Control & Coordination
NCERT Exemplar Problems
Long Answer Questions
Question 45: Draw the structure of a neuron and explain its function.
- Cyton or cell body: The cell body or cyton is somewhat star-shaped, with many hair-like structures protruding out of the margin. These hair-like structures are called dendrites. Dendrites receive the nerve impulses.
- Axon: This is the tail of the neuron. It ends in several hair-like structures, called axon terminals. The axon terminals relay nerve impulses.
- Myelin Sheath: There is an insulator cover around the axon. This is called myelin sheath. The myelin sheath insulates the axon against nerve impulses from the surroundings.
Question 46: What are the major parts of the brain? Mention the functions of different parts.
Answer: The major parts of the brain and their functions are as follows:
- Cerebrum: It controls the voluntary actions and is the site for sensory perceptions.
- Cerebellum: It coordinates the motor function and maintains posture and balance.
- Medulla: It controls involuntary functions; such as heart rate, breathing, etc.
Question 47: What constitutes the central and peripheral nervous systems? How are the components of central nervous system protected?
Answer: The central nervous system is composed of the brain and the spinal cord. The peripheral nervous system is composed of cranial nerves, spinal nerves and the autonomous nervous system.
Brain gets the maximum protection, as it is housed inside the skull. Spinal cord gets protection by the vertebral column. Additionally, the brain and the spinal cord are surrounded by a system of three layers; called meninges. The cerebrospinal fluid; filled between these membranes; provides a cushion against mechanical shocks.
Question 48: Mention one function for each of these hormones:
Answer: General metabolism
Answer: Controls blood sugar level
Answer: Prepares the body for fight or flight response.
- Growth hormone
Answer: Promotes growth and development
Answer: Triggers sperm production and is responsible for the development of secondary sexual characters in males.
Question 49: Name various plant hormones. Also give their physiological effects on plant growth and development.
Answer: Various plant hormones and their effects are as follows:
- Auxin: Promotes cell elongation and thus promotes growth of a plant part.
- Gibberellins: Promotes growth.
- Cytokinin: Promotes cell division and thus promotes growth.
- Abscissic acid: Inhibits growth and is responsible for shedding or older parts.
Question 50: What are reflex actions? Give two examples. Explain a reflex arc.
Answer: Reflex action is a special case of involuntary movement in voluntary organs. When a voluntary organ is in the vicinity of a sudden danger, it is immediately pulled away from the danger to save itself. For example; when your hand touches a very hot electric iron, you move away your hand in a jerk. All of this happens in flash and your hand is saved from the imminent injury. This is an example of reflex action.
Reflex Arc: The path through which nerves signals; involved in a reflex action; travel is called the reflex arc. The following flow chart shows the flow of signal in a reflex arc.
Receptor ⇨ Sensory Neuron ⇨ Relay neuron ⇨ Motor neuron ⇨ Effector (muscle)
- The receptor is the organ which comes in the danger zone.
- The sensory neurons pick signals from the receptor and send them to the relay neuron.
- The relay neuron is present in the spinal cord.
- The spinal cord sends signals to the effector via the motor neuron.
- The effector comes in action and moves the receptor away from the danger.
Question 51: Nervous and hormonal systems together perform the function of control and coordination in human beings.” Justify the statement.
Answer: The nervous system controls and coordinates all the functions in the body. It carries out its functions in close coordination with the hormonal system.
Nerves don’t reach every nook and corner of the body and hence need assistance from the hormones to control all the parts of the body. Moreover, while the nervous control is somewhat faster, hormonal control is slower.
Hormonal control is mainly based on feedback mechanism and tells the body to either pace up or slow down, as per the situation. Nervous control, on the other hand, is more of a direct control.
Both of them complement each other. Thus, it can be said that nervous and hormonal systems together perform the function of control and coordination in human beings.
Question 52: How does chemical coordination take place in animals?
Answer: Chemical control takes place through hormones in animals. Hormones are directly released in the bloodstream and reach an effector. Hormones tell the brain when to pace up or slow down a particular function. It is mainly based on the feedback mechanism.
Question 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: Channels for receiving neurotransmitter are present only at the dendritic end of neuron. Such receptor channels are absent at axonal end of neuron. Due to this, neurotransmitters can come out from the axonal end and can enter the dendritic end of neuron. You can imagine receptor channels at the dendritic end as a valve which permit only inward movement of neurotransmitters. On the other hand, the channels at the dendritic end permit only outward movement of neurotransmitters. Due to this, there is one way movement of nerve signals. Hence, the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse.