Biology 2 Marks Questions

The cones are responsible for color vision. There are three types of cones cells that respond to green light, blue light and red light according to their characteristics. These cells are stimulated by different lights, from different sources. The combinations of the signals generated help us see the different colors.

Cerebrum and cerebellum:

Cerebrum	Cerebellum
It is the part of the forebrain that controls voluntary functions. It is the place where intelligence, will power, memory, etc., reside.	It is the part of the hindbrain that controls voluntary functions and controls the equilibrium.

It is located between the thalamus region of the forebrain and pons region of hindbrain. The dorsal surface of midbrain consists of superior and inferior corpora bigemina and four round lobes called corpora quadrigemina. A canal known as cerebral aqueduct passes through the midbrain. Midbrain is concerned with the sense of sight and hearing.

Choroid and retina:

	Choroid		Retina
1.	Choroid is the middle vascular layer of eye.	1.	Retina is the innermost nervous coat of eye.
2.	It contains numerous blood vessels that provide nutrients and oxygen to retina and other tissues.	2.	It contains photoreceptor cells, rods and cones that are associated with twilight and colour vision respectively.

Thalamus and hypothalamus:

Thalamus	Hypothalamus
Thalamus is the part of the forebrain that receives nerve impulses of pain, temperature, touch, etc., and conducts them to the cerebral hemisphere.	Hypothalamus is the part of the forebrain that controls involuntary functions such as hunger, thirst, sweating, sleep, fatigue, sexual desire, temperature regulation, etc.

Cranial nerves and spinal nerves:

	Cranial nerves		Spinal nerves
1.	Cranial nerves arise from the brain.	1.	Spinal nerves arise from the spinal cord.
2.	There are 12 pairs of cranial nerves.	2.	There are 31 pairs of spinal nerves.

Pupil is the small aperture surrounded by the iris that regulates the amount of light entering the eye. This expand in case of low light and contract in case of intense light thereby regulating the amount of light falling on the retina.

Organ of corti is the hearing organ. It is located on the basilar membrane that contains hair cells. Hair cells act as auditory receptors. They are present on the internal side of organ of corti.

Impulse conduction in a myelinated nerve fibre and an unmyelinated nerve fibre:

	Impulse conduction in a myelinated nerve fibre		Impulse conduction in a unmyelinated nerve fibre
1.	In a myelinated nerve fibre, the action potential is conducted from one node to another.	1.	In an unmyelinated nerve fibre, the action potential is not conducted from node to node. It is carried along the whole length of the nerve fibre.
2.	The conduction of impulses is faster.	2.	The conduction of impulses is slower.

Afferent neurons and efferent neurons:

Afferent neurons	Efferent neurons
Afferent neuron conducts nerve impulses toward the brain or the spinal cord.	Efferent neuron conducts nerve impulses from the brain or spinal cord to the effector organs such as muscles or glands.

1. The neurotransmitters involved in the conduction of nerve impulse across the synapse, are present only in the axon terminals and not in the dendrites or cell body.
2. In a synapse, the impulse travels from the axon terminal to the dendrite or cell body of the next neuron; hence, the flow of nerve impulse is unidirectional.

The parasympathetic neural system is part of autonomic neural system. This system has some sort of inhibitory effect. The inhibitory effect minimizes the over functioning of certain functions. Functions, like salivating, digestion, are under control of parasympathetic neural system.

1. Medulla: It has centres to control respiration, cardiovascular reflex and gastric secretion.
2. Hypothalamus: Hypothalamus regulates body temperature, urge for eating and drinking and secretes hormones for posterior pituitary.

The cones are responsible for color vision. There are three types of cones cells that respond to green light, blue light and red light according to their characteristics. These cells are stimulated by different lights, from different sources. The combinations of the signals generated help us see the different colors.

Brain and spinal cord constiture the CNS. A blow on the back can result in serious injury to the soinal cord and eventually to the nerve cord. Nerve cord is an integer part of the CNS. Any damage to the CNS can hamper many normal functions in the body. A person can also be paralysed.

Cerebrum and cerebellum:

Cerebrum	Cerebellum
It is the part of the forebrain that controls voluntary functions. It is the place where intelligence, will power, memory, etc., reside.	It is the part of the hindbrain that controls voluntary functions and controls the equilibrium.

Limbic system is concerned with:

1. Olfaction.
2. Autonomic responses.
3. Regulation of sexual behavior.
4. Expression of emotions.
5. Motivation.

It is located between the thalamus region of the forebrain and pons region of hindbrain. The dorsal surface of midbrain consists of superior and inferior corpora bigemina and four round lobes called corpora quadrigemina. A canal known as cerebral aqueduct passes through the midbrain. Midbrain is concerned with the sense of sight and hearing.

Choroid and retina:

	Choroid		Retina
1.	Choroid is the middle vascular layer of eye.	1.	Retina is the innermost nervous coat of eye.
2.	It contains numerous blood vessels that provide nutrients and oxygen to retina and other tissues.	2.	It contains photoreceptor cells, rods and cones that are associated with twilight and colour vision respectively.

1. Neurotransmitters are the chemicals that are involved in the transmission of nerve impulse across the chemical synapses.
2. They are present in the synaptic vesicles in the synaptic knobs of axon terminals.
3. When the neurotransmitters are released in the synaptic cleft, they diffuse across the synaptic cleft and bind to the specific receptors present on the membrane of the post-synaptic neuron.
4. This binding opens the ion-channels and the entry of ions generates an action potential on the post synaptic neuron.

The visceral nervous system consists of the whole complex of nerves, fibres, ganglia and plexus by which impulses travel form the central nervous system to the viscera and from the viscera to the CNS.

1. There exists an electrical potential difference across the resting membrane.
2. The outer surface is positively charged, with more of Nations.
3. The inner surface is negatively charged, with more of negatively charged proteins.

• Medulla contains centres for regulation of many vital functions like respiration, cardiovascular reflexes and gastric secretions.
• It also continues as spinal cord; hence any damage to medulla can be fatal.

The neural system is composed of specialized cells called neurons. It detects stimuli and transmits neural signals. The neural system of complex animals is composed of two parts, viz. central neural system and peripheral neural system. The brain and nerve cord comprise the central neural system and other nerves comprise the peripheral neural system.

Thalamus and hypothalamus:

Thalamus	Hypothalamus
Thalamus is the part of the forebrain that receives nerve impulses of pain, temperature, touch, etc., and conducts them to the cerebral hemisphere.	Hypothalamus is the part of the forebrain that controls involuntary functions such as hunger, thirst, sweating, sleep, fatigue, sexual desire, temperature regulation, etc.

1. It equalises the air pressure on either side of the tympanum, so that the tympanum can vibrate freely.
2. Hypothalamus controls body temperature, hunger and thirst and secretes some neurohormones.

Cranial nerves and spinal nerves:

	Cranial nerves		Spinal nerves
1.	Cranial nerves arise from the brain.	1.	Spinal nerves arise from the spinal cord.
2.	There are 12 pairs of cranial nerves.	2.	There are 31 pairs of spinal nerves.

Pupil is the small aperture surrounded by the iris that regulates the amount of light entering the eye. This expand in case of low light and contract in case of intense light thereby regulating the amount of light falling on the retina.

• The resting membrane is impermeable to the negatively charged proteins of the axoplasm.
• An active sodium pump transports three sodium ions to the outside, but two potassium ions only come inside.

1. The sense organs detect the changes in the environment and send appropriate signals to the central nervous system.
2. Here, all the inputs are processed and analysed.
3. Signals are sent to different centres of the brain and hence one can sense the changes in the environment.

Organ of corti is the hearing organ. It is located on the basilar membrane that contains hair cells. Hair cells act as auditory receptors. They are present on the internal side of organ of corti.

1. Olfactory receptors are the mucus-coated receptors, specialised for receiving the sense of smell.
2. They are parts of the olfactory epithelium.
3. The neurons extend from the outside environment directly to the pairs of olfactory bulbs, which are parts of forebrain.

Afferent neurons and efferent neurons:

Afferent neurons	Efferent neurons
Afferent neuron conducts nerve impulses toward the brain or the spinal cord.	Efferent neuron conducts nerve impulses from the brain or spinal cord to the effector organs such as muscles or glands.

S. No.	Somatic nervous system	Autonomic nervous system
1.	It relays impulses from the CNS to the skeletal muscles.	It relays impulses from the CNS to the involuntary muscles and glands of the body.