Question 1.
What is the difference between a reflex action and walking?
Answer.
A reflex is an involuntary, rapid response
to a stimulus. It does not involve any thinking. For example, we pull back our
hand on touching any hot surface. It is an instant reaction. We do not have
any control over the movement. On the other hand, walking is a voluntary
action. It is a part of our routine and we have a full control over walking.
Question 2.
What happens at the synapse between two
neurons?
Answer.
The gap between the two neurons is called
synapse. At the synapse, the nerve impulse from one neuron gets transmitted to
the other neuron. This takes place by the virtue of special neurotransmitters
released by the axon terminal of a neuron. These neurotransmitters travel
through the synapse to reach the dendrites of the adjacent neuron. The nerve
impulses travel along with these neurotransmitters.
Question 3.
Which part of the brain maintains posture
and equilibrium of the body?
Answer.
Cerebellum
Question 4.
How do we detect the smell of an agarbatti
(incense stick)?
Answer.
We have some olfactory receptors in our
nose. These receptors are specialised to pick up the smell. Once they detect
any smell, they send the message to the brain. The brain interprets and
analyses those signals and tells the body that it is the smell of an incense
stick.
Question 5.
What is the role of the brain in reflex
action?
Answer.
Brain does not play any direct role in
reflex action. Reflex action is mainly controlled by the spinal cord. The
brain function as a relay centre for transferring impulses from sensory to
motor neurons in the form of cerebral reflexes Control and Coordination such
as closure of eyes on exposure to flash of light and salivation in the mouth
at the good smell of food. In spinal reflexes, it acts as a collection centre
of information without any direct involvement in reflex action.
Question 6.
What are plant hormones?
Answer.
Plant hormones are the special chemicals
which help in the growth of various parts of the plant.
Question 7.
How is the movement of leaves of the
sensitive plant different from the movement of a shoot towards light?
Answer.
The movement of leaves of the sensitive
plant exhibits nastic movement. This means that the movement does not depend
on the direction of the stimulus. Whereas, the movement of a shoot towards
light is an example of tropic movement. This movement is dependent on the
direction of the light.
Question 8.
Give an example of a plant hormone that
promotes growth.
Answer.
Auxin
Question 9.
How do auxins promote the growth of a
tendril around a support?
Answer.
The concentration of, auxin hormone varies
in different parts of the plant. It is more in the part of the tendril which
is away from the support. Auxin hormone promotes the cell division. Hence,
there is increased cell division in that part compared to the part which is
nearer to the support. So, the external part of the tendril grows more than
the internal part making the tendril coil around the support.
Question 10.
Why is the use of iodised salt advisable?
Answer.
Iodine is an important constituent required
by the body to synthesise thyroxin hormone. The deficiency of iodine leads to
a disease called ‘goitre’. In this disease, the neck region swells up. Hence,
it is advisable to consume iodised salt to prevent chances of goitre.
Question 11.
Design an experiment to show hydrotropism.
Answer.
Procedure:
- Take a big tray which should be able to accommodate a porous pot.
- Fill the tray with sand. Put some seeds in it.
- Make a pit in the sand to insert the pot in it.
- Fill the porous pot with water.
- Do not disturb the set up for about a week.
- After a week, locate the seeds and observe.
Observation: When seeds are taken out, you will see that the roots show bending towards the direction from which water is diffusing. This shows the hydrotropic movement in roots.
Question 12.
How does chemical coordination take place
in animals? .
Answer.
Chemical coordination in animals involves
hormones which are secreted by endocrine glands. These hormones help in
regulating different metabolic functions in the body. For example, growth
hormone is a hormone which regulates the growth of the body. If this hormone
is secreted in excess, it leads to ‘gigantism’. If this hormone is secreted in
less quantity, it leads to ‘dwarfism’.
Question 13.
How does our body respond when adrenaline
is secreted into the blood?
Answer.
Adrenaline is commonly known as ‘fight or
flight’ hormone. This is because, the hormone prepares the body for any
emergency situation. If there is an increased secretion of this hormone in the
blood, it causes increased blood supply to limbs and face. It also increases
the heart rate and breathing rate. All of these responses enable the body to
deal with any situation-be it a fight or; if need be; a flight from the scene.
Question 14.
Why are some patients of diabetes treated
by giving injections of insulin?
Answer.
Insulin controls the sugar levels of the
body. In some diabetic patients, insulin hormone level is not normal. Hence,
insulin injection is given to such patients to compensate for the reduced
insulin hormone secretion. Such cases of diabetes are called Insulin Dependent
Diabetes Mellitus (IDDM). such as closure of eyes on exposure to flash of
light and salivation in the mouth at the good smell of food. In spinal
reflexes, it acts as a collection centre of information without any direct
involvement in reflex action.
Chapter End Questions
Question 1.
Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin
Answer.
(d) Cytokinin
Question 2.
The gap between two neurons is called a
(a) dendrite
(b) synapse
(c) axon
(d) impulse
Answer.
(b) synapse
Question 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
Question 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 sensory structures which
provide information about the external environment to the body. This helps the
brain to instruct a related organ to take the required action. Receptors are
very important for our survival. For example, if a person is blind, performing
certain ordinary task may be very difficult for him. Since, one of the
receptors (eyes) are not functional in his body, he may not be able to see the
obstruction in his path or may even fall in a pit.
Question 5.
Draw the structure of a neuron and explain
its function.
Answer.
Structure of neuron:
Function: Neuron helps in transmitting the nerve impulses.
Question 6.
Which signals will get disrupted in case of
a spinal cord injury?
Answer.
The spinal cord is a junction where various
nerves meet. In case of spinal cord injury, the communication between the
spinal nerves and the brain would get disturbed.
Question 7.
How does phototropism occur in plants?
Answer.
The concentration of auxin differs in
different parts of the plant in response to the direction of light. For
example, in a stem the concentration of auxin is more in the parts which are
away from the light. Presence of auxin hormone increases the cell division in
that part. This causes the stem to bend towards the light. That is how
phototropism occurs in plants.
Question 8.
How does chemical coordination occur in
plants?
Answer.
Plant hormones play a very important role
in chemical coordination. Most of the plant hormones stimulate growth in
certain parts of the plant. For example, hormones auxin and gibberellins
stimulate growth. However, hormone abscisic acid inhibits the growth of the
plant.
Question 9.
What is the need for a system of control
and coordination in an organism?
Answer.
A living organism constantly interacts with
its external environment. For example, a deer has to move in search of its
food. It also needs to quickly run in case there is some danger. Hence, there
is a need for control and coordination in not just deer but any organism.
Question 10.
How are involuntary actions and reflex
actions different from each other?
Answer.
Involuntary actions are those reactions
which take place during our daily routine activities, e.g. beating of heart,
peristaltic movement of intestines, etc. Reflex actions are the reactions
which are involuntary in actions that evoked in response to a sudden danger.
Question 11.
Compare and contrast nervous and hormonal
mechanisms for control and coordination in animals.
Answer.
|
Nervous control
mechanism |
Hormonal control
mechanism |
|
1. It is a fast mechanism.
|
1. It is a slow mechanism.
|
| 2. The information is conveyed in form of nerve impulses. |
2. The information is conveyed in form of chemical messengers.
|
|
3. It is facilitated by neurotransmitters.
|
3. It is facilitated by hormones.
|
Question 12.
What is the difference between the manner
in which movement takes place in a sensitive plant and the movement in our
legs?
Answer.
The movement in a sensitive plant is
controlled by hormones which are a part of hormonal mechanism. The movement in
our legs is controlled by nervous control mechanism.