CONTROL AND COORDINATION IN LIVING ORGANISMS - II : BRIEF AND LONG ANSWERS

ANSWER AS ASKED

*INDEX-TOPIC SEARCH

1. Explain : Tropism
   
   ANS:
   
   
   
   • The movement of curvature of plants in the direction of stimuli is known as tropism.
     
   • Phototropism : When illuminated by a unidirectional light, the response of a growing plant by bending towards that light is called phototropism.
     
     
     
   • Geotropism : The downward movement of the roots of the plants, for fixation and absorption, as a response to the gravitational force is called geotropism.
     
   • Chemotropism : The movement of a plant or its part as a response to certain chemicals is called chemotropism. For example, germination of pollen grains and development of pollen tubes as a response to the chemicals secreted by the surface of the stigma.
     
   
   
   
2. Explain : Explain : Nastic movement
   
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   • The response by some plants to the external stimuli without any directional movement of growth or curvature towards that external stimuli is called nastic movement.
     
   • Examples :
     
     
     
     1. The leaves of Mimosa (touch-me-not) are sensitive to touch. They droop when touched.
        
     2. All insectivorous plants bend down or curl up when touched by insects.
        
     3. A sunflower plant bends towards the sun.
        
     
     
   • Of the above examples, (i) and (ii) are examples of thigmonastic response and (iii) is an example of photonastic response.
     
   
   
   
3. Distinguish between tropic movement and nastic movement.
   
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4. Explain : Photoperiodism.
   
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   • Photoperiodism is the phenomenon in which the duration of light decides the flowering and germination in plants.
     
   • Plants are (i) Long-day plant and (ii) Short-day plant on the basis of the duration of light received by them.
     
   • Day natural plants do not respond to photoperiodism.
     
   • Plants respond to photoperiodic stimulus by a specialised pigment present in them called phytochrome.
     
   
   
   
5. Explain : Coordination in animals.
   
   ANS:
   
   
   
   • All multicellular organisms, except porifera, have well-developed nervous system.
     
   • Hydra and other cnidarians possess nerve cells which form a nerve net in the body.
     
     
     
   • In invertebrates, the nerve net condenses into nerve mass called 'ganglion'.
     
   • Insects have a bilobed nerve mass (brain), nerve cord and nerve ganglia.
     
     
     
     
   • Higher organisms possess sensory organs (receptors) related to light, hearing, taste, touch and smell.
     
   • Receptors receive the stimulus and pass on the message to the brain through sensory neuron.
     
   • The brain transmits information to the effector organ (generally muscles and glands) through motor neuron.
     
   • The brain acts as the center for the analysis of information.
     
   • Motor neurons stimulate the muscles of the organ to respond.
     
   • Hormones also play an important role in control and coordination in animals.
     
   • In vertebrates there is a successive development of nervous system.
     
   • The nervous system of human beings is highly developed.
     
   • Hormones secreted by endocrine glands control various biochemical and mechanical activities carried out in the organisms. This is chemical control.
     
   
   
   
6. Write an explanatory note on HUMAN BRAIN.
   
   ANS:
   
   
   
   
   
   • Human brain is the main coordinating center for all the activities of the human body.
     
   • It is protected by a bony box in the skull called cranium and three membranes called meninges.
     
   • There is a fluid called cerebrospinal fluid in the space between these membranes.
     
   • Cerebrospinal fluid acts as a cushion and protects the brain from mechanical shocks.
     
   • The brain is divided into three regions : (i) fore-brain (ii) mid-brain and (iii) hind-brain.
     
   • FORE-BRAIN consists of cerebrum and olfactory lobes.
     
     
     
     • Cerebrum is the most complex and specialised part of the brain.
       
     • It consists of two cerebral hemispheres.
       
     • It has sensory area to receive impulse from the sense organs and motor area to send impulse to muscles and effector organs.
       
     • Cerebrum has four regions having different centers of activity : (i) frontal lobe (ii) parietal lobe (iii) temporal lobe (iv) occipital lobe.
       
       
       
     • The frontal lobe possesses centres for voluntary muscular activities.
       
     • Parietal lobe possesses the centres for temperature control, smell and touch.
       
     • Temporal lobe possesses the centres for auditory and olfactory reception.
       
     • Occipital lobe possesses the centres for visual reception.
       
     
     
   • MID-BRAIN is a part of the brain stem and possesses the regions for visual reception, auditory reception and touch.
     
   • HIND-BRAIN consists of cerebellum, pons and medulla oblongata.
     
     
     
     • Cerebellum is situated on the posterior side of the fore-brain and it controls the rhythmic movement of muscles, body balance and posture.
       
     • Pons connects various parts of the central nervous system and cerebellum by the transverse bands of nerves.
       
     • Pons takes part in the regulation of respiration and helps in the movement of head as per audio-visual perception in coordination with medulla oblongata and spinal cord.
       
     • Medulla oblongata possesses the centres to regulate heartbeats, breathing, blood-pressure, sneezing, coughing, vomiting, swallowing, hiccups, etc.
       
     
     
   
   
   
7. Write in brief about Spinal cord.
   
   ANS:
   
   
   
   • Spinal cord is a cylindrical structure.
     
   • It is the posterior extension of of medulla oblongata.
     
   • The vertebral column and meninges protect the spinal cord.
     
   • There are 31 pairs of spinal nerves arising from the spinal cord.
     
   • These nerves connect various organs of the body to the brain.
     
   • They help in the conduction of impulses from brain to organs and from organs to brain.
     
   • They also perform reflex action.
     
   
   
   
8. Explain : Reflex action
   
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   • An unconscious and involuntary response of effectors to the stimulus is called reflex action.
     
   • Due to reflex action we suddenly withdraw our leg when we step on a very hot or pricking object.
     
   • Similarly, our response towards very hot or very cold water is sudden and involuntary.
     
   • The reflex action is performed by the spinal cord when the brain is busy or at rest.
     
   • In reflex action, a message from the receptors is relayed by sensory nerves to the spinal cord and the spinal cord sends response via motor nerve to the effector organ.
     
   • This entire pathway is called 'REFLEX ARC'.
     
   
   
   
9. Write a note on Autonomous nervous system.
   
   ANS:
   
   
   
   • The system which is responsible for the intervention in the activities of the organs located in the body cavity without the awareness of brain is called autonomous nervous system.
     
   • This system controls heart, blood vessels, glands, uterus and coelomic organs.
     
   • Autonomous nervous system is of two types : (i) sympathetic (ii) parasympathetic.
     
   • The involuntary actions of the body are controlled and regulated by the coordination of these two systems.
     
   • The effects of sympathetic and parasympathetic nervous systems are complimentory and contradictory.
     
   • For example : If the sympathetic system increases the heartbeats abnormally, the parasympathetic system decreases it and brings it back to normal.
     
   
   
   
10. Mention characteristics of hormones.
    
    ANS:
    
    
    
    • They are specific chemical messengers.
      
    • Generally the origin and the target area of hormones are different.
      
    • They are directly poured into the blood (from the gland) and carried by blood circulation.
      
    • The effect of a hormone is either rapid or slow (i.e. it may increase or decrease the speed of some process). For example, acetylcholine increases the speed of the conduction of impulses whereas decreases (slows down) the effect of sex hormones.
      
    
    
    
11. Write a note on endocrine glands.
    
    ANS:
    
    
    
    • Endocrine glands play an important role in coordination (in animals).
      
    • These are ductless glands and secrete hormones which are specific chemical messengers.
      
    • The main endocrine glands are hypothalamus, pituitary,, pineal, thyroid, parathyroid, pancreas, adrenal, testis and ovary.
      
    • Pituitary gland is called the master gland as it regulates the secretion of hormones by other endocrine glands.
      
    • The function of the pituitary gland is controlled by the secretion of hypothalamus.
      
    
    
    
12. Mention different endocrine glands, hormones secreted by them and the functions of these hormones.
    
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13. How is brain protected ?
    
    ANS : The brain is surrounded by cranium, a bony box in the skull and three membranes called meninges. In the space between these membranes there is a fluid called cerebrospinal fluid. This fluid protects the brain against mechanical shocks. Thus brain is protected.