NCERT Exemplar Class 10 Science Solutions Chapter 7 Control and Coordination

NCERT Exemplar Class 10 Science Solutions Chapter 7 MCQ

Different forms of questions, like MCQs, short answers, and long answers with the required diagrams, are provided below. Practising these will help you understand the pattern and these concepts easily and effectively.

Question:1

Which of the following statements is correct about receptors?
(a) Gustatory receptors detect taste while olfactory receptors detect smell
(b) Both gustatory and olfactory receptors detect smell
(c) Auditory receptors detect smell and olfactory receptors detect taste
(d) Olfactory receptors detect taste and gustatory receptors smell

Answer: A
Solution: A receptor is a cell or group of cells that help in detecting external stimuli.
Gustatory receptors are taste receptors present on the papillae of the tongue. Olfactory receptors help in detecting smell and are present on the roof of the nasal cavity. Both the receptors send the information to the brain to interpret the stimulus and generate an appropriate response. Auditory receptors in the ears help in detecting voices.

Question:2

The electrical impulse travels in a neuron from
(a) Dendrite $\to$ axon $\to$ axonal end $\to$ cell body
(b) Cell body $\to$ dendrite $\to$ axon $\to$ axonal end
(c) Dendrite $\to$ cell body $\to$ axon $\to$ axonal end
(d) Axonal end $\to$ axon $\to$ cell body $\to$ dendrite

Answer: C
Solution: The stimulus is received by dendrites and transmitted to cyton through the axon from where it reaches the terminal branches called as axonal end from where they are transmitted to another neuron.

Question:3

In a synapse, a chemical signal is transmitted from
(a) dendritic end of one neuron to the axonal end of another neuron
(b) axon to the cell body of the same neuron
(c) cell body to the axonal end of the same neuron
(d) axonal end of one neuron to the dendritic end of another neuron

Answer: D
Solution: Neurons communicate with one another at junctions called synapses In a synapse, the electrical signal is converted into a chemical substance called a neurotransmitter by the presynaptic neuron.
This chemical diffuses across the synaptic cleft and reaches the other neuron. The signal thus travels from the axonal end of one neuron to the dendritic end of another neuron.

Question:4

In a neuron, the conversion of the electrical signal to a chemical signal occurs/in
(a) cell body
(b) axonal end
(c) dendritic end
(d) axon

Answer: B
Solution: The signals are transferred from one neuron to another with the help of a synapse. The electrical signals are very fast as compared to that of chemical signals. At the axonal end, the electrical signal is converted into a chemical signal with the help of chemical messengers called neurotransmitters that are received by the receptors present on the dendrites of another neuron.

Question:5

Which is the correct sequence of the components of a reflex arc?
(a) Receptors$\to$ Muscles$\to$ Sensory neuron$\to$ Motor neuron$\to$ Spinal cord
(b) Receptors$\to$ Motor neuron $\to$ Spinal cord $\to$ Sensory neuron $\to$ Muscle
(c) Receptors $\to$ Spinal cord $\to$ Sensory neuron $\to$ Motor neuron $\to$ Muscle
(d) Receptors $\to$ Sensory neuron $\to$ Spinal cord $\to$ Motor neuron $\to$ Muscle

Answer: D
Solution: The reflex arc is a neural pathway that controls a reflex. The reflex arc is a part of the PNS and is responsible for actions performed in response to certain stimuli, such as pulling a hand away from a hot object. It consists of 5 components- a receptor that receives the initial stimulus, such as skin, muscles or organs, a sensory neuron that carries the signal to the central nervous system (the spinal cord), an interneuron that relays the information to the central nervous system, and one or more motor neurons that relay the information to the final component of the arc, the effector. The effector could be a muscle, a gland or both.

Question:6

Which of the following statements arises?
(i) Sudden action in response to something in the environment is called reflex action
(ii) Sensory neurons carry signals from spinal cord to muscles
(iii) Motor neurons carry signals from receptors to spin the record
(iv) The path through which signals are transmitted from a receptor to a muscle or a gland is called reflex arc
(a) (i) and (ii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (i), (ii) and (iii)

Answer: C
Solution: The statements (ii) and (iii) are false because sensory neurons carry signals from receptors to the spinal cord and motor neurons carry signals from the spinal cord to the muscles.
The statement (i) and (iv) are true.

Question:7

Which of the following statements are true about the brain?
(i) The main thinking part of the brain is the hind brain
(ii) Centres of hearing, smell, memory, sight etc are located in the forebrain.
(iii) Involuntary actions like salivation, vomiting, and blood pressure are controlled by the medulla in the hindbrain
(iv) Cerebellum does not control posture and balance of the body
(a) (i) and (ii)
(b) (i), (ii) and (iii)
(c) (ii) and (iii)
(d) (iii) and (iv)

Answer: C
Solution: The hindbrain forms the lower part of the brain stem and it consists of the medulla oblongata, pons, and cerebellum.
Medulla oblongata controls involuntary actions such as heartbeat, breathing etc. The cerebellum helps in maintaining posture, balance, and equilibrium. The cerebrum forms part of the forebrain and is the main thinking part of the brain. It coordinates the voluntary actions of the body. It has different areas for performing functions such as centres of hearing, smell memory, etc.

Question:8

Posture and balance of the body is controlled by
(a) cerebrum
(b) cerebellum
(c) medulla
(d) pons

Answer: B
Solution: Cerebellum is the part of the hindbrain and plays a major role in coordinating voluntary motor movements of the body. It also helps in maintaining balance and equilibrium. Cerebellar damage causes decreased coordination, speed, posture and motor learning.

Question:9

The spinal cord originates from
(a) cerebrum
(b) medulla
(c) pons
(d) cerebellum

Answer: B
Solution: The brain is subdivided into the cerebrum, thalamus, hypothalamus, cerebellum and brain stem. The brain stem consists of the midbrain, pons and medulla oblongata. The medulla oblongata is the lowest part of the brain stem from where the spinal cord originates. The spinal cord is a long cylindrical structure consisting of a bundle of nerve fibres, running through the vertebral column of the backbone.

Question:10

The movement of the shoot towards light is
(a) geotropism
(b) hydrotropism
(c) chemotropism
(d) phototropism

Answer: D
Solution: Tropism is the growth in response to external stimuli. Geotropism is the growth of roots towards the gravitational force of the earth. Hydrotropism is the growth of shoots towards water. Chemotropism is the growth of shoots towards the chemical stimulus. Phototropism is the growth of shoots towards the direction of the light.

Question:11

The main function of abscisic acid in plants is to
(a) Increase the length of cells
(b) promote cell division
(c) inhibit growth
(d) promote the growth of stem

Answer: C
Solution: Abscisic acid is the plant hormone. It is also called a stress hormone because it shows different responses to stress conditions. It leads to seed dormancy and ensures seed germination only when favourable conditions return. It also causes the closing of stomata when plants don’t get enough water.

Question:12

Which of the following is not associated with the growth of plants
(a) Auxin
(b) Gibberellins
(c) Cytokinins
(d) Abscisic acid

Answer: D
Solution: Abscisic acid is the stress hormone that causes different plant responses acting against stress conditions. It is responsible for the dormancy of seeds and inhibition of seeds. It stimulates the closure of stomata inhibits shoot growth, stimulates the storage of proteins in seeds, and so on.

Question:13

Iodine is necessary for the synthesis of which hormone?
(a) Adrenaline
(b) Thyroxin
(c) Auxin
(d) Insulin

Answer: B
Solution: The thyroid gland secretes the hormone thyroxine or T4 into the bloodstream. The major function of the thyroid gland is to produce thyroid hormones required by the body for metabolism. Iodine is required to make thyroid hormone. If iodine is not available in the diet, the thyroid gland may produce an insufficient amount of hormone.

Question:14

Choose the incorrect statement about insulin
(a) It is produced by the pancreas
(b) It regulates the growth and development of the body
(c) It regulates blood sugar level
(d) Insufficient secretion of insulin will cause diabetes

Answer: B

Insulin doesn't regulate the growth and development of the body.

Question:15

Select the mismatched pair
(a) Adrenalinepituitaryyry gland
(b) Testosterone: Testes
(c) Estrogen: Oary
(d) Thyroxin Thyroid gland

Answer: A
Explanation: Adrenaline is a hormone produced by the adrenal glands and triggers the body's fight-or-flight response while the pituitary gland produces growth hormone.
Testosterone is a hormone produced by the testes in males and is responsible for the development of male sexual characteristics.
Estrogen is produced by ovaries in the females and is responsible for the development of female sexual characteristics.
Thyroxine is produced by the thyroid gland whose function is to regulate the metabolism in the cells of the body.

Question:16

The shape of guard cells changes due to changes in the
(a) protein composition of cells
(b) temperature of cells
(c) amount of water in cells
(d) position other the nuclei in the cells

Answer: C
Solution: Stomata is a pore-like structure present on the epidermis of the leaves. It is guarded by the guard cells that help to regulate the rate of transpiration by opening and closing the stomata. If the guard cells are turgid or swollen, the stomatal opening is large. This turgidity is caused by the accumulation of K+ ions in the guard cells.
As K+ levels increase in the guard cells the water potential of the guard cells drops and water enters the guard cells. In the second case, the guard cells have lost water, which causes the cells to become flaccid and the stomatal opening to close. This may occur when the plant has lost an excessive amount of water.

Question:17

The growth of tendrils in pea plants is due to
(a) effect of light
(b) effect of gravity
(c) rapid cell divisions in tendrillar cells that are away from the support
(d) rapid cell divisions in tendrillar cells in contact with the support

Answer: C
Solution: Pea plants grow in winter when the days are shorter and the exposure to sunlight is less. Tendrils are hair-like structures that grow with the help of any support so, they are not seen to grow with the impact of gravity.
On the other hand, tendrils that come in contact with the side of the object grow slowly and the side opposite to it is seen to grow at a very fast rate which causes rapid division of cells on the opposite side. This causes the tendril to bend to the side where it touches the object helps in clinging and does not flow with the wind.

Question:18

The growth of pollen tubes towards ovules is due to
(a) hydrotropism
(b) chemotropism
(c) geotropism
(d) phototropism

Answer: B
Solution: Chemotropism is growth towards the chemical stimulus. For fertilization to take place, pollen grains follow a chemotropic mechanism where the growth of the pollen tube is towards the ovules. During fertilization, the ovary releases chemicals that trigger the chemotropic response from developing pollen tubes Hydrotropism is growth towards the water, phototropism is towards the light, and geotropism is towards the force of gravity.

Question:19

The movement of the sunflower by the path of the sun is due to
(a) phototropism
(b) geotropism
(c) chemotropism
(d) hydrotropism

Answer: A
Solution: Tropism is growth towards an external stimulus. It is of different types. In phototropism, the growth of plants is towards the direction of light. Thus, the movement of the sunflower by the path of the sun is due to phototropism.

Question:20

The substance that triggers the fall of mature leaves and fruits from plants is due to
(a) auxin
(b) gibberellin
(c) abscisic acid
(d) cytokinin

Answer: C
Solution: Abscisic acid is a plant hormone that plays an important role under stress conditions. It promotes the senescence of leaves and causes the abscission of flowers and fruits by forming a layer of abscission. This layer disconnects the living tissue of the leaf from the other parts.

Question:21

Which of the following statements about the transmission of nerve impulses is incorrect?
(a) Nerve impulse travels from the dendritic end towards the axonal end
(b) At the dendritic end electrical impulses bring about the release of some chemicals which generate an electrical impulse at the axonal end of another neuron
(c) The chemicals released from the axonal end of one neuron cross the synapse and generate a similar electrical impulse in a dendrite of another neuron
(d) A neuron transmits electrical impulses not only to another neuron but also to muscle and gland cells

Answer: C
Solution: Sensory neurons carry the nerve impulses generated at the sensory receptor towards the CNS. The nerve impulse is transmitted through the axon of one neuron to the dendrite of another neuron. At the end of the axon, neurotransmitters are released which flow through the synapse to the dendrite of another neuron.

Question:22

Involuntary actions in the body are controlled by
(a) medulla in forebrain
(b) medulla in their mid-brain
(c) medulla in the hind brain
(d) medulla in the spinal cord

Answer: C
Solution: The medulla oblongata is located in the hindbrain. It is a cone-shaped structure that forms the lower part of the brain stem and connects the brain to the spinal cord. It performs various functions of the autonomous nervous system (ANS) like:

• heart rate,
• breathing,
• swallowing,
• sneezing and
• digestion

by the sympathetic and parasympathetic response.

Question:23

Which of the following is not an involuntary action?
(a) Vomiting
(b) Salivation
(c) HeHeartbeatd) Chewing

Answer: D
Solution: Involuntary actions are not under the control of a person’s will. Vomiting, salivation and heart are controlled by the autonomous nervous system and are therefore involuntary. Chewing is a voluntary action that a person performs according to his/ her will and involves voluntary skeletal muscles.

Question:24

When a person is suffering from a severe cold, he or she cannot
(a) differentiate the taste of an apple from that of an ice cream
(b) differentiate the smell of a perfume from that of an agarbatti
(c) differentiate red light from green light
(d) differentiate a hot object from a cold object

Answer: B
Solution: Common cold is a respiratory disease that involves the clogging of the nose with phlegm. It results in the blockage of the perception of smell. The olfactory receptors fail to send the olfactory signals to the nose as a result of which a person won't be able to differentiate between the smell of agarbatti and perfume.

Question:25

What is the correct direction of the flow of electrical impulses?

Answer: C
Solution: For the generation of nerve impulses, nerve cells should be in contact with each other. The nerve impulse is transmitted in the following sequence:
Axon end-synapse dendrites- dendron- cyton- axon body- axon end.
The nerve impulse travels in the form of electrical signals from one end of the axon to the synapse. At the synaptic cleft, the electrical impulse is converted to the chemical impulse. Further, this nerve impulse flows from the synaptic cleft to dendritic tips, converting the chemical impulse to an electrical impulse. Thus, the flow of impulse is always from one axonal end of a neuron to the dendritic end of another neuron.

Question:26

Which statement is not true about thyroxin?
(a) Iron is essential for the synthesis of thyroxin
(b) It regulates carbohydrates, protein and fat metabolism in the body
(c) The thyroid gland requires iodine to synthesise thyroxin
(d) Thyroxin is also called thyroid hormone

Answer: A
Solution: The thyroid gland produces a hormone called thyroxine in the bloodstream. It regulates the rate of metabolism in the body. Iodine is necessary for the production of thyroid hormones- T3 and T4.

Question:27

Dwarfism results due to
(a) Excess secretion of thyroxin
(b) Less secretion of growth hormone
(c) Less secretion of adrenaline
(d) Excess secretion of growth hormone

Answer: B
Solution: The pituitary gland releases growth hormone (GH) also called somatostatin. The over-secretion of GH stimulates abnormal growth of the body leading to gigantism and low secretion of GH results in stunted growth resulting in dwarfism. The symptoms of dwarfism include shortened arms and legs, a short neck, a broad, rounded chest, slightly flattened cheekbones, a slow growth pattern and an unusually small stature.

Question:28

Dramatic changes in body features associated with puberty are mainly because of the secretion of
(a) oestrogen from the testes and testosterone from the ovary
(b) estrogen from the adrenal gland and testosterone from the pituitary gland
(c) testosterone from the testes and estrogen from the ovary
(d) testosterone from the thyroid gland and estrogen from the pituitary gland

Answer: C
Solution: Puberty leads to dramatic physical and mental changes in the body of a person. It is the transition stage towards attaining sexual maturity. Sex hormones play a key role here.
In humans, testosterone is the male hormone produced by testes that promotes the development of secondary sexual characteristics. Oestrogen produced by the ovaries in females is responsible for the development of secondary sexual characteristics in females.

Question:29

A doctor advised a person to take an injection of insulin because
(a) his blood pressure was low
(b) his heart was beating slowly
(c) he was suffering from goitre
(d) his sugar level in his blood was high

Answer: D
Solution: The specialised cells called beta cells in Islets of Langerhans in the pancreas produce insulin. It plays a key role in the absorption of blood sugar by the cells. Thus, the patient who is advised to take insulin injections might be suffering from high blood sugar levels in the body.

Question:30

The hormone which increases fertility in males is called
(a) oestrogen
(b) testosterone
(c) insulin
(d) growth hormone

Answer: B
Solution: Testosterone is the male sex hormone produced in the testes of males which promotes maleness. It helps in promoting spermatogenesis, the process of production of sperm. It also promotes secondary sexual characteristics in the case of males.

Question:31

Which of the following endocrine glands is unpaired?
(a) Adrenal
(b) Testes
(c) Pituitary
(d) Ovary

Answer: C
Solution: Except pituitary, all endocrine glands given here are paired in nature.
Adrenal glands are paired and present on the top of each kidney. The testes are a paired gland in males which produces male sex hormones. Ovary is a paired gland in females, which produces female sex hormones. The pituitary gland is unpaired and present below the brain. It is also called as master gland as it has several hormones.

Question:32

The junction between two neurons is called

(a) cell junction
(b) neuromuscular junction
(c) neural joint
(d) synapse

Answer: D
Solution: In the nervous system, a synapse is a junction between two neurons where there is a small gap that allows a neuron to pass an electrical or chemical signal to another neuron.
Cell junction provides contact between neighbouring cells. The neuromuscular junction is a synapse between the axon terminals of a motor neuron and a muscle fibre while the neural joint is present in the nervous system.

Question:33

In humans, life processes are controlled and regulated by
(a) reproductive and endocrine systems
(b) respiratory and nervous systems
(c) endocrine and digestive systems
(d) nervous and endocrine systems

Answer: D
Solution: Reproductive, respiratory and digestive systems have no role to play in control and regulation of the life processes. It is the nervous system and the endocrine system that control and regulate all the processes including the reproductive, respiratory and digestive systems.
The nervous system consists of a network of neurons that allows signals to move between the brain and the body. The endocrine system releases hormones into the body that regulate a variety of functions such as metabolism, digestion, blood pressure and growth. The endocrine system is not directly linked to the nervous system. They two interact in different ways.

NCERT Exemplar Class 10 Science Solutions Chapter 7-Short Answer

Question:34

Label the parts (a), (b), (c) and (d) and show the direction of flow of electrical signals in Figure 7.2.

Answer:

(a) Sensory neuron- It receives the signals (heat) from the stimulus (hot pan) and carries it directly to the spinal cord.
(b) Spinal cord (CNS)- It is a cylindrical structure that carries bundles of nerve fibres. It receives the signal from the sensory neurons and processes and sends them back through the motor neurons.
(c) Motor neuron- It transmits the signals to the effector muscle (muscle in the m) so that the muscle can take action immediately.
(d) Effector (Muscle in the arm)- They act in response to the stimuli and show contraction.

Question:35

Name the plant hormones responsible for the following
(a) elongation of cells
(b) growth of stem
(c) promotion of cell division
(d) falling of senescent leaves.

Answer:

(a) Auxin helps in the elongation of cells
(b) Gibberlin helps the growth of stem
(c) Cytokinihelpslp the promotion of cell division
(d) Abscisic acid leads to the falling of senescent leaves.

Question:36

Label the endocrine glands in Figure 7.3.

Answer:

a) Pineal Gland- It is located in the brain and produces a hormone called melatonin.
b) Pituitary gland- It is called the master gland because it controls the secretions of other glands and releases various hormones like growth hormone.
c) Thyroid gland- It secretes the hormone thyroxine which helps in regulating the metabolism of the body.
d) Thymus- It produces the hormone thymosin which stimulates the development of T-cells.

Question:37

In Figure 7.4 (a), (b) and (c), which appears more accurate and why?

Answer:

Figure a) is more accurate. The roots of a plant always grow downwards in response to gravity and in the figure, a plant root shows positive geotropism. While the shoot of the plant shows positive phototropism by growing towards the light.

Question:38

Label the parts of a neuron in Figure 7.5.

Answer:

a) Dendrites These are branch-like structures that receive messages from other neurons and help in the transmission of impulses to the cell body.
b) Cellbody-It is also called soma. It is a star-shaped structure with a nucleus, Golgi body, endoplasmic reticulum, mitochondria etc.
c) Axon- It is a tube-like structure that carries electrical impulses from the cell body to the axon terminals that pass the impulse to another neuron.
d) Axon terminal- It is the end of an axon that helps in the transmission of electrical impulses to the dendrites of another neuron.

Question:39

Match the terms of Column (A) with those of Column (B)Column (A) Column (B)
(a) Olfactory receptors (i) Tongue
(b) Thermo receptors (temperature receptors) (ii) Eye
(c) Gustatoreceptors (iii) Nose
(d) Photoreceptors (iv) Skin

Answer: (a)- 3. (b)-4, (c)-1, (d)-2
Sensory receptors are nerve receptors present in different organs of a body and respond to stimulant receptors, thermoreceptors, and gustatory receptors, photoreceptors are different sensory receptors. Olfactory receptors present in the nose help to recognise different types of smell. Thermoreceptors are non-specialised sensory neurons which connect the skin to the hypothalamic region of the brain and detect temperature changes Gustatory receptors also called taste receptors are present in the tongue and detect taste. Photoreceptors are present in the es. There are two types of photoreceptors, .i.e., rods and cones. They contain coloured pigments which help to differentiate between colours.

Question:40

What is a tropic movement? Explain with an example.

Answer:

Tropic movement is the directional growth of the plant in response to the external stimulus present in the environment, this movement is in response to root and shoot growth. Movement can be either toward the stimulus or away from the stimulus. They are mainly of five types:
Phototropism,

• Geotropism,
• Chemotropism,
• Hydrotropism and
• Thigmotropism

Ex: Roots show positive geotropic movement as they grow downwards the gravity whereas shoots show negative geotropic movement.

Question:41

What will happen if the intake of iodine in our diet is low?

Answer:

Iodine is essential for the synthesis of the hormone thyroxin. The thyroid gland secretes the hormone thyroxin which controls the rate of metabolism of carbohydrates, fats and proteins in the body. If iodine is deficient then thyroxine hormone will be deficient in the body and will cause goitre. The neck appears to be swollen due to enlargement of the thyroid gland which is also called a goitre.

Question:42

What happens at the synapse between two neurons?

Answer:

The transmission of nerve impulses between two neurons takes place through the synapse. The axon terminal of a neuron releases chemical substances called neurotransmitters e.g. acetylcholine. These chemicals travel through the synapse and reach the dendrites of the next neuron. The nerve impulses travel along with the neurotransmitters.

Question:43

Answer the following :
(a) Which hormone is responsible for the changes noticed in females at puberty?
(b) Dwarfism results due to deficiency of which hormone?
(c) Blood sugar level rises due to deficiency of which hormone?
(d) Iodine is necessary for the synthesis of which hormone?

Answer:

(a) Oestrogen hormone is responsible for the changes noticed in females at puberty.
(b) Dwarfism results due to a deficiency of growth hormone.
(c) Blood sugar level rises due to deficiency of Insulin hormone.
(d) lodine is necessary for the synthesis of Thyroxine hormone.

Question:44

Answer the following :
(a) Name the endocrine gland associated with the brain.
(b) Which gland secretes digestive enzymes as well as hormones?
(c) Name the endocrine gland associated with the kidneys.
(d) Which endocrine gland is present in males but not in females?

Answer:

a) The pituitary gland is associated with the brain.
b) The pancreas secretes digestive enzymes as well as hormones.
c) The adrenal gland is associated with the kidneys.
d) Testis is present in males but not in females.

NCERT Exemplar Class 10 Science Solutions Chapter 7-Long Answer

Question:45

Draw the structure of a neuron and explain its function.

Solution:
Neurons are the building blocks of the nervous system. They receive and transmit signals to different parts of the body. Different types of neurons help in the transmission of information. The following are the different parts of a neuron:
Dendrites
These are branch-like structures that receive messages from other neurons and allow the transmission of messages to the cell body.
Cell Body
Each neuron has a cell body with a nucleus, Golgi body, endoplasmic reticulum, mitochondria and other components.
Axon
An axon is a tube-like structure that carries electrical impulses from the cell body to the axon terminals that pass the impulse to another neuron.
The myelin sheath acts as an insulator around the axon. It insulates axons from the electrical 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 human brain are-
Cerebrum: The cerebrum is the largest part of the human brain. It is divided into two hemispheres; called cerebral hemispheres. The cerebrum controls voluntary motor actions. It is the site of sensory perceptions and the seat of learning and memory.
Hypothalamus: The hypothalamus lies at the base of the cerebrum. It controls the sleep and wake cycle of the body. It also controls the urge to eat and drink.
Cerebellum: Cerebellum lies below the cerebrum and at the back of the whole structure. It is responsible for the voluntary actions of the body and helps in maintaining the equilibrium of the body.
Medulla: Medulla forms the brain stem; along with the pons. It lies at the base of the brain and continues into the spinal cord. The medulla controls various involuntary functions: like a heartbeat, respiration, etc.

Question:47

What constitutes the central and peripheral nervous systems? How are the components of the central nervous system protected?

Answer:

The central nervous system consists of the brain and the spinal cord. The peripheral nervous system consists of all the nerves in the body that lie outside of the spinal cord and brain.
The central nervous system has a well-developed system for its protection. The brains are enclosed in a hard shell known as the skull. The spinal cord is enclosed in a vertebral column for its protection. Along with these, there is a cerebrospinal fluid which protects the brain from mechanical shocks.

Question:48

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

Answer:

(a) Thyroxin regulates carbohydrate, protein and fat metabolism in the body to provide the best balance for growth.
(b) Insulin regulates blood sugar levels in the body.
(c) Adrenaline increases heart rate and supply of blood to various organs.
(d) Growth hormone regulates growth and development in the body.
(e) Testosterone controls the changes in body features associated with puberty in males.

Question:49

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

Answer:

Auxin - It promotes plant growth and fruit growth.
Gibberlins- It helps in fruit growth and cell division.
Cytokinins –They promote cell division, fruit growth and opening of stomata.
Abscisic acid- It promotes dormancy and inhibits plant growth. It is also responsible for the falling of leaves fruits and flowers.

Question:50

What are reflex actions? Give two examples. Explain a reflex arc.

Answer:

The sudden involuntary movement in a voluntary organ; in response to a stimulus; is called reflex action.
Examples of reflex action:

• (a) Moving your hand away from a hot pan.
• (b) Blinking of eyes

Reflex The reflex arc is a path of electrical impulse during a reflex action. It is composed of sensory neurons the spinal cord, motor neurons and
muscle.
Steps of the reflex arc
• The sensory neuron picks signals from the stimulus and carries the signals to the spinal cord.
• Spinal cord processes the signals and sends the message through the motor neuron.
• Motor neuron transmits the signals to the effector's muscle so that the muscle can take immediate action

Question:51

“Nervous and hormonal systems together perform the function of control and coordination in human beings.” Justify the statement.

Answer:

The control and coordination in human beings are because of the nervous and endocrine systems. These two systems work in different ways. The brain controls all the functions of the body with the help of a network of neurons which carry signals through neurotransmitters in the form of electric impulses to the brain and from the brain. The hormonal system consists of hormones secreted by various glands in our body.
The hormonal system coordinates the function of the nervous system. Hormones indirectly control the life processes by a feedback mechanism. They can produce hormones when required and can stop production when not required.

Question:52

How does chemical coordination take place in animals?

Answer:

The chemical coordination in animals takes place through hormones produced by the ductless glands i.e. endocrine glands of the body. Hormones are directly released into the bloodstream to reach the target site. Hormones control the behaviour of the target tissue.
Example: Adrenaline hormone is secreted by the adrenal gland which reaches the lungs and gastrointestinal tract. The heart speeds up its pumping action so that more blood can be supplied to the limbs and facial muscle muscles, the cactiactivityI tract is slowed down to ensure better blood supply in limbs. Thus, adrenalin prepares the body for a fight-or-flight situation.

Question:53

Why is the flow of signals in the synapses from the axonal end of one neuron to the dendritic end of another neuron but not the reverse?

Answer:

The electrical signal travels through a neuron. To be transmitted to another neuron, it needs to be passed in the form of neurotransmitters. Neurotransmitters are chemical substances that can enter a neuron only through specialized channels which are present only in dendrites not in axons.
Due to this, the flow of signals in a synapse is from the axonal end of one neuron to the dendritic end of another neuron but not the reverse.