Chapter at a Glance
1.Introduction: The adjustment of all the vital activities of life is called as coordination. The vital processes of life are controlled by endocrine system and nervous system.
2. Control and coordination in animals
(i) Nervous system
1) It comprises of neurons, nerves organs like brain, spinal cord etc. which control the activities of different organs of the body.
2) Nervous system of human consists of three parts – central nervous system (which includes brain and spinal cord); peripheral nervous system (comprises of nerves arising from brain and spinal cord) and autonomic nervous system (comprises of sympathetic and parasympathetic nervous systems).
(a) Neuron: It is the structural and functional unit of nervous system. Neuron (or nerve cell) has three components:
- Dendrites: It branch out in tree-like fashion and serve as the main apparatus for receiving signals from other nerve cells.
- Cyton: It is the spherical part of the neuron and contains the nucleus. It maintains the cell and keeps the neuron functional.
- Axon: It is the elongated fibre which transmits information away from the cell body. It is the main conducting unit of the neuron.
Both axon and dendrites arise from cyton of the neuron.
(b) Synapse: The neurons transmits the messages to the nervous system in the form of electrical signals. They pass the impulse to the cell body and then along the axon. The axon passes the impulse to another neuron through a junction called synapse.
(c) Reflex action: It is rapid, automatic, definite response to stimulus by an organ without involving brain for its initiation. The pathway which is followed by this is called reflex arc.
(d) Components of reflex are
- Sensory structure (receptor organ) – e.g. skin
- Afferent (sensory) neuron
- Interneuron (association neuron)
- Efferent (motor) neuron
- Effector organ – e.g. muscle or gland
(e) Brain: Brain controls all the functions in the human body, hence it is considered as the main coordinating centre. It is divided into three parts
Cerebrum is the largest part of brain. It is involved with higher brain function like memory, reasoning, judgement, etc.
Thalamus sends motor and sensory signals to the cerebral cortex. Hypothalamus plays an important role in nervous as well as endocrine system. It secretes releasing and inhibiting hormones that stimulate or inhibit production of pituitary hormones.
Midbrain controls involuntary actions, e.g., reflexes of eye and ear.
Medulla oblongata, located in brainstem, controls a number of involuntary functions. It helps regulate breathing, digestion, sneezing, swallowing, heart and blood vessel function, etc. Hence, also considered as a centre for respiration and circulation.
Pons is a part of brainstem. It transfers information between cerebrum and cerebellum and regulates respiration.
Cerebellum manages voluntary movements like posture, balance, co-ordination, and speech, resulting in smooth and balanced muscular activity. It also helps in learning motor behaviour.
(ii)Hormones in animals
•Hormones are the chemical messenger which help in control and coordination of the body activities.
•Exocrine glands: It includes mammary glands, salivary gland, sweat gland.
•Endocrine glands: It includes pituitary, thyroid, adrenal, pineal, testes, ovary etc.
•Pancreas,testes and ovary are endocrine as well as exocrine gland. •Hypothalamus, pituitary, pineal, thyroid, parathyroid, adrenal, testes, ovary are endocrine glands of human being.
• Hypothalamus :The hypothalamic hormones are alsocalled releasing hormones, e.g.,TSH, ACTH, FSH, LH etc.
• Pineal gland secretes melatonin hormone that helps to maintain circadian rhythm and regulate reproductive hormones.
• Pituitary gland,also called master gland, produces a number of hormone, for example, adrenocorticotropic hormone (ACTH), anti diuretic hormone (ADH), or vasopressin, follicle-stimulating hormone (FSH), growth hormone (GH), luteinising hormone (LH), prolactin (PRL), and thyroid-stimulating hormone (TSH).
• Thymus gland is the main organ of lymphatic system. It secretes thymosin hormone that stimulates the development ofT-lymphocyte and helps in immune function.
• Thyroid gland secretes two most important hormones – T (triiodothyronine) and T3(thyroxine). These hormones regulate protein, fat, and carbohydrate metabolism,
• Iodine is necessary for the formation of thyroxine hormone secreted from thyroid gland. Therefore, its deficiency will lead to low secretion of thyroid hormone.
•Parathyroid gland secretes parathyroid hormone that regulates calcium levels in the blood, largely by increasing the levels when they are too low.
•Adrenal gland, also called gland of emergency, is composed of two distinct parts: adrenal cortex (outer part) and adrenal medulla (inner part).
•Adrenal cortex secretes aldosterone, cortisol whereas adrenal medulla secretes epinephrine (or adrenaline) and nor-epinephrine (or noradrenaline).
•Pancreas contains both exocrine as well as endocrine glands.
Exocrine part of pancreas helps in digestion by secreting digestive enzymes like trypsin. Endocrine part consists ofislets of Langerhans that secretes and releases hormones directly into the bloodstream. Insulin and glucagon are two main important hormones secreted by pancreas.
•Insulin, secreted by beta cells, acts to lower blood sugar, and glucagon, secreted from alpha cell, acts to raise blood sugar.
•Gonads produce gametes (testes in male and ovary in female) for reproduction and secrete sex hormones.
•Testosterone (secreted from testes) and oestrogen (secreted from ovary) are associated with male and female puberty respectively.
•Progesterone hormone helps in the maintenance of pregnancy, hence also known as hormone of pregnancy. It is secreted from ovary, placenta and adrenal gland.
Excess or deficient secretion of hormones has harmful effect on body that may lead to many disorders.
Control and coordination in plants
(i) Coordination in plants: The plants coordinate their behaviour against environmental changes by using hormones.
Plants show two types of movements:
- (a) Movement dependent on growth: Environmental triggers such as light, or gravity will change the directions that plant parts grow in. These directional, or tropic, movements can be either towards the stimulus, or away from it. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the earth.
- (b)Movement independent on growth: Growth independent movements are also called nastic movements. In nastic movements, the movement of plant part is neither towards the stimulus nor away from the stimulus. This movement is not a directional movement of the plant part with respect to the stimulus. In nastic movements, growth may or may not take place.
(ii) Immediate response to stimulus: The plant movements made in response to external stimuli fall into two main categories: tropism and nastic.
(a) Tropism (tropic movements): Agrowth 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.
Types of tropic movements
- In phototropism, plants grow towards or away from the light. It is caused due to differential growth of part of plant like root or stem. Stems show positive phototropism while roots show negative phototropism.
- When plant grows in response to touch, the condition is called thigmotropism, e.g., climbing vines.
- The tropic movement of plant in response to stimulus of water is called hydrotropism. The growth of root towards water is due to positive hydrotropism. The shoot grow away from water is called negative hydrotropism.
- The tropic movement in response to some chemical is called chemotropism. The hyphae of the fungi are chemotropic.
- Geotropism is the growth of plant parts in response to the force of gravity.
- The movements that occur in response to external stimuli but unlike tropic movements, the direction of the response is not dependent on the direction of the stimulus.
(b) Nastic (nastic movements): The movements that occur in response to external stimuli but unlike tropic movements, the direction of the response is not dependent on the direction of the stimulus.
Types of nastic movement
- Thigmonasty: It is the non-directional movement of a plant part in response to the touch ofan object, e.g., Mimosa pudica (Chui-mui).
- Photonasty: The non-directional movement of a plant part (usually petals of flowers) in response to light is called photonasty.
(iii) Hormones in plants: Plant hormones, also known as phytohormones, are chemicals that regulate plant cell processes. They are signal molecules produced within the plant functioning in extremely low concentrations. Various plant hormones are as follows:
- (i) Auxins: It stimulates growth, phototropism, geotropism. Auxins
- prevent potato sprouting.
- (ii) Gibberellins: It increase the height of plant, can induce parthenocarpy, stimulate flowering.
- (iii) Cytokinins: It promotes cell division, inhibit or delay ageing, organ formation.
- (iv) Ethylene: It is a gaseous plant hormone, used in artificial ripening of fruits, promote ageing in plants, breaks dormancy of several organs.
- (v) Abscisic acid (ABA): It also known as stress hormone. It is a growth inhibitor, inhibit the process of flowering, seed development.
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