NOTES PREPARED BY
ASHAQ HUSSAIN BHAT
TEACHER SCHOOL
EDUCATION DEPARTMENT
JAMMU AND KASHMIR
INTRODUCTION
Movements are one of the important characteristics of living beings All plants and animals depict different kind of movements. They may be growth movements in plants (e.g growth of germinating seed enabling the seedling to come out of soil) , non-growth movements in plants eg folding and drooping of leaves of the plant Mimosa pudica) or non-growth movement in animals eg, running of cat, children playing on swings, cow and Buffalo chewing the cud ete). Al movements in living organisms , In fact, occur in response to changes in the environmental factors,
The changes in the environment (or environ mental factors) to which the organisms respond and react are called stimuli
Environmental factors such as light, heat , touch taste, smell, sound, water current, force of gravity etc, act as stimuli to induce responses and reactions in all living organisms. For instance, plants grow towards sunshine, cat is running after a mouse or away from a dog, children are getting fun and pleasure out of swinging and cow and buffalo chew the cud to break tough food in order to digest it better Similarly, we close our eyes on exposure to bright light or we with draw our hand when suddenly touch a hot object In all these examples, we find that movements (responses and reactions) in living organisms occur to provide advantage to them.
Different organisms respond and react to stimuli differently. Most of the plants do not have nervous system and they, therefore, do not possess any special structure for the perception of external stimuli. Also, most of them can not move from one place to another because they are fixed to the substratum or soil by roots or root-like structures. Still, plants respond/react to the external stimuli. They do so due to the action of plant hormones. The plant hormones coordinate their behaviour either by effecting for growth of the plants slowly (eg, plants respond to light by bending towards it) or by affecting the shape of plant cells by changing the amount of water in them (eg, response of touch me not plant, Mimosa pudica to touch by folding-up and drooping its leaves). On the other hand, responses of different animals to light, touch or other stimuli vary a great deal. Among animals, simple organisms respond to external stimuli by moving towards them (positive response) or away from them (negative response), Amoeba (a single celled organism), for instance, reacts to the presence of food by moving towards the food particle (positive chemotaxis). Also, number of amoebae respond to heat stimulus and tend to go towards the warm water.
COORDINATION IN ANIMALS
Unicellular organisms respond to environmental stimuli by moving towards or away from the source of stimulus. Such responses of unicellular organisms (e.g. Amoeba) are termed as taxes (singular taxis). If they move towards the source of stimulus, their response is termed positive taxis and if they move away from the source of stimulus, their response is termed negative taxis. The responses of multicellular animals to stimuli, however, are not as simple.
Evolution of multicellularity in animals necessitated the development of some system for the control and coordination of the activities of various cells of the body. Such a control and coordination, in fact, requires
(i) gathering information about changes in the external environment,
(ii) transmitting this information to the internal cells located away from the body surface, and
(iii) exchange of information between the cells situated away from each other.
In lower multicellular animals, the coordination takes place through the nervous system. However, in higher animals, coordination takes place through two types of control systems : nervous system and endocrine
1. Nervous System. The nervous system is composed of specialized cells called neurons (nerve cells) which exercise control by sending electrical signals called nerve impulses. The nervous control is speedy and flexible but its effect is localized,
2. Endocrine System. The endocrine system consists of specialized glands (endocrine glands) which bring about control by sending chemical messengers termed hormones. The hormonal control is usually slow acting and its effect is diffuse.
In the following account, we describe nervous system in animals explaining the structure of neuron, arrangement of neurons, types of neurons, sensory receptors, reflex actions, involuntary and voluntary actions and finally components and functions of human nervous system,
(ii) Dendrites (singular dendron). These are several short, tapering, much branched protoplasmic processes stretching out from the cell body of a neuron. Dendrites are the parts of neuron where sensation (information) is acquired. The information then travels as an electric impulse towards the cell body, Dendrites contain Nissi's granules and neurofibrils.
(iii) Axon. It is a single, very long, cylindrical protoplasmic process (nerve fibre) of uniform diameter arising from the cell body. At its terminal end, axon is highly branched. The terminal branches are called terminal arborization. Axon terminals are often knob-like and these may end in nerve fibres (forming neuromuscular junction) or glands or form synapses with dendrites of other neurons. The axon conducts nerve impulses away from the cell body.
Axon is covered with one or two sheaths. Sheathed axon is termed nerve fibre . he cell membrane of the axon is called axolemma and its cytoplasm is termed axoplasm. It lacks Nissl's granules. However, neurofibrils are present. The single sheath present over the axon is made of Schwann cells and is called neurilemma. The axon may have an additional insulating and protective sheath of myelin around it. It is present between neurilemma and axon. Nerve fibres (axons) having myelin sheath are termed myelinated nerve fibres and those without this sheath are termed non-myelinated nerve fibres. Myelinated nerve fibres conduct impulses more efficiently than non-myelinated nerve fibres. At intervals, myelinated nerve fibres possess unmyelinated areas called nodes of Ranvier.
Neurons transmit messages in the form of nerve impulses. They have following special properties:
(i) They do not divide.
(ii) From shortly after birth, new neurons do not develop.
(iii) They are not repaired, when injured.
(iv) They use only glucose as a respiratory substrate.
(v) They die if deprived of oxygen for over five minutes.
Arrangement of Neurons
The neurons lie end-to-end in chains to transmit nerve impulses in the animal body. Each neuron receives an impulse through its dendrites and passes it on to the next neuron in the chain through its axon via cell body.
Synapse. The neurons connected. There occurs a very minute gap between terminal portion of axon of one neuron and the dendron of other neuron. This minute gap is called synapse. At the synapse, axon terminal comes in close proximity to the dendron terminal of next neuron
Nerve impluse is a self propagated electrochemical current that travels from one neuron to another neuron for the passage of message.
Passage of Impulse. The receptor (s), ie, sensory neuron (s) present in the body receives the stimulus. The stimulus generates a message in the form of an electrochemical impulse which then travels from the receptor (sensory neuron) to another neuron. The pathway followed is :
stimulus → dendrite + cell body + axon → axon terminal → passage of impulse through synapse.
As the nerve impulse reaches the presynaptic knob, the synaptic vesicles get stimulated to release a chemical called neurotransmitter in the synaptic cleft. The neurotransmitter molecules diffuse across the gap (synapse) to come in contact with the chemoreceptor sites in the post-synaptic membrane. In this way, nerve impulse passes across the minute gap (synapse) to stimulate dendron of other neuron.
The synapse acts as a one-way valve to conduct nerve impulse in one direction only. This is so because chemical substance, called neurotransmitter, is secreted by. synaptic vesicles only on one side of the gap, i.e, on axon's side. The neurotransmitter carries message across the synapse and passes it to the dendron of the other neuron.
- A receptor is a nerve cell or group of nerve cells which is sensitive to a specific stimulus or to specific change in the environment.
- An effector is some muscle or gland in specific part of the body which produces suitable response(s)
(i)Central nervous system (CNS).
(b) Cerebrum : - It is the largest part of brain. It covers about part of the brain. It is divided into two halves by a longitudinal groove. Each half is called cerebral hemi-sphere. The two hemi-spheres are joined together by a broad, curved, thick band of nerve fibres called corpus callosum. It has the sensory areas where information (impulse) is received from sense organs (receptors) and motor areas from where messages are sent. It is the site of intelligence, memory, learning, reasoning and stores information and experiences in association centres. The cerebral hemi-sphere has an outer region of densely packed nerve cells called cerebral cortex. The intelligence of an animal is measured by an amount of cerebral cortex. The folds are called gyri and depressions are called sulci.
(c) Diencephalon :- It encloses a slit like cavity. The thin roof of this cavity is known as epithalamus, the thick right and left sides as the thalami and the floor as hypothalamus.
(i) Epithalamus: It is not formed of nervous tissue. It consists of pia matter only.
(ii) Thalamus: It is for the integrity of sensory impulses sent from sense organs like eyes, ears and skin. Hence it deals with sensation of pain, temperature, pressure or touch.(iii)Hypothalamus: It is the part below thalamus. It deals with water balance in body (thirst and hunger), behavioural patterns of sex, sleep and menstrual cycle in females.
(ii) Mid brain: It consists of two groups of nerve cells cereb peduncles or crura cerebri on ventral side and two swellings, termed superior and inferior colliculi on each side of dorsal surface. It connects the fore brain to hind brain. It has the reflex centres for eye movements and hearing response.
(iii) Hind brain: It is the last part of brain. It has three parts:
(a) Cerebellum: It is in the bottom part of the head. It helps in maintaining posture and balance of the body. It also enables us to make precise and accurate movements. It coordinates smooth body movements such as walking, dancing, riding a bicycle and picking up a pencil, etc
(b)Pons-varolli :An oval mass called pons varolii lies above the medulla oblongata, It regulates respiration,
Medulla-oblongata: This is long connecting part of brain to spinal cord. It represents floor of brain. It deals with control of heart beat, blood vessels, breathing, coughing, vomiting, salivary secretions, swallowing and most of the reflex and involuntary movements.
2. Spinal cord
Spinal cord is a cylindrical structure and is about 45 cm long. It begins in continuation with the medulla oblongata of brain and extends downwards upto early part of lumbar region. It then extends to the end of vertebral column as fibrous connective called filum terminale. Internally, the spinal cord possesses a narrow, fluid-filled cavity called central canal. Spinal cord is enclosed in the vertebral column or backbone which protects it. Like brain, spinal cord too is surrounded by meninges. Thirty one pairs of spinal nerves arise from the spinal cord. Spinal cord performs two important functions :
(i) It conducts sensory and motor impulses to and from the brain.
(ii) It acts as a centre for the reflex actions. Thus, it reduces brain's work.
Functions of brain
The functions of the brain are as under;
(i)It receives information carrying nerve impulse from all sensory organs of the body.
(ii) The brain responds to the impulses brought in by sensory organs by sending its own instruction to muscles and glands causing them to function accordingly.
(iii)In its association centres it correlates various stimuli and different sense organs.
(iv)It stores information so that behaviour can be modified according to the past experience. This function makes the brain the organ of thought and intelligence.
(v)It controls mental activities such as thinking, memory, reasoning, intelligence, sense of responsibility, etc. It gives perception of pain, temperature, sense of touch, hearing, taste, smell and site.
Peripheral Nervous System
It connects CNS with different parts of the body. It has two components, voluntary and involuntary.
Voluntary peripheral nervous system is under the control of will. It consists of nerves that arise directly from CNS connecting different body parts for voluntary (conscious) control of the brain.
Involuntary peripheral nervous system (autonomic nervous system), on the other hand, is not under the control of human will. It develops from branches of some cranial and spinal nerves called visceral nerves. Peripheral nervous system, thus, consists of all the three types of nerves namely,
(i) Cranial nerves,
(ii) Spinal nerves, and
(ii) Visceral nerves.
(i) Cranial nerves. Cranial nerves arise from the brain and spread to various parts of the head. They are 12 pairs in number. Cranial nerves I, II and VIII are sensory nerves ; cranial nerves III, IV, VI, XI and XII are motor nerves; and cranial nerves V, VII, IX and X are mixed nerves (containing both sensory and motor nerve fibres),
(ii) Spinal nerves. Thirty one pairs of spinal nerves arise from the spinal cord along most of its length and spread throughout the body (except head region). They are all mixed nerves as they carry both sensory and motor nerve fibres.
(iii) Visceral nerves. Apart from regulating normal functions of the body, many activities of the internal organs such as heart, kidney, lungs, urinary bladder, blood vessels, glands etc. are controlled by specific set of nerves called visceral nerves which mostly arise from spinal cord but a few from the brain also. These form the autonomic nervous system.
Autonomic or automatic nervous system
(ix) Ovary: - These are the glands which are present in females only. Ovaries make three female sex hormones called Oestrogen; progesterone and relaxin. The function of Oestrogen hormone is to control the development of female sex organs and female features such as famine voice, soft skin and mammary glands. The function of progesterone hormone is to control uterus changes in menstrual cycle. It also helps in the maintenance of pregnancy. Relaxin helps in the widening of pelvis at birth.
Explain reflex action and refiex arc?
Reflex action:- The sudden action in response to something in the environment is called reflex action. The simplest form of response in the nervous system is reflex action. A reflex action is one which we perform automatically. Or
The quick responses which are given immediately and are controlled by spinal cord are called reflex actions. If we unknowingly touch a hot plate, we immediately move our hand away from it. So moving our hand on touching a hot plate is an example of reflex action. Similarly, moving our foot away when we step on something sharp is also an example of reflex action. A knee jerk, movement of diaphragm, coughing, yawning, blinking of eyes and sneezing are all reflex actions. The reflex which involve only the spinal cord are called spinal reflexes. The contraction of pupil of our eye automatically in the presence of bright light is an example of cerebral reflex. Some reflex arcs involve the brain, rather than the spinal cord. They are called cerebral reflexes
Reflex arc:- The pathway or route taken by nerve impulses in a reflex action is called the reflex arc. Reflex arcs allow rapid response. The receptor triggers an impulse in a sensory neuron, which transmits the message to the spinal cord. Here, the impulse is passed on to a relay neuron, which in turn, passes it to a motor neuron. The motor neuron passes the impulse to a muscle in our arm. The muscles then contract and pulls our hand away from the receptor.
COORDINATION IN PLANTS
Control and coordination in plants is not as elaborate as in animals. Plants do not have nervous system, muscles and sense organs (e.g., eyes, ears, nose etc.) like the animals. Still, they can respond and react to various environmental stimuli such as light, gravity, water, touch, chemicals etc. Plants, in fact, show two different types of movements in response to various stimuli . One type of movements are independent (e.g.,movement of leaves of 'touch-me-not' plant, also called chhui-mui or 'sensitive plant', in response to touch). Other type of movements are dependent on growth (e.g., directional movement of seedling with root going down and stem coming up). Both these types of movements are effected by the action of plant hormones (phytohormones). In other words, plants coordinate their responses against environmental stimuli by using hormones. Plants, thus, possess only chemical coordination.
The mode of action of hormones in plants is different from that in animals. In plants, the hormones coordinate their behaviour in two ways:
(i) effecting the growth of the plant and as a result part of the plant shows movement, and
(i) affecting the shape of plant cells by changing the amount of water in them (turgor changes),resulting in swelling or shrinking.
Thus, growth and movements in plants are regulated by both external (environmental stimuli) and internal (hormones) factors.
Since plants lack nervous system, they generally can not respond as quickly as animals. plants respond to various stimuli very slowly by revealing growth. Therefore, generally the response of the plants to various stimuli can not be observed immediately or in other words, the effect of stimulus on a plant is observed after a considerable time in most of the cases. Chhui-mui or 'touch-me-not' plant of Mimosa family (also called sensitive plant), however, shows very quick response to touch.
Plant hormones or phytohormones. Name of various plant hormones.
Ans: Plants in addition to water, CO2, light and minerals require certain chemical substances for their proper growth and development. These chemical substances are called plant hormones or phytohormones or growth receptors. Growth hormones or phytohormones are defined as organic substances which are synthesized in minute quantities in one part of the plant body and transported to another part of the plant body where they influence specific physiological processes. There are 5 main groups of plant hormones:
Auxins, gibberellins, cytokinin, abscisic acid (dormin) and ethylene.
Plant hormones with their functions. Plant harmone are of five types namely auxiri, gibberellin, cytokinin, abscisic acid and ethylene.
(1) Auxins : Of all the plant hormones, Auxins were the first to be observed. F.w.went in 1928 was the first to isolate this growth substance from the tips of oat coleoptiles in the plant body. Auxins are found in the growing tips of stem and root. The common naturally occurring auxin is indole-3-acetic acid (IAA). Synthetic auxins, (compounds made in the laboratory which have cixin like properties) include Naphthalene acetic acid (NAA) and 2, 4-dichlorophenoxy acetic acid (2,4-D); indole-3-propionic acid(IPP): 2,4,5 tri chlorophenoxy acetic acid (2,4,5-T): 2,3,6 trichloro benzoic acid.
functions:
(i)It promotes cell enlargement and cell differentiation
ii) It stimulates the tissue near the extreme tip to show rapid cell division.
ii) It stimulates seed germination,
iv) It helps in weed control.
It helps in production of seedless fruits (parthenocarpy).
vi) It helps in prevention of leaf and fruit drops.
(2)Gisberellins: These are also growth hormones which promotes cell elongation. These were discovered by Kurosawa in 1926. The discovery of gibberellins was made by Japanese worker in rice fields. Some rice seedlings were found to be much more taller than the others. It was found that these tall plants were infected with a fingus called gibberella fujikuroi. This fungus secretes a substance which was found to be responsible for causing tallness. This substance was called gibberellic acid or gibberellins. Gibberellins are produced in apical buds, young growing roof tips, embryo and endosperm.
Functions:
(i)It induces stem elongation
(ii)Its treatment results in formation of female flowers,
(iii)It induces flowering and promotes seed germination.
(iv)its treatment increases the size of leaves and therefore helpful in increasing photosynthetic activities.
(v) It also initiates the formation of parthenocarpy.
(3)Cytokinin: There are growth hormones which promote cell division. The discovery was first of all made by 2 scientists: F.Skoog and C.O.Miller in 1955. Main sources of naturally occuring cytokinins are coconut milk, yeast exiract and maize. First naturally occurring cytokinin called zeatin was found in maize,
Functions:
Functions: -
(i) It is responsible for breaking the dormancy of buds and seeds.
(ii) It helps in stimulation of fruit ripening.
(iii) It also helps in growth of fruits.
(iv) It inhibits growth of lateral buds.
(v) If stimulates abscission.
(vi) It helps in flowering in pineapple, mango and various other plants.
Plant movements and Their types
The movement of plants or parts of plant due to some external stimuli like light, force of gravity, chemical substance, water and touch are known as plant movements. The plant movements made in response to external stimuli fall in two categories: tropism (tropic movement) and Nasties (nastic movement).
Classification of Induced Plant Movements
Induced plant movements are broadly classified into two types
1. Nastic movements
2. Tropic movements
(1). Nastic movements. These are non-directional induced variation movements that occur due to turgor changes. These reveal immediate response to stimulus but do not involve growth. Nastic movements are induced by external stimuli such as light, temperature, touch. However, these are not directional movements. Here, the part of the plant does not respond towards or away from the stimulus .Nastic movements include:
(i)Seismo nostic movements
 |
| Seismonastic movement in sensitive plant (Mimosa pudica, Normal leave and,Drooping leave) |
(ii)Nyctinastic movements
Nyctinastic movements include
Photonostic and Thermonastic movements
2. Tropic movements or tropisms. Tropic movements are induced growth movements of curvature that occur due to differential growth. These are directional movements or orientations that occur in response to external stimuli such as light, force of gravity, chemicals, water etc. When some stimulus is received by the plant, specific part of the plant shows response in the form of growth movement due to unequal growth in its two sides by the action of plant growth hormones (phytohormones). Directional movements or orientations of specific part of a plant revealing growth in response to external stimuli are called tropisms or tropic movements.
Tropic movements are very slow. The movement of the plant part can be either towards the stimulus or away from the stimulus.
• If the movement of the plant part is towards the stimulus, it is termed as positive tropism.
. If the movement of the plant part is away from the stimulus, it is termed as negative tropism.
Tropism and its types
A growth movement of a plant part in response to an external stimulus in which the direction of stimulus determines the direction of response is called tropism. If the growth of a plant part is towards the stimulus, it is called positive tropism. If the growth of a plant part is away from the stimulus, then it is called negative tropism.
Types of tropism
There are 5 common stimuli in the environment which are (light) , (gravity) (chemicals), (water) and (touch). though These 5 stimuli give us 5 types of tropism:
phototropism (light),
Geotropism (gravity),
Chemo tropism (Chemical)
Hydro tropism (Water)
Thigmo tropism (Touch)
(i) Phototropism. If the plant part moves towards the light, it is called positive phototropism. If the plant part moves away from light, it is called negative phototropism. The stems of a plant shows positive phototropism while the roots show negative photo-tropism.
(ii) Geotropism: The movement of a plant part in response to gravity is called geotropism. If the plant part moves in the direction of gravity, it is called positive geotropism. If the plant part moves against the direction of gravity, it is called negative geotropism. The roots of a plant show positive geotropism while as stem of a plant shows negative geotropism.
(iii) Chemotropism: The movement of a plant part in response to a chemical stimulus is called chemotropism. If the plant part shows movement towards the chemical, it is called positive chemotropism. If the plant part shows movement away from the chemical, it is called negative chemotropism. e.g.: growth of pollen tube through stigma and style towards the embryo sac with the stimulus of chemical substances present in the carpel.
(iv) Hydrotropism: The movement of a plant part in response to water is called hydrotropism. If the plant part moves towards water, it is called positive hydrotropism. If the plant part moves away from the water, it is called negative hydrotropism. The roots of a plant are positively hydrotropic while as the stem of a plant is negatively hydrotropic.
(v) Thigmotropism: The directional growth movement of a plant part in response to the touch of an object is called thigmotropism. The climbing part of the plant such as tendrils are positively thigmotropic.
Nastic Movement (or Nasties)And Its Types
Ans: The movement of a plant part in response to an external stimulus in which the direction of response is not determined by the direction of stimulus is called nastic movement. The main difference between tropic and nastic movement is that tropic movement is a directional movement of a plant part but nastic movement is not a directional movement of the plant part with respect to the stimulus. Nastic movement is of two types: thigmonasty and photo nasty.
(i) Thigmonasty: The non-directional movement of a plant part in response to touch of an object is called thigmonasty. The folding up of leaves of a sensitive plant 'Mimosa pudica (or touch me not or chhui-mui) on touching, is an example of thigmonastic movement in plants. The sensitive plant has pad-like swellings called pulvini at the base of each leaf. The folding up of leaves of a sensitive plant on touching is due to the sudden loss of water from the pulvini present at the base of each leaf of the sensitive plant which make the pulvini lose their firmness causing the leaves to droop and fall. The folding up of leaves of a sensitive plant on touching is not a growth movement.
(ii)Photo nasty: The non-directional movement of a plant part usually petals of flower in response to light is called photo nastic movement. The opening and closing of petals of Dandelion flower in response to the intensity of light is an example of nastic movement. The opening and closing of flowers in response to light are growth movements.
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