that the shoot of the plant fixed on the stationary klinostat bends
upwards showing negative geotropism and the root bends downwards showing positive
geotropism. But there is no bending in the root and shoot of the plant fixed on the
rotating klinostat. This is due to the fact that gravitational stimulus is not unilateral as it
affects the sides of the rotating organs equally.
C. Hydrotropism
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Growth movements in response to unilateral stimulus of water are known as
hydrotropism.
Roots are positively hydrotropic as they bend towards the source of water.
D. Chemotropism
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This is the movement caused by unilateral stimulus of some chemicals.
Movement of pollen tube through the style towards the ovary is an example
of chemotropism.
2. TACTIC MOVEMENTS
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Tactic movements are movements of locomotion, which are induced by some
unidirectional external stimuli.
Their direction is controlled by the direction of the stimulus.
Depending upon the nature of stimuli, these movements are of following types:A) Phototactic
B) Chemotactic
C) Thermotactic
A. Phototactic :
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These tactic movements are in response to unidirectional light.
Examples: Free swimming algae, zoospores, gametes when swim towards the diffused
light are said to be positively phototactic and when they move away from the strong
light, they are called negatively phototactic.
B.
Chemotactic
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The unidirectional movements of locomotion in response to certain chemicals is called
chemotactic.
The movement of antherozoids of bryophytes and pteridophytes towards egg due to
chemicals.
C. Thermotactic
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The movement of locomotion in response to certain unidirectional temperature stimulus.
Examples: Rapid rotational cytoplasmic movement in the leaf of Vallisneria due to
increase in temperature and movement of algae form a cloder to a warmer place.
3. NASTIC MOVEMENTS
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The movement can be due to changes in turgor or changes in growth
Depending upon the nature of stimuli, these movements are of following types:A) Nyctinasty
B) Chemonasty
C) Seismonasty
A. Nyctinasty
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These movement of plant organs occur in response to day and light and thus are also
known as sleep movement.
Photonastic: If these movement when induced by change in light intensity.
Examples: Flowers of Oxalis, Portulaca, Nicotiana, Oenothera etc.
Thermonastic :
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If these movement when induced by change in temperature intensity.
Examples : Tulip and Saffron (Crocus)
A temperature rise of only 0.36 degrees is enough to begin to open a crocus.
B. Chemonasty
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These movement occur in response to some
chemical stimulus.
Eg. Strong chemonasty is exhibited by long
peripheral tentacles of sundew leaves
(Drosera) which respond to the presence of
organic nitrogenous compounds by bending
towards the middle of leaf.
C.
Seismonasty
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These movements are in response to shock by a touch stimulus.
BQ: Give a brief account of turgor movement shown by Mimosa pudica.
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The base of the petiole is swollen (Pulvinus) and similar but smaller pulvinus are present
at the baseof each leaflet.
Lower half thin walled and upper half thick walled.
If the terminal pinnule is struck a blow or touched, the stimulus is conducted to its base
and then other pinnules.
This stimulus causes fall in turgor of lower cells due to loss of water.
Upper half retain turgidity.
Turgid half presses flaccid lower half lower half/ leaf droops.
When the touch stimulus is removed regains turgidity.
Motility
In biology,
motility is the ability to move spontaneously and actively, consuming energy in the
process.
Sessile
Sessile animals are usually permanently attached to a solid substrate of some kind, such as a part
of a plant, a dead tree trunk, or a rock. For example, barnacles attach themselves to the hull of a
ship, but corals lay down their own substrate.
The Basic Types of Movements
Movement involves 3 basic mechanisms. They are amoeboid, ciliary and muscular.
Amoeboid movement is typically found in amoeba, a unicellular animal. Amoeba moves by
producing pseudopodia, which are cytoplasmic projections. This involves change in the shape of
the cell body and streaming movement of cytoplasm into the pseudopodium. The movement due
to pseudopodia in amoeba is termed as amoeboid movement. Amoeboid movement is
characteristic of certain cells in other organisms. For example, the movement of white blood
cells or leucocytes, in human blood.
Amoeba moves about to obtain food or to avoid dangers or to escape from energy. Leucocytes
like phagocytes or macrophages of the lymph, show amoeboid movements to engulf antigen or
microbes and to immigrate in the circulatory fluid.
Ciliary movement is the method by which ciliated protozoans like paramoecium, move from
plate to place in water medium. Paramoecium uses cilia not only for moving from one plate to
another (locomotion) also to drive water and food into their gullet.
Cilia can perform a variety of functions:
1. In certain molluscs, cilia help to pass water currents over the gills
2. In echinoderms cilia helps to drive water through the water vascular system, (locomotion)
3. Cilia of the cells lining the respiratory tract of humans help to drive away the microbes and
dust particles towards the nose or mouth
4. Cilia in the oviduct or fallopian tubes of human female transport ova
Flagellum also helps in the movement in certain protozoans like euglena. Flagellum is a long,
thread like cytoplasmic projection. Flagellum in sperms also helps in the swimming movement.
Muscular movement
Muscular movement is the method used in most of the vertebrates, including man. Muscular
movement is based on the use of muscle fibres. Muscle fibres have the unique property of ability
to contract and relax, which exerts a force. This force is responsible for movement of body parts
and locomotion.
Human movement and locomotion also results from co-operation between muscles and bones.
Hence study of both skeletal and muscular system in the human body becomes essential.
Types of Muscles
Muscles constitute nearly 40 - 50% of the total human body weight.
Muscles have the unique properties of:
(a) Excitability (b) Contractibility (c) Extensibility and (d) Elasticity
In man, muscles are classified into 3 categories:
1) Skeletal Muscles
These muscles are under the control of the will of an individual. Therefore called are Voluntary
muscles. These muscles are found in arms, legs, body wall, face, neck etc. They are attached to
the bones by tendons and help in the movement of the parts of skeleton. Under the microscope
these muscle fibres show transverse stripes and hence also called as striated muscles. These
muscles are responsible for movement and locomotion.
2) Smooth muscles
These are not under the direct control of one's will. Hence called as Involuntary muscles and are
innervated by autonomic nervous system. These muscles are composed of stender, tapering
muscle fibres which are non-striated. These are found in the wall of internal organs like
alimentary canal, reproductive tract, blood vessels etc. Smooth muscles help in the movement of
materials through tubular internal organs. For example movements of passage of food in the
intestine.
3) Cardiac muscles
These muscle fibres are striated and comparatively short. Unlike other muscles, cardiac muscle
fibres are branched. It is found only in the heart. It is involuntary.
Structure of Skeletal Muscle
When a typical skeletal muscle is viewed under a microscope, it consists of many elongated,
cylindrical cells called muscle fibres or muscle cells. Each muscle fibre is enveloped by a plasma
membrane called the sarcolemma. The sarcolemma surrounds a quantity of cytoplasm called
sarcoplasm. Within the sarcoplasm are many nuclei and a number of mitochondria. Skeletal
muscle fibres are thus multi-nucleate. Also within the muscle fibre is the sarcoplasmic reticulum.
The mitochondria are called sarcosomes.
Myofibrils of a Muscle Fibre
Bundles of muscle fibres are grouped in a fascicule, which are held together and enclosed by
collagen fibres and by connective tissue. A tough outer layer called fascia, lying below the skin,
surrounds the bundles of fascilli.
A highly magnified view of skeletal muscle fibre reveals thread-like structures (about 1-2 mm in
diameter) called Myofibrils. These bear the characteristic cross -striations. The myofibrils are
stacked in compartments called sarcomeres. Narrow zones of dense material called Z lines
separate sarcomeres from one another. A dark anisotropic band (A-band) is present in the centre
of the sarcomere. Adjacent to this lies a light isotropic band (I-band). Alternate arrangement of
dark and light bands produces the striated appearance to the skeletal muscle. At the centre of the
A-band, a less dark zone called H-zone is present. In the centre of H-zone, M-line is present,
made up of fine threads that connect the myofilaments. The Z-line is present at the centre of the
I-band.
The sarcoplasm has many thick and thin filaments. In each sarcomere, the thin filaments are
present at the two ends and the thick one at the centre.
The H-zone contains thick myofilaments only. The I-band is composed of thin myofilaments
only. The rest of A-band has both thick and thin filaments.
Components of Thin and Thick Filaments
The thin myofilaments are composed mostly of the protein actin. The thick myo-filaments are
composed mostly of the protein myosin. Both are contractile proteins. Actin has low molecular
weight and it occurs as G-actin and F-actin. The thin filaments also contain two other protein
molecules - tropomyosin and troponin.
The myosin molecule is shaped like a rod with a round head. Myosin rods form the long axis of
the thick myofilaments and the heads form projections called cross-bridges, which connect to the
active site present on the actin.
Elbow muscles are commonly referred to as flexors or extensors, depending on how they affect
elbow movement. Extensors are on the inside of the arm and help extend the arm
outward. Flexors are at the back of the elbow and pull it closer to the body by bending the elbow.
The major muscles involved in moving the elbow include:
powerfully twists the forearm, turning the palm upward.
Triceps brachii: This muscle at the back of the upper arm extends the arm and stabilizes the
elbow when the hand is used for fine movements.
Biceps brachii: The large muscle of the upper arm flexes the arm and Brachioradialis: A forearm
muscle that flexes the arm at the elbow.
Anconeus: This muscle helps extend the forearm at the elbow.
Brachialis: This muscle helps flex the elbow inward toward the body.
Pronator teres: This muscle extends from the head of the humerus over the elbow to the ulna
bone to help flex the elbow, and also enables pronation of the forearm.
Several tendons connect the bones and muscles that meet at the elbow. As the elbow creates a
fulcrum, these tendons can be worn and torn with repetitive stressful use.
Tendon tears can be partial or complete, in which the muscle becomes completely detached from
the bone. Symptoms of a tendon tear include swelling, bruising, pain, and weakness.
Repetitive stress injuries, due to activities such as playing sports or using a keyboard, can cause
inflammation and pain. Collectively, these injuries are known as tendonitis. If the tendon on the
outside of the elbow joint is affected, it is called “tennis elbow.” If it is the tendon on the inside
of the elbow, the condition is known as “golfer’s elbow.”
Also, improper lifting, such as carrying a heavy item with your arms extended, can cause
unnecessary strain on the elbow muscles and tendons.
The roles of bones, muscles, tendons, and ligaments in
movement.
The bones of the skeletal system provide a framework for the muscles of the muscular system to
work against, promoting motion within the organism itself. Take your biceps muscle, the top
part of your upper arm, the one we flex when trying to show off how big our muscles are. When
that muscle contracts, which means to get shorter, it pulls on the lower arm to cause it to come
closer to the body. It is attached to the bones by means of tendons. thick elastic tissue that binds
the end of the muscle to a connection point on the bone. Ligaments are similar in composition to
tendons, but they differ in function. Ligaments bind bone to bone in junctions in the skeleton
called joints. When the biceps muscle relaxes, the muscle on the other side of the upper arm
contracts and causes the lower arm to extend. Muscles that cause limbs to extend are called
extensors, while those that cause limbs to come in closer to the body are called flexors.