NCERT & SEBA SCIENCE CLASS 10 SOLUTION
IMPORTANT NOTES:
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NCERT & SEBA SCIENCE CLASS 10 SOLUTION
CONTROL AND COORDINATION
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| CONTROL AND COORDINATION |
NCERT Textbook Questions
Q.1 What is the difference between a reflex action and walking?
Answer: Reflex action is a
rapid, automatic response to a stimulus that is not under the voluntary
control of the brain. It is a kind of involuntary action that involves only the
spinal cord. A reflex action is not based on our thinking. On the other hand,
walking is a voluntary action that we undertake knowingly. The action of
walking involves thinking by the brain. The central nervous system (brain and
spinal cord) takes part in the action of walking.
Q.2 What happens at the synapse between two neurons?
Answer: The synapse is a
microscopic gap between any two adjacent neurons. Electrical impulses (or nerve
impulses)carrying messages pass over the synapse when going from one neuron to
another. Actually, the synapse between two neurons acts as a one-way valve which
allows electrical impulses to pass in one direction only. This happens as
follows: When an electrical impulse coming from the receptor reaches the end of
the axon of sensory neuron, then the electrical impulse releases a tiny amount of
a chemical substance (called neurotransmitter substance) into the synapse (or
gap) between two adjacent neurons. This chemical substance crosses the synapse
(or gap) and starts a similar electrical impulse in the dendrite of the next
neuron. In this way, the electrical impulses (or messages) are passed from one
neuron to the next across the synapse.
Q.3 Which part of the brain maintains posture and equilibrium of the
body?
Answer: Cerebellum.
Q.4 How do we detect the smell of an agarbatti (incense stick)?
Answer: When the agarbatti
burns, it produces vapours having a characteristic pleasant smell. This smell
is detected by the olfactory receptors present inside our nose. The action of the smell of agarbatti on receptors sets off chemical reactions that generate
electrical impulses. The sensory neurons carry these electrical impulses to the
sensory area of the forebrain (called cerebrum). This makes us detect the smell of
burning agarbatti.
Q.5 What is the role of the brain in reflex action?
Answer: Reflex action takes
place in the spinal cord. Only the information that a reflex action has taken
place goes on to reach the brain.
NCERT & SEBA SCIENCE CLASS 10 SOLUTION
Q.6 What are plant hormones?
Answer: The organic
chemical substances produced in plants that control growth, development and
responses in plants, are called plant hormones. The examples of plant hormones
are: Auxins, Gibberellins, Cytokinins, and Abscisic acid.
Q.7 How is the movement of leaves of the sensitive plant different
from the movement of a shoot towards light?
Answer:
Q.8 Give an example of a plant hormone that promotes growth.
Answer: Auxin
Q.9 How do auxins promote the growth of a tendril around a support?
Answer: When tip of tendril
supports the growth of a tendril, the auxin moves away to the
opposite part. It helps the cell grow longer. When a tendril comes in contact
with a support, auxins stimulates faster growth of the cells on the opposite
side. This continual growth of shoot tip forms tendril and starts coiling
towards the support.
Q.10 Design an experiment to demonstrate hydrotropism.
Answer:
(i). Take
two glass troughs A and B.
(ii). Fill
each one of them with two-thirds of soil.
(iii). In
trough B, we plant a similar seedling and place a small clay pot inside the
soil.
(iv). Water
the soil in the trough A daily and uniformly.
(v). Do not
water the soil in trough B, but put some water in the clay pot placed in the
soil.
(vi). Leave
both the troughs for a few days.
On examining the
roots later, it will be found that the root in trough B has bent towards the
source of water. Roots in trough A grew normally straight.
Q.11 How does the chemical coordination take place in animals?
Answer: The chemical
coordination in animals takes place through the action of chemicals called
‘hormones’. Hormones are the chemicals which are made inside the animal body in
very small amounts by certain glands. Hormones are released directly into the
blood. They are carried by the blood circulatory system to other parts of the
body. Hormones travel all over the body but affect only particular organs at
particular places. The organs which they affect are called target organs. The
hormones control and coordinate several functions of the animal body such as growth,
development, metabolism, behaviour and secondary sexual characteristics, etc.
Q.12 Why is the use of iodised salt advisable?
Answer: Iodine is necessary
for the thyroid gland to make thyroxine hormone. Thyroxine hormone regulates
the metabolism of carbohydrates, fats and proteins so as to produce the best
balance for growth. If there is a deficiency of iodine in our diet, the formation
of thyroxine hormone will be reduced and lead to a disease called goitre. One
of the symptoms of goitre disease is that the neck of the person appears to be
swollen. Iodised salt contains appropriate amounts of iodine compounds. Iodised
salt can provide all the iodine needed by the thyroid gland to make sufficient
thyroxine hormone for the body. So, if we take iodised salt, there can be no
deficiency of iodine (or thyroxine) in the body and hence goitre disease can be
prevented.
Q.13 How does our body respond when adrenaline is secreted into the
blood?
Answer: The adrenaline
hormone prepares our body to function at maximum efficiency during emergency
situations like danger, anger, excitement, etc. This happens as follows: When
we are faced with a dangerous situation (like being chased by a ferocious dog),
then our nervous system stimulates the adrenal glands to secrete more adrenaline
hormone into our blood. This adrenaline hormone increases our ‘heartbeats’,
‘breathing rate’, ‘blood flow into muscles’ and causes liver ‘to put more
stored glucose into our blood’. All these actions of adrenaline hormone produce
a lot of energy in our body very, very quickly. And this energy helps us to
cope up with emergency situations (like running away very fast from a ferocious
dog or fighting an enemy, etc.).
Q.14 Why are some patients of diabetes treated by giving injections
of insulin?
Answer: Insulin is a hormone
which is produced and secreted by a gland called pancreas. The function of the insulin hormone is to lower the blood sugar level. The deficiency of insulin
hormone in the body raises the blood sugar level causing a disease known as
diabetes. The high sugar level in the blood of a diabetic person can lead to
many harmful effects. Some persons having diabetes are treated by giving
injections of insulin because addition of insulin hormone to blood lowers the
blood sugar level.
NCERT & SEBA SCIENCE CLASS 10 SOLUTION
NCERT EXERCISE:
Q.1 Which of the following is a plant hormone?
(a) Insulin (b)
Thyroxin (c) Oestrogen (d) Cytokinin
Answer: (d)
Cytokinin.
Q.2 The gap between two neurons is called a:
(a) dendrite (b)
synapse (c) axon (d) impulse
Answer: (b) synapse.
Q.3 The brain is responsible for:
(a) thinking (b)
regulating the heartbeat (c)
balancing the body
(d) all of the above
Answer: (d) all of
the above.
Q.4 What is the function of receptors in our body? Think of
situations where receptors do not work properly. What problems are likely to
arise?
Answer: Receptors are the
special cells present in our sense organs. Receptors detect all the information
from our environment and feed it to the nervous system. For example, gustatory
receptors present in our tongue detect the taste of our food whereas olfactory
receptors present in our nose detect the smell. Now, if the gustatory receptors of
our tongue do not work properly, we will not be able to know the taste of
different types of foods (whether sweet, salty, sour or bitter, etc.). And if
the olfactory receptors present in our nose do not work properly, we will not
be able to smell things (like the flavour of a food or the fragrance of a
perfume).
Q.5 Draw the structure of a neuron and explain its function.
Answer: A neuron consists of
three parts: cell body, dendrites and axon (see Figure on the next page). The cell
body of a neuron is like a typical animal cell which contains cytoplasm and a
nucleus. A number of long and thin fibres stretch out from the cell body of a
neuron. They are called nerve fibres. The shorter fibres on the cell body of a
neuron are called dendrites.
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| NEURON |
NCERT & SEBA SCIENCE CLASS 10 SOLUTION
Q.6 How does phototropism occur in plants?
Answer: The bending of a
plant stem towards light is an example of phototropism. The plant stem responds
to light and bends towards it due to the action of ‘auxin hormone’. This
happens as follows: The auxin hormone is present in the tip of the stem of the
growing plant. The auxin hormone prefers to stay in shade, away from light. So,
when sunlight falls on the stem from one side, auxin hormone gets concentrated
on the side of the stem which is away from light. Auxin promotes growth. So,
due to more auxin, the shady side of the stem (which is away from light) grows to
be longer than the side of stem which is facing the light, and makes the stem bend towards the light. For example, in Figure given here, the left side A of the stem (which is
away from light) has more auxin hormone and grows faster than right side B
which is towards the light. Since side A of the stem becomes longer than side B, the
stem bends towards the right side (in the direction of light).
Q.7 Which signals will get disrupted in case of a spinal cord
injury?
Answer: Reflex actions and
involuntary actions will get disrupted in case of a spinal cord injury.
Q.8 How does chemical coordination occur in plants?
Answer: The plants do not
have nervous system but they can still sense things. The plants can sense the
presence of stimuli such as light, gravity, chemicals, water, and touch, etc.,
and respond to them by the action of hormones. Thus, the plants coordinate
their behaviour against environmental changes by using organic chemicals called
hormones. This is called ‘chemical coordination’. The hormones in plants
coordinate their behaviour by affecting the growth of a part of the plant
resulting in the movement of that plant part in response to a stimulus. For
example, when sunlight falls on a shoot from one side, the auxin hormone causes
the shady side of shoot to grow faster, making the shoot bend towards sunlight.
Q.9 What is the need for a system of control and coordination in an
organism?
Answer: An organism needs a system of control and coordination for its
survival in this world. The system of control and coordination is necessary in
plants as well as animals (including human beings).
(i) The
plants need carbon dioxide, water and sunlight. It is due to the presence of a
hormonal system of control and coordination in plants that the stomata in their
leaves open to allow in carbon dioxide gas, the roots bend towards water and
the shoots grow towards the sunlight. It is also due to control and coordination
that tendrils in plants having weak stems make them climb on to neighbouring
supports.
(ii) In
human beings, the system of control and coordination is needed for all our
actions, thinking and behaviour. The human nervous system receives information
from the surroundings, processes it and then responds accordingly. Our heartbeats, breathing, reading, writing, cycling, dancing and various reflex actions
are all because of the nervous system. The hormonal system (endocrine system)
helps in controlling and coordinating activities like metabolism, development,
reproduction and preparing our body to cope up with grave situations.
Q.10 How are involuntary actions and reflex actions different from
each other?
Answer: Involuntary actions
are those which we cannot control even if we want to. There is no stimulus
involved in the involuntary actions. They take place on their own. For example,
our heart beats all the time without our thinking about it. So, the beating of
heart is a purely involuntary action. Involuntary actions are regulated by the
brain. The reflex actions are also a kind of involuntary actions but they take
place in response to a stimulus. For example, the decrease in the size of the
pupil of our eye on stepping out in bright light is a reflex action which takes
place in response to a stimulus ‘light’. Reflex actions are usually regulated
by the spinal cord.
Q.11 Compare and contrast nervous and hormonal mechanisms for
control and coordination in animals.
Answer:
Q.12 What is the difference between the manner in which movement
takes place in a sensitive plant and the movement in your legs?
Answer: The movement of a
sensitive plant are due to nastic movements which take place due to the change
in turgor pressure at the base of the leaves. The change in turgor pressure
causes leaves to droop. The movement in our legs is due to the contraction and
relaxation of muscles.
IMPORTANT NOTES:
1.
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| CONTROL AND COORDINATION IN ANIMALS |
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| THE ENDOCRINE SYSTEM IN HUMANS |
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| THE REPRODUCTIVE PHASE |
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| REPRODUCTION IN HUMANS |
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| SPINAL CORD |
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| STRUCTURE OF NEURON |
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| CENTRAL NERVOUS SYSTEM (CNS) |
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| PERIPHERAL NERVOUS SYSTEM (PNS0 |
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| HUMAN NERVOUS SYSTEM |
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| THE ENDOCRINE SYSTEM DYSFUNCTION |
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| THE ENDOCRINE SYSTEM IN HUMANS |
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| SEXUALLY TRANSMITTED DISEASES |
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