SUPPORT AND MOVEMENT
As we know that all living organisms are made up of cells and cell having living material called protoplasm, possesses special characteristics of irritability due to change in its environment.
*Irritability is the ability that living organisms have to respond to changes in their environment.
This lieu of this irritability, living organism take sonic (quick) actions, these actions are called movement. In other words, we can say that movement is a response shown by a living organism towards stimuli.
All living organisms having this property of movement, fulfil the need of their nutritition, protection, shelter and reproduction. Plants and animals respond to environmental stimuli in different ways.
Animals are usually motile, they respond mainly by behavioral mechanisms by moving towards or away from stimuli. Plants are usually sessile which respond to environmental factors by adjusting their pattern of growth and development.
In living organisms movement can occur at cellular level, for example cytoplasmic streaming (cyclosis) and swimming of gametes, at organ level like movement of limbs and heart.
Plants show cellular and organ movement. They do not locomote in search of food. They are usually capable of slow movement in response of light, gravity and water.
As the animals or plants grow in size they need support to maintain their shape and posture to stand erect for having balanced, fast and rhythmic movement. In terrestrial organisms, the need of support is much pronounced because air does not provide support like water.
Support is provided by:
• Skeletal system in animals i.e. exo, endo and hydrostatic skeleton.
• Mechanical tissues with thick cell-walls in woody parts of plant.
• Turgidity in soft parts of plants.
SUPPORT IN PLANTS
The body of higher plant can be divided into two major parts, the root and the shoot. These two parts are distinguished on the basis of their specialized morphological and physiological characteristics.
*Physiology is the scientific study of functions and mechanisms in a living system.
*Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features.
They both have many tissues which are growing throughout the entire axis and keep their body erect, they require some supporting tissues and materials. These tissues and materials are present in all parts of their body e.g. root, stem branches and leaves.
Young stem has special type of anatomical arrangement, which also helps in supporting plant. The outermost layer of thin walled cells called epidermis.
Regions beneath epidermis are generally called cortex and the central portion called stele, which mainly consist of vascular tissues and some soft tissues.
This type of stem depends for its mechanical support on the following tissues:
i) Thin walled parenchyma-having turgidity.
ii) Thick walled living tissues like collenchyma and dead tissues like sclerenchyma.
iii) Stele as cylindrical core of vascular bundles.
Parenchyma
Parenchyma a kind of simple tissue found in the epidermis, cortex and pith. These are relatively unspecialized vegetative cells. The whole body of lower plants (Bryophytes) is made up of these tissues. They usually have thin primary walls but no secondary walls. They have a large central vacuole surrounded by at peripheral layer of cytoplasm. They are loosely packed with intercellular spaces in leaves and green herbaceous stem. They contain chloroplasts therefore photosynthesis largely occurs in these cells.
They take in water by endosmosis and become extended, these extended parenchyma are turgid, exert an internal pressure called turgor pressure. Due to this turgor pressure these parts remain firm and rigid. If these cells lose water, they also lose turgidity, which causes wilting in herbaceous stem and leaves. Therefore, these turgid parenchyma are important for support and shape of the soft plant.
Collenchyma
Collenchyma is another type of simple tissue, which is important to provide support in plants. They are also living tissues more elongated structurally similar to parenchyma except that their walls are irregularly thickened. The thickened areas are usually more prominent at edges. They function as an important supporting tissue in young plants, in the stem of non-woody older plants and in leaves.
Sclerenchyma
Sclerenchyma is another type of supporting tissues. They are simple fundamental dead tissues. They have uniformly thick, heavily lignified secondary walls, which gives strength to the plant body. Often these walls are so thick that the lumen of the cell becomes nearly vanished.
Sclerenchyma cells are of two types: fibers and sclereids.
Fibers are very long cells with tapered ends. They are tough and strong but flexible while sclereids are variable, often irregular in shape.
The simple unbranched sclereids are variable, often irregular in shape. The simple unbranched sclereids are generally called stone cells, they are common in nut and hard parts of the seeds.
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References:
stimulus and response
http://www.funscience.in/studyzone/Biology/NervousSystem/StimulusAndResponse.php#sthash.QkIiiTdy.dpbs
Cyclosis / Cytoplasmic streaming in plant cells
https://www.youtube.com/watch?v=BB5rvjZzgFU&feature=emb_title
Leaf Epidermis
https://irrecenvhort.ifas.ufl.edu/plant-prop-glossary/01-biology/02-cell-types/07-celltypes-parenchyma.html
Epidermis, Cortex, stele
https://www.toppr.com/ask/question/rearrange-the-following-in-a-proper-logical-sequenceepidermis-cortex-root-hair-xylem-endodermis/
lycopodium stem tshttps://www.plantscience4u.com/2014/04/lycopodium-stem-anatomy-cs.html#.XwCaMygza1s
CELLS OF THE GROUND TISSUES
http://www.bio.miami.edu/dana/226/226F09_5.html
PArenchyma
https://irrecenvhort.ifas.ufl.edu/plant-prop-glossary/01-biology/02-cell-types/07-celltypes-parenchyma.html
turgid vs plasmolysed cell
https://www.slideshare.net/SECBIO/osmosis-diffusion-active-transport
Difference Between Parenchyma Collenchyma and Sclerenchyma
https://pediaa.com/difference-between-parenchyma-collenchyma-and-sclerenchyma/
Plant cell type collenchyma
https://en.wikipedia.org/wiki/Ground_tissue
Plant cell type sclerenchyma fibers
https://en.wikipedia.org/wiki/Ground_tissue
Sclerenchyma
https://www.onlinebiologynotes.com/permanent-tissue-characteristics-types-functions/
Difference Between Fibres and Sclereids
https://pediaa.com/difference-between-fibres-and-sclereids/#:~:text=The%20main%20difference%20between%20fibres,of%20the%20sclereids%20are%20blunt.
Fiber Cell
https://www2.palomar.edu/users/warmstrong/traug99.htm
sclereids of pear
https://www.instagram.com/p/BpnSLK6F7i0/?utm_source=ig_web_copy_link
Magnified view of a Yucca leaf cross section
https://www2.palomar.edu/users/warmstrong/traug99.htm
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Tracheids
Tracheids are elongated tubular heavily lignified dead cells having large hollow cavities. They have oblique transverse walls making tracheids spindle shaped. They are found in the xylem acting as supporting tissues in addition to transport of water and dissolved inorganic salts.
Vessels
Vessels (Tracheae) are like tracheids but have no transverse walls and placed end to end forming a structure like open water pipe line. They are also found in xylem acting like tracheids.
Sclerenchyma cells provide the fibers of hams and jute, which are used for making rope. Other type of sclerenchyma cells form nutshells, outer covering of Peach Pits and gritty texture of pears.
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References:
Tracheid and Vessel
https://www.quora.com/What-is-the-function-of-tracheid-cells
Cells of the xylemhttps://www.britannica.com/plant/angiosperm/Organization-of-the-vascular-tissue#ref596770
Difference Between Tracheids and Vessels
https://pediaa.com/difference-between-tracheids-and-vessels/
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Secondary tissues and their significance:
Secondary tissues are those which are formed by the activity of lateral meristem vascular cambium and cork cambium during secondary growth which takes place in a number of vascular plants (spermopsids). It occurs in all gymnosperms. Many dicot angiosperms undergo secondary growth but very few monocot plants.
1. Vascular cambium
It first appears between the primary xylem and primary phloem and called fusiform initials (fascicular cambium). Then few cells of each medullar ray, lying in line with fusiform initials become meristematic to form interfascicular cambium. The two cambium combine to form a ring of meristematic tissue called vascular cambium. Vascular cambium cuts off new cells inside as well as outside. The cells formed inside give rise to secondary xylem. The cells formed outside give rise to secondary phloem.
During secondary growth, the primary epidermis splits, dries and fall off. To protect the exposed tissues and to increase the diameter cork cambium (phellogen) arises in the cortex.
2. Cork cambium or phellogen
It appears when the layers of hypodermal cells regain the power of division to form a ring of meristematic tissue. Cork cambium cuts off new tissues inside called secondary cortex or phelloderrn. The cells cuts off outside are rectangular and arranged in radial rows. They have waxy deposition of suberin and become dead, they are called cork tissue or functions as a barrier and protects the stein from physical damage and from pathogens. It also prevents from water loss.
In older trees many chemical and physical changes occur in the rings of xylem towards the center of stem. The conducting cells become blocked, parenchyma cell die while pigment, resin, tannins and gums are deposited.
When these changes take place. xylem becomes non-functional for transport and emerges as strong supportive component of tree. The part of ring where these changes have occurred is known as heart-wood whereas the outer part of ring which contains comparatively young tissues remain functional in transport, constitute the sap-wood. Only youngest secondary phloem functions in sugar transport.
In between the cork, is a spongy region in the bark, with loosely arranged cells having intercellular spaces. These masses of loose cells, through which gases and water vapour readily pass out are known as lenticels.
Sheets and plugs of cork come from the cork of oak trees, native of Spain, Portugal and Algeria.
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References:
Meristematic Tissue
https://byjus.com/biology/meristematic-tissue/
Lateral Meristems
http://www.phschool.com/science/biology_place/biocoach/plants/lateral.html
A Woody Twig Has Both Primary and Secondary Tissues
https://www.macmillanhighered.com/BrainHoney/Resource/6716/digital_first_content/trunk/test/hillis2e/hillis2e_ch24_4.html
cork tissue
https://www.toppr.com/ask/question/what-is-the-other-name-for-the-cork-tissue/
Natural gum of plum tree
https://en.wikipedia.org/wiki/Natural_gum#/media/File:Natural_gum_of_plum_tree_01.jpg
LEnticel
http://www.sbs.utexas.edu/mauseth/weblab/webchap17bark/17.3-1.htm
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Significance of Secondary Tissues:
Secondary growth meets the need of more water, minerals and food conduction for growing plant. It also provides the firm support to it by producing new conducting and mechanical tissues. In addition to these, the cambium forms callus on or around the wound. The parenchymatous tissues are rapidly formed below the damaged surface of stem and root. Callus also develops during grafting to unite the graft with the plant.
Annual rings: The plants of temperate region accumulate secondary xylem in the form of concentric layers every year and called annual rings. Each annual ring consists of two zones, the inner zone of spring wood or summer-wood having larger vessels and an outer zone of winter-wood or autumn-wood having smaller vessels. A fairly accurate estimate of age of an old tree can be made by counting annual rings. Study of the rings of large sample of very old tree can also give clue to the climate of an area. Tree ring dating have been used in archeological studies.
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References:
Wound healing in plants
https://www.thehindu.com/sci-tech/science/how-wounded-plants-heal-survive/article31010471.ece
Secondary Growth in Various Parts of Dicotyledonous Stems:
https://www.biologydiscussion.com/shoot-system/stems/dicotyledonous-stems/secondary-growth-in-dicotyledonous-stems-with-diagram-botany/20516
Explain Formation of Annual Ring
https://www.qsstudy.com/biology/explain-formation-annual-ring
This basswood (Tilia americana) trunk cross section has 24 distinct annual rings.
Cross section of a conifer
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MOVEMENT IN PLANTS
Plant movements occur in response to certain stimuli, because movement is defined as any action taken by living organs to reduce its irritability produced by stimuli. Stimulus is the change in environment either external or internal which affect the living organism by developing irritation in their protoplasm. A stimulus can be diffused or directional, it may be replied with a prompt or delayed response.
Types of movement in plants:
On the basis of stimuli, there are two main types of movement found in plants.
1 Autonomic or spontaneous movement
2. Induced or paratonic movement
1-Autonomic or spontaneous movement:
Movement which occur due to internal stimuli, factors inside the plant body itself are known as autonomic or spontaneous movements. Autonomic movements are of following types:
i) Growth and curvature movement:
Advantageous changes in the form and shape of plants or plant organs or to the differences in the ratio of growth of different parts are called growth and curvature movement. These movements are due to unequal growth on two sides of plant organs like; stem, root, tendrils, buds, leaves etc.
There are two types of growth movement.
(a) Nutation: The growth in the apex of young stem takes place in zig zag manner due to an alternate change in growth rate on opposite side of the apex, this type of movement is called nutation. A nutation movement may be circumnutation when apex makes rotational growth around its long axis e.g. movement of climber around the rope as found in railway creeper.
(b) Nastic movement: Movement that occurs due to differences in the rate of growth on two opposite sides of a plant organ. Opening of the petals and circinately coiled leaves of fern are good example of nastic movement. When movement occurs due to faster growth on the upper side of the organ is known as epinastic movement and when it occurs due to faster growth on lower surface of the growing organ, it is known as hyponastic movement.
(ii) Turgor movement:
Movement that occurs due to change in the turgidity and size of cells as a result of loss or gain of water called turgor movement.
2- Paratonic or Induced movement:
Movements which occur due to external stimuli are known as induced or paratonic movements. They may be tropic or nastic. The external stimuli which cause these movements may be light, temperature, water, chemicals, gravity etc.
i) Tropic movement: (Directional movement)
Tropism or tropic movement are growth responses that result in curvatures of whole plant organs towards or away from stimuli. It is derived from a Greek word tropos means 'turn'. Movement caused due to external stimuli coming from one side, controlled by the direction of stimulus, respond in the form of growth of curvature in one direction called tropic movement. It is commonly found in radially symmetrical organs of plant such as root and stem. On the basis of stimuli following are the types of tropic movement found in plants.
a) Phototropism (photo = light, tropos = turn): It is a curvature movement that takes place when plant is exposed to light coming only from one direction. If this curvature movement is towards the source of light called positive phototropism and if sway from the source of light called negative phototropism. Phototropic curvature is due to light effect on the distribution of auxin (plant growth promoting hormone).
b) Geotropism: It is the movement caused in response to gravitational stimulus. Positive geotropism is observed in the primary roots of many plants and negative geotropism in their shoot.
c) Chemotropism (Chemo = chemical, tropos = turn): Chemotropism is the movement caused due to chemical for example pollen tube grows through the style awards ovary due to chemical stimulus.
d) Hydrotropism: (Hydro = water, tropos = turn): The movement of plant organs in response of water stimulus is called hydrotropic movement. This also results in curvature of the organ due to unequal growth on its two sides. Roots are positively hydrotropic.
e) Thigmotropism (Thigmos = touch, tropos = turn): Thigmotropism is the curvature movement of plant in response to touch stimulus. It can be observed in twinner and climbers. When they touch the solid object the growth on the opposite side of contact increases and the tendrils coiled around the support.
ii) Nastic movement (Non-directional movement:
The term nastic movement is used for the movement which is unrelated to direction of stimuli and direction of stimulus is not fixed. This type of movement is mostly observed in leaves and petals etc. The types of nastic movements depend on the type of stimulus, they may be photonastic, thermonastic, seismonastic, vctinastic and haptonastic.
a) Photonastic movement or photonasty: The nastic movement caused by light. The flowers open and close due to light intensity e.g. the flowers of oxalis and portulaca open in day and close at night while flowers of Nicotia close in day and open at night.
(b) Thermonastic movement (Therme (Gr.)= heat): Nastic movement caused due to high atmospheric temperature e.g. Indian telegraph plant.
(c) Seismonastic movement (Seismos (Gr.)= to shake): When the compound leaf of sensitive plant (mimosa pudica) is touched, it collapses and its leaflets fold together as it is undergone a shock. It results from a rapid loss of turgor by cells of the leaflets.
(d) Nyctinastic movement (Nyctos = Night/ sleep): Bean plants and many other members of legume family lower their leaves in the evening and raise them to a horizontal position in the morning. These movements are called sleep movement which are powered by daily changes in the turgor pressure of the cells of the leaves.
(e) Haptonastic movement: Haptonastic movement are caused due to stimuli of touch and they can be observed in many insectivores plants in which touch causes the movement. The distinctive feature is that, in case of thigmotropism, plant part touches the object whereas in haptonastic movement, an object (any insect) touches the plant part.
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References:
Nutation in Plants
https://www.semanticscholar.org/paper/Chapter-2-Nutation-in-Plants-Mugnai-Azzarello/158f88df3f0b6e528288d8f8de02449a0aeb7be6
railroad creeper
https://www.alamy.com/mile-a-minute-vine-messina-creeper-cairo-morning-glory-coast-morning-glory-and-railroad-creeper-image247268446.html
Nutation video
https://www.youtube.com/watch?v=HLDPovgehaE
Nastic movement
http://lifeofplant.blogspot.com/2011/03/nastic-movements.html
Tomato Plant Time Lapse Recover From Wilting
https://www.youtube.com/watch?v=UnsqkvYQJ2E&feature=emb_title
Positive Phototropism | Demonstration
https://www.youtube.com/watch?v=DhITXtENPrU&feature=emb_title
Negative Gravitropism | Demonstration
https://www.youtube.com/watch?v=Rb55mj8xkxk&feature=emb_title
Pollen tube growth
https://www.youtube.com/watch?v=4Kw2U2E1POM&feature=emb_title
thigmotropism
https://www.youtube.com/watch?v=yMHmU3eZsYk&feature=emb_title
Oxalis Triangularis
youtube.com/watch?v=GubQ6vAR4KQ&feature=emb_title
The Telegraph Plant
https://www.youtube.com/watch?v=J-fIKlcCbSU&feature=emb_title
Touch-me-not plant
https://www.youtube.com/watch?v=nPf3FbR6eQE&feature=emb_title
Cucumber Nyctinasty 2
https://www.youtube.com/watch?v=_qu09TKSNso&feature=emb_title
Venus flytrap
https://www.youtube.com/watch?v=O7eQKSf0LmY&feature=emb_title
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ROLE OF GROWTH SUBSTANCES IN PLANT MOVEMENT
Plant as sessile organism shows its movement mainly in the form of growth. This movement is controlled by phytohormones (auxins, cytokinin, giberellins, abscisic acid). It is found that the phototropic curvature is due to light effect on the distribution of auxin. Went (1928) found that the illuminated side of Oat Coleoptile possessed only 27% auxin whereas unilluminated side possessed 57% auxin. This distribution of auxin is due to light response. The region rich in auxin grows rapidly which results in growth curvature towards the light. Auxins also play role in geotropic responses. It is responsible for positive geotropism of roots and negative geotropism of stem. The growth rate increase with the increased accumulation of auxin and as a result a shoot will grow away showing negative geotropic property and a root because of inherent differences in response will grow towards the lower side showing positive geotropic property.
Ratio between growth inhibitors like abscisic acid and growth regulator gibberellin also play an important role in nastic movement. The epinasty is found due to auxin while gibberellin causes hyponastic movement. Role of growth substance on plant movement will be discussed in chapter 3 in plant growth regulators.
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