Class 10 Science Chapter 6 Question Answers - Control and Coordination

Q1: What is a neuron?

Ans: A neuron is a nerve cell that is the basic building block of the nervous system. Neurons are specialized to transmit information throughout the body.

These highly specialized nerve cells are responsible for communicating information in both chemical and electrical forms. There are also several different types of neurons responsible for different tasks in the human body.

Q2: How does the feedback mechanism regulate the hormone action? Explain with the help of an example.

Ans: The presence or absence of a particular hormone can regulate its further formation with the help of a regulatory mechanism called the feedback mechanism.
Example: Hypothalamus regulates thyroxin levels in blood by secreting thyroid stimulating hormone (TSH). If the thyroxine levels increase then the hypothalamus stops secreting TSH in order to reduce the production of thyroxine from the thyroid gland.
Low levels of thyroxin in blood again switch on the release of TSH from the hypothalamus to increase levels of thyroxin in blood.

Q3: Name any two types of tropism.

Ans: The two types of tropism are phototropism and geotropism.

Q4: How do control and coordination take place in plants?

Ans: Plants have a unique mechanism of controlling and coordinating their various physiological and biological processes. Plants respond to light, touch, gravitational force, and other stimuli. Growth and movements in plants are regulated by both external and internal factors. The functions of control and coordination in plants are performed by chemical substances known as plant hormones or phytohormones.
(i) Coke on heating in air, catches fire and liberates a large amount of heat. 

C + O₂  →  CO₂ + ΔT 
(ii) Carbon dioxide and water react in the presence of chlorophyll and sunlight to form glucose and oxygen. 6CO₂ + 6H₂O → C₅H₁₂O₆+ 6O₂ 
(iii) Molten lead bromide decomposes into lead metal and bromide on the passage of electric current. 

PbBr₂→ Pb + Br₂ 
(iv) The reaction between red hot iron and steam is reversible. 

3Fe + 4H₂O ⇆  Fe₃O₄ + 4H₂
(v) When magnesium burns in air or oxygen it liberates a large amount of heat. 

2Mg + O₂ →  2MgO + ΔT.

Q5: Describe the central nervous system in human beings.

Ans: 

• The brain is the highest coordinating center in the body, protected by a bony box in the skull called the cranium.
• It is covered by three membranes known as meninges, with the space between them filled with cerebrospinal fluid that protects the brain from mechanical shocks.

The brain is broadly divided into three regions:
i. Forebrain
ii. Midbrain
iii. Hindbrain

i. Forebrain: Includes the cerebrum and olfactory lobes.

The cerebrum is the most complex and specialized part, consisting of two cerebral hemispheres.

It contains:

• Sensory areas: Receive information from sense organs.
• Motor areas: Send impulses to muscles or effector organs.
• Specific regions for each kind of stimulus and its response.
• Pairs of cranial nerves arise from the brain.

ii. Midbrain:

• The midbrain is located between the forebrain and the hindbrain.
• It acts as a relay center for auditory and visual information.
• The midbrain controls some reflex actions and is involved in the regulation of eye movements.

iii. Hindbrain: Consists of three centers: cerebellum, pons, and medulla oblongata.

• Medulla oblongata: Regulates swallowing, coughing, sneezing, and vomiting.
• Pons: Participates in the regulation of respiration.
• Cerebellum: Controls coordination and the adjustment of movement and posture.

Spinal Cord: Part of the central nervous system, located in the vertebral canal, and is a downward continuation of the medulla oblongata. The spinal cord's structure:

The arrangement of white matter (myelinated axons) and grey matter (cytons) is reversed compared to the brain:

• Grey matter is the inner region.
• White matter is the outer region.
• A small central canal runs through the center of the spinal cord, continuous with the brain's ventricles.

The spinal cord has an H-shaped structure in the transverse section due to fissures on the ventral and dorsal sides:

• The dorsal fissure almost reaches the grey matter.
• The anterior median fissure falls short of it.
• The spinal cord gives off 31 pairs of nerves.

Q6: Write the functions of any one part of the hindbrain.

Ans: The cerebellum is the part of the hindbrain that controls and coordinates the movements of our body and helps adjust posture. It functions even when the person is asleep.

Q7: Differentiate between the central nervous system (CNS) and the peripheral nervous system (PNS). Explain the functions of each system in maintaining control and coordination.

Ans: The Central Nervous System (CNS) and Peripheral Nervous System (PNS) are two integral components of the nervous system, each playing distinct roles in maintaining control and coordination within the human body.Central Nervous System (CNS):

• The CNS consists of the brain and spinal cord.
• It acts as the control center, processing information, making decisions, and sending out commands.
• The brain is responsible for higher functions such as thinking, memory, emotion, and voluntary muscle movements.
• The spinal cord serves as a conduit for nerve impulses between the brain and the rest of the body, and it also controls reflex actions.
• The CNS integrates sensory input, processes it, and sends appropriate responses to effectors (muscles or glands) through the PNS.

Peripheral Nervous System (PNS):

• The PNS includes all the nerves outside the CNS, extending to the body's extremities.
• It is divided into the sensory (afferent) division and the motor (efferent) division.
• Sensory neurons transmit sensory information from receptors (such as the skin, eyes, and ears) to the CNS for processing.
• Motor neurons carry commands from the CNS to effectors, resulting in muscular contractions or glandular secretions.
• The motor division is further divided into the somatic nervous system (voluntary control over skeletal muscles) and the autonomic nervous system (involuntary control over smooth muscles, cardiac muscles, and glands).
• The autonomic nervous system is subdivided into the sympathetic and parasympathetic divisions, which regulate bodily functions in response to different situations, such as stress (sympathetic) and relaxation (parasympathetic).

Q8: Define reflex action with suitable examples.

Ans: When we suddenly withdraw our hands on pricking a pin, it is a reflex action. This type of sudden response to a stimulus is involuntary. A reflex action is defined as an unconscious and involuntary response of effectors to a stimulus. In reflex actions, a message from the receptors is relayed by sensory nerves to the spinal cord, which sends information for response via motor nerves to effectors. The pathway is called a reflex arc. The simplest type of reflex action is the knee-jerk reflex. In this case, while sitting with freely hanging legs, a strike below the kneecap kicks the leg forward. Other reflex actions are coughing, sneezing, yawning and blinking of eyes.

Q9: Name the hormones secreted by the thyroid, parathyroid, and pancreas.

Ans: 

(i) Thyroid secretes thyroxin,
(ii) Parathyroid secretes calcitonin and
(iii) Pancreas secrete insulin and glucagon.

Q10: List the functions of testosterone and estrogen.

Ans: The functions of testosterone are the regulation of male accessory sex organs and secondary sexual characters like moustache, beard, and voice.
The functions of estrogen are the regulation of female accessory sex organs and secondary sexual characters like mammary glands, hair pattern and voice, and the maintenance of pregnancy.

Q11: Write the name of three hormones secreted by the pituitary gland.

Ans: The three hormones secreted from the pituitary gland are
(i) Growth hormone
(ii) adrenocorticotrophic hormone
(iii) follicle-stimulating hormone (FSH).

Q12: Why is the flow of signals in a synapse from the axonal end of one neuron to the dendritic end of another neuron but not the reverse?

Ans: The information received by the dendrites of neurons present at receptors is transferred in the form of electrical impulses to the cell body, axon, and the nerve endings at the ends of the axon. At the axonal ends, chemicals are released between the junction of two neurons called synapses. The chemical diffuses towards the dendrite of the next neuron where it generates an electrical impulse again. So, the electrical signals change to chemical signals and again to electrical signals for the next neuron.
Since the chemicals Eire are released at the axonal ends and absent at the dendrite end, the signal travels from the axonal end to the dendritic end of another neuron but not the reverse i.e., the flow of electrical impulse is unidirectional only. 

Q13: Describe the reflex arc and its significance in maintaining the body's safety and coordination.

Ans: The reflex arc is a neural pathway that mediates a reflex action. It involves a simple and rapid sequence of events in response to a specific stimulus, often without involving the brain's conscious processing.The reflex arc consists of the following components:

• Receptor: The sensory organ or cell that detects the stimulus and converts it into a nerve impulse.
• Sensory neuron: Transmits the nerve impulse from the receptor to the spinal cord or brainstem.
• Interneuron (optional): In some reflex arcs, an interneuron located in the spinal cord or brainstem relays the impulse from the sensory neuron to the motor neuron.
• Motor neuron: Carries the nerve impulse from the spinal cord or brainstem to the effector organ (usually a muscle or gland).
• Effector: The muscle or gland that responds to the nerve impulse by producing a specific action.

Significance of the reflex arc:

The reflex arc serves as a protective mechanism that enables rapid responses to potential dangers, often without conscious thought. This is crucial for the body's safety and coordination in the following ways:

• Swift response: Reflex actions occur quickly, helping the body to react promptly to potential threats, such as withdrawing a hand from a hot object.
• Avoidance of injury: Reflexes help prevent injuries by causing immediate muscle contractions or other responses that can move the body away from harm.
• Maintaining posture and balance: Reflexes help in maintaining balance and posture, contributing to the body's overall coordination and stability.
• Diversion of excessive sensory input: In cases of overwhelming sensory input, reflexes can divert the excessive input away from higher brain centers, allowing the brain to focus on more critical tasks.