NCERT Exemplar Class 10 Science Solutions

Chapter 07-Control and Coordination-Long Answers

Long Answer Type Questions
Q.45. Draw the structure of a neuron and explain its function.
Answer. Neuron is the structural and functional unit of nervous system. It serves to carry nerve impulse from one part of body to other. It has dendrites, cell body and axon. Dendrite receives signals from sensory receptors or other neurons. The long extension of cell body of nerve cell is called as axon that serves to conduct the nerve impulse away from the cell body. Cell body is the metabolic center of neuron.


Q.46. What are the major parts of the brain? Mention the function of different parts.
Answer. Brain is the most important coordinating centre in the body. It has three major parts namely: fore-brain, mid-brain and hind-brain.
1. Fore brain:


2. Mid brain:


3. Hind brain:


Q.47. What constitutes the central and peripheral nervous systems? How are the components of central nervous system protected?
Answer. The central nervous system consists of the brain and the spinal cord.
(i) Brain is the main centre of coordination of sensory information in the body. It is located in protective brain box or cranium and is covered by membranous meninges. Cerebrospinal fluid is the clear tissue fluid which makes protective cushion around and within CNS. It is present in central canal of spinal cord and in brain ventricles.
(ii) Spinal cord is a long cylindrical structure that begins from the medulla oblongata and extends downwards. It is enclosed in a protective bony cage vertebral column and is also surrounded by meninges.
Peripheral Nervous System (PNS): It lies outside the central nervous system and consists of somatic and autonomic nervous system.
It includes cranial, spinal and visceral nerves.
(i) Cranial nerves: Thses consist of the 12 pairs that emerge from the brain mostly concerned with head, neck and facial region of the body.
(ii) Spinal nerves: 31 pairs of spinal nerves arise from the spinal cord and spread throughout the body.
(iii) Visceral nerves: These arise from the spinal cord and are connected to the internal organs of the body.

Q.48. Mention one function for each of these hormones
a) Thyroxin
b) Insulin
c) Adrenaline
d) Growth hormone
e) Testosterone
Answer.


Q.49. Name various plant hormones. Also give their physiological effects on plant growth and development.
Answer.


Q.50. What are reflex actions? Give two examples. Explain a reflex arc.
Answer.
Reflex action: A reflex action, is an involuntary and nearly instantaneous movement in response to a stimulus.
For example:
(i) Moving away your hand upon touching a hot object.
(ii) Closing your eyes on sudden exposure to bright light.
Reflecx arc: Reflex arc is a simple nervous pathway and consists of receptors, sensory neurons, interneurons, motor neurons and muscles. The sensory neurons transmit the sensory information from sensory receptors to spinal cord or brain. The interneurons integrate the incoming information and signal is relayed to motor neurons. The motor pathway transmits the signal from motor neurons to the effector organs (usually muscles and glands).


Q.51. ‘Nervous and hormonal systems together perform the function of control and coordination in human beings. Justify the statement.
Answer. Nervous system serves to pass the sensory information from receptor to effector organs and thereby generate response. The afferent/sensory neurons transmit the sensory information from sensory receptors to spinal cord or brain. The interneurons integrate the incoming information and signal is relayed to motor/efferent neurons. The efferent/motor pathway transmits the signal from motor neurons to the effector organs (muscles and glands etc).
The effector organs generate response in terms of secretion of either any activity or secretion of hormones. It can be said that secretion of hormones is under regulation of nervous system. Hormonal system can regulate wise range of target tissues as compared to nervous system. Hence, together, nervous system and hormonal system serve the function of control and coordination.
Q.52. How does chemical coordination take place in animals?
Answer. Hormones are the long range chemical messengers that are released into blood by endocrine gland in response to some signal. These hormones exert their effect on the target cells present distantly from their site of release. These hormones serve the function of chemical coordination in animals.
Hormones are released into the blood stream and can reach all cells but they affect only target cells. This is followed by generation of stimulus specific biochemical or physiological activity. In this way, hormones regulate functioning of different organs and tissues. Each hormone is under regulation of feedback mechanism which in turn ensures reliability of the system.
Q.53. Why is the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse?
Answer. Two neurons are never in physical contact of each other and the junction between two neurons is referred to as synapsis. The synapse serves like a one-way valve as axonal ends of synapse release the chemical substance that diffuse into synapse. This chemical diffuses towards the dendrite end of next neuron and propagates an electrical signal.
Diffusion of chemical from axonal end followed by its diffusion in synapse and fusion with dendrite of next neuron ensures the transmission of electrical signal. Since, the dendritic end of neuron does not release the chemicals; the nerve impulse can go across only in one direction.