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Solutions for Biology, Class 8, ICSE
Assertion (A): Synapse is the junction between two neurons which communicates impulses/ messages.
Reason (R): Neurons must be connected with each other through some means in order to transmit the unidirectional flow of impulses.
Both A and R are true.
Explanation — At synapse, the message is transmitted from the axon of one neuron to the dendrites of the next neuron. Messages relayed in this manner from one neuron to the next allow the unidirectional flow of impulses.
Both A and R are false.
Explanation — The main function of cerebellum are muscular coordination and body balance. Cerebrum, the largest portion of the brain, is the seat of intelligence, consciousness and will power. Hence, it enables us to remember, think and reason. Therefore both the Assertion and the Reason are incorrect.
Assertion (A): The glands and muscles are considered as effector organs.
Reason (R): Muscles and glands are highly affected by the impulses carried through the sensory nerves from sense organs to the central nervous system (brain/ spinal cord).
A is true and R is false.
Explanation — Muscles and glands are called effector organs because they carry out the response when they receive signals from the nervous system. Muscles and glands respond to impulses sent from the CNS via motor nerves, not sensory nerves.
Assertion (A): The sympathetic and parasympathetic nervous systems are antagonistic (opposite) in their actions.
Reason (R): Sympathetic nervous system becomes active when a person is in fear whereas parasympathetic nervous system gets activated when in anger.
A is true and R is false.
Explanation — While the sympathetic nervous system is indeed activated during states of fear, the parasympathetic nervous system is associated with rest and digestion, not anger. Anger is more closely linked to the sympathetic nervous system's activation.
Assertion (A): The arrangement of white and grey matter is reversed in spinal cord from that in the brain.
Reason (R): In brain, the outer portion is white and the inner portion is grey. In spinal cord, the outer portion consists of cytons of neurons whereas the inner portion contains the axons of neurons.
A is true and R is false.
Explanation — In the brain, the outer portion of cerebrum contains the grey matter and the inner portion of cerebrum contains the white matter. In the spinal cord, the arrangement is reversed. In the spinal cord, the inner part is the grey matter made up of cell bodies, while the outer part is the white matter made up of axons.
Difference between Stimulus and Response on the basis of definition:
| Stimulus | Response |
|---|---|
| Any change in the environment that usually results in change in the activity of the body. | The activity of the body due to the stimulus. |
Difference between Receptor and Effector on the basis of examples:
| Receptor | Effector |
|---|---|
| The nerve cells in the skin that receives the stimulus is the receptor. | The muscle of the hand receiving the command from the brain is an effector. |
Difference between Motor nerve and Sensory nerve on the basis of their function:
| Motor Nerve | Sensory Nerve |
|---|---|
| Motor nerve carries impulses from the brain and spinal cord to the muscles and glands. | Sensory nerve carries impulses from the sense organs to the spinal cord or brain. |
Difference between Cranial and Spinal nerves on the basis of their number in pairs:
| Cranial Nerves | Spinal Nerves |
|---|---|
| There are 12 pairs of cranial nerves. | There are 31 pairs of spinal nerves. |
Difference between Cerebrum and Medulla oblongata on the basis of their function:
| Cerebrum | Medulla oblongata |
|---|---|
| The cerebrum is the seat of intelligence, consciousness and will power. It controls all the voluntary activities. | Medulla oblongata controls the activities of the internal organs. |
Difference between Cerebrum and Spinal cord on the basis of arrangement of white and grey matter:
| Cerebrum | Spinal cord |
|---|---|
| In Cerebrum, the outer portion contains grey matter and inner portion contains white matter. | In Spinal cord, the inner part contains grey matter and the outer part contains white matter. |
Draw a neat and labeled diagram of a neuron and answer the following questions :
(a) What are the two main parts of a neuron?
(b) Is this structure unicellular or multicellular?
(c) Which part of the neuron contains nucleus?
(d) Name the two parts of the human body where neurons are found abundantly.
(e) How are neurons significant to us?
Labeled diagram of a neuron is shown below:
(a) Axon and Cyton
(b) Unicellular
(c) Cyton
(d) Brain and Spinal cord
(e) Neurons are significant to us as they are the fundamental building blocks of the nervous system. Neurons carry impulses between sense organs and brain or spinal cord as well as between themselves. They keep us informed about the outside world and bring about control and coordination in our body. They also help in regulating our involuntary activities.
The peripheral nervous system and spinal cord together control certain actions where the brain is not involved, e.g. when we touch a hot object or get pricked by a pointed object, we instantly remove our hand, without thinking about it. Such an action is called a reflex action.
Difference between Voluntary and involuntary action is given below:
| Voluntary Action | Involuntary Action |
|---|---|
| Voluntary actions occur knowingly. | Involuntary actions occur unknowingly. |
| Cerebrum controls voluntary actions. | Medulla oblongata and Spinal cord controls involuntary actions. |
| Eating apple, watching TV are examples of voluntary actions. | Breathing, beating of heart are examples of involuntary actions. |
Difference between Inborn and acquired reflexes is given below:
| Inborn Reflexes | Acquired Reflexes |
|---|---|
| No previous experience or learning is required for inborn reflexes. | Acquired reflexes develop with experience and learning during the lifetime. |
| Blinking, coughing, sneezing, vomiting are examples of inborn reflexes. | Typing on the keyboard, playing a musical instrument are examples of acquired reflexes. |
Name:
(a) The long, extended process of a neuron.
(b) The point of contact between two neurons.
(c) The kind of nerve which carries both sensory and motor neurons.
(d) The nerve which connects the eyes to the brain.
(e) The nerve which connects the nose to the brain.
(f) The nerve which connects the ears to the brain.
(g) Two sub-divisions of the peripheral nervous system.
(h) Two parts of the autonomic nervous system.
(a) Axon
(b) Synapse
(c) Mixed nerve
(d) The Optic nerve
(e) Olfactory nerve
(f) Auditory nerve
(g) Somatic nervous system and Autonomic nervous system.
(h) Sympathetic and Parasympathetic systems
This is a Conditioned or Acquired Reflex action. This reflex is one which is developed during the lifetime due to experience or learning.
Beating of heart and respiratory movement
Reason — Medulla oblongata controls breathing, heart function, blood vessel function, digestion, sneezing, and peristalsis of the alimentary canal, etc.
Peripheral nervous system consists of different types of nerves which connect the central nervous system to all parts of the body. Cranial nerves, spinal nerves, sympathetic and parasympathetic nerves are all connected to different parts of the body. Which of the following does not belong to cranial nerves ?
Sympathetic nerves
Reason — Cranial nerves emerge from the brain. Some of the cranial nerves are — the olfactory (for nose), optic (for eyes) and auditory (for ears). While cranial nerves are a part of Somatic nervous system, Sympathetic nerves are a part of Autonomic nervous system.
Ayush, a student of class 8 was preparing for his biology annual exam but could not understand the terms Receptor, Effector, Stimulus and Response. Which of the following statements explains 'receptor' ?
P. Receptors are sense organs.
Q. Receptors send impulses to CNS through sensory nerves.
R. Receptors receive messages from the central nervous system.
Only P and Q
Reason — Receptors are the sense organs that receive the stimulus. They send impulses to CNS through sensory nerves. For example, eyes, ears, skin, etc.
